By harnessing SABRE, strong signals for [1‐13C]‐ and [2‐13C]pyruvate in addition to a long‐lived singlet state in the  form are readily created; the latter can be observed five minutes after the initial hyperpolarisation step. We also demonstrate how this development may help with future studies of chemical reactivity.Hyperpolarisation methods that premagnetise agents such as pyruvate are currently receiving significant attention because they produce sensitivity gains that allow disease tracking and interrogation of cellular metabolism by magnetic resonance. Here, we communicate how signal amplification by reversible exchange (SABRE) can provide strong  Signal amplification by reversible exchange (SABRE) can provide strong 13C pyruvate signal enhancements in seconds through the formation of the novel polarisation transfer catalyst [Ir(H)2(η2‐pyruvate)(DMSO)(IMes)]. By harnessing SABRE, strong signals for [1‐13C]‐ and [2‐13C]pyruvate are readily created. Pyruvate lies at the junction of many metabolic processes in living cells, being produced from glucose before it enters cellular energy production pathways.p‐H2) induced polarisation (PHIP). This approach utilises the reactivity and nuclear spin orientations of p‐H2 to create highly visible hydrogenation products.Hyperpolarisation can also be created by parahydrogen  process, which is shown in Figure p‐H2, which is one of a growing range of molecules that exists as a nuclear spin singlet. When this molecule binds to a transition‐metal centre to form a dihydride complex, it is possible to transfer polarisation from p‐H2 into a ligand if there are different hydrides coupling to the nucleus that receive it. The potentially long lifetime of such states makes them ideal fuels for polarisation transferp‐H2 can be formed in >95 % purity by simply cooling H2 gas to <40 K in the presence of a suitable conversion catalyst.SABRE harnesses 13C pair with a singlet‐state lifetime that exceeds one hour.13C2 singlet state in pyruvate using DNP13C2 isotopologue in a process that proceeds spontaneously without the need for complex instrumentation or pulse sequences.In a remarkable development, Levitt and co‐workers created a molecular spin singlet state by radiofrequency excitation in 2004,cis,cis‐1,5‐cyclooctadiene), the well‐known SABRE catalyst precursor,2, and sodium pyruvate to form [Ir(H)2(η2‐pyruvate)(DMSO)(IMes)]. The resulting high‐field NMR spectra and characterisation data that confirm this product formation are detailed in the Supporting Information, and its structure is represented in Figure 13C]‐ (1), [2‐13C]‐ (2), and ‐pyruvate (3) isotopologues of sodium pyruvate (4) are used in this work.In order to achieve this goal, we first had to overcome the challenge of weak iridium pyruvate binding, which prevents typical hyperpolarisation of pyruvate using SABRE. The presence of an appropriate dimethyl sulfoxide (DMSO) co‐ligand allows for the assembly of a highly reactive polarisation transfer catalyst that overcomes poor pyruvate ligation. This is achieved by the reaction of [Ir(Cl)(COD)(IMes)] imidazol‐2‐ylidene, COD=2(η2‐pyruvate)(DMSO)(IMes)] yields two inequivalent hydride ligands such that at low magnetic fields, an [AA′B] spin system is formed. Modelling the propagation of hyperpolarisation from the p‐H2‐derived hydride ligands of this product into the bound pyruvate 13C nuclei predicts optimum polarisation transfer at a magnetic field strength of ±(−JHH+JHC*)/ΔγJHH corresponds to the J coupling between the hydride ligands, JHC* is (JHC+JH′C)/2, the combined hydride–carbon cross‐coupling in the complex, and Δγ is the difference in magnetogyric ratios (γH−γC) of proton and carbon nuclei. The predicted field strengths are about 100 times lower than the Earth's natural magnetic field and were achieved experimentally by housing the sample in a mu‐metal shield in conjunction with a field top‐up solenoid as detailed in the Supporting Information.Because of the low symmetry of pyruvate,  precatalyst, and DMSO with 3 bar p‐H2 was therefore prepared. This was shaken in the mu‐metal‐shielded solenoid for 20 s at 9 mG. Upon transfer into a 9.4 T magnet, strongly hyperpolarised 13C resonances corresponding to free pyruvate were observed. Subsequently, polarisation transfer between +20 to −21 mG confirmed that ±9 mG reflects the maximum signal intensity as portrayed by both Figure 13C polarisation level of about 1 % results for a sample containing [Ir(Cl)(COD)(IMes)] (5 mm), DMSO, and the corresponding pyruvate isotopologue in a 1:8:5 ratio after shaking with 3 bar of p‐H2 for 20 s. When a similar sample containing 2 was examined, the corresponding maximum polarisation level proved to be 0.6 % when transfer took place at ±3 mG. This reduction in efficiency is due to a smaller J1H-13Ctransfer coupling and shorter spin‐state lifetime 2(η2‐pyruvate)(DMSO)(IMes)] and pyruvate (3) as illustrated in Figure 3, present at 1.1 % natural abundance, confirms the impressive nature of the signal amplification that is achieved. The 13C relaxation times and polarisation levels of these species are detailed in Table 13C signals of 1 and 2, which are close to the normal values of 35.4±0.5 s and 20.1±0.5 s, respectively. Hence, the presence of the SABRE catalyst in these solutions does not significantly change their value. This reflects the fact that magnetisation build up by this catalyst is slow due to slow ligand exchange and small propagating JHC values, which differs from the typical response achieved when nitrogen‐containing heterocycles are examined.A sample of 1 and 2, isotopomer 3 is predicted to give a singlet‐based response after polarisation transfer between 0 G and 1 kG , DMSO, and 3 in a ratio of 1:8:5. The lifetime of this magnetisation was assessed after sample storage at both low and high field as a function of catalyst loading (IMes)(DMSO)] catalyst. The hyperpolarised 13C signals appear with intensities that are three orders of magnitude above their thermal values. Furthermore, when pyruvate is employed, the ready formation of a long‐lived singlet state with a low field lifetime of 85.4±8.5 s is achieved. We demonstrate that these polarisation levels allow in vitro images to be collected of a 70:30 D2O/[D6]ethanol mixture and a simple organic transformation to be viewed. We expect that the signal gain can be improved by optimisation of the ligand exchange processes within the polarisation transfer catalyst and by using higher pressures of p‐H2 with continuous bubbling.In conclusion, we have presented an approach to hyperpolarise pyruvate directly by SABRE in just a few seconds. This simple process harnesses a solenoid housed within a mu‐metal shield to optimise the polarisation transfer pathway within a novel [Ir(H)W.I., S.S.R., B.J.T., and S.B.D. are inventors on a University of York patent application on this work .As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.SupplementaryClick here for additional data file.


The reversible redox process was then applied in the catalytic hydrosilylation of 4,4′‐difluorobenzophenone, where the reaction rate could be reversibly controlled as a function of the catalyst oxidation state. The new NHC exhibits high electrophilicity and nucleophilicity, which was demonstrated in the reversible activation of alcohols and amines. The electronic structure of the resulting complexes was investigated through various spectroscopic and computational methods.A new redox‐active N‐heterocyclic carbene (NHC) architecture is obtained using N‐methylated pyrazinediimine iron complexes as precursors. The new species exhibit strong π‐accepting/σ‐donating properties and are able to ligate two metal centres simultaneously. The redox activity was demonstrated by the reversible chemical oxidation of a heterobimetallic Fe Symbiosis: A novel redox‐switchable N‐heterocyclic carbene architecture based on pyrazine‐diimine systems is presented. We demonstrate its ambiphilicity in the reversible activation of alcohols and amines. This scaffold is capable of ligating two metals simultaneously, and the resulting heterobimetallic complexes can be reversibly oxidised and reduced. Herein, we wish to introduce a new, non‐ ferrocene based redox‐active carbene architecture, which makes use of a Fe0‐ligated pyrazinediimine ligand (PPzDI), where both the iron centre and the ligand framework can be involved in the redox activity.(a) as the formally Fe0 centre in PDI/PPzDI‐type ligands  is more easily oxidised than the FeII centre in ferrocene, milder oxidation conditions would allow access to the oxidised form(b) while in ferrocene, the iron centre is more reluctant to engage in reactivity, iron‐PDI complexes display very rich chemistry ranging from catalysis to small molecule activation, making them the systems of choice for a considerable number of transformations(c) the PPzDI‐ligand is itself redox active through the reversible reduction of the imine functionality or ligand core, therefore allowing access to more redox states. Herein, we wish to communicate the synthesis of the new iron‐PPzDI NHC‐like precursors, the redox chemistry of the corresponding rhodium complexes and examples of reversible alcohol and amine activation at the in situ generated carbene centre.N‐heterocyclic carbenes (NHCs) have had a significant impact on the field of organometallic chemistry and of homogenous catalysis, where they have become widespread ligands for a myriad of transformations. Key to their success was the ability to accommodate a large number of transition metals, as well as facile tunability of steric bulk and electronic σ‐donating/π‐accepting properties. The parametrisation of these properties through the buried volume 2 and even Li(OEt)2NCytBu4 and 5 could be observed by 1H NMR spectroscopy in [D6]benzene or [D8]THF solutions, suggesting also that the pyrazine core is dearomatised (vide infra). While stable in solution for at least 24 h, complexes, 3–5 cannot be isolated as solids: removal of the respective solvent under vacuum, followed by re‐dissolving the reaction mixture in the same NMR solvent shows a complex mixture of species. The reactivity pattern suggests that the addition of the weakly nucleophilic base is reversible, and points towards an unstable NHC 2 intermediate, generated upon subjecting the reaction mixture to high vacuum.3–5 we assume that the steric bulk of the added base is the driving force for regenerating the free carbene.2, we could not observe any evidence for a Wanzlick‐type dimerization; the resulting reaction mixture likely contains paramagnetic species as judged by the broad signals observed by 1H NMR spectroscopy.Deprotonation of the iron‐based methylpyrazinium complex 2 with very poor nucleophiles testifies to the strong electrophilic character of the transient carbene species. In order to further assess this characteristic experimentally, 4 was treated with elemental selenium, which allowed the clean conversion to the selenourea derivative 6  and SIPr congeners (δSe=181 ppm),δSe=492 ppm) and bicyclic(amino)carbenes BICAAC (δSe=645 ppm),The reactivity of ers δSe=81 ppm,1 2, we have synthesised the corresponding Rh complexes. As described previously, the hexamethyldisilazane (HMDS) adduct proved to be a good precursor for 2, and reacting a freshly prepared solution of 4 with either [Rh(COD)Cl]2 or [Rh(CO)2Cl]2 readily afforded the heterobimetallic Fe/Rh complexes 7 and 8 . 