Specifically, liquid‐phase ultrasonication is applied to exfoliate a [Co4(bIm)16] zeolite‐imidazole framework (ZIF), named as ZIF‐9(III) phase, into nanoscale sheets. ZIF‐9(III) is selectively prepared through simple mechanical grinding of cobalt nitrate and benzimidazole in the presence of a small amount of ethanol. The resultant exfoliated nanosheets exhibit significantly higher OER activity in alkaline conditions than the corresponding bulk phases ZIF‐9 and ZIF‐9(III). The electrochemical and physicochemical characterization data support the assignment of the OER activity of the exfoliated nanosheet derived material to nitrogen coordinated cobalt oxyhydroxide N4CoOOH sites, following a mechanism known for Co‐porphyrin and related systems. Thus, exfoliated 2D nanosheets hold promise as potential alternatives to commercial noble metal electrocatalysts for the OER.2D layered materials, including metal‐di‐chalcogenides and transition metal layered double hydroxides, among others, are intensively studied because of new properties that emerge from their 2D confinement, which are attractive for advanced applications. Herein, 2D cobalt ion (Co The2, cubic system) and “ZIF‐9(II)” (Co9(bIm)18 triclinic system) were obtained by heating ZIF‐9‐I. The permanently nonporous third phase “ZIF‐9(III)” was produced by a slurry aging experiment after leaving ZIF‐9‐II in water at room temperature for one week. Most importantly, the dense coordination network structure of ZIF‐9(III) features a  square planar grid layer structure formed by fourfold linked corner‐shared Co(II) benzimidazole tetrahedra as Co4(bIm)16 . The 2D layers stack along the crystallographic c direction and are interconnected by weak van der Waals interactions  represent an important subgroup of chemically highly robust MOFs, especially in alkaline solution.We demonstrate herein that very simple and easy scalable mechanochemical synthesis by grinding of the reactants cobalt nitrate, benzimdazole and sodiumbicarbonate in the presence of ethanol ≈1 mL) for 2 min selectively yields bulk Co‐ZIF‐9(III) . As revealed by field emission scanning electron microscopy (FESEM), the as‐synthesized grinded product consists of multiple, closely packed bundles of crystalline plates of micrometric thickness  for 20 min to obtain a milky colloidal suspension comprising a mixture of fully exfoliated and partially exfoliated nanosheets . The obtained colloidal solution exhibited the Tyndall effect . Extending the sonication time in the presence of ethanol as dispersant solvent yields a higher degree of exfoliation. Powder XRD of the collected exfoliated material shows only one broad peak, which can be indexed to the (002) planes of ZIF‐9(III)  method; Figure S12, left, Supporting Information).The interlayer space of Co‐ZIF‐9(III) is occupied by the hydrophobic benzimidazole groups and the layers are held together only by weak van der Waals interactions Figure a. Thus, m KOH) along with its bulk phases. A suspension of the catalyst (5.0 mg mL−1) dispersed in a water/ethanol mixture containing 0.2 vol% Nafion was drop cast on a finely polished glassy carbon electrode to form a film with a catalyst loading of 210 µg cm−2. The material underwent irreversible electrochemical transformation upon potential application as depicted by the changes that take place during potential cycling between 0.9 and 1.6 V vs RHE  nanosheets with potential cycling. Specifically, under oxidizing conditions, the Co2+ sites are stepwise transformed to Co3+, which is most likely coordinated to a hydroperoxide moiety ([OOH]−). Such kind of species are the expected form of the catalytic active site prior to oxygen evolution. A noteworthy feature of the Co2+ ↔ Co3+ + e redox processes is their high reversibility, which is important for fast kinetics of reactions involving a redox catalytic mechanism  and thus a clear indication that the four coordination nitrogen atoms of the imidazole ligands strongly mediate in the Co2+ ↔ Co3+ + e redox processes. The OER activity of the exfoliated Co‐ZIF‐9(III) nanosheets in 1.0 m KOH is shown in Figure −1 and electrode rotation at 1600 rpm. The results are presented together with the OER data of bulk phases of ZIF‐9(I) and ZIF‐9(III). The comparison demonstrates superior OER activity of the 2D nanosheets in relation to the bulk materials. The 2D nanosheets required 1.61 V ) to drive a current density of 10 mA cm−2 whereas bulk Co‐ZIF‐9‐I and Co‐ZIF‐9(III) required 1.65 V (η = 0.42 V) and 1.65 V (η = 0.43 V), respectively, to drive the same current density. The Tafel slope ∂E∂(lni)=−2.303RTαF of the OER was 55, 57, and 56 mV dec−1, respectively, on the exfoliated Co‐ZIF‐9(III) 2D sheets, bulk phases of Co‐ZIF‐9(I) and Co‐ZIF‐9(III). The Tafel slopes are close to the theoretical value of −2.303RTαFor 59 mV, where the first electron transfer step is rate limiting and the coverage with adsorbed species is low. The similarity of the Tafel slopes indicates that the mechanism of the OER was similar on all the catalysts and further, that the active sites are most certainly the same. The exceptionally high OER activity of the 2D Co‐ZIF‐9(III) nanosheets compared to its bulk counterparts must therefore arise from its comparatively much higher active site density due to a higher degree of exposure of the edge sites in addition to the basal sites. The performance of the exfoliated 2D Co‐ZIF‐9(III) nanosheets, expressed by average overpotential at a current density of 10 mA cm−2, was further compared against that of selected cobalt based OER catalysts as well as IrO2 and RuO2  nanosheets are expected to be superior in catalytic performance as compared to the corresponding bulk phase materials due to a high active site density arising from enhanced accessibility of the active sites with a smaller diffusion barrier for substrate molecules. As a proof‐of‐concept, the electrocatalytic performance of the obtained 2D exfoliated Co‐ZIF‐9(III) nanosheets towards the oxygen evolution reaction (OER) was studied in alkaline conditions . The resistances to interfacial charge transfer across the electrocatalytic films derived from bulk Co‐ZIF‐9(I), bulk Co‐ZIF‐9(III), and exfoliated 2D Co‐ZIF‐9(III) nanosheets were determined from the diameter of the semicircles in the corresponding Nyquists plots . The resistances decreased in the order Co‐ZIF‐9(I) (40.7 Ω) > bulk Co‐ZIF‐9(III) (23.0 Ω) > exfoliated 2D Co‐ZIF‐9(III) nanosheets (≈0.0 Ω). This sequence indicates inherently higher electronic conductivity of the films derived from the exfoliated material as compared to the bulk materials, which partly accounts for the superior OER activity of the 2D Co‐ZIF‐9(III) nanosheet‐derived electrode coating.−1 (mole Co)−1 . This value is one order of magnitude higher than that for Co3O4 (0.04 s−1) at the same conditions. The TOF essentially depicts the inherent activity of the active sites for a given catalyst and the results indicate that the cobalt sites in the Co‐ZIF‐9(III) nanosheets are potently more active than the cobalt sites in Co3O4. This observation is attributed to the 2D confinement of the cobalt centers in the ZIF‐nanosheets and their synergistic interaction with nitrogen, as well as fast mass transport of reactants and products owing to the unique morphology of the catalyst.The average OER performance of the exfoliated 2D Co‐ZIF‐9(III) nanosheets based on three replicate measurements is superior to the performance reported for most cobalt‐based catalysts on a passive support.−2, then decreased gradually afterward. Nonetheless, despite the observed activity, the average current density after 10 h remained higher than the initial value. The initial increase of the current density is due to activation of the catalyst and concomitant increase in accessibility of the active sites. Physical detachment of the catalyst films was visible and it is certainly one of the major causes of the decline in activity following the initial activation.The long‐term performance of the exfoliated 2D Co‐ZIF‐9(III) nanosheets was investigated by a sequence of chronoamperometric measurements at 1.7 V versus RHE for 900 s followed by LSV activity measurements, repeating the protocol for a total duration of 10 h. Figure Figure−1. The band at ≈521.3 cm−1 is assigned to Co(OH)2 species and is due to ν(Co–O) (Ag) symmetric stretching mode, while that at ≈548.1 cm−1 is due to ν(Co–N) stretching mode.−1 and at 548.1 cm−1 diminish in intensity while the one at 523 cm−1 is accentuated. Meanwhile, the band at 778.5 cm−1, ascribed to deformation of the complex, also decreases in intensity with increase of the applied potential. The band initially centered at 642 cm−1 at OCP, becomes less sharp and its center moves to a slightly lower Raman shift. These modifications were irreversible. The original Raman bands were not regenerated upon reversal of the applied potential in similar steps. Thus, under the influence of the applied potential, the exfoliated 2D Co‐ZIF‐9(III) nanosheets underwent irreversible transformation due to formation of pendant hydroxide and oxyhydroxide groups at the uncoordinated Co sites of the nanosheets. In the following we denote these sites as N4CoX  in order to emphasize the particular molecular N‐donor coordination environment being similar to the Co‐ZIF‐9(III) base material, however in contrast to CoX species being present at inorganic Co oxide surfaces. A survey of the literature did not disclose any published data on the Raman spectral features of N4CoOOH type species under alkaline conditions as a reference for comparison with our spectroscopic studies. The Raman spectral features of CoOOH surface species at inorganic cobalt oxides, which is most closely related to the proposed molecular N4CoOOH species, was thus used as the reference for comparison and basis for discussion. Note, the notation “CoOOH” refers to oxo and hydroxo species being simultaneously present at the Co‐oxide surface. The most intense Raman band of CoOOH species is expected at about 503 cm−1 with additional less intense peaks at about 641, 572, and 705 cm−1, on the basis of Raman studies on a reference CoOOH material by Yang et al.2 species exhibits its most intense Raman peak at about 523 cm−1. Owing to evidence of the prevalence of the Co–N coordination moieties, we therefore attribute the broad band stretching from about 500 to 570 cm−1, whose intensity increased with applied potential, to be a convolution of N4CoO (Co4+), N4CoOH (Co3+), and probably also N4CoOOH (Co3+). The proposed formation of such kind of coordinated “N4CoOOH” species in the exfoliated Co‐ZIF‐9(III) nanosheets as equivalent to the inorganic “CoOOH” species under OER conditions is consistent with the expected preoxidation steps that proceed the evolution of oxygen at inorganic metal/metaloxide active sites,− → MOH + e−; ii) MOH + OH− → MO + H2O + e−; iii) MO + OH− → MOOH; iv) MOOH + OH− → MO2 + H2O + e−, and v) MO2 → M + O2 + e− . We transfer this mechanism to our case. Thus, equations (i)–(iii) refer to the formation of oxo, hydroxo, and possibly hydroperoxo groups at the Co centers exposed on the exfoliated 2D ZIF‐9(III) sheets, where in (i) and (ii) the cobalt site is stepwise oxidized from the Co2+ to the Co4+ state, in (iii), the proposed N4CoOOH hydroperoxo species (Co3+) is formed and in steps (iv) and (v) O2 isoxidatively released and the N4Co2+ active site is finally regenerated to repeat the cycle  nanosheets Co is present as Co2+, reaction (iii) is identified as the rate‐determining step, yielding excellent agreement between the electrochemical data and in situ Raman spectroscopy observation. Importantly, the N4Co coordination between the cobalt ions and the benzimidazole ligand remains intact during the OER as confirmed through operando Raman imaging of the Co–N band  exhibits no peaks corresponding to ZIF‐9(III) because of randomly organized nanosheet and confirms no presence of oxide based impurities. The post‐mortem Raman spectrum shows an absorption band positioned at 548 cm−1 assigned to Co–N. Figure We probed the structure of the material derived from exfoliated 2D Co‐ZIF‐9(III) nanosheets under OER conditions by coupled in situ Raman spectroscopy, to get insight into the active state of the catalyst during OER. 4CoOOH, O=C and O—C, respectively , O 1s (18.8%), Si 2p 4.1%), Co 2p (3.9%), and N 1s (3.2%) . The O 1s peak was deconvoluted into three components at 529.82, 531.91, and 533.79 eV corresponding to N.1%, Co 23+/4+ sites of the Co‐ZIF‐9(III) nanosheets does not significantly alter the intrinsic, overall crystallographic features of the material. Therefore, besides the high active site density of the 2D nanosheets, the N atoms coordinated to Co are obviously expected to influence the electronic properties of the Co sites, and thus of the various intermediates, leading to the excellent OER activity of the exfoliated 2D ZIF‐9(III) nanosheet derived catalyst, and subsequently, to the observed enhancement of the OER activity.Post‐mortem TEM images show a layer morphology and elemental mapping by electron energy loss spectroscopy (EELS) also confirms the presence of cobalt, carbon, nitrogen, and oxygen distributed throughout the sample . All these characterizations indicate that the various oxygen species coordinated to the Co4CoOOH as the key species, a schematic representation of a conceptual mechanism for activation of OH− ions at the Co‐ZIF‐9(III) 2D nanosheets is illustrated in Figure − ions is initiated by their chemisorption  via step i) at the initially tetra‐N‐coordinated Co2+ site (structure I). Due to the structural flexibility of the 2D MOF nanosheets, a local transformation to a pseudo square‐planer pyramidal coordination environment of the cobalt center is suggested (structure II). Note that it is also possible to coordinate two hydroxyl units to obtain a (trans) Co(OH)2 species with an octahedral cobalt center . Accordingly, during step i) this cobalt site is electrochemically oxidized to Co3+, hydroxylated and still coordinated to four nitrogen atoms. Thus, the OH− (hydroxo), O2− (oxo), OOH− (hydroperoxo), and O22− (peroxo) attachment and transformations all occur at the axial positions of cobalt sites (structures II–V) of different oxidation states as depicted in the steps (i)–(iv). Finally, electrochemical oxidation of the structures IV and V liberates O2  and regenerates the N4Co2+ center in structure I. It should be noted that such a situation of the coordinatively flexible Co‐ZIF‐9(III) nanosheets, with Co2+/3+/4+ coordinated to four benzimdazole groups efficiently mimics the active site structure of porphyrin based cobalt complexes commonly employed as homogeneous water oxidation catalysts.For a better understanding of the data assignment and our reasoning based on the reversible formation of Nm KOH is significantly higher in terms of current density and overpotential compared to the bulk Co‐ZIF‐9 counterparts. The exfoliated 2D Co‐ZIF‐9(III) derived electrocatalyst obviously exhibits the advantage of more accessible active sites as compared to 3D bulk MOF crystals. This work therefore opens up new avenues for efficient production of electrocatalytic materials based on or derived from exfoliated 2D metal–organic frameworks or 2D coordination polymers.In summary, the unique physical and chemical properties of 2D materials, possessing large lateral dimensions and nanometric thickness, makes them ideal for various applications in energy conversion. 2D cobalt‐based ZIF‐9(III) nanosheets synthesized by simple and facile mechanochemical grinding with subsequent ultrasonication assisted liquid‐phase exfoliation, exhibited excellent OER electrocatalytic performance. The electrocatalytic activity of the 2D Co‐ZIF‐9(III) nanosheet derived electrocatalyst coating in 1.0 The authors declare no conflict of interest.SupplementaryClick here for additional data file.


The type of lanthanide emission can be fine-tuned by adjusting the thickness of each layer, and the layered structure allows for emission from otherwise incompatible lanthanide pairs. This novel multi-layered approach enables high sensitivity over a broad temperature range. The highest relative sensitivity was achieved for a dual layered YVO4: Eu3+/YVO4: Dy3+ sample, exhibiting a maximum sensitivity of 3.6% K−1 at 640 K. The films were successfully deposited on all tested substrates , and can be applied homogenously to most surfaces without the use of binders. The films are unaffected by water, enabling non-contact temperature sensing in water, where IR thermometers are not an option.Below the Earth’s crust, temperatures may reach beyond 600 K, impeding the batteries used to power conventional thermometers. Fluorescence intensity ratio based temperature probes can be used with optical fibers that can withstand these conditions. However, the probes tend to exhibit narrow operating ranges and poor sensitivity above 400 K. In this study, we have investigated single and dual layered YVO As the signal from a luminescent probe is optical, it can pass through robust silica fibers, making them attractive for use in harsh conditions where the combination of electrical wiring and batteries is not a realistic option, e.g. in boreholes where temperatures can reach above 600 K7. The advantages of luminescent temperature sensors over other non-contact temperature sensors, such as IR-thermometers, are mainly their fast response, high spatial resolution and sensitivity, self-referencing, and that they do not rely on the emissivity of the material where the temperature is to be measured, as previously reviewed10.Luminescent temperature sensors are gaining attention as remote real-time temperature sensors due to their fast response, high spatial resolution and sensitivity, and low perturbation of the sample temperature during measurements. This enables them to be used for monitoring of moving parts, such as a working engine and 11, or non-thermally coupled (NTCS)15. Measurements based on the lifetime of temperature sensitive excited states requires sophisticated read out, time-consuming data fitting, and becomes less reliable if the lifetimes are not single-exponential. FIR measurements can be performed with simple read-out at significantly reduced cost. This signal is also intrinsically referenced, as variations in emission intensity, indicator concentration, geometry, source intensity, and light field are cancelled out when the relative emission of two different states are considered9. Probes based on the FIR methodology tend to either exhibit a high temperature sensitivity over a narrow operating range or poor sensitivity over a broad range due to how these parameters are linked. As luminescence eventually quenches with temperature, most materials do not exhibit sufficient emission intensity to be useful above 500 K, severely limiting the usefulness of FIR based probes for high-temperature applications. In this study, we demonstrate how it is possible to achieve high sensitivity over large operating ranges by employing multilayered thin films produced by the atomic layer deposition (ALD) technique.Optical thermometry using luminescent materials can either be performed by measuring the changes in the lifetime of the excited state of the phosphor, or by measuring the difference in fluorescence intensity ratio (FIR) between two excited states that can either be thermally coupled (TCS)3+, Nd3+ exhibits three different kinds of FIRs in the same material1. By selecting luminescent ions whose emission quenches in different temperature ranges, it is possible to achieve high temperature sensitivity over a broad temperature range. Figure A layered thin film can contain different luminescent ions in separate layers, resulting in numerous intensity ratios, each with an independent temperature sensitivity, similar to how e.g. YAG: Cr16, shape17, crystalline phase19, doping concentration20, and surrounding medium21. In layered samples, the luminescence is also affected by the thickness of the layers, and the order of the layers. As the thermal sensitivity depends on the luminescence intensity, there are consequently a wide range of parameters that can be used to further optimize the sensitivity for a specific temperature range.While there may be TCS within each individual layer, there will be several NTCS that may be used for temperature sensing when considering the FIRs arising from the emission of the different layers. The emission ratio of NTCS is affected by several factors, such as particle size4: Ln3+  thin films deposited by ALD is affected by temperature in the 300–850 K range. We then demonstrate how ALD can be used to make layered films that contain different luminescent ions and thus provide ratiometric temperature sensitive emission over a broad temperature range. The films can be deposited on a probe and attached to a surface, or alternatively deposited directly on the surface where the temperature is to be determined.In this study, we start by investigating how the emission in various single and dual layered YVO4 is a well-known host for lanthanides due to the strong absorption of (VO4)3−, fairly low phonon energies, high transparency in the visible range, non-hygroscopicity, and a low symmetry Y3+ site that can be substituted with lanthanides without distorting the structure24. As the films are only 100–150 nm thick, it is important that they are made of a highly absorbing material, and the films need to exhibit intense luminescence. Highly crystalline YVO4 is thus considered an optimal host. With YVO4 as host material, either temperature sensitive emission or excited state lifetimes have been reported for Eu3+ 25, Dy3+ 26, Nd3+ 30, and co-doped Er3+/Yb3+ 32, or Er3+/Ho3+ 33. Previously, we determined that crystalline growth of YVO4 can be achieved by using a 1-to-1 pulse ratio of Y(thd)3/O3 and VO(thd)2/O3 at 300 °C. The crystallinity, and as a consequence the luminescence intensity, can be further increased through post-deposition annealing34. Hansen