15N NMR chemical shifts for 6–8 suggest that the pyrazine ring retains aromaticity (δN (NMe)=170.6 ppm in 6, 176.1 in 7, 171.4 in 8, similar to 145.5 in [1]⋅I).avRh‐CO) is generally used to measure the overall donor capabilities of NHCs. Dichloromethane solutions of compound 8 exhibit three main CO stretching frequencies, as a result of the overlapping between the Fe‐CO and Rh‐CO vibrational modes.−1 to the Rh‐CO fragments . The average value suggests that despite the high electrophilicity, 2 has high electron donating capacity—higher than the standard imidazolin‐2‐ylidene and imidazolidin‐2‐ylidene derivatives, but lower than certain cyclic alkyl amino carbenes (cAACs). Nevertheless, taken together, the spectroscopic data suggest that 2 has an ambiphilic character.2 fragment. While the diazine ring is π‐acidic, the iron‐ligated nitrogen atom is unable to stabilise the carbene formally empty pπ orbital as it is already engaged in interaction with the iron centre (vide infra). To the best of our knowledge, using a pyrazine ring as a scaffold for the generation of NHCs to give well‐defined metal complexes is so far unreported.To further explore the electronic properties of 7 and 8 could be determined by single crystal X‐ray diffraction  in 1⋅[I]8 precluded us from discussing the metric parameters; however, the connectivity could be established unambiguously.The molecular structures of n Figure .21 The m7 and 8. Both complexes exhibit one quasi‐reversible redox wave at very similar peak potentials , which we assign to the reversible redox chemistry of the formally Fe0 centre. This is followed by two irreversible oxidation waves, which we tentatively assign to the oxidation of the rhodium centre.II/FeIII redox potentials (of ca. 370 mV), the same variation of substituents appears to have negligible influence on the redox potentials of the Fe0/FeI couple. The marked cathodic shift in diaminocarbene[3]ferrocenophane is explained by through space Fe⋅⋅⋅Rh interactions, which would be absent in 7 and 8. Nevertheless, the attenuated shift in 7 and 8 could also be explained by CO/COD ligand scrambling between the two metal centres in 7, which is facilitated by the labilisation of the Fe−CO bond as a result of the oxidation of the iron centre, effectively reducing the amount of backbonding interactions.In order to probe the redox‐switchability of the isolated heterobimetallic complexes, we have initially performed cyclic voltammetry of 8 with a ferrocenium salt ([Fc][BArF24]) which gave rise to a paramagnetic compound 9 (Scheme μeff=1.91 μB). In contrast to the diaminocarbene[3]ferrocenophanes system described by Bielawski,9 product is stable enough to be isolated, even though we could not obtain X‐ray quality crystals despite numerous attempts. Dichloromethane solutions of 9 display three main IR stretching frequencies, as a result of the overlapping between the Fe‐CO (2007 and 1948 cm−1) and Rh‐CO (2081 and 2007 cm−1) vibrational modes. These values are shifted to higher frequencies compared to the parent compound 8, in line with the reduced amount of backbonding expected for 9. Overall, the IR data suggest a significant alteration of the electronic properties of 9  compared to 8 , with the overall donating properties of 9 being similar to the established IMes and IPr NHCs. This variation in the TEP is comparable to the values reported for other redox‐switchable NHCs.9 with one equivalent of cobaltocene cleanly regenerates 8 alongside [CoCp2][BArF24]  which gnocarbeneferroceno9 was investigated by X‐band CW‐EPR spectroscopy. The data, recorded at 6 K (Scheme 1/2), with no distinguishable hyperfine structure and with very small g anisotropy, centred at g=2.0080 (ge=2.0023). These data suggest reduced spin density on the iron centre and are consistent with significant spin delocalisation. A signal possessing the same characteristics could also be observed at room temperature in THF solutions, albeit with reduced intensity (see the supporting information).As the formal oxidation of the iron centre has a marked effect on the stretching frequencies of the Rh‐CO unit, we wondered whether the resulting unpaired electron resides on the iron centre, or it is delocalised over the entire conjugated system. As a Fe (or Rh) based radical would have a specific EPR signature compared to an organic radical, K Scheme , right, PzDI)Fe(CO)2][BArF24] 10 (Scheme PzDI)Fe(CO)2 in the presence of [Fc][BArF24]  is iron‐based rather than ligand‐based. The characteristics of 10 are similar to the pyridine‐based FeI analogue, [(PDI)Fe(CO)2][BArF24] reported by Chirik.In order to ascertain whether the radical delocalisation over the entire ligand scaffold is a result of the carbene functionality, we have prepared [(PO)2]BArF2 10  and IR  spectroscopy. In order to minimise the induction time, the more labile COD substituted [FeRh] pre‐catalyst 7 was chosen. Initial catalytic runs were performed in the presence of neutral (7) and the in situ‐oxidised analogue (+7) respectively  and oxidised species (+7), the temporal control was depicted through three “on/off” cycles, which could be performed without apparent loss of catalytic activity.Taking the significant difference in the reaction rate between the oxidised and reduced forms into account, we sought to demonstrate that the change between the two kinetic regimes was possible through in situ oxidation and reduction. Conducting the catalytic hydrosilylation reaction in a cell fitted with an IR probe allowed us to detect rapid changes in the kinetic profile as a function of external stimuli. Sequential addition of [Fc][BArF1⋅[I] with bulky alkoxides and amides readily affords the corresponding alcohol and amine adducts 3–5, which act as carbene precursors, but cannot be isolated as solids due to the kinetic lability of the bases employed. In order to get more insight in the structure and reactivity of carbene 2, the structure and reactivity of these adducts would provide valuable information. We therefore envisaged that replacing the bulky amine or alcohol fragments with OMe would increase the stability of the resulting adducts. Reacting derivative 3 with methanol affords indeed the OMe substituted derivative 11 in quantitative yield, alongside tBuOH as observed by 1H NMR spectroscopy  to 94.8, when compared to the 145.5 value measured for 1⋅[I]. The imine character of the C19=N2 bond adjacent to the MeOH is also diminished, as shown by the significant upfield shift 15N NMR signal (δN2=188.2 ppm vs. δN1=231.4 ppm in 1⋅[I]) . The decrease of electron density on the imine arm revealed by 15N NMR spectroscopy is also reflected in the elongation of the C19=N2 bond to 1.361(4) Å compared to the average value of 1.325 Å observed for 1⋅[I] and 7 °) is significantly compressed compared to ∡C2‐C1‐N4 (122.0(3)°) suggesting a tetrahedral geometry at C17, in line with a change of hybridisation from sp2 in 1⋅[I] to sp3, as a result of formal methanol addition.Unlike s Figure , top. NM−1 in 11), as expected for a more electron rich system, which enhances backbonding from Fe to the carbonyl ligands.The CO stretches determined by solid state IR spectroscopy are also responsive to the alteration of the electronic environment and shift to lower frequencies  of the corresponding alcohols or amines, the conversion to 13 and 14 was around 75 % and 66 % respectively, suggesting an equilibrium reaction.12 and 13 could however be achieved when starting directly form 3. Methoxide and isopropoxide derivatives 11 and 12 are stable and could be isolated as solids, whereas benzylic alcohol and amine derivatives 13 and 14 show clear signs of decomposition upon solvent removal. While the fate of the iron species could not be hitherto elucidated, in the case of the benzylic alcohol adduct 13, benzaldehyde formation could be observed by 1H NMR spectroscopy and GC‐MS. The formation of benzaldehyde could be explained by a 1,3‐hydride shift followed by α‐elimination.The unconventional way of synthesising 3 Scheme . Similar2 and its rhodium complexes, we have performed DFT calculations at a B3LYP/def2‐TZVP(‐f) level of theory.1, 7 and 10, geometry optimisations produced features which were in good agreement with the metric data from X‐ray crystallography, as well as vibrational data from IR spectroscopy (See the supporting information for details). Potential ligand redox non‐innocence for complexes 2, 7, 8 and 11 was investigated through broken‐symmetry (BS) calculations, where all strategies employed converged to the same BS  (i.e. closed‐shell) solution, similar to the one observed for the starting material 1⋅[I], as well as (PPzDI)Fe(CO)2.0 metal centre supported by a neutral ligand, in line with the diamagnetism observed for the investigated complexes. We have then proceeded by examining the frontier molecular orbitals (MOs) Fe(CO)2, with a narrow HOMO–LUMO separation (2.60 eV), most likely due to the extended π‐conjugation over the pyrazine ring and imine arms. Interestingly, the carbene based Eσ and Eπ* are the HOMO−1 (stabilised by 0.68 eV compared to the HOMO) and LUMO+1 (destabilised by 0.50 eV compared to the LUMO). This distribution of molecular orbitals is similar to the one observed for the bisoxazoline‐based NHC IBioxMe4,[36] where, in some cases, the Eσ (HOMO−1) is stabilised by ca. 0.50 eV compared to the HOMO. In the case of Siemeling's neopentyl‐substituted diaminocarbene[3]ferrocenophane, the carbene Eσ is in the HOMO , whereas the carbene Eπ* is the LUMO+2, while the LUMO and the LUMO+1 are ferrocene‐based (see the supporting information for a full MO diagram).EST) for 2 appears significantly narrow , however, the magnitude is not directly comparable with the other reported NHCs, given the fact that in 2, the carbene‐based orbitals are not the frontier MOs. A natural bond orbital (NBO) analysis4‐C1 and N3‐C18 σ* MOs . The p‐type orbital located at C18 is also strongly delocalised into the adjacent imine bond C19‐N2, as well as the pyrazine N4‐C17 π* orbitals (see supporting information for details). These data suggest that the carbene π‐symmetry orbital is strongly delocalised over the entire diiminopyrazine ligand, and this stabilization is in line with the strong π‐accepting properties determined experimentally. The bonding picture strongly resembles the one in the 1,3‐imidazol‐4‐ylidenes, which belong to the category of mesoionic N‐heterocyclic carbenes (MICs).2, and therefore a π* molecular orbital that satisfies the symmetry criteria in order to accept electron density from a metal centre is too high in energy.2, a molecular orbital of appropriate symmetry is low in energy, accounting for the good π‐accepting properties  Figure . In the 2, four resonance structures can be envisaged  is significantly influenced by the nature of the ligand on the rhodium atom, that is, the HOMO is stabilised by 0.26 eV in the case of 8 (−5.12 eV), which contains the strong π‐accepting CO ligands, compared to 7 (−4.86 eV). As expected, this stabilisation is even more pronounced for the rhodium‐based HOMO−1 (by 0.70 eV). An NBO analysis reveals a bonding situation very similar to the one described for 2. Additionally, the carbene lone pair is involved in a 3c/4e interaction with the trans Rh−CO bond, whereas the cis Rh−CO bond is involved in a 3c/4e interaction with the chloride ligand.11, NBO analysis reveals that the N2‐C19‐C18 .In the case of the neutral metal complexes ed to 7 −.86 eV. A9 (ligand‐based) and 10 (Fe‐based) observed by EPR.10, the SOMO was found to be a Fe‐based MO with a predominant d‐character, while the spin‐density plot obtained from a Mulliken‐population analysis reveals 0.71 spin density on the iron centre  the spin density is more delocalised over the entire ligand framework, with 0.56 spin density on the iron centre  the SOMO (−8.70 eV) is stabilised by 0.21 eV compared to the rhodium‐based HOMO (−8.49 eV). The extent of spin delocalisation on the ligand explains the low g anisotropy observed by EPR spectroscopy.Lastly, we wanted to address the discrepancy between distribution of the unpaired electron in e Figure , right. PzDI‐type systems are able to support a bimetallic architecture, where the heterocyclic core is able to ligate both a NNN pincer‐type chelating system, while simultaneously acting as an N‐heterocyclic carbene, which can coordinate to a second metal centre. For the heterobimetallic Fe/Rh system studied herein, the NHC exhibits strong σ‐donating/π‐accepting properties. The carbene exhibits a special bonding situation, possessing both the characteristics specific to mesoionic carbenes, explaining the strong σ‐donating properties. Furthermore, the system possesses low lying π* molecular orbitals of the appropriate symmetry for backbonding, due to extensive delocalization of the π electrons over the PPzDI system. These properties can be modulated through reversible chemical oxidation. As both oxidised and reduced forms are isolable, we could directly compare the effect of oxidation on the carbene properties by spectroscopic and computational methods. These studies reveal that, in contrast to standard iron PDI chemistry, where oxidation takes place at the metal, in the case of the heterobimetallic complexes, the unpaired electron is evenly distributed on the ligand core, therefore impacting the electronic properties of both metals involved. The reversible modulation of electronic properties was then applied in the catalytic hydrosilylation reaction of 4,4′‐difluorobenzophenone, where the oxidised species shows a ten‐fold increase in the reaction rate. We have shown that the switch between a slow‐rate regime and a fast‐rate regime could be achieved in situ through the addition of the appropriate external stimulus (oxidising or reducing agent) We have also demonstrated the ability of the NHC‐type Fe‐PPzDI fragment to reversibly activate various alcohols and amines, likely through successively reversible formal oxidative addition/reductive elimination steps at the Cα. The formal oxidative addition of alcohols and amines is accompanied by the dearomatisation of the pyrazinium ring. This reactivity pattern is likely due to the ambiphilicity of the systems as a result of combining a π‐acidic pyrazine system with a Fe(CO)2 fragment which prevents the second nitrogen atom from engaging in the stabilisation of the carbene atom. It remains to be established if the redox‐state dependent change in reaction rate or chemoselectivity of the bimetallic species is general, and can be fostered for the design of redox‐switchable bimetallic catalysts. It is also to be expected that increasing the steric bulk of the substituents at the periphery of the carbene centre would allow the isolation of the free NHC. These directions are currently pursued in our laboratory.We have shown that PThe authors declare no conflict of interest.As a service to our authors and readers, this journal provides supporting information supplied by the authors. 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Herein reported are the reactions of an electron‐rich, Lewis acidic diborane with N‐heterocyclic aromatics to give first members of an unprecedented family of highly charged cationic cyclophanes with diboranyl units. Tetracationic cyclophanes with 4,4‘‐bipyridine/ 1,2‐bis(4‐pyridyl)ethylene and diboranyl units were synthesized and their redox chemistry was studied. Cyclisation of two diboranyl and two pyrazine units is accompanied by electron transfer from the diboranyl unit to the pyrazine. Our results pave the way for the integration of redox‐active diboranyl units into cyclophanes and supramolecular structures. Electron‐Rich cyclophanes: Unprecedented, highly charged cyclophanes with diboranyl units are synthesized and their redox and optical properties studied. This reaction led to the new diboron dication 2 as colorless needles in a yield of 52 % diborane(4) with phthalazine in toluene yielded the first N,N‘‐diboryl‐2,3‐dihydrophthalazine (after 10 min reaction time) and then in 8 h 1,2‐bis(borylimidoyl)benzene, in which the N−N bond was completely cleaved.1 with phthalazine resulted in the complexation of one phthalazine molecule to give monocationic diborane(4) derivative 3 in 90 % yield as yellow crystals (Scheme The recently reported reaction of the highly Lewis acidic tetra(11B NMR spectrum of 3(OTf) at δexp=5.9 and 1.9 ppm confirm the asymmetric substitution pattern and are in a good agreement with the quantum chemically calculated values of δcalc=4.8 and 2.4 ppm . Moreover, the B−B bond length (1.717(6) Å) is similar to that in the starting material 1 (1.708(4) Å),Two singlets in the 1 with bpy or dpe resulted in the formation of an unprecedented tetracationic tetraboron cyclophane , 1,2‐di(4‐pyridyl)ethylene (dpe) and pyrazine (pz) were in the focus of the following experiments. Reacting compound e Scheme  a. Durin4(OTf)4 and 5(OTf)4, were crystallized from a 1:1 mixture of methylene chloride and n‐pentane giving deep‐red needles 4 grew likewise from a concentrated aqueous solution demonstrating the quite remarkable stability of the tetracation towards hydrolysis. Due to the persistent disorder of the triflate anions it was not possible to obtain satisfying crystal structures both of 4(OTf)4 and 5(OTf)4. To overcome this difficulty, we replaced the anion in a metathesis reaction with four equivalents of Na[B(C6F5)4]. The experimentally determined structure of the tetracations 4 and 5 are shown in Figure Both compounds, s Figure  in 31 an4 amounts to only 4.0 Å, in line with the quantum chemically calculated value of 3.9 Å (B3LYP‐D3/def2‐TZVPP). The observed distance is significantly shorter than the value of 6.8 Å previously determined for the well‐known CBPQT4+ 4 and 5(OTf)4 are stable in solution. The 11B NMR spectra in [D3]acetonitrile display in both cases one singlet signal and the chemical shifts are very similar (δ=3.9 ppm for 4 and δ=3.2 ppm for 5).Further NMR studies clearly showed that both compounds 4(OTf)4  displays one broad absorption band in the visible region (λmax=397 nm) and an additional sharp band at 251 nm. A comparison with the carbon analogue, methylviologen (MV2+) points to an intriguing similarity. The parent dication MV2+ possesses only one strong absorption band at 257 nm, close to the value measured for 4.4 are closely conform we postulate a boron‐to‐ligand charge transfer.The experimental UV/Vis spectrum of on λmax=7 nm and 4 contains two bpy units, up to four one‐electron reduction steps can occur.2Cl2 solution three waves were observed, that were assigned to two reversible one‐electron reduction processes (at E1/2=−1.10 and −1.30 V) followed by a reversible two‐electron reduction process at E1/2=−1.71 V, converting the initial tetracation eventually to a neutral molecule.We investigated on the nature of the interactions between the linkers by cyclic voltammetry Figure , top. Gi3CN solution exhibiting a reduction peak separation of 230 mV, presumably a consequence of the steric and electronic constraints associated with the rigid geometry of the cyclophane .5, the last two‐electron reduction process is clearly separated in two one‐electron steps  are separated by 516 mV.4+, shows no interaction between the aromatic systems as no wave splitting occurs in the CV and only two two‐electron processes are visible.4 and 5 between those in o‐ExBox and CBPQT.We observed a further wave splitting of the reversible two‐electron couple in CHs Figure , bottom.4 by reacting it with an excess of zinc in CH3CN. During the reaction we observed a slight color change to orange brown, but only isolated the starting material. We also tried to isolate the side products involved in the formation of 4(OTf)4 by crystallization from the concentrated mother liquor. Indeed, a few yellow box‐shaped crystals were obtained at room temperature. The X‐ray analysis revealed a tetrameric octacationic macrocycle as byproduct  demonstrating that even larger macrocyclic structures are possible. The solution NMR spectra of the reaction mixture showed no clear evidence for an equilibrium between 4 and the tetrameric species at room temperature, but small amounts of the dimer of 4 were observed together with five triflate counterions in an high‐resolution ESI+ mass spectrum recorded after heating of 4(OTf)4 in CH2Cl2. Traces of the trimeric hexacation and the pentamer decacation were detected as well .Motivated by the promising cyclic voltammograms we attempted a chemical reduction of the tetracation 1 with one equivalent of pyrazine. The product 6(OTf)2, isolated in a yield of 17 %, turned out to be again a tetraboron ring  which at last is cleaved. Consequently, the boron atoms of each diborane unit are now separated by 2.45 Å. In this context it should be noted that complexation coupled with electron transfer was previously observed in some reactions of the ditriflato‐diborane 1.The electron transfer occurs from the B−B bond (B6(OTf)2 decomposes in polar solvents like acetonitrile, DMF, or DMSO. Among commonly used organic solvents, it is only stable in dry, degassed methylene chloride. Unfortunately, the solubility of the compound is very low. Therefore, it was only characterized by solid‐state analytics and UV/Vis spectroscopy. In the UV/Vis spectrum, a broad band at 449 nm appeared, indicating reduction of the 1,4‐diazine and agreeing with the solid‐state structure. The value recorded for 6(OTf)2 is 92 nm redshifted in comparison to the absorption band reported for 1,4‐bis(dimesitylboryl)‐1,4‐dihydropyrazine, λ=357 nm).Compound 1 with a mixed organic system containing both the pyrazine and bipyridine units, 2,3‐di‐2‐pyridinyl‐pyrazine (dpp). As we observed in the past, the diborane dication forms Lewis acid–base adducts with 2,2‐bipyridine whereas pyrazine becomes reduced.1 are reacted with one equivalent of the organic ligand (Scheme 7(OTf)2 (formed in ca. 70 % yield), featuring only one diborane unit. The B−B bond (1.7131(3) Å) was confirmed by structural analysis . The methodology reported herein might be used for the synthesis of a variety of new redox‐active cyclophanes.In summary we presented here the synthesis of new remarkably stable, highly charged tetraboron ring compounds being the first cyclophanes with integrated diborane units. Given that the spatial separation of the organic linkers is small due to the constraints imposed by the diboryl units, there is a significant degree of electronic communication. In the case of pyrazine, ring formation is accompanied by electron transfer, leading to pyrazine reduction and oxidation of the boron atoms  should be addressed to the authors.SupplementaryClick here for additional data file.