et al. have previously reported on the growth of most of the lanthanide oxides from Ln(thd)335, enabling the doping of lanthanides by substituting some of the Y(thd)3 pulses with other Ln(thd)3 pulses.YVO3  were used as the lanthanide precursors. Y(thd)3, VO(thd)2 and O3 were used as the yttrium, vanadium and oxygen precursor, respectively. All information pertaining to the precursors is presented in Table 3 that is being pulsed. The actual concentrations are not determined in this study and will be termed as pulse% RE(thd)3, which will be abbreviated p% RE from here on. Previously, we have determined that the relation between p% and mol% is approximately 1:2 at these pulsing levels and a deposition temperature of 300 °C34, e.g. YVO4: 1 p% Dy3+ is expected to result in a Dy0.02Y0.98VO4 stoichiometry. Nitrogen was used as both carrier and purge gas and was supplied from gas cylinders , run through a Mykrolis purifier, and maintained at a 300 cm3 min−1 primary flow rate. All depositions were preceded by an in situ 10 min ozone cleaning consisting of 100 cycles of 1 s O3 pulse and 5 s N2 purge at the deposition temperature in order to remove any organic remains while letting the reactor stabilize its temperature.The thin films investigated in this study were deposited with an F-120 research-type ALD-reactor (ASM Microchemistry Ltd) at 300 °C at a reactor pressure of ~3.6 mbar. The β-diketonate chelates Ln(thd)3/purge/O3/purge/VO(thd)2/purge/O3/purge cycles. These are longer pulse and purge times than what would be required to achieve saturating conditions for all precursors35, but optimizing these parameters was not the focus of this study and it was thus kept constant for all precursors. Si (100) and SiO2 were used as substrates for the depositions. The thickness of the native oxide layer on the silicon substrates ranged from 3–20 nm and was measured by spectroscopic ellipsometry prior to each deposition.Pulse durations were 3/3/3/3/3/3/3/3 s for all the RE(thd)4)3− to absorb >90% of <300 nm light34. The samples are crystalline and luminescent as deposited, however, both these properties can be improved through post-deposition annealing above 700 °C. For each deposition, a sample was annealed post deposition in air at 1000 °C for 10 h. The graphs, images and figures in this study refers to annealed samples unless states otherwise.The deposited films have a thickness between 100–145 nm, which previously was determined to be sufficient in order for  measurements in the visible range were performed with a 280 nm 1 mW diode and an OceanOptics USB4000 spectrometer for the high-resolution measurements shown in the supplementary section, while an USB2000+ spectrometer with high sensitivity was used for all the spectra collected above 300 K presented in the paper. An OceanOptics NIR-Quest spectrometer was used for recording emission spectra in the 900–1700 nm NIR. The detectors were not calibrated with respect to each detectors wavelength dependent response, and while this affects the absolute FIR values, it does not affect the relative change in the FIR and consequently not the reported relative sensitivity.−1, and then kept at the max temperature for 10 min, before being cooled down by turning off the heater (ca. −0.5 K min−1 on average).The temperature sensitivity measurements were conducted by positioning the samples vertically inside a tube furnace and threading a quartz rod through a hole in the insulation. This setup allows photons to travel from the excitation source through a split fiber and then through the quartz rod aimed at the sample inside the furnace. The emitted light from the sample is passed back through the rod and the split fiber, before being collected at the spectrometer. A thermocouple was used to monitor the temperature inside the furnace. The resolution of the controller for the thermocouple was 1 K. The samples were heated to 700–875 K at a ramp rate of 2 K minα1 radiation and a Ge(111) monochromator. UV-Vis measurements were conducted on films deposited on fused silica in the range 200–900 nm with a Shimadzu UV-3600 instrument and an integrating sphere. A Hitachi SU8230 field emission scanning electron microscope (FE-SEM) was used to study the surface morphology of some of the samples.The crystallinity of the samples was determined with a Bruker D8 Discovery X-ray diffractometer, using CuK4: Yb3+ had been previously deposited by ALD34, the first step to making multilayered films was to deposit YVO4 films doped with different lanthanides by ALD and to determine which of them are most promising for temperature sensing in multilayered films. The normalized emission spectra of all the deposited YVO4: Ln3+  thin films after annealing are presented in Fig. 4: 1 p% Tb3+ and YVO4: 1 p% Pr3+ were also prepared, but exhibited no detectable luminescence, which is to be expected since these ions easily oxidize to Tb4+ and Pr4+. The as-deposited samples are crystalline with a highly preferential orientation along the growth direction 37.Among the lanthanides whose emission is depicted in Fig. 4 thin films, a preliminary investigation was done where the total emission from the most emissive state of each sample was monitored in the 300–875 K range , providing a fitted value for ΔE of 623 cm−1, which is in good agreement with the emission spectra (ca. 650 cm−1). The relative thermal sensitivity, S, of the probe, defined as relative change in the FIR with temperature43:16, shape17, crystalline phase19, doping concentration20, surrounding medium21, and in layered samples also the thickness of the layers and the order of the layers. Therefore, while the absolute sensitivity is relevant for the practical operation, it is not a meaningful parameter for comparison between probes, and thus only the relative sensitivities will be presented in this study. For the investigated temperature range, the S of this sample spans from 1.23% K−1 at 300 K to 0.21% K−1 at 660 K, making it reasonable for measuring temperature changes in e.g. water. The FIR between 295–370 K, and a picture of the experimental setup of YVO4: 1 p% Er film submerged in water, is given in Fig. 4, the Er3+ emission is unaffected by water, which will be demonstrated for YVO4: Eu3+ in the next section, and the resulting FIR is thus similar to that of Fig. In the YVO3+ emission has previously been investigated for use as ratiometric temperature sensors in several hosts51, including YVO425. Previous studies have primarily investigated the thermal dependence of FIR between the emission from the 5D1 and 5D0 excited states. The study on YVO4: Eu3+ investigated ratios between the emissions from two stark sublevels of the 7F2 excited state the 293–333 K range, with S being in the order of 0.1% K−1. As the emission from these two levels overlaps significantly . The average experimental value for ΔE was determined to be 1991 cm−1, which is in good agreement with previous studies45. A lower ΔE (1872 cm−1), which is closer to the experimental value suggested by the PL spectra (1735 cm−1), is obtained by extracting ΔE from an Arrhenius-plot representation of the data, as shown in Fig. The thermal dependence of the emission spectrum of YVOS, which reaches a maximum of 0.59% K−1 at 550 K. While S is fairly low, it is still higher than e.g. YVO4: Er3+ in the 450–800 K range, making YVO4: Eu3+ a reasonable alternative for measurements in this temperature range. Discrepancies between heating and cooling are attributed to thermal mass in the system, and that the thermocouple used to measure the temperature was positioned 1–2 cm from the sample.Figure 4 is non-hygroscopic material, it will not absorb water, and submerging the films in water should thus not affect their luminescence. This was verified by submerging an YVO4: 2 p% Eu3+ sample in water for 60 hours while recording the PL emission. The total emission of the sample depends proportionally on the power of the excitation source, which fluctuates significantly over the course of such a long experiment. Changes in the background, in the atmosphere, or with the equipment is only expected to yield minor variations. Instability of the excitation source can be accounted for by recording the reflected UV signal  emission of Dy3+ and 700 nm (5D0–7F4) emission of Eu3+ (FIR 1) is presented in Fig. r2 = 0.998), and seems to capture the changes in the FIR well in the temperature sensitive 500–750 K range.Note that while it has been demonstrated that the FIR methodology can still be used even when there is no thermal coupling between the involved states4F9/2–6H13/2 emission of Dy3+ and the 5D1–7F1 transition of Eu3+ (FIR 2) is presented in Fig. r2 = 0.999). The FIR that was used in YVO4: Eu3+, i.e. the ratio between the 538 nm and 700 nm emission of Eu3+, is also present in this sample (FIR 3). The thermal dependence of this FIR is given in Fig. S compared to a sample without any Dy3+.The ratio between the S of the three FIRs in the layered YVO4: 2 p% Eu3+/YVO4: 1 p% Dy3+ thin film is presented in Fig. 4: Dy3+ layer on top of YVO4: Eu3+ enhances S significantly in the 500–750 K range, with a maximum of 3.6% K−1 at 640 K. The FIR resulting from TCS on Dy3+ is not included in Fig. S of 0.9–1.8% K−1 below 400 K26, enabling high S over the entire 300–800 K range.The thermal dependence of Smax and operating range is presented in Table Smax due to the differences in operating range. While the listed systems still exhibit luminescence above 473 K, their Smax may be at a much lower temperature, and the sensitivity in the 473–750 K range may be significantly lower than the value listed. E.g. the Smax observed for the YVO4: Er3+ film presented in this study was 1.2% K−1 at 300 K, while above 473 K, S is less than 0.5% K−1 and gradually decreasing, resulting in an average S of only 0.30% K−1 in the 473–673 K range. On the other hand, the dual-layer YVO4: Eu3+/YVO4: Dy3+ thin film has an average S of 2.2% K−1 over the 475–750 K range (2.4% in the 500–750 K range). An average sensitivity over a certain operating range would be more sensible to compare, though such numbers have not been compared in previous studies, as such comparisons only make sense if the systems are compared for use in a specific application requiring a certain operating range. A recent study on the Pr3+: Y2Ti2O7 system, using the FIR of host trap emission and the 1D2–3H4 emission of Pr3+, demonstrated an impressive Smax of 5.25% K−1 at 289 K in the operating range 289–573 K53. However, above 473 K it is less than 1.5% K−1 and decreasing, clearly making it less suitable than the dual layer YVO4: Eu3+/YVO4: Dy3+ thin film in the 500–750 K range. To the authors’ knowledge, there are no previously investigated materials that exhibit higher average S than that of the dual layer YVO4: Eu3+/YVO4: Dy3+ presented in this study for FIR measurements in the 500–750 K temperature range, making this currently the most attractive material for non-contact temperature sensing in this range.A list of phosphor materials