Pectobacterium cause soft rot in various plants, and result in important economic losses worldwide. We understand much about how these pathogens digest their hosts and protect themselves against plant defences, as well as some regulatory networks in these processes. However, the spatiotemporal expression of genome‐wide infection of Pectobacterium remains unclear, although researchers analysed this in some phytopathogens. In the present work, comparing the transcriptome profiles from cellular infection with growth in minimal and rich media, RNA‐Seq analyses revealed that the differentially expressed genes (log2‐fold ratio ≥ 1.0) in the cells of Pectobacteriumcarotovorum subsp. carotovorum PccS1 recovered at a series of time points after inoculation in the host in vivo covered approximately 50% of genes in the genome. Based on the dynamic expression changes in infection, the significantly differentially expressed genes (log2‐fold ratio ≥ 2.0) were classified into five types, and the main expression pattern of the genes for carbohydrate metabolism underlying the processes of infection was identified. The results are helpful to our understanding of the inducement of host plant and environmental adaption of Pectobacterium. In addition, our results demonstrate that maceration caused by PccS1 is due to the depression of callose deposition in the plant for resistance by the pathogenesis‐related genes and the superlytic ability of pectinolytic enzymes produced in PccS1, rather than the promotion of plant cell death elicited by the T3SS of bacteria as described in previous work.Bacterial pathogens from the genus  Pectobacterium PccS1 infection, transcriptomic analysis using a two‐control gene expression experiment reveals more differentially expressed genes with different expression change types, which are related to virulence, adaptation, and host response.In  It is well known that SREs use plant cell wall‐degrading enzymes (PCWDEs) as the main pathogenic determinants to successfully infect host plants, and encode all six known protein secretion systems involved in attacking host plants and competing with environmental bacteria  encoding enzymes in the metabolic pathways of carbohydrates are crucial to the virulence of Shigella flexneri, Listeria monocytogenes, and P. carotovorum  genes (sDEGs) were identified and classified into five types of expression pattern. Some key genes that encode enzymes for acetyl‐CoA production from sucrose/glucose and pectin via pyruvate were significantly up‐regulated in PccS1 infection. While expression changes in genes for pathways of acid production were not widely detected, these results are helpful to our understanding of the bacterial response to environmental nutrients. Additionally, virulence in host plants and the hypersensitive response in nonhost plants were determined for mutants with one of the sDEGs deleted independently. The results demonstrate that the extensive host maceration by PccS1 is due to (a) the depression of callose deposition in plants by pathogenesis‐related genes or resistance being decreased by the host itself; and (b) the superlytic ability of pectinolytic enzymes in Pectobacterium PccS1.RNA‐Seq has been widely used in to help understand pathogen–plant interactions. Based on dynamic expression changes, RNA‐Seq approaches have identified genes that function in pathogen infection and adaption processes, such as pathogenicity, metabolism, signalling regulation, and response to complex environmental factors , similar to previous results that demonstrated that the threshold of bacterial population should be 106–107 cfu to effectively elicit expression of the genes participating in a variety of cell density‐dependent physiological processes , and the quantity of PccS1 cells in planta was measured as previously described . Our results showed a good overall quality of clean reads with Q20 > 98% obtained in each sample, and over 97% genes in the reference genome were uniquely mapped. Subsequent analyses showed that 48.72% and 57.50% of genes of the cells recovered were differentially expressed  at the early stage of infection (4 HAI) versus that of the cultures in LB and MM, respectively  analysis, as previously described (Allie 2.4http://www.genome.jp/keeg/)  database  Figure . The res) Figure . The exp) Figure . In some) Figure . Previou2.5PccS1_00151 and PccS1_00152 were classified as special genes   were up‐regulated in infection, belonging to the positively plant‐induced gene type. These results emphasize the role of pectate lyase (PL) in PccS1 infection, which is similar to previous work that showed that all nine PLs (pelABCDEILNZ) in D. dadantii  was not significantly changed in PccS1 infection compared to the references, except that four genes for polygalacturonases (pehX and three peh genes) were differentially expressed with a ratio of log2‐fold of approximately 2–3 in the samples of PccS1 recovered at some time points  and five protease genes  are positively plant‐induced genes, and celB , like rplY, is a nutrient‐level susceptible gene  metabolism and the regulation of PCWDE expression, to some extent, which represents the adaption of PccS1 gene expression to environmental nutrient status.In our recent work, we demonstrated that genes crucial to virulence, such as 2.7carI and expR) and on those for regulation of pectin catabolism   (such as rsmA (PccS1_00073 and PccS1_00521), rsmB (PccS1_00733 and PccS1_02891), rsmC (PccS1_01829 and PccS1_01902), and rpoS (PccS1_00230). It is well known that RsmA is an RNA‐binding protein responsible for response to bacterial metabolic status  suggests that RsmA might be a switch for cellular processes including infection. The result that the rsmA deletion mutant showed an increase in both virulence .The results revealed that the expression patterns of the seven genes related to construction of RNA are different  and ExpR (PccS1_01370), were nearly the same as for the controls, except there was less down‐regulation of expR at the final stage of infection compared to the control in LB only. Similarly, the expression of carI showed no difference compared with the references, although it was repressed at a lower level in the PccS1 samples recovered at 12 and 16 HAI compared with the reference from MM , three were differentially expressed based on nutrient levels, with gene expression levels and nutrient levels inversely correlated, while narX was expressed at a similar level under the three different nutrition levels (Table ntrC‐ntrB) were undetected, although narX‐narL expressed at a log2‐fold change of 1–2 , transcriptional regulation (marR) and anaerobic regulation . Two genes of undetected expression change (oxyR and ohrR) are linked to hydroperoxide , the related genes (dspF), and a gene for the chaperone of HrpW. The gene expression pattern showed that the clusters of both T3SS and T6SS were all significantly up‐regulated in planta compared with the references  out of the 11 genes outside the T2SS cluster were expressed at higher levels when nutrient levels decreased, and the 14 genes in the T2SS cluster expressed at a similar level to the references, except six of them were up‐regulated at a log2‐fold ratio of 2–3 versus the LB reference  and motility related to the pilus assembly crossing the inner membrane (tadA and rcpA) were more susceptible to nutrient conditions than those in the cluster encoding Gsp proteins for assembling the secretion tunnel. We deduced that the T2SS secretion tunnel might be assembled for secretion at any cellular processes regardless of growth conditions in Pectobacterium PccS1. The genes with functions for pathogenicity, including those for the Tat export pathway and pili for motility in T2SS, are activated only in the presence of host plants.It is well known that several secretory systems in bacterial pathogens secrete enzymes or toxins into host cells or the surrounding environment  presented a similar level of maceration on the hosts as the wild type  showed no differences in lesion development compared with the wild‐type PccS1  or rpoS . Callose rarely deposited in the in vitro N. benthamiana leaves infiltrated with ΔPccS1_03557 and ΔPccS1_03557 (pBBR) showed evidence that the leaves lost the ability of resistance to the invasion of the bacterial strains, but more callose was deposited in the leaves in vivo after inoculation of these two mutants  was down‐regulated when PccS1_03557 was impaired in PccS1 2SO4, 20 mM K2HPO4 and 15 mM KH2PO4) containing 0.5% (wt/vol) glucose  at 40 μg/ml, rifampin (Rif) at 100 μg/ml (Sangon Biotech). Bacterial growth (OD600) was measured in a BioPhotometer (Eppendorf) at 600 nm.The bacterial strains and plasmids used in this study are listed in Table 3.2et al., 600 = 1.2) onto the petioles of the approximately 45‐day‐old calla (Z. odorata) or B. rapa subsp. pekinensis plants in vivo or in vitro. Bacterial population dynamics in the host after inoculation were assayed as previously described  or the detached leaves of N. benthamiana using a needleless syringe as in previous work  were mixed with 3 ml ice‐cold transcriptional stop solution, and then centrifuged at 13,800 × g at 4 °C for 20 min. The pellets were frozen in liquid nitrogen and stored at −80 °C for RNA extraction.Previous research has indicated that the growth medium of the bacteria is an important consideration during the experimental design for any experimental protocol  according to the manufacturer's instructions. RNA samples were treated with RNase‐free DNase I (Thermo Fisher Scientific Inc.) to remove any DNA contamination. Purity and concentration of RNA were determined by a microspectrophotometer NanoDrop ND‐1000 (Thermo Fisher Scientific Inc.). The quality of the RNA was analysed using a 2,100 Bioanalyzer (Agilent Technologies). RNA that passed quality control was depleted using a Ribo‐Zero rRNA Removal Kit (Bacteria) (Illumina) and then broken into short fragments (approximately 200 bp). These short fragments were used as templates to synthesize cDNA libraries using the NEBNext Ultra RNA Library Prep Kit (Illumina). The cDNA libraries were purified using the Beckman AMPure XP beads (Illumina). The quality of the cDNA libraries was measured using a 2,100 Agilent High Sensitivity DNA Kit (Agilent Technologies). Quantification of the cDNA libraries was performed with an ABI 7,500 real‐time PCR system (Applied Biosystems) using a KAPA SYBR Green fast universal 2 × qPCR master mix kit (Vazyme).3.5N percentage (the percentage of the nucleotides that could not be sequenced in the read) over 5%, and those with Q‐value of both the 5′ and 3′ ends lower than 20 . The sequences were then re‐evaluated using software FastQC v. 0.10.1 and the clean reads were assembled.Pair‐end (PE) index libraries were constructed with a TruSeq PE Cluster Kit v. 3 according to the manufacturer's protocol . The libraries with different indexes were multiplexed and loaded onto an Illumina Hiseq 2,500 according to the manufacturer's instructions (Illumina). Sequencing was carried out using a 2 × 125 paired‐end configuration. In order to obtain clean reads, raw reads were first filtered using statistical software Trimmomatic v. 0.30. Adapter sequences and low‐quality sequences were removed. Low‐quality sequences included reads of base number less than 75, reads with 3.6et al., et al., p value threshold in multiple tests was determined by the false discovery rate (FDR)  value . The hypothesis test of percentages  was used to determine significant differences in the assays described above.The authors have declared no conflicts of interest.FIGURE S1 Images of Zantedeschia odorata plants inoculated with Pectobacterium carotovorum subsp. carotovorum PccS1Click here for additional data file.FIGURE S2 Bacterial population of Pectobacterium PccS1 recovered at different time points after inoculation in Zantedeschia odorata plantsClick here for additional data file.FIGURE S3 The activities of plant cell wall degrading enzymes determined for the wild type and mutants of Pectobacterium PccS1Click here for additional data file.FIGURE S4 Growth curves of Pectobacteriumcarotovorum subsp. carotovorum wild type (PccS1) and the derived strains in Luria Bertani mediumClick here for additional data file.TABLE S1 The number of the differentially expressed genes (log2‐fold ≥ 1.0) in Pectobacterium PccS1 recovered from the petioles of calla lily (Zantedeschia odorata) plants at four different time points after inoculation compared with in vitro controls grown in both Luria Bertani and minimal mediaTABLE 1.2 Log2‐fold ratio (≥ 2.0) of the significantly differentially expressed genes in PccS1 recovered at four different time points after inoculation in the petioles of calla lily plants in vivo compared with the cultures in Luria Bertani mediumTABLE 1.3 Log2‐fold ratio (≥ 2.0) of the significantly differentially expressed genes in PccS1 recovered at four different time points after inoculation in the petioles of calla lily plants in vivo compared with that of the cultures in minimal mediumClick here for additional data file.TABLE S2 Expression pattern of the genes encoding for cyclic nucleotide‐related proteins in Pectobacterium PccS1 recovered at different times after inoculation compared with that of the cells in Luria Bertani and minimal mediaClick here for additional data file.TABLE S3 Log2‐fold ratios of the genes for the components of T3SS in Pectobacterium PccS1 recovered from Zantedeschia odorata at different times after inoculation compared with those for the cells in Luria Bertani and minimal mediaClick here for additional data file.TABLE S4 Log2‐fold ratios of the genes in T6SS cluster and the homologues dispersed in the genome of Pectobacterium PccS1 recovered from Zantedeschia odorata at different times after inoculation compared with those of the cells in Luria Bertani and minimal mediaClick here for additional data file.TABLE S5 Log2‐fold ratios of the genes for the components of T2SS in Pectobacterium PccS1 recovered from Zantedeschia odorata at different times after inoculation compared with those of the cells in the mediaClick here for additional data file.TABLE S6 The sequences of oligonucleotides for molecular modification used in this studyClick here for additional data file.TABLE S7 Bacterial strains and plasmids used in this studyClick here for additional data file.TABLE S8 The sequences of RT‐qPCR primers used in this studyClick here for additional data file.


Being the most prevalent environmental factors in daily life, temperature and related thermal effects have tremendous potential for practical applications. To increase the practicality in everyday life, bismuth telluride nanoplates (Bi2Te3 NPs), serving as an efficient thermocatalyst, are coated on a carbon fiber fabric (Bi2Te3@CFF) to develop a thermocatalytic filter with antibacterial function. Temperature difference induced H2O2 generation by thermocatalysts results in the oxidative damage of bacteria, which makes thermocatalysts highly promising for disinfection applications. Antibacterial activity as high as 95% is achieved only by the treatment of low-temperature difference cycles. The current work highlights the horizon-shifting impacts of thermoelectric materials for real-time purification and antibacterial applications.The highly reactive nature of reactive oxygen species (ROS) is the basis for widespread use in environmental and health-related fields. Conventionally, there are only two kinds of catalysts used for ROS generation: photocatalysts and piezocatalysts. However, their usage has been limited due to various environmental and physical factors. To address this problem, herein, we report thermoelectric materials, such as Bi 2O2 generation by thermoelectric materials is an attractive strategy for environmental remediation purposes. Here the authors demonstrate Bi2Te3 nanoplates based antibacterial filter as an effective candidate for indoor disinfection applications.Temperature difference induced H Among all different types of ROS, hydrogen peroxide (H2O2) is more stable than others9. As an environmentally friendly chemical, H2O2 not only plays an important role in various organic syntheses12 but can also be used as a bleaching agent and fuel in industry14. Conventionally, H2O2 is produced by the anthraquinone method, which involves some serious limitations, such as complicated reaction steps, where the products and byproducts are hardly separated16. Recently, photocatalysis and piezocatalysis have emerged as promising alternatives to produce ROS. In particular, the utilization of renewable energies to generate ROS has been widely investigated in recent years instead of traditional chemical methods20. Light irradiation and mechanical vibration provide the necessary stimuli in photocatalysis and piezocatalysis, respectively. Activated by external triggers, the electron-hole pairs are separated in photo/piezocatalysts and promote surface electrochemical reactions to generate ROS21. However, photocatalytic reactions are greatly affected, where suspended matter in wastewater causes low solution transmittance and thus restricts its quantum efficiency below 10%23. Moreover, in practical applications, round-the-clock performance is also hindered in photocatalysis due to the unavailability of sunlight24. On the other hand, the unavailability of suitable mechanical forces in nature creates a serious bottleneck for the realization of effective piezocatalytic performance. Hence, it is imperative to design efficient catalysts that can be exploited in an uninterrupted manner for ROS generation.The generation of reactive oxygen species (ROS) is the backbone of advanced oxidation processes leading to widespread applications such as organic pollutant degradation26. In general, thermoelectric materials can convert thermal energy to electrical energy by means of the temperature difference-induced separation of positive and negative charges27. Temperature difference-induced charge separation and consequent voltage generation inside a thermoelectric material can also be expected to realize ROS generation and the corresponding catalytic activity29. Thermoelectric materials that can be used as catalysts are called thermocatalysts and are endowed with multiple advantages over traditional photo/piezocatalysts. Unlike photocatalysts or piezocatalysts, thermocatalysts show great promise towards the uninterrupted generation of ROS, as a temperature difference always exists in nature. Moreover, temperature difference-induced charge separation in thermocatalysts is beneficial for prohibiting electron-hole recombination, which further ensures higher ROS generation. However, despite these striking advantages, the investigation of ROS generation by thermocatalysts remains almost unexplored in the literature. Since the thermoelectric voltage under a particular temperature difference plays the key role in influencing the thermoelectric effect, a thermoelectric material whose Seebeck coefficient is high should be selected for achieving efficient thermocatalytic performance. Near room temperature, bismuth telluride (Bi2Te3) has a higher Seebeck coefficient32 than other common thermoelectric materials such as antimony telluride (Sb2Te3) and lead telluride (PbTe) due to its excellent physical properties and distinctive electronic structure33.Temperature is one of the most important environmental factors, and a temperature difference exists almost everywhere in our living environment. The discovery of thermoelectric materials has paved the path to harness this waste heat or temperature difference for various applications, such as energy convertors and sensors2O2 generation and the consequent antibacterial activity of selected thermoelectric materials such as Bi2Te3, Sb2Te3, and PbTe. Since the early 1800s, H2O2 has been used as a disinfectant owing to its high oxidative and biocidal efficiency34. The thermocatalytic efficiency and subsequent H2O2 generation were further enhanced 20 times by narrowing down the Bi2Te3 size. For convenient applications, Bi2Te3 nanoplates (NPs) were coated on a carbon fiber fabric (Bi2Te3@CFF), and for simulating real-life conditions, Bi2Te3@CFF was utilized as a thermocatalytic filter under an indoor temperature difference. Bi2Te3@CFF exhibits significant antibacterial activity with either a positive or negative temperature difference and shows good durability as the antibacterial activity remains intact for more than one month. The concepts and results presented in this paper strongly highlight the bright prospects of thermocatalysts for H2O2 generation and environmental disinfection applications.In this work, we demonstrate H2O2 is illustrated in Fig. 2Te3 is a narrow bandgap semiconductor with a bandgap of ∼0.2 eV, and the conduction band potential of Bi2Te3 is more negative than the redox potential of O2/.O2−. In thermal equilibrium, free charges present on the crystal surface quickly exhaust before reacting with the contaminant solution because of the large potential difference between the conduction band and the redox potential of O2/.O2−. As a result, no significant catalytic activity is noticed. However, with the application of a temperature difference, negative charges rush from the hot side to the cold side of the material and produce a potential difference between the hot and cold ends. As a result of this thermoelectric potential, the band energy decreases at the positive potential side and increases at the negative potential side. To follow this variation in energy, both the valence band and conduction band tilt across the material and the conduction band comes very close to the redox potential for generating superoxide (.O2−) radicals. Consequently, electrons from the conduction band can easily migrate to the solution and produce H2O2 afterward via the reaction. O2− + e− + 2H+ → H2O2. However, the thermocatalytic property can be exclusively observed in thermoelectric materials, which are capable of producing electron-hole separation under an applied temperature difference. In previous studies, thermoelectric materials have been deployed to realize thermoelectric nanogenerators to harvest thermal energy from the environment and convert it into electrical energy36. In a similar way, it is expected that the temperature difference-induced potential of thermoelectric materials can be utilized for realizing efficient thermocatalysts.The concept of the thermocatalytic generation of H2Te3, Sb2Te3, and PbTe, (purchased from Alfa Aeser) were used for the thermocatalytic reactions  cannot produce H2O2 under the same conditions. The obtained results vividly verify the potential of the thermoelectric materials for using as thermocatalysts. Furthermore, the amount of H2O2 generated in the thermocatalytic reaction is strongly correlated with the Seebeck coefficient37 and the dimension of the thermoelectric materials. The Seebeck coefficient of both Sb2Te3 and PbTe is much smaller than Bi2Te3 in the low temperature range32, resulting in the highest amount of H2O2 production in the case of Bi2Te3. As any catalytic reaction is accelerated with a large surface area, the small size of Bi2Te3 is also responsible for demonstrating superior thermocatalytic activity as compared to Sb2Te3 and PbTe  can generate up to 30 μM H2O2 with a temperature difference of 30 K. It is noteworthy that regardless of whether the temperature difference is positive or negative, H2O2 can still be generated.In an attempt to boost the thermocatalytic efficiency, nanometer-sized BiTe3 Fig. . The obtnce Fig. . Bi2Te3 2Te3 NPs are also estimated  of a hot plate. When the temperature of the hot end of the device is increased from 40 to 100 °C, the generated thermoelectric voltage is also enhanced from 0.72 mV to 19.83 mV  are plotted as a function of actual temperature difference (ΔT) and the slope obtained from the linear fitting of ΔV vs. ΔT curve denotes the Seebeck coefficient (S)  is lower than that generated under a +10 K temperature difference (18 μM). Obtained results strongly signify that the generated thermoelectric voltage of a thermocatalyst plays a crucial role in controlling surface electrochemical reaction and consequent catalytic activity.Since the Seebeck coefficient of a thermoelectric material plays the pivotal role in controlling the thermocatalytic activity, the thermoelectric voltage and corresponding Seebeck coefficient of Bi mV Fig. . The act(S) Fig. . The syn2O2 generation efficiency is significantly higher in the case of cyclic heating condition than the continuous heating condition  exhibited very little antibacterial activity under the same experimental conditions as Bi2Te3 NPs  between the KPFM tip and sample increases compared to thermal equilibrium conditions. A higher contact potential difference also indicates a reduction in the work function of Bi2Te3 under the applied temperature38. The observed output voltage is a direct consequence of temperature difference-induced electron-hole separation in Bi2Te3. Moreover, the generation of H2O2 by Bi2Te3 was tested under different environmental conditions, including O2, N2, and air. It was found that the N2-filled environment led to the generation of the lowest amount of H2O2, indicating that superoxide radical derivation from dissolved O2 was the key factor in H2O2 generation  positions are calculated from the equation ECB = EVB − Eg . Considering the bandgap of Bi2Te3 as 0.2 eV40, the CBM position is calculated to be −0.61 eV. The obtained conduction band potential is more negative than the redox potential of O2/·O2− (−0.33 eV vs. NHE)42. The more negative conduction band potential readily implies that formation ·O2− radical and consequent H2O2 generation is thermodynamically possible. Furthermore, the efficiency of H2O2 generation by the Bi2Te3 NPs was compared to that of bulk Bi2Te3  incorporated with a thermal stage to heat the samples Fig. . While tion Fig. . It is aTe3 Fig. , reveali2Te3 NPs was further employed to design an antibacterial filter with potential applications in our daily life. The antibacterial filter was fabricated by coating the Bi2Te3 NPs on a CFF, as illustrated in Fig. 2Te3 NPs over CFF is clearly visible from the FESEM images shown in Fig. 2Te3 NPs retain their hexagonal shape even after dip-coating on the CFF. As expected, the developed antibacterial filter is capable of producing H2O2 by a thermocatalytic effect when it is exposed to a temperature difference  is also less in this condition as compared to cooling fan experiment. Moreover, it was also noticed that without the application of cold air or