that can be used for temperature detection above 473 K, and their 4: Tm3+/YVO4: Eu3+ is another dual layered material that seemed promising based on Fig. 4: Tm3+ quenches at a slower rate, but over a slightly broader temperature range compared to YVO4: Dy3+. The emission spectra in the 300–850 K temperature range of a dual layered thin film consisting of 20 nm YVO4: 2 p% Eu3+ deposited on top of 125 nm YVO4: 1 p% Tm3+ is presented in Fig. 3+ emission indicates that the large difference in thickness between the Eu3+ and Tm3+ layer is required for a balanced ratio of the emission intensity. It has previously been determined that there is resonant energy transfer from Tm3+ to Eu3+ 54, and thus the emission properties will be dominated by Eu3+ when mixed together. By making a layered structure, the energy transfer from Tm3+ to Eu3+ can be reduced, enabling intense emission from both lanthanides.YVO4: Tm3+, Eu3+ system there are at least three FIRs suitable for temperature measurements. The FIR of the 1G4–3H6 transition of Tm3+ and 5D0–7F4 of Eu3+ is presented in Fig. r2 = 0.998), indicating that this is indeed a valid approach for this system as well. The FIR of the 1G4–3H6 transition of Tm3+ and 5D1–7F1 transition of Eu3+ is presented in Fig. 5D0–7F4 and the 5D1–7F1 transition of Eu3+ in this sample (FIR 3) is provided in Fig. S of the three FIRs. FIR 2 exhibits a maximum S of 1.9% K−1 at 675 K, and displays a reasonable sensitivity over the 500–775 K range (average S = 1.35% K−1). S is lower compared to YVO4: Dy3+/YVO4: Eu3+, but the operating range is slightly broader.In the YVO4: Ln3+  by ALD was achieved, both as single layers and as multilayers, and the thermal dependence of the photoluminescence in the 300–875 K range of the samples doped with Eu3+, Dy3+, Tm3+, Sm3+, Er3+ and Yb3+ was investigated. FIR measurements using TCS on Er3+ and Eu3+ demonstrated maximum sensitivities reaching 1.2% K−1 for YVO4: Er3+ at 300 K, and 0.6% K−1 for Eu3+ at 575 K. FIR measurements were also performed using excited states situated on different lanthanides in layered YVO4: Eu3+/YVO4: Dy3+ and YVO4: Tm3+/YVO4: Eu3+. The dual layered materials exhibit a Smax of 3.6% K−1 at 640 K, with S significantly improved in the whole 500–775 K range compared to the single layer YVO4: Eu3+ thin film, and also compared to any other previously investigated materials in this range. The dual layered films are particularly attractive for use in boreholes where the temperatures exceed 500 K. The films were successfully deposited on all tested surfaces , indicating that they can be applied to most industrially relevant surfaces. It was also demonstrated that the luminescence of the films is unaffected by water, which enables monitoring of the temperature of transparent liquids inside e.g. sealed ampoules, Schlenk lines or hydrothermal pressure vessels. The study shows that it is possible to make highly customizable, chemically and physically robust coatings by ALD that can provide ratiometric temperature sensing over a broad temperature range and with high sensitivity.In this study, controlled deposition of luminescent YVOFigure S1–18


The reaction with imidazole (Him) goes to completion whereas those with pyrazole (Hpyz) and 2‐mercaptoimidazole (HimSH) give up to 41 and 36 % conversion, respectively. The BET surface areas for the Mannich products are reduced from that of UiO‐66‐NH2, but the compounds show enhanced selectivity for adsorption of CO2 over N2 at 273 K. The thiol‐containing MOFs adsorb mercury(II) ions from aqueous solution, removing up to 99 %. The Mannich reaction with pyrazole succeeds on [Zn4O(bdc‐NH2)3] (IRMOF‐3), but a similar reaction on [Zn2(bdc‐NH2)2(dabco)]  gave [Zn3(bdc‐NH2)1.32(bdc‐NHCH2pyz)1.68(dabco)]⋅2 C7H85, whereas the reaction with imidazole gave the expected PSM product. Compound 5 forms via a dissolution–recrystallisation process that is triggered by the “free” pyrazolate nitrogen atom competing with dabco for coordination to the zinc(II) centre. In contrast, the “free” nitrogen atom on the imidazolate is too far away to compete in this way. Mannich reactions on [In(OH)(bdc‐NH2)] (MIL‐68(In)‐NH2) stop after the first step, and the product was identified as [In(OH)(bdc‐NH2)0.41(bdc‐NHCH2OCH3)0.30(bdc‐N=CH2)0.29], with addition of the heterocycle prevented by steric interactions.The Mannich reaction of the zirconium MOF [Zr Metal‐organic frameworks (MOFs)6O4(OH)4(bdc‐NH2)6] ,4O(bdc‐NH2)3] (IRMOF‐3),2(bdc‐NH2)2(dabco)] 2)] (MIL‐68(In)‐NH2)The Mannich reaction, first reported over 100 years ago,6O4(OH)4(bdc‐NH2)6], UiO‐66‐NH2, is an attractive PSM precursor due to the high chemical stability of the zirconium‐dicarboxylate framework, its high crystallinity and relatively large pore windows (≈6 Å),2 were undertaken as shown in Scheme DMSO. For the reaction with pyrazole (Hpyz), the 1H NMR spectrum of 1  shows a number of new signals in addition to those corresponding to the aromatic protons of the unmodified groups, present as D2bdc‐NH2 . The aromatic protons of D2bdc‐NHCH2pyz were observed at δ=7.62d, 7.25s and 7.08d ppm, overlapping with the signals from D2bdc‐NH2 and others attributed to minor (<10 %) by‐products. The presence of the pyrazole ring on the digested framework of 1 was confirmed by the signals at δ=7.57 and 6.28 ppm. Attempts to remove the by‐products by thorough washing with a variety of solvents were unsuccessful, suggesting that these compounds are also derived from PSM reactions, with a double‐Mannich product the most likely. Formylated by‐products can be present in UiO‐66‐NH2, deriving from reaction with DMF during the MOF synthesis.2 showed no evidence for formylation, suggesting this is not the origin of the by‐products present in 1.The effectiveness of the PSM reactions in terms of the percentage conversion of amino groups into the Mannich products was gauged by δ=7.13 and 6.28 ppm, the percentage conversion from −NH2 into ‐NHCH2pyz groups was estimated to be 41 %. Ignoring the minor by‐products, this gives the formula for 1 as [Zr6O4(OH)4(bdc‐NH2)3.54(bdc‐NHCH2pyz)2.46]. Attempts to increase the degree of conversion by carrying out the reaction at a higher temperature or for a longer time period were unsuccessful, though it should be noted that higher conversion to the methoxymethyl amine in the first step might not be observable in the 1H NMR spectra of the digested product, given the likely reversion of any D2bdc‐NHCH2OMe to D2bdc‐NH2 under the acidic digestion conditions.By comparison of the integrals for the signals at 2 with imidazole (Him) as the nucleophile was more successful than that with pyrazole, with the amino groups fully converted into ‐NHCH2im groups. This was confirmed by the disappearance of the signals which correspond to the aromatic protons of the starting MOF, UiO‐66‐NH2, in the 1H NMR spectrum of the digested product. Instead, new signals at δ=7.56d, 7.14s and 7.07d ppm were observed . The signal at δ=7.03 ppm corresponds to two chemically similar but non‐identical protons from the imidazole ring, and this overlaps with the doublet from one of the aryl protons, whereas the singlet at δ=7.75 ppm arises from the remaining proton peak of the imidazole ring. The signal attributed to the methylene protons can be seen at δ=4.56 ppm, close to the broad HDO peak resulting from the digestion solvent. The chemical formula of this PSM product is [Zr6O4(OH)4(bdc‐NHCH2im)6] 2.The Mannich reaction of UiO‐66‐NH2, the comparable Mannich reaction with 2‐mercaptoimidazole (HimSH) as the nucleophile gave only partial conversion. The 1H NMR spectrum  of the digested product 3 shows the presence of new peaks in addition to the aromatic proton peaks which correspond to the starting MOF, UiO‐66‐NH2. The signals attributed to the aromatic protons of D2bdc‐NHCH2imSH are observed at δ=7.68d, 7.26s and 7.08d ppm, respectively, although these peaks overlap with others from minor by‐products. The presence of new peaks at δ=6.98 and 6.76 ppm, from the imidazole ring, indicates that the 2‐mercaptoimidazole ring was successfully grafted onto the MOF framework.In contrast to the complete conversion observed for 2 into ‐NHCH2imSH was calculated as approximately 36 % by comparing the integrals for the signals at δ=7.16 and 6.76 ppm. Ignoring minor by‐products, this gives a formula for 3 of [Zr6O4(OH)4(bdc‐NH2)3.84(bdc‐NHCH2imSH)2.16].The percentage conversion from ‐NH1–3, further evidence for successful PSM came from the ESI mass spectra of the digested products. The negative ion ESI mass spectra of digested 1 and 3 confirmed the presence of the deprotonated anions of H2bdc‐NHCH2pyz and H2bdc‐NHCH2imSH at m/z=260.0664 (predicted [M−H]−=260.0671) and m/z=292.0400 (predicted [M−H]−=292.0392), respectively. In both cases a peak was also observed for H2bdc‐NH2 . Digested 2 gave better results in the positive ion rather than the negative ion ESI mass spectrum, with the protonated cation of H2bdc‐NHCH2im observed at m/z=262.0824 (predicted [M+H]+=262.0828).For 1–3 are summarised in Table 2OCH3, leading to a higher conversion. The steric demands of the nucleophile also have some influence on the extent of the reaction, with the lowest conversion achieved in the case of 2‐mercaptoimidazole, the largest of the nucleophiles employed. This can be rationalised by the more restricted diffusion of 2‐mercaptoimidazole within the pores of the MOF.The percentage conversions for the PSM reactions generating 3 was anticipated to be able to coordinate to soft metal centres such as mercury(II). In order to probe the effect of different ‐NHCH2imSH loadings on HgII uptake, a second thiol‐containing MOF was prepared, using the same conditions as for 3, but with the temperature for the second step reduced from 80 to 50 °C. It was anticipated that the lower temperature during the second step would lead to a lower conversion to the ‐NHCH2imSH group.The thiol substituent in 1H NMR spectrum  of the digested product formed under these conditions, 3 a, showed the presence of the modified group (‐NHCH2imSH), though present in a lower relative concentration than in 3. The percentage conversion from ‐NH2 into ‐NHCH2imSH groups was estimated as 21 %, giving a formula for 3 a of [Zr6O4(OH)4(bdc‐NH2)4.74(bdc‐NHCH2imSH)1.26]. This confirms that the reaction temperature has a significant impact on the degree of modification, with a lower temperature leading to lower conversion.The 1–3 and 3 a exhibit similar features to that for UiO‐66‐NH2 . There is an initial mass loss (up to 110 °C) corresponding to removal of 1,4‐dioxane from the pores. A small, gradual mass loss, observed in the range 110–470 °C, is attributed to the loss of residual solvent in the pores and/or the dehydroxylation of the Zr6O4(OH)4 nodes.1 has 4.0, 2 has 3.0, 3 has 5.0, 3 a has 5.5 and UiO‐66‐NH2 has 7.0 molecules of 1,4‐dioxane per Zr6O4(OH)4 unit in the unactivated MOFs. This shows that the amount of 1,4‐dioxane in the pores decreases as the degree of post‐synthetic modification increases. This is