hot air, no antibacterial activity was observed, which proves the necessity of the thermocatalyst for effective antibacterial performance in the presence of a temperature difference.The temperature difference needed for HCFF Fig. . The com2Te3@CFF was fabricated for utilization as a domestic antibacterial filter. An air conditioner (AC) is a commonly used machine to control the temperature and humidity in indoor surroundings. Herein, we used an air conditioner as a platform to demonstrate the concept of indoor air purification technology. The antibacterial filter was installed in the air conditioner in such a way that it could be easily removed or changed. The temperature inside the air conditioner was lower than the air in the surroundings, creating a temperature difference to trigger the thermocatalytic reaction. Since the air conditioner was set at 17 °C, it can be concluded that the temperature difference across the Bi2Te3@CFF was similar to that in the case of cooling fan experiment. This fact is also clear from the disinfection results which reveal that thermocatalytic reaction at air conditioner also leads to ~ 60% bacterial degradation as in the case of cooling fan experiment. A comparison of the SEM image shown in Fig. 2Te3@CFF does not undergo any degradation even after 30 days of operation. XRD and Raman spectra of the Bi2Te3@CFF  after three thermal cycles. For the effective utilization of the developed catalysts in daily life applications, Bi2Te3 NPs were coated on a CFF and used as an antibacterial filter in a domestic air conditioner. As long as a temperature difference exists, the thermocatalyst can generate ROS to kill the bacteria. As a whole, the concepts presented here highly promote the merits of thermocatalysts for round-the-clock ROS generation that can open a new direction towards sustainable environmental remediation applications.In summary, Big for 10 min. The supernatant was discarded, and the process was repeated 3 times. Finally, the filtered Bi2Te3 NPs were redispersed in 30 mL of isopropyl alcohol and were used for further experiments.First, a stock solution was prepared by dissolving 0.8 g sodium hydroxide in 10 mL ethylene glycol at 45 °C in a water bath. Then, 0.1 g bismuth nitrate pentahydrate, 0.067 g sodium telluride, and 0.235 g polyvinylpyrrolidone (PVP) were loaded into a 25 mL three-neck flask, to which 10 mL stock solution was added. The mixture was stirred for 10 min at room temperature. After that, the three-neck flask was placed in the water bath at 45 °C for 20 min. Until the precursors were dissolved in the solution, a three-neck flask was kept in the oil bath and stirred for 3 h at 190 °C. After the reaction, 30 mL of isopropyl alcohol and 10 ml of acetone were added to the solution, and the mixture was centrifuged at 6700 × 2Te3 NP (1 mM) solution. Finally, the as-prepared carbon fiber was dried in a hot air oven to completely remove the water.To clean the surface of the carbon fiber fabric, it was soaked in acetone, isopropanol, and DI water for 5 min, respectively. Then, the carbon fiber fabric was cut into a size of 1 × 1 cm and dipped in 100 μL of Bi2Te3 NPs were coated on a glass slide and placed on a hot plate to remove water. The morphology of the Bi2Te3 NPs was analyzed by using scanning probe microscopy . The morphology of the Bi2Te3@CFFs was analyzed via field emission scanning electron microscopy . For FESEM analysis, the Bi2Te3 NPs were drop-coated on a Si wafer and placed in a 60 °C incubator overnight. Cs-corrected STEM (JEOL ARM200F) and energy dispersive spectrometry  were used to analyze the lattice and elemental distribution of the Bi2Te3 NPs, respectively. Amplitude modulated Kelvin probe force microscopy (AM-KPFM) equipped with a thermal stage was employed to monitor the surface potential distribution of the Bi2Te3 NPs. Raman spectra were recorded by a UniRam Raman spectrometer (ProTrus. Tech. Co. Ltd.) equipped with a 532 nm laser. Valence band XPS (VB-XPS) spectra were collected by X-ray photoelectron spectrometer  having monochromatic Al Kα X-ray source.X-ray diffraction  was employed to investigate the structural properties of the prepared nanomaterials. For XRD analysis, the Bi2 was used for the thermoelectric voltage measurement and a hot plate was used to create the temperature difference. For measuring the thermometric voltage below room temperature, a PID controlled cooling stage was used. The temperature difference between the surface of the hot-plate/cooling stage and the top surface of device induces temperature difference across the device and the consequent thermoelectric voltage is generated. The generated thermoelectric voltages were recorded with a low noise voltage preamplifier (SR-560). To determine the actual temperature difference created across the device, the temperature at the surface of the hot-plate (T1) and top of the device (T2) were monitored with the help of IR camera.A device size of 1cmE. coli K12 cells were grown in lysogeny broth (LB) medium. The original E. coli K12 cells were added to LB medium for 16 h at 37 °C in an incubator. After 16 h, the E. coli K12 cells were diluted to an optical density of 0.06 at 670 nm (OD670 = 0.06). Then, the bacterial cell suspension was diluted 10 times in 0.85% sodium chloride, which was equal to 2 × 107 CFU per 1 mL for the antibacterial investigation.2Te3 and Bi2Te3 NPs. The masses of the bulk Bi2Te3 and Bi2Te3 NPs were 0.05 g and 0.005 g, respectively. These materials were added to 1 mL bacterial solution (2 × 106 CFU per 1 mL) for the thermocatalysis experiments.Thermocatalysis experiments were conducted in a water bath where the thermocatalysts in the contaminant solutions were subjected to 3 thermal cycles denoted as C1, C2, and C3. In each cycle, the materials at first were allowed to react at specific temperature (15/35/45 °C) for 5 min and then were returned to room temperature (RT) for 5 min. Two separate groups of experiments were carried out, one without a thermal cycle (under RT) and the other with thermal cycles. The materials were bulk Bi2Te3 NPs were mixed with XTT (50 μM) and then, the solution was subjected to different temperature difference at water bath. After the reaction Bi2Te3 was separated by centrifugation and the absorbance spectra of supernatants were monitored at 470 nm.The generation of superoxide radicals during the thermocatalysis reaction was estimated quantitatively by using XTT −2H-tetrazolium-5-carboxanilide) assay. Typically, aqueous dispersion of bulk and Bi2O2 detection. In general, Amplex Red reacts with H2O2 to produce the red-fluorescent oxidation product resorufin. First, two different stock solutions were prepared. One was 0.4 mg Amplex Red powder dissolved in 3.1 mL dimethyl sulfoxide (DMSO), and the other was 0.5 mg of HRP dissolved in phosphate-buffered saline . The materials  were first added to a 1 mL sodium chloride (0.85% NaCl) solution, and the solution was then kept in a water bath for 15 min where it was subjected to different temperatures . After the temperature treatment, the solution was filtered by a 0.2 µm PVDF membrane filter, and 270 µL of filtrate solution was added to a mixture of 30 µL Amplex Red solution and 3 µL HRP solution. A photoluminescence spectrophotometer (HITACHI F-7000) was used to detect the generated fluorescent product. The samples were excited at 530 nm, and emission spectra were scanned from 560~750 nm.Amplex Red reagent with HRP enzyme was used for H2Te3@CFF as an antibacterial filter, the disinfection tests were conducted using a hairdryer and a cooling fan. At first 1 mL of bacterial solution (2 × 106 CFU/mL) was added to 1 × 1 cm Bi2Te3@CFF and further treated for a total time of 20 min under the temperature difference created by hairdryer and cooling fan. Control experiments were also performed under the same conditions without the temperature difference. Both the treated and untreated Bi2Te3@CFF were immersed in 1 mL of 0.85% sodium chloride solution. Aliquots of 100 μL of bacterial solution were collected from each group and plated on an aseptic plate. The bacterial colonies were counted from the plates after 24 h of incubation at 37 °C. The survival rates were determined by using the formula C/C0 × 100% where C0 is the concentration of the bacteria solution before thermal treatment and C is the remaining concentration of the bacteria after the thermal treatment.To demonstrate the performance of Bi2Te3@CFF with dimensions of 8 × 15 cm was mounted on an indoor part of a split air conditioner. The temperature of the air conditioner was set to 17 °C in order ensure similar range of temperature difference as in case of cooling fan experiment. In this case, the same bacterial concentration (2 × 106 CFU/mL) was used to react the Bi2Te3@CFF as in the case of cooling fan experiment. The treatment was the same as the air for the disinfection test. The treatment was repeated for 30 days.This test was conducted by using an air conditioner. BiFurther information on research design is available in the Supplementary InformationPeer Review FileReporting Summary


Using first‐principles defect calculations, here, a systematic computational screening of potential efficient n‐type lanthanide dopants is conducted for Mg3Sb2. In addition to La, Ce, Pr, and Tm, it is found that high electron concentration (≳1020 cm−3 at the growth temperature of 900 K) can be achieved by doping on the Mg sites with Nd, Gd, Ho, and Lu, which are generally more efficient than other lanthanide dopants and the anion‐site dopant Te. Experimentally, Nd and Tm are confirmed as effective n‐type dopants for Mg3Sb2 since doping with Nd and Tm shows higher electron concentration and thermoelectric figure of merit zT than doping with Te. Through codoping with Nd (Tm) and Te, simultaneous power factor improvement and thermal conductivity reduction are achieved. As a result, high zT values of ≈1.65 and ≈1.75 at 775 K are obtained in n‐type Mg3.5Nd0.04Sb1.97Te0.03 and Mg3.5Tm0.03Sb1.97Te0.03, respectively, which are among the highest values for n‐type Mg3Sb2 without alloying with Mg3Bi2. This work sheds light on exploring promising n‐type dopants for the design of Mg3Sb2 thermoelectrics.The recent discovery of n‐type Mg 3Sb2 thermoelectrics. Experimentally, Nd and Tm are confirmed as efficient n‐type dopants and high thermoelectric figure of merit zT values above 1.6 at 775 K are obtained in n‐type ‐codoped and ‐codoped Mg3Sb2 without Mg3Bi2 alloying.A systematic computational screening reveals that Nd, Gd, Ho, and Lu are strong candidates as efficient n‐type dopants for Mg The performance of TE materials is typically determined by the dimensionless figure of merit zT = α2σT/κ, where α is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the total thermal conductivity.Thermoelectric (TE) materials show great promise in waste heat recovery and solid‐state refrigeration applications since they can directly convert heat into electricity or vice versa purely by solid‐state means.1, 23Sb2‐based compound is one such material that shows exceptionally high TE performance with low‐cost and earth‐abundant chemical compositions. The excellent TE performance with zT ≈ 1.6 at 725 K was first reported in n‐type Mg3Sb1.5Bi0.5 with Te as an effective electron dopant on the anion sites, where the good TE performance is dominantly attributed to the multiple conducting electron pockets and light conductivity effective mass. Later, many experimental efforts have been made to improve the low‐temperature performance of n‐type Mg3+δSb2−xBix. Theoretically, accurate electronic structure, chemical bonding, and phonon transport properties have been revealed for understanding the outstanding TE properties of n‐type Mg3Sb2‐based TE materials. Despite many significant studies on n‐type Te‐doped Mg3Sb2‐based compounds, the optimization of transport properties requires efficient n‐type dopants for the broad tunability of carrier density. For the anion site doping, Se and S also have been reported as effective n‐type dopants for Mg3Sb2, whereas they are less efficient than Te due to the higher substitution defect formation energies. Recent defect calculations predicted that the group‐3 elements (Sc and Y) as well as several lanthanides including La, Pr, Ce, and Tm are efficient n‐type cation‐site dopants for Mg3Sb2 and doping with these elements on the Mg sites is able to achieve higher electron concentration than doping with chalcogens on the anion sites. The subsequent experiments confirmed Sc, Y, La, Pr, and Ce as efficient n‐type dopants on the Mg sites for Mg3+δSb2−xBix. Despite these significant theoretical and experimental efforts on exploring efficient n‐type dopants, the n‐type doping behavior of many other lanthanide dopants in Mg3Sb2 remains largely unexplored so far.Low‐cost high‐performance materials are required for the widespread application of TE technology. The recently discovered n‐type Mgive mass.4, 53Sb2 TEs. It is shown that, in addition to La, Ce, Pr, and Tm, several other lanthanides including Nd, Gd, Ho, and Lu are efficient n‐type dopants on the cation sites for Mg3Sb2. The predicted free electron concentrations for doping with these lanthanide elements in Mg3Sb2 generally approach or exceed 1020 cm−3 at the growth temperature of 900 K under the Mg‐rich condition, which are higher than those of doping with the chalcogens. For the experimental validation, we have successfully synthesized n‐type Nd‐doped, Tm‐doped, ‐codoped, and ‐codoped Mg3Sb2 without alloying with Mg3Bi2. In agreement with the theoretical calculation, the experimental electron concentrations of Nd‐doped and Tm‐doped Mg3Sb2 samples are indeed higher than those of the Te‐doped ones. Among n‐type Nd‐doped and Tm‐doped samples, optimal zT values of 0.16–1.30 and 0.27–1.38 at 300–775 K are obtained in Mg3.5Nd0.04Sb2 and Mg3.5Tm0.03Sb2, respectively. By codoping with the appropriate amount of Nd (Tm) and Te, simultaneous power factor enhancement and thermal conductivity reduction can be achieved. As a result, high zT values of ≈1.65 and ≈1.75 are obtained at 775 K, respectively, in Mg3.5Nd0.04Sb1.97Te0.03 and Mg3.5Tm0.03Sb1.97Te0.03, outperforming any reported n‐type Mg3Sb2 samples without alloying with Mg3Bi2.In this work, we perform first‐principles defect calculations to explore potential n‐type dopants from all lanthanides for Mgh Mg3Bi2.353Sb2. Point defects in Mg3Sb2 can exist as either electron‐producing donors with positive charges or electron‐capturing acceptors with negative charges, which are indicated by defect plots with positive or negative slopes , respectively. Because of the high vapor pressure and easy oxidation of Mg, Mg3Sb2‐based compounds prepared by traditional melt methods are usually Mg‐deficient. Under the Mg‐poor condition, the negatively charged Mg vacancies, acting as the electron‐capturing acceptors, are the dominant native defects showing low defect formation energies within the bulk gap , which pin the Fermi level close to the valence band maximum (VBM) and thereby make pure Mg3Sb2 samples persistently p‐type.The intrinsic point defects under different growth conditions play a crucial role in understanding the doping behavior of Mgy p‐type.3618 cm−3) since the compensating acceptor defects Mg vacancies can spontaneously form when the Fermi level is close to the conduction band minimum (CBM), which pin the Fermi level well below the CBM. Thus, the efficient n‐type doping in Mg3Sb2 requires Mg‐rich growth condition as well as the extrinsic donor defects with sufficiently low formation energies to avoid the electron compensation by the negatively charged Mg vacancies.In contrast, under the Mg‐rich situation, the defect formation energies of Mg vacancies are notably increased and the Mg interstitials (donor defects) become the dominant native defects , which means that the Fermi level can move above the middle of the bandgap (mid‐gap) and n‐type conductivity can be achieved. However, the free electron concentration contributed by the positively charged Mg interstitials is very low (in order of ≈1018 cm−3)23 sin3Sb2, we investigated the effect of n‐type doping with all lanthanide elements. The formation energies of all the extrinsic defects LnMg  were calculated using density functional theory (DFT). The results as well as their comparison with the native defects and other extrinsic defects  under Mg‐rich conditions are shown in Figure 3Sb2, where the Mg1 atom occupies the octahedral site between the [Mg2Sb2]2− slabs while the Mg2 atom resides in the tetrahedral site within the [Mg2Sb2]2− slabs. The formation energies of the extrinsic defects LnMg1 are lower than those of LnMg2, which indicates that the lanthanides prefer to substitute Mg1 over Mg2. This might be attributed to the Mg1 atom showing relatively weaker adjacent bonds as well as the larger void space induced by the octahedral site. All extrinsic defects LnMg1 generally show no electron compensation by the native defects within the bulk gap since they show much lower formation energies than those of the Mg vacancies and the extrinsic defect TeSb. In defect plots, the slope of the energy line corresponds to the charge state of the defect and the Fermi energy at which the slope changes represents the transition energy level. The substitution defects LnMg1 generally have +1, 0, and −1 charge states. For n‐type doping, it is favorable to form the donor defect with the charge state +1, while it is detrimental to form the defect with the charge state −1 (or 0) since it can compensate (or limit) the electron concentration.To explore potential efficient n‐type dopants for Mg2− slabs.37 TheMg1 and YbMg1 show very low (or deep) (+1/0) transition levels even close to or below the VBM, which pin the Fermi level only slightly above the mid‐gap . In contrast, Y, La, Ce, and Tm are very efficient as n‐type dopants for Mg3Sb2 because the extrinsic defects LnMg1  show high donor transition levels (+1/0) and (+1/−1) well above the CBM  below the CBM, very high transition level (0/−1) located at ≈0.5 eV above the CBM as well as the low formation energy allows the Fermi energy to shift well above the CBM  close to the CBM , (0/−1), and (+1/−1) very close to or well above the CBM so that the Fermi level is able to shift close to or above the CBM. It is clear that Eu and Yb are very unfavorable as n‐type dopants since Eu3Sb2 under the Mg‐rich condition. Consistent with the results of defect formation energies , Eu and Yb are largely ineffective as n‐type dopants showing poor free electron concentrations. It is evident that Sm, Dy, Er, Pm, and Tb are a bit less efficient and show lower free electron concentrations than Te for n‐type doping since they show a bit deeper donor levels even though they have lower formation energies. Besides La, Ce, Pr, and Tm that have been confirmed by previous calculations, Nd, Gd, Lu, and Ho, as expected, are more effective as n‐type dopants than Te and doping with these lanthanide elements results in high maximum achievable electron concentrations ≳1020 cm−3 at 900 K. Among these efficient n‐type dopants, Nd and Tm show the lowest formation energies of the donor defects NdMg1 (+1) and TmMg1 (+1) throughout the bulk gap. The predicted maximum achievable free electron concentrations at the growth temperature of 900 K for the potential n‐type dopants Nd, Gd, Lu, and Ho are respectively 9.90 × 1019, 1.30 × 1020, 1.27 × 1020, and 1.17 × 1020 cm−3, which are slightly lower than those (>2 × 1020 cm−3) of the n‐type dopants La, Ce, and Pr. Recent experiments have already confirmed La, Ce, and Pr as effective n‐type dopants for Mg3Sb2−xBix, while other predicted efficient n‐type dopants such as Nd, Gd, Lu, Ho, and Tm still require the experimental confirmation.Figure ulations,25 Nd,3Sb2. The Nd‐doped, Tm‐doped, ‐codoped, and ‐codoped Mg3Sb2 bulk samples were prepared by the previously proposed spark plasma sintering (SPS) method followed by annealing in the Mg‐rich condition. According to our previous work, the specific amount of excess Mg (Mg3.5) is used to compensate for the evaporation loss of Mg so that the as‐SPS‐pressed pellets show no Mg deficiency. All as‐synthesized bulk samples are dense with relative densities larger than 95% . Powder X‐ray diffraction (PXRD) patterns confirm that all samples are virtually phase pure with a very small amount of MgO ‐codoped samples show a small amount of secondary phase, which can be indexed to the NdSb cubic phase (space group: Fm3¯m). Similarly, a small amount of secondary phase TmSb is found in several Mg3.5TmySb2−xTex samples . For Nd‐doped samples Mg3.5NdySb2, the lattice parameters show a gradually increasing trend as the fraction y increases from 0.01 to 0.03 (see Table S2 in the Supporting Information). This can be understood by the larger ionic radius of Nd3+ than that of Mg2+. On the other hand, the lattice parameters decrease when the fraction y increases from 0.03 to 0.04, which is likely induced by the formation of the secondary phase NdSb. A similar trend in the lattice parameters is found in Tm‐doped samples , which can be understood in the same manner.To verify the theoretical prediction, here, we experimentally examine the potential of Nd and Tm as n‐type dopants for MgS) method38 fol3.5Nd0.03Sb1.97Te0.03 sample shows that the sample is virtually homogeneous with nearly uniform distributions of the constituent elements . The chemical composition measured by scanning electron microscopy (SEM)‐EDS reveals that the actual Mg content of the Mg3.5Nd0.03Sb1.97Te0.03 sample increases from Mg3.05 to Mg3.3 after annealing in the Mg‐rich condition in an Argon atmosphere . The evolution of the PXRD patterns confirms that the amount of MgO shows nearly no change after annealing , which indicates that the 10% excess Mg after annealing should not exist dominantly as the MgO secondary phase at the grain boundaries. The increase in cell parameters after annealing in the Mg‐rich condition could be an indication of the excess Mg partially entering the interstitial sites of the structure . However, only a small proportion of the excess Mg might exist as the Mg interstitials within the structure due to the small solubility. Therefore, the excess Mg should be dominantly contributed by the elemental Mg that diffuses into the grain boundaries of the sample during the Mg‐rich annealing, which is confirmed by the elemental Mg peaks in the PXRD pattern of the Mg3.5Nd0.03Sb1.97Te0.03 sample right after the annealing .The energy dispersive X‐ray spectroscopy (EDS) elemental mapping of the Mglubility.34 The3Sb2, several Y‐doped samples Mg3.5YySb2 (y = 0.01–0.04) were also prepared using the same method as for Nd‐doped samples and the corresponding experimental results are shown in Figures S10–S13 in the Supporting Information. With the experimental data of the Nd‐, Tm‐, and Y‐doped samples, we can compare the results with those of the reported Te‐ and Sc‐doped samples prepared using a similar synthesis method. It is found that n‐type Nd‐doped and Tm‐doped Mg3Sb2 samples show slightly lower electron concentrations than those of the Y‐doped samples but higher electron concentrations than those of Sc‐doped and Te‐doped samples  to 3.17 × 1019 cm−3 (y = 0.03), while the electron concentrations vary from 7.32 × 1018 to 2.36 × 1019 cm−3 in Mg3.5TmySb2 samples. Nearly all experimental electron concentration data points of Nd‐ and Tm‐doped samples fall exactly within the pink region shown in Figure 3Bi2.For the better comparison of the doping effect on the carrier concentration and mobility in n‐type Mgs method.30 It Figure   to minimize the grain boundary scattering, the electron mobility of Nd‐doped Mg3Sb2 samples still shows a temperature dependence of T1.5 at low temperatures. This is very different from the Y‐doped, Sc‐doped, or Te‐doped samples synthesized using a similar method, which show dominant acoustic phonon scattering at low temperatures . The increasing temperature dependence of the mobility at low temperatures results in poor room‐temperature electron mobility (≈20.8–32.3 cm2 V−1 s−1) of Nd‐doped samples in comparison with those of Te‐doped samples (≈51.0–73.8 cm2 V−1 s−1). By codoping with Nd and Te, acoustic phonon scattering becomes dominant throughout the entire temperature range as indicated by