unsurprising, since the greater the degree of conversion, the lower the residual space available to accommodate guest solvent molecules.The TGA profiles of the PSM products 1–3 and 3 a were determined based on their N2 adsorption isotherms at 77 K  is similar to previously reported values.2, with SBET values of 528 m2 g−1 for 1, 290 m2 g−1 for 2, 352 m2 g−1 for 3 and 608 m2 g−1 for 3 a. BET surface areas are governed by the degree of conversion and the size of the modified groups. In general, the BET surface area reduces as the percentage conversion increases and 2, with complete conversion, has the lowest surface area. The presence of larger pendant groups in the pores also leads to lower BET surface areas, with the value for 3 less than that for 1, despite 1 possessing a higher degree of modification.The BET surface areas of 2 adsorption isotherms of the PSM products were measured at 273 K  to assess the influence of the modified groups on the CO2 uptake capacities. All PSM products show lower CO2 uptake capacities than UiO‐66‐NH2, attributable to the reduction in pore volume and the lower percentage of −NH2 groups in the pores. Of the PSM products, 1 shows the highest CO2 uptake which is probably due to the favourable interactions of CO2 molecules with the nitrogen atom in the pyrazole ring. Compound 2 shows a lower CO2 uptake than 1, despite having higher percentage of heterocycles in the pores, which is consistent with the lower BET surface area, itself a consequence of the high degree of modification. Compounds 3 and 3 a show the lowest CO2 uptake capacities at 1 bar and this may be due to pore blocking caused by higher steric hindrance of the modified groups. Nonetheless, the proportion of thiol groups in the pores has little impact on the CO2 uptake capacities, as evidenced by the relatively small difference in CO2 uptake between 3 and 3 a. The modified MOFs show enhanced CO2/N2 selectivity over UiO‐66‐NH2, though this is largely a consequence of their low N2 uptake at 273 K.The CO6O4(OH)4(bdc‐NH2)3.84(bdc‐NHCH2imSH)2.16] 3 and [Zr6O4(OH)4(bdc‐NH2)4.74(bdc‐NHCH2imSH)1.26] 3 a were also investigated for their ability to remove mercury(II) from aqueous solutions. The HgII uptake experiments were carried out by immersing the MOF samples in an aqueous solution of HgCl2 (100 ppm) and stirring the solution for 12 h at ambient temperature. The HgII‐treated MOFs were isolated by centrifugation and atomic emission spectroscopy (AES) was used to quantify the residual HgII concentration in the supernatant.The thiol‐containing PSM products, .The effectiveness of the PSM reaction was gauged by 4 confirms the presence of the deprotonated anions of H2bdc‐NHCH2pyz and H2bdc‐NH2 at m/z=260.0669 (predicted [M−H]−=260.0671) and m/z=180.0308 (predicted [M−H]−=180.0297), respectively. The PXRD pattern of 4  shows the similarities in peak positions with the starting MOF, IRMOF‐3, indicating that the bulk framework structure remained unchanged upon PSM. Nonetheless, a degree of degradation was observed, as evidenced by the broadening of peaks and reduced intensities. The presence of stoichiometric MeOH in the first step and as a side product in the second step may cause some crystal degradation. Attempts to analyse 4 by single crystal X‐ray crystallography were unsuccessful due to poor diffracting power of the sample.The negative ion ESI mass spectrum of the digested product 2(bdc‐NH2)2(dabco)], DMOF‐1‐NH2, is a flexible MOF which consists of Zn2(dicarboxylate)2 sheets that are linked by dabco pillars into a three‐dimensional network.2 due to it having little effect on the pore geometry and it not unduly affecting the crystallinity.−=260.0671) and m/z=180.0364 (predicted [M−H]−=180.0375), respectively. The disappearance of ‐NH2 stretching bands (3287 and 3457 cm−1) of DMOF‐1‐NH2 in the FTIR spectrum of 5  indicates the successful conversion of primary into secondary amine.The negative ion ESI mass spectrum of the digested product 5 is completely different to that of DMOF‐1‐NH2 , revealing a significant structural difference between the two materials. Indeed, the PXRD pattern of 5 does not match any of the PXRD patterns reported in the literature for DMOF‐1 type materials. Inspection of 5 under an optical microscope revealed the presence of small colourless crystals and the absence of brown block crystals, characteristic of DMOF‐1‐NH2 and its derivatives. This observation suggests that DMOF‐1‐NH2 has undergone a complete structural change upon reaction.The PXRD pattern of 5 was successfully elucidated by single crystal X‐ray crystallography and is shown in Figure R‐3m, and the asymmetric unit  contains one quarter of a zinc atom , one twelfth of a dabco ligand and one quarter of a ligand which is comprised of bdc‐NH2 and bdc‐NHCH2pyz, disordered in a 34:56 ratio.The crystal structure of 5 indicates a mass loss that corresponds to two toluene molecules for every three zinc centres present, and this provides a formulation of 5 as [Zn3(bdc‐NH2)1.32(bdc‐NHCH2pyz)1.68(dabco)]⋅2 C7H8.Attempts to accurately determine the structural void volume via the PLATON SQUEEZE algorithm were hampered by pendant group site‐occupancies, disorder and the smearing of electron density. The TGA of 5 contains three zinc centres, one 6‐coordinate and two 4‐coordinate 6 SBUs are pillared by the dabco ligands along the c axis and these pillars are linked in the ab plane by the substituted bdc linkers to form a three‐dimensional network containing infinite one‐dimensional triangular channels 6 SBU exhibited by 5 has previously been observed in other MOF systems. For example, a three‐dimensional MOF, [Zn3(bpdc)3(bpy)],  prepared by Li and co‐workers,5.The Zn2 into 5, a series of control studies were carried out. No structural change was observed when DMOF‐1‐NH2 crystals were heated in toluene, or when the crystals were treated separately with paraformaldehyde, MeOH or pyrazole . This suggested that the formation of the methoxymethyl amine intermediate DMOF‐1‐NHCH2OCH3 in the first step was unproblematic, but that the structural transformation occurred in the second step of the Mannich reaction. In order to confirm this, the reaction of DMOF‐1‐NHCH2OCH3 with pyrazole was monitored under an optical microscope equipped with a camera. The reaction conditions were modified in order to be able to view the reaction in this way. In particular, DMOF‐1‐NHCH2OCH3 crystals were dispersed on a microscope slide containing a solution of pyrazole in toluene at room temperature. After five minutes, the crystals began to dissolve, with complete dissolution observed after 40 minutes. A new phase, corresponding to the crystals of 5, was first observed after approximately twenty minutes , so is unable to compete with it for coordination. Moreover, a diaza‐[18]‐crown‐6 ligand functionalised with pendant pyrazole groups using a Mannich reaction also exhibited fragmentation behaviour in the presence of transition metals,After the first step of the Mannich reaction, the methoxymethyl amine species is localised in close proximity to the bridging dabco ligands. Upon addition of pyrazole, a facile reaction displacing methanol can occur to yield the ‐NHCH5 show the presence of more than one phase, so the degree of occupancy of the pores by toluene in the crystal structure is an estimate, and although the ratio of linkers in the 1H NMR spectra are consistent between samples, this too may have been different in the crystal analysed crystallographically.It should be noted that PXRD patterns for bulk samples of 2 with imidazole as the nucleophile was carried out using the same conditions as with pyrazole  shows aromatic protons from D2bdc‐NH2 and D2bdc‐NHCH2im, and from the integrals the percentage conversion of amino into ‐NHCH2im groups was calculated to be 65 %, giving a formula for 6 as [Zn2(bdc‐NH2)0.7(bdc‐NHCH2im)1.3(dabco)]. The negative ion ESI mass spectrum of the acid‐digested product 6 confirmed the presence of the deprotonated anions of H2bdc‐NHCH2im and H2bdc‐NH2 at m/z=260.0661 (predicted [M−H]−=260.0671) and m/z=180.0339 (predicted [M−H]−=180.0297).The Mannich reaction of DMOF‐1‐NH6 and the starting MOF, DMOF‐1‐NH2 closely match one another , demonstrated that PSM does not affect the gross structure or the crystallinity of the product. Furthermore, visual inspection of 6 confirmed the presence of only brown block crystals and the absence of new phases. Attempts to analyse 6 crystallographically were hampered by crystal twinning. Nonetheless, a screening experiment suggested that there were similarities in the unit cell parameters of 6 (a=15.2955(17) Å, b=15.2860(15) Å, c=19.207(2) Å) and those of DMOF‐1 (a=15.063(2) Å, c=19.247(5) Å).The PXRD pattern of 2OCH3, by eliminating the possibility of coordinative competition with dabco. The “free” nitrogen atom in imidazole is positioned beyond the coordination sphere of the zinc(II) centre and, as a consequence, the process shown in Figure Based on these results, it is clear that framework dissolution does not occur when imidazole is used as a nucleophile. It is believed that substituting pyrazole by imidazole prevents the dissolution of DMOF‐1‐NHCH2 with 2‐mercaptoimidazole as the nucleophile was attempted using the same conditions as in the reaction with imidazole. However, the 1H NMR spectrum of the digested solid showed only signals corresponding to the aryl protons of DMOF‐1‐NH2 , indicating that the inclusion of 2‐mercaptoimidazole onto this MOF framework was unsuccessful. The PXRD pattern  is similar to that for DMOF‐1‐NH2, implying that the framework was retained throughout the experiment. The unsuccessful grafting of 2‐mercaptoimidazole onto the MOF framework is likely to be due to its larger size than imidazole, which makes it too big to pass through the pore windows (2‐mercaptoimidazole: 8.4×6.6 Å. DMOF‐1‐NH2 channels: 5.3×4.8 Å).The Mannich reaction of DMOF‐1‐NH2)], MIL‐68(In)‐NH2, is a three‐dimensional MOF that is constructed from chains of InO4(OH)2 octahedral units that are linked together by bdc‐NH2 ligands to form triangular (≈6 Å) and hexagonal (≈16 Å) one‐dimensional channels. In MIL‐68(In)‐NH2, the amino groups are oriented towards the InO4(OH)2 octahedral chains rather than projecting into the pores. However, this has not prevented successful tandem post‐synthetic modifications involving formation of the azide and subsequent click reactions from being carried out,.This finding validates the hypothesis that 7  confirms the presence of the deprotonated anions of H2bdc‐NHCH2OCH3 , H2bdc‐N=CH2  and H2bdc‐NH2 , and provides good evidence for the identity of the tag groups in the products. The PXRD pattern of 7 is similar to that of MIL‐68(In)‐NH2 , indicating that framework integrity is maintained and the PSM reaction did not alter the crystallinity of the product.The negative ion ESI mass spectrum of the base‐digested product 7⋅0.8 dioxane was successfully elucidated by single crystal X‐ray crystallography. The asymmetric unit  consists of