the temperature dependence of the mobility following T−p (1  ≤  p  ≤  1.5). As a result, the ‐codoped Mg3Sb2 samples show enhanced room‐temperature electron mobility values of ≈38.4–54.6 cm2 V−1 s−1, which, however, are still lower than those of many reported Te‐doped Mg3Sb2 samples. By comparing the calculated density of states (DOS) of the defect structure Mg53Nd1Sb36 (Mg2.944Nd0.056Sb2) with the perfect structure Mg54Sb36 (Mg3Sb2), it is found that the f states of the impurity atom Nd exist largely below the CBM within the bulk gap . Moreover, the Nd f states show hybridization with the electronic states (Mg 3s states) of the near‐edge conduction bands resulting in the enhanced DOS of the CBM. The relatively localized feature of the f states below the CBM as well as the enhanced DOS (effective mass) of the CBM induced by the hybridization of the f states with the near‐edge electronic states is likely the origin of low electron mobility in Nd‐doped Mg3Sb2. The appearance of the f states below the CBM as well as their hybridization with the conduction band in Nd‐doped samples can be attributed to the relatively small energy separation between the atomic orbital levels of the Nd f states and Mg 3s states. Similarly, the above mechanism may be used to explain the low electron mobilities in previously reported La‐, Pr‐, and Ce‐doped Mg3Sb2−xBix samples because of the small energy separation between the atomic orbital energies of the f states of the dopants  and 3s states of Mg (see Table S5 in the Supporting Information).The low carrier mobilities in Nd‐doped samples in comparison with Y‐, Sc‐, and Te‐doped samples  of Tm‐doped samples are comparable to those of many reported Te‐doped Mg3Sb2 samples. This is because that the f states of the Tm dopant mainly contributed to the electronic states of the valence bands (rather than within the bulk gap and conduction bands) in Tm‐doped Mg3Sb2 due to the much lower atomic orbital energies of the Tm f states .In comparison with Nd‐doped samples, Tm‐doped Mg samples.30 ThiFigures 3Sb2 samples. The Seebeck coefficient and electrical resistivity of all samples show typical degenerate semiconductor behaviors with increasing temperature dependence at elevated temperatures. The resistivity of several Nd‐doped and Tm‐doped samples shows a clear decreasing trend with increasing temperature at low temperatures, which is induced by the increasing temperature dependence of the mobility. Unlike the reported Te‐doped samples showing clear hysteresis, the resistivity data of Mg3.5NdySb2 and Mg3.5TmySb2 samples show virtually no hysteresis upon thermal cycling , indicating the enhanced stability and good repeatability. With increasing y from 0.01 to 0.03 in Mg3.5NdySb2 and Mg3.5TmySb2, the resistivity and absolute values of the Seebeck coefficient decreases as the electron concentration increases ‐codoped samples exhibits a significant enhancement over the Nd‐doped samples  at 775 K in Mg3.5Nd0.04Sb1.97Te0.03 (Mg3.5Tm0.03Sb1.97Te0.03).s Figure . Because3 Figure . The tot Figures  and 5d. Figure 3.5NdySb2 samples, an optimal zT of 1.30 at 775 K is obtained in the sample with y = 0.04, which is superior to the reported Te‐doped Mg3Sb2 samples. In comparison with Nd‐doped samples, a higher zT of 0.27–1.38 at 300–775 K is achieved in n‐type Mg3.5Tm0.03Sb2 ‐codoped and ‐codoped samples generally show strongly enhanced zT values in comparison with those of singly doped samples. Peak zT values of 1.65 and 1.75 at 775 K are achieved, respectively, in Mg3.5Nd0.04Sb1.97Te0.03 and Mg3.5Tm0.03Sb1.97Te0.03, which are higher than those of previously reported n‐type Mg3Sb2 samples without alloying with Mg3Bi2 ‐codoping and ‐codoping in Mg3Sb2, we achieve optimal zT values of 1.65 and 1.75 at 775 K, respectively, superior to any reported n‐type Mg3Sb2 samples without alloying with Mg3Bi2. We can expect further improvements in TE performance through optimizing carrier concentration as well as reducing thermal conductivity via alloying with Mg3Bi2. This work provides insight into the exploration of potential effective n‐type dopants for the development of Mg3Sb2 TE materials using an integrated computational and experimental approach.In summary, we have conducted a complete computational screening of promising n‐type dopants from all lanthanide elements for Mg in Vienna Ab initio Simulation Package (VASP). The defect calculations were conducted in a 3 × 3 × 2 supercell with 90 atoms using the hybrid functional HSE06. A mixing parameter of 25% was used for the calculations with the HSE06 functional. The energy and Hellmann–Feynman force convergence criteria were 10−4 eV and 0.01 eV Å−1, respectively. An energy cutoff of 400 eV was used for the plane‐wave expansions. A Γ‐centered 2 × 2 × 2 k mesh was applied for the crystal structure optimization and the total energy calculation. For the optimization of defect structures, the lattice parameters were fixed at the optimized values of the perfect supercell and all atomic positions in the defect supercell were allowed to be fully relaxed into their equilibrium positions. The symmetry was switched off during the structural relaxation. Spin polarization was included in all defect calculations. Due to the slow convergence of structural relaxations, the extrinsic defects SmMg, DyMg, TbMg, and ErMg were calculated using the Perdew‐Burke‐Ernzerhof (PBE) functional and a Γ‐centered 4 × 4 × 4 k mesh with the band edge shifting correction  so that the bandgap is corrected to be equal to the result (0.51 eV) with the HSE06 functional. The density of states of the relaxed defect supercell Mg53Nd1Sb36 (Mg53Tm1Sb36) with one Nd (Tm) atom substituting on the Mg1 site and the bulk supercell Mg54Sb36 shown in Figures S15b and S16 in the Supporting Information were calculated with the TB‐mBJ potential and a Γ‐centered 6 × 6 × 6 k mesh.All calculations in this work were conducted using the projector augmented wave method41 in qd, the formation energy can be calculated usingFor a point defect d with a charge state Etotd is the total energy of the supercell with the point defect d, and Etotbulk is the total energy of the perfect supercell. in represents the number of atoms of type i that is added to (in > 0) or removed from (in < 0) the supercell when the point defect is formed, and iµ represents the atomic chemical potentials of these species. εF is the Fermi level, which is referenced to the valence‐band maximum EV of the perfect bulk structure. Ecorris the correction term induced by the finite size of charged supercells. Here, the image charge and potential alignment corrections for charged defects were taken into account.Here, 3Sb2, the chemical potentials of Mg and Sb must fulfill the thermodynamic stability condition: 3ΔμMg + 2ΔμSb = 5ΔHf(Mg3Sb2). To avoid the precipitations of the constituent elements, the chemical potentials should satisfy the condition: Δμα=μα−μα0≤0, in which μα0 denotes the total energy per atom in the pure bulk crystal of the element α. Under the Mg‐rich condition, the chemical potentials of Q  are limited by the formation energies of the competing phases QSb (ΔμQ + ΔμSb ≤ 2ΔHf(QSb)), the chemical potentials of M (M = Eu and Yb) are constrained by M5Sb3 (5ΔμM + 3ΔμSb ≤ 8ΔHf(M5Sb3)), and the chemical potential of Te is limited by MgTe (ΔμMg + ΔμTe ≤ 2ΔHf(MgTe)). For the calculations of defect formation energies of QSb  under the Sb‐rich condition (ΔμSb =  0), the chemical potentials of Q are also limited by the formation energies of the competing phases QSb. For PmSb , the structure is assumed to be the same as NdSb. Formation energies of the bulk phase and competing phases are in units of eV per atom.In MgUnder the thermodynamic equilibrium, the Fermi energy at different growth temperatures can be obtained by self‐consistently solving the charge neutrality equation46(2)c0d is the concentration of defect sites for the point defect d, and kB is the Boltzmann constant. In the dilute limit, the electronic structure is assumed to be the same as that of the perfect neutral bulk cell. The numbers of holes and electrons are calculated, respectively, byTaking the approximation of the free energy by the defect formation energy, the defect concentration can be calculated using47(3)EC is the energy of the conduction band minimum. f is the Fermi–Dirac distribution. For N(ε), the accurate density of states of the Mg3Sb2 unit cell calculated by the HSE06 functional with the tetrahedron method and a dense Γ‐centered 16 × 16 × 10 k mesh was used. For solving the equilibrium Fermi level of the lanthanide (Ln) doping in Mg3Sb2 with Equation , Mg3+δTmySb2−xTex , and Mg3+δYySb2 , and mixed in a mixer  without using ball pestles for 15 min. The excess Mg here was typically used for the purpose to compensate for the evaporation loss of Mg during the high‐temperature synthesis. The mixed powders were loaded into a 12.7 mm diameter graphite die protected with the graphite paper. The above processes were conducted inside an argon‐filled glove box. Afterward, the mixed powders loaded in the graphite die were immediately sintered and consolidated in dynamic vacuum under a uniaxial pressure of 60 MPa using an SPS‐515S instrument . The SPS process was conducted at 673 K with a 10 min dwell and then heating to 1073 K with another 10 min dwell. Following the SPS, the annealing of the pellets was conducted in the Mg‐rich environment similar to the procedure proposed by Wood et al. The as‐pressed pellets together with Mg turnings  were placed in a glassy carbon crucible with a lid and annealed in Ar flow at 888 K for 3 days. After annealing in the Mg‐rich condition, the pellets were taken out and slightly polished before property measurements.Stoichiometric amounts of high‐purity Mg powder , Sb powder , Nd powder , Tm powder , Te powder , and Y powder  were weighed according to the nominal compositions of Mgα1 source. The lattice parameters were determined by the Le Bail method using the JANA2006 program. The microstructure, elemental distribution, and chemical composition were characterized using a scanning electron microscope (FEI Nova NanoSEM 600) equipped with an energy dispersive spectrometer.The phase purity of the bulk samples was checked by the PXRD measured on a Rigaku Smartlab in the Bragg–Brentano (BB) geometry using a Cu Kρ and Hall coefficient (RH) were implemented using the van der Pauw method in dynamic vacuum (<10−4 mbar) under a magnetic field up to 1.25 T. Hall carrier concentration (nH) and mobility (μH) were evaluated respectively by 1/eRH and RH/ρ, where e is the elementary charge. The Hall measurements of the pellets were carried out with the heating and cooling processes for 3 thermal cycles (300–725 K), in which the final stabilized cycle is used for discussion in the main text. The temperature‐dependent Seebeck coefficients of the pellets were then measured with the slope method using chromel‐niobium thermocouples in dynamic vacuum (<10−4 mbar) on an in‐house system, whose geometry is similar to the one reported by Iwanaga et al. The thermal diffusivity (D) was measured using the laser flash method . The density (d) was estimated from the mass and volume of the pellets. Thermal conductivity was then determined using the formula κ  =  dDCP. In the main text, the thermal conductivity and zT were evaluated using the heat capacity (CP)  calculated with the polynomial equation proposed by Agne et al. For comparison, the thermal conductivity and zT estimated with the heat capacity (CP) from the LFA457 setup using a Pyroceram 9606 standard sample are shown in Figures S20 and S21 in the Supporting Information. For simplicity, here, the cooling curves of transport properties were adopted for discussion in the main text. The Seebeck coefficient, electrical resistivity, and thermal conductivity typically have the measurement uncertainties of 7%, 5%, and 7%, respectively. The uncertainty for zT is about 20%.Measurements of electrical resistivity ficient RH were imficient RH were imficient RH were imficient RH were imficient RH were imficient RH were imficient RH were imficient RH were imThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.