two indium(III) centres with site occupancies of 0.5 and 0.25 for In1 and In2, respectively, one half and one quarter of a dicarboxylate ligand and two OH ligands (based on O1 and O5) with combined site occupancies of 0.75. Finally, there was evidence for some diffuse solvent present in the framework which was modelled as four‐fifths of a dioxane molecule per indium centre based on TGA evidence.Crystals were grown from dioxane, and the crystal structure of 2, in agreement with the PXRD data. Although there is some evidence for the nitrogen atoms of the tag groups, disordered over several positions, further evidence for the nature of the substituents was unavailable.As can be seen in Figure 7 is the short distance between the nitrogen atoms on neighbouring benzene rings ‐NH2 into a range of azole‐functionalised MOFs with conversions of up to 100 %. It did not prove possible to prepare the azole‐functionalised acids using similar procedures, and the instability of N−CH2−N linkages to hydrolysis is well established.The results presented herein demonstrate a previously unreported post‐synthetic modification process on MOFs, whereby catalyst‐free Mannich reactions were used to convert the primary amines of UiO‐66‐NH2, the degree of conversion from ‐NH2 into ‐NHR  depends on the strength and size of the nucleophiles. Complete conversion was achieved with the strongest nucleophile (imidazole) whereas a lower conversion (41 %) was obtained with the isosteric weaker nucleophile, pyrazole. The use of a larger nucleophile, 2‐mercaptoimidazole, led to the lowest conversion (36 %) and this is most likely due to the restricted diffusion of the nucleophile within the pores of UiO‐66‐NH2. The modified MOFs have lower BET surface areas than UiO‐66‐NH2, but show enhanced selectivity for CO2 over N2. In addition, the thiol‐containing products show excellent uptake of mercury(II) from aqueous solutions.With regards to the PSM reactions on UiO‐66‐NH2 into ‐NHCH2pyz was achieved whilst using pyrazole as a nucleophile. However, the successful PSM reaction comes at a cost of decreased product crystallinity as evidenced by the broadening of peaks and reduction in peak intensities in the PXRD pattern of the PSM product.With regard to the PSM reaction on IRMOF‐3, 75 % conversion of ‐NH2, using pyrazole as the nucleophile, unexpectedly afforded [Zn3(bdc‐NH2)1.32(bdc‐NHCH2pyz)1.68(dabco)]⋅2 C7H8, 5, which was characterised by single crystal X‐ray crystallography, 1H NMR spectroscopy and TGA analyses. The framework transformation occurs when the intermediate MOF, DMOF‐1‐NHCH2OCH3, dissolves in the presence of pyrazole and re‐precipitates 5. In contrast, the Mannich reaction of DMOF‐1‐NH2 with imidazole afforded a product, 6, bearing the same gross structure as DMOF‐1‐NH2, showing that substituting pyrazole for imidazole prevents the dissolution of DMOF‐1‐NHCH2OCH3. This difference in reactivity has been rationalised on the basis of a functionality‐dependent dissolution process, in which the “free” nitrogen atom on pyrazole is in a position to compete with the dabco ligand for coordination to zinc, whereas the equivalent atom on imidazole is too far away to coordinate.The Mannich reaction on DMOF‐1‐NH2 to a similar PSM reaction with pyrazole, gave a modified product 7 that did not contain the heterocycle. The first step of the Mannich reaction proceeded, but the methoxymethyl amine intermediate did not react with pyrazole in the expected manner. The X‐ray crystal structure of 7 suggests that this is a consequence of the location and orientation of these groups which are inaccessible to the pyrazole molecules, thus preventing the second step in the Mannich reaction from occurring.Subjecting MIL‐68(In)‐NHThis work has demonstrated that the post‐synthetic Mannich reaction represents a versatile route to introducing complex functionalities into a range of metal‐organic frameworks, and we are currently working to further develop the breadth of this approach.2 with formaldehyde and imidazole is presented here. UiO‐66‐NH2  and paraformaldehyde  were added into a glass vial containing methanol (5 mL). The vial was placed in an oven and heated at 50 °C for 24 h. The powder was then washed with methanol (three times) via centrifugation to remove any residual paraformaldehyde in the pores or on the solid surfaces. The powder was subsequently treated with imidazole  in 1,4‐dioxane at 80 °C for 24 h before quenching the reaction by rinsing the sample with fresh 1,4‐dioxane. The product was soaked in 1,4‐dioxane for 3 days, replacing the solvent with fresh solvent every 24 h, before isolation by centrifugation. Prior to characterisation, samples were left to dry in air for 2 h to obtain free‐flowing powders.Full experimental details are presented in the electronic supplementary information. As an example, the reaction of UiO‐66‐NH5 and 7⋅0.8 dioxane are given in the Supplementary Information. The structures have also been deposited with the Cambridge Structural Database .Full details of the X‐ray crystal structures of The authors declare no conflict of interest.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.


Inorganic chemical cells (iCHELLs) are compartment structures consisting of polyoxometalates (POMs) and cations, offering structured and confined reaction spaces bounded by membranes. We have constructed a system capable of efficient anisotropic and hierarchical photo‐induced electron transfer across the iCHELL membrane. Mimicking photosynthesis, our system uses proton gradients between the compartment and the bulk to drive efficient conversion of light into chemical energy, producing hydrogen upon irradiation. This illustrates the power of the iCHELL approach for catalysis, where the structure, compartmentalisation and variation in possible components could be utilised to approach a wide range of reactions. The electrolysis of water is a mature, scalable technology for H2 production and if the energy source is renewable, for example, sunlight, the process can be sustainable.Photosynthesis is the process by which plants and other organisms convert solar energy to chemical energy. It is a widely studied topic due to the many potential applications of synthetic photochemical systems for sustainable solar fuels, such as hydrogen.In order to mimic the compartmentalisation advantages found in cells, self‐assembled soft materials  have often been used as platforms.3]2+, bpy=2,2′‐bipyridyl), an electron mediator (methyl viologen (MV)), a catalyst (Pt colloid), and a sacrificial electron donor (triethanolamine (TEOA)).12O40]3− or [SiW12O40]4− polyoxometalate (POM) anions and MV2+ cations, we were able to construct a system in which efficient and sustained HER was driven by anisotropic and hierarchical electron transfer across the membrane, see Figure Herein, we used inorganic chemical cells (iCHELLs)+, Na+ etc.), into a similarly dense aqueous solution of larger cations 3]Cl2  etc.). A diverse range of cations and POMs with various functions can be used as building blocks, allowing the membrane to be readily functionalised.iCHELLs are hybrid inorganic chemical cells consisting of organic cations and POM anions.3]2+→MV2+→POM→Pt colloid), it is possible to separate the MV from the Pt colloid, reducing the problem of MV degradation.While HER is known to proceed efficiently at low pH, due to the reduction potential of protons being more favourable, the performance of sacrificial electron donors drastically declines at low pH due to degradation.12O40]4− and [Ru(bpy)3]2+ as a platform for a photochemical HER. [SiW12O40]4− is a clear choice here, as it is a POM capable of being incorporated into iCHELLs, and its reduced form is known to drive rapid HER in presence of Pt/C.12O40]4− on the membrane, electron transfer across membrane could not be confirmed. This was likely because of reverse electron transfer ([SiW12O40]5−→[Ru(bpy)3]3+) due to the proximity of the [SiW12O40]4− and [Ru(bpy)3]2+. To suppress this reverse electron transfer, the distance between these components was increased by addition of an intermediate electron mediator, MV2+, which was integrated into the membrane in the place of [Ru(bpy)3]2+.Initially, we investigated iCHELLs composed of [SiW3]2+, MV2+, and TEOA are in the bulk solution. The membrane is primarily composed of POMs and MV2+, so hierarchical electron transfer from the outside to the inside of the iCHELL was expected. H3[PW12O40] and H4[SiW12O40] are very strong acids, so the pH inside the iCHELL was very low (<1). Conversely, the pH of the bulk solution was maintained at 7.2 using Bis‐Tris buffer (100 mm). This way, the optimum conditions for efficient HER were achieved without the degradation problems found in homogenous systems. Evaluating the reaction system from the viewpoint of its energy diagram (see SI), the reduction potentials [PW12O40]5−/[HPW12O40]6− or [SiW12O40]5−/[SiW12O40]6−, are lower than that of a proton at pH <7 , and these can be further reduced by MV+⋅, so theoretically, HER should occur spontaneously in this system.A schematic model for the photochemical HER with iCHELLs along with the strategy above is given in Figure 12O40]3− and MV2+. As a result of Xe light irradiation to the membrane and solution, the colour of the upper phase immediately turned dark blue due to the generation of MV+⋅. After a short lag period, the colour of the lower phase gradually turned to dark blue from the membrane boundary, see Figure 12O40]3− corresponding to WVI/V transition , and it is assumed that the colour change of the lower phase was induced by reduction of [PW12O40]3−. It should be noted that reduced species of [PW12O40]3− were surprisingly stable even in air, as observed when the membrane was left (without irradiation) for 100 h. This is still under investigation, but the membrane may act as barrier for oxygen.Electron transfer across the membrane was initially evaluated using a bulk plane membrane composed of PW1O403− and2+ and [PW12O40]3− were fabricated (see SI for detailed procedure) by injection of a dense aqueous solution of H3[PW12O40] (100 mm) into another dense aqueous solution of MV (25 mm). iCHELLs were formed at various concentrations of H3[PW12O40] (50–500 mm), but those prepared with high concentrations of H3[PW12O40] were found to swell over time due to osmotic pressure, and low concentrations of H3[PW12O40] resulted in flat and fragile iCHELLs. Thus, 100 mm of H3[PW12O40], which resulted in a stable structure, was used for most of the experiments described . As a result of light irradiation, a colour change of iCHELLs to black was observed in presence of [Ru(bpy)3]2+ and TEOA , but the TON was lower than with [PW12O40]3−. A mixture of H4[SiW12O40] and Pt NPs resulted in small precipitations within a few hours, presumably resulting in low efficiency for the HER.Photochemical HER was conducted using iCHELLs consisting of POM and MVns Table . Hydroge2+ and PW2O403− br12O40]6− is essential to drive proton reduction, and therefore all the [PW12O40]3− in the iCHELLs must be reduced to [PW12O40]5− before hydrogen evolution can begin. After a few hours of irradiation of the iCHELLs, a rapid increase in the HER rate was observed (ca. 3–12 hrs). We hypothesise that in this phase electrons transferred into the inside of the iCHELLs are used for proton reduction directly. After this period, a decay in the hydrogen evolution was observed due to deactivation of [PW12O40]3− or Pt NPs, or a decreased concentration of protons in the iCHELLs.Time course measurements for hydrogen production in Experiments 1–4 are shown in Figure To verify the reason for the decay, photochemical HER was conducted with various initial concentrations of Pt. The total volume of hydrogen produced was similar when the Pt concentration was halved (Expts. 1 & 2), suggesting that the dominant reason for the decay was not deactivation of Pt NPs. However, upon reducing the Pt concentration further (by a factor of ca. 5×), the total volume of hydrogen produced somewhat smaller (Expt. 3), so the effect of Pt availability on the decay is not negligible.3[PW12O40] is a strong acid, and three protons are almost completely dissociated in aqueous solution. Therefore, increasing the concentration of H3[PW12O40] provides an increased concentration of protons inside of iCHELLs. Time courses of hydrogen production where the concentration of H3[PW12O40] was varied  are shown in Figure 3[PW12O40] resulted in a greater volume of hydrogen in total, confirming that the available concentration of protons is strongly linked to the decay of hydrogen production, and defines the total volume of hydrogen that can be produced. The length of induction period also shows a correlation with the H3[PW12O40] concentration. At lower concentrations, the total amount of [PW12O40]3− in the iCHELLs is small, requiring fewer electrons for reduction to [PW12O40]5−, resulting in a shorter induction period for HER. It should be noted however, that the concentration of H3[PW12O40] also affects morphology of the membrane , as described above, and these morphological changes could also influence the induction period.As described previously, H3PW12O0 is a st2 reduction are under investigation. iCHELLs represent a unique approach to structuring multicomponent catalytic systems in a similar manner to the spatial organisation critical to many biological processes, and one could foresee the ability to design structures with active sites akin to those in enzymes.In conclusion, we achieved a minimal photosystem involving hierarchical and anisotropic electron transfer from the photosensitizer across a membrane, and successfully observed photochemical HER from Pt NP inside the iCHELL structure with a high TON. The unique properties of the iCHELLs allowed optimum conditions for both proton reduction and sacrificial electron donor stability by utilising a membrane and providing a compartmentalised low pH environment for HER and a high pH for electron donor stability. An induction period, which is not normally observed in homogeneous HER, was observed in the iCHELLs due to membrane transport, and its length was controllable by changing building block concentration. The effect of size was not investigated here, but it is presumed that larger numbers of smaller iCHELLs would be favourable for HER, due to the larger overall surface area for surface reduction of POMs. Mass‐production and precise size control of iCHELLs by using microfluidic devices,) dichloride hexahydrate ([Ru(bpy)3]Cl2⋅6 H2O). Phosphotungstic acid hydrate (H3[PW12O40]⋅n H2O) was purchased from Wako. Methyl viologen dichloride (MV) and Triethanolamine (TEOA) were purchased from TCI. PVP‐protected colloidal Pt (2 nm in particle size) was purchased from Tanaka Holdings Co., Ltd. Silicotungstic acid hydrate (H4[SiW12O40]⋅n H2O) and all other materials were purchased from Sigma Aldrich. 1H‐NMR analyses were measured with JEOL 600 MHz NMR. UV/Vis absorption spectra were measured with JASCO V‐630. Visible‐light irradiation  was conducted using Xenon Light Source XFL‐300.General experimental remarks: All chemicals were purchased from commercial sources and used without further purification, except for Trisruthenium(II12O40]4− or [PW12O40]3− and [Ru(bpy)3]2+: 20 μL of aqueous solution of POM (H4[SiW12O40] or H3[PW12O40]) (100 mm) was intermittently injected into 1.4 mL of another aqueous buffer solution of [Ru(bpy)3]Cl2 (26.5 mm) and TEOA (53.5 mm) with micro syringe to form iCHELLs. Volume per one iCHELL was about 5 μL, so approximately four iCHELLs were prepared.Fabrication of iCHELLs consisting of [SiW12O40]3− and MV2+: 2.0 mL of aqueous solution of H3[PW12O40] (100 mm) in 10 mL glass vial was degassed by argon bubbling for 30 minutes. 2.0 mL of dichloromethane (DCM) degassed with Ar in advance was added on the top of the H3[PW12O40] solution. Then, 2.0 mL of degassed mixture of MV (25 mm), [Ru(bpy)3]Cl2⋅6 H2O (0.1 mm), and TEOA (50 mm) was also added on the top of dichloromethane. Dichloromethane was removed with syringe, and plane bulk membrane was formed.Fabrication of bulk membrane composed of [PW4[SiW12O40] or H3[PW12O40]) (100 mm) was intermittently injected into 1.4 mL of another aqueous buffer solution of MV (26.5 mm), [Ru(bpy)3]Cl2⋅6 H2O (0.107 mm), and TEOA (53.5 mm) with micro syringe to form iCHELLs (Scheme S4 in SI). The volume per iCHELL was approximately 5 μL, so around twenty iCHELLs were prepared.Fabrication of iCHELLs consisting of MV and POM for HER: 100 μL of aqueous solution of POM  should be addressed to the authors.SupplementaryClick here for additional data file.


Borane dimethylsulfide complex and catecholborane were used as a hydride source. Surprisingly, the less sterically hindered 1 a exhibited lower catalytic activity than the bulkier 1 b. A similarly unexpected discrepancy was found with the lower catalytic activity of 10+ in comparison to the one of the bis(NHI) 12. The latter is incorporated as the ligand to the boron center in 10+. To elucidate possible mechanisms for CO2 reduction the compounds were subjected to stoichiometric reactivity studies with the borane or CO2. Aluminum carboxylates 4, 6, and 7+ with two, four, and one formate group per two aluminum centers were isolated. Also, the boron formate salt 11+[OTs]− was characterized. Selected metal formates were subjected to stoichiometric reactions with boranes and/or tested as a catalyst. We conclude that each type of catalyst  follows an individual mechanistic pathway for CO2 reduction.The previously reported dimeric NHI aluminum dihydrides  2 reductionCO: Aluminum‐ and boron hydrides bearing the N‐heterocyclic imino ligand show activity as (pre)catalysts in the hydroboration of carbon dioxide with borane dimethylsulfide complex and catecholborane. A bis(NHI) ligand proved as an organocatalyst with highest activity among the tested compounds. Metal formate complexes of B and Al were isolated. Nowadays, a chemical transformation of outstanding importance to the biosphere is the catalytic reduction of carbon dioxide. The massive amounts produced by combustion of fossil fuels are commonly acknowledged to promote climate change and sea‐water acidification.2.2 transformations, particularly with regard to hydrogenation/reduction, started to surge.A) or triazabicyclodecenes  are typically implemented to promote chemical reduction of CO2  have also been used as catalysts for this type of transformation.D) reported by Wehmschulte and coworkers and a non‐ionic catalytic system based on boron‐ and aluminum Lewis acids are to be pointed out, as well catalytic reduction of CO2 Figure . In recel Figure .6a, 6d, 2 has, however, not been described. In 2018, the group of Aldridge outlined the reactivity of 1,3‐diketimino aluminum hydride (E) and selected derivatives with CO2, catecholborane and borane dimethylsulfide complex  hydrides bearing an N‐heterocyclic imino (NHI) group3 to an atmosphere of CO2 (1.0–1.1 bar) in the presence of catalytic amounts (1–5 mol%) of 1 or 2. No notable conversion of the hydridoborane was recognized. Even when heating a reaction setup containing 1 b as a (pre)catalyst to 60 °C for several hoursRecently, we described the catalytic hydroboration of terminal alkynes and of carbonyl compounds  with pinacolborane using NHI aluminum hydrides as catalysts Figure .9b Accor11B NMR analysis. This agrees with the generally lower susceptibility of CO2 towards hydroboration because the second oxygen atom as a highly electronegative entity renders the C=O bond less electron‐rich than the one in aldehydes or ketones. Thus, we switched to borane dimethylsulfide complex as a reductant which is commonly known to be a stronger hydroboration reagent than pinacolborane. In the outcome, major transformation of CO2 into methoxyborane equivalents was observed within hours at ambient temperature using 1 as a catalyst (Table 1 a) exhibited decreased catalytic activity as compared to the bulkier 1 b  had been reported to yield the aluminum borohydride 3  within 2 hours to yield the dicarboxylate 4 (Scheme 1H NMR spectrum (CDCl3) with 2H relative intensity. Also, we obtained a single crystal of 4 that was determined to the diformate by XRD analysis with the formate groups at the four‐membered ring in trans‐position relative to each other 4]−) and B(C6F5)3 (uncharged) in CDCl3 solution were probed in an NMR sample tube (Scheme F=C(CF3)3). The trityl salt afforded a clean conversion to a new NHI species (1H NMR spectroscopic control) upon reaction in a one‐to‐one ratio. In contrast, two equivalents of B(C6F5)3 were required until the signal pattern of the proton resonances produced by the NHI ligand matched the 1H NMR spectrum of the trityl salt conversion of 4. A singlet at 7.69 ppm integrates to 1H and is assigned to a formate group which resonates at significantly lower field as the carboxylate groups in 4 or 6. Also, the formation of triphenylformylmethane and of the [HCO2(B(C6F5)3)2]− anion, respectively, is concluded from 1H and 11B NMR analysis. As the 1H NMR spectrum of 7+ in CDCl3 suggests high symmetry for the complex we surmise the single formate group to assume a bridging position between the aluminum centers decorating the four‐membered Al2N2 ring. Consequently, we postulate the structural formulation 7+  in CDCl3 in an NMR sample tube. Monitoring the progress of the reaction revealed the formation of an untraceable mixture of NHI ligand species in the 1H NMR in both cases . Counterintuitive to the expectation from the steric properties the bulkier 4 had decomposed completely within one hour while the less congested 6 was still observed as the major component within the same timeframe though the latter was exposed to a larger excess of the borane (7 h later 6 was found to have quantitatively disintegrated). The decomposition rates of 4 and 6 correlate to the catalytic activities of 1 b and 1 a for which bulkier 1 b was also found to exhibit the higher CO2 conversion rate  showed two broad resonances  and a sharp quintet of weaker intensity . The −37 ppm signal is in agreement with the value reported for the aluminum borohydride 3 while the most upfield shifted resonance can clearly be assigned to [BH4]−. Such resonances were found in the 11B spectrum of the conversion of 6 with excess borane, however, aside from the far slower conversion rate the relative intensity of the [BH4]− signal was considerably increased and only traces of the two broader resonances were shown . The formation of [BH4]− is of particular interest because traces of Na[BH4] had been reported to catalyze the reduction of CO2 to trimethoxyboroxine with H3B ⋅ thf in THF.In order to further elucidate the mechanism for CO7+) shows that dimeric aluminum complexes of type 4 may readily act as carboxylate group transfer agents. However, after consideration of the reaction profile of 4 towards excess H3B ⋅ SMe2 (vide supra) we do not propose that the respective complex 7+ constitutes a relevant intermediate in the reduction of CO2 with this borane and 1 b as a precatalyst. Taking into account the conversions described above we conclude that the catalytic CO2 reduction with 1 commences with insertion of CO2 into the Al−H bonds rather than initial reaction with the borane because a resulting complex of type 3 would be an ending path. It is conceivable, however, that a mixed Al(H)BH4 species promotes CO2 reduction but its existence could not be verified albeit the assigned 11B NMR signal at −40 ppm from conversions of 4 or 6 with excess borane (vide supra) could be produced by such type of complex. Nevertheless, the absence of CO2 insertion to occur for 2 and 3 renders this “mixed‐species‐pathway” unlikely. Considering that aluminum carboxylate reactions with exc. H3B ⋅ SMe2 lead to ill‐defined product mixtures supports speculations that a non‐aluminum‐containing compound promotes CO2 reduction and it is likely to include the tetrahydroborate anion as a potent hydride transfer group.The reactivity towards carboxylate group acceptor reagents (i. e. synthesis of 4 and 7+ we conceived that the bulkier bis(NHI) aluminum dihydride 9+  would be a suitable target to provide insight into (i) the difference between complexes with one Al center (9+) and two Al centers (1), and (ii) the difference between cationic and uncharged aluminum dihydrides with regard to catalytic activity for CO2 reduction. Compound 9+[OTs]− readily forms upon conversion of the bis(iminiumtosylate) 8 ⋅ (HOTs)2 with lithium aluminum hydride as concluded from 1H and 13C{1H} NMR spectroscopy and verified by SCXRD study and elemental analysis (Scheme p‐tolylsulfonyl). We tested the suitability of 9+[OTs]− as a (pre)catalyst for CO2 reduction (i. e. hydroboration) with H3B ⋅ SMe2 and it exhibited substantially lower activity as 1 a  ligand with mesityl substituents at the imidazoline nitrogen atoms of the ligand. centers , and  furnished the borocarboxylate 11+[OTs]− within 12 h . The introduction of the carboxylate group at boron is indicated by the rise of a singlet at 5.51 ppm in the proton NMR spectrum (CDCl3) that integrates to 1H. A signal at −1 ppm (JBH not resolved) in the 11B NMR analysis is shifted to lower field with regard to the one of the precursor  and suggests that the boron nucleus remains four‐coordinate but has one hydride replaced by a more electron‐withdrawing ligand. Moreover, the structural formulation is established by SCXRD analysis . Continued exposition of 11+[OTs]− in CDCl3 to CO2 did not result in further transformation (i. e. to the borodicarboxylate) over 24 h which might reflect the generally weaker hydride donor character with respect to the one of aluminum hydrides (1).We had previously described the bis(NHI) substituted boron dihydride salt − Scheme .14d It w2 with H3B ⋅ SMe2 and use of the boron dihydride salt 10+[OTs]− as a catalyst resulted in a conversion rate similar to the one of aluminum hydride 1 a (Table 2 reduction using 10+ we reacted 11+[OTs]− with an excess of H3B ⋅ SMe2 (7 equiv) in CDCl3. It occurred that in theCatalytic reduction of CO1H NMR spectrum a clean transformation to 10+ was indicated. In addition, a singlet at 3.65 ppm appeared which suggests the formation of a methoxy group. The 11B NMR spectrum shows a broad resonance at −8 ppm assigned to 10+ (JBH not resolved) and a signal at 19 ppm which hints towards the formation of a trialkoxy boron species. This well‐defined conversion of 11+ to 10+ with excess H3B ⋅ SMe2 is in sharp contrast to the respective reactions of the aluminum formates 4 and 6. It reveals that 10+ can be transformed by CO2 and replenished by the reductant (i. e. H3B ⋅ SMe2).2 reduction with 10+ is outlined in Scheme 11+ via CO2 insertion into the B−H bond. With concomitant release of boron formate the catalyst (10+) is reformed via metathesis reaction between hydridoborane (i. e. reducing agent) and 11+ (Path A). Alternately, the carbonyl group in 11+ can be hydroborated by the reducing agent to produce 1Int which liberates boronic acetal upon reaction with hydridoborane (Path B).The proposed mechanism for the catalytic CO12 with H3B ⋅ SMe2 (2 equiv) to 10+[BH4]−  of H3B ⋅ SMe2 in CDCl3 containing 5 mol%  of 12 is near‐quantitatively converted to alkoxyborane equivalents at 1.0–1.1 bar CO2 pressure  that differs from the mechanism for the use of a bidentate organic superbase naphthalene, 12) as proposed by Fontaine.12 can form 10+ when reacted with H3B⋅SMe2 we assume that its activity as a (pre)catalyst might rely on a dual mechanism running in part via 11+ (Scheme 4) and in part following the catalytic cycle of Fontaine which does not involve the formation of an analoguous bis(amino) boron formate.In 2018 we had published a study on the auto‐ionization of the “free” bis(NHI) ligand to 10+BH−  and 9‐BBN−H  as alternate reductants. These boranes are commonly acknowledged to be less potent hydroboration agents than H3B ⋅ SMe2. Still, when using 12 as a (pre)catalyst we observed near‐quantitative conversion of either borane within 13 h when exposed to a CO2 atmosphere (1.0–1.1 bar) in CDCl3. In case of HBcat 1H and 11B NMR analysis confirmed the formation of H3COBcat and O(Bcat)2 2 and HCO2Bcat, see the SI). When the dialkylborane is used the NMR analysis suggested the formation of a mixture of H3COBBN, O(BBN)2, H2C(OBBN)2, and HCOO(BBN) similar to the report of Cantat and coworkers on the analogous conversion using various organic nitrogen bases as catalysts .12 promotes the CO2 reduction with HBcat we also probed selected boron and aluminum complexes as catalysts for comparison. The results are outlined in Table 3B ⋅ SMe2 the conversions generally take longer and a lower ratio of methoxy containing products is obtained. Unsurprisingly, the relative catalytic activity of the compounds follows the trend from the trihydridoborane reactions  ligand 12 was found to be the most active (pre)catalyst. The bulkier aluminum hydride 1 b exhibited comparable conversion rates while the less congested aluminum hydride 1 a was significantly less active. The bis(NHI) aluminum dihydride salt 9+[OTs]− possessed lower activity than 1 a. The boron dihydride salt 10+[OTs]− proved to be a far more potent catalyst than its cationic aluminum congener (9+). The metal(loid) hydrides  were demonstrated to form metal formate complexes  upon conversion with CO2. The tetracarboxylate 6, the dicarboxylate 4, and the monocarboxylates 7+[HCO2(B(C6F5)3)2]−, as well as 11+[OTs]− were isolated at room temperature under an atmosphere of argon or nitrogen. The aluminum formates 4 and 6 were shown to form ill‐defined product mixtures upon reaction with an excess H3B ⋅ SMe2. From the boron formate 11+ the dihydride 10+ was replenished by reaction with H3B ⋅ SMe2. For 1 a,b it is hypothesized that an aluminum formate is initially formed which converts with the borane to a complex product mixture that contains the actual catalytically active species. For 10+ the relevant processes  are supposed to majorly occur at the bis(NHI)‐bonded boron center. For 12 the [BH4]− anion formed via auto‐ionization between bis(NHI) and H3B ⋅ SMe2 is believed to function as the hydride transferring species.In summary, we have demonstrated the applicability of various aluminum and boron hydride complexes The authors declare no conflict of interest.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.


E. halophila HiPIP I, many NMR structures were determined for several Fe–S proteins in different oxidation states. It was found that differences in chemical shifts, in patterns of unobserved residues, in internal mobility and in thermodynamic stability are suitable data to map subtle changes between the two different oxidation states of the protein. Recently, the interaction networks responsible for maturing human mitochondrial and cytosolic Fe–S proteins have been largely characterized by combining solution NMR standard experiments with those tailored to paramagnetic systems. We show here the contribution of solution NMR in providing a detailed molecular view of “Fe–S interactomics”. This contribution was particularly effective when protein–protein interactions are weak and transient, and thus difficult to be characterized at high resolution with other methodologies.Iron–sulfur proteins were among the first class of metalloproteins that were actively studied using NMR spectroscopy tailored to paramagnetic systems. The hyperfine shifts, their temperature dependencies and the relaxation rates of nuclei of cluster-bound residues are an efficient fingerprint of the nature and the oxidation state of the Fe–S cluster. NMR significantly contributed to the analysis of the magnetic coupling patterns and to the understanding of the electronic structure occurring in [2Fe–2S], [3Fe–4S] and [4Fe–4S] clusters bound to proteins. After the first NMR structure of a paramagnetic protein was obtained for the reduced  Whi3+ proteins, the electron spin relaxation times of the paramagnetic centers are shorter than those in the [4Fe–4S]2+ and [4Fe–4S]+ clusters, because of larger magnetic couplings among iron ions. Therefore, signals are sharper and easier to be sequence specifically assigned  iron ions and a delocalized valence pair , which are antiferromagnetically coupled each other giving rise to a S = 1/2 ground state [+ case.Individual oxidation states of iron ions in [4Fe–4S] clusters were identified for the first time in [4Fe–4S]ned Fig. i. Theorend state , 56, ess3+ cluster and the availability of a series of homologous proteins from different bacterial sources, characterized by high reduction potential values, spanning the + 450/+ 50 mV range  provided NMR spectroscopists with an exemplary case. Sequence-specific assignments of Cys residues bound to the cluster were performed, and the two iron ions constituting the mixed valence pair and those forming the purely ferric pair were identified  proteins, but not necessary for the maturation of mitochondrial [2Fe–2S] proteins in eukaryotes  cluster is de novo synthesized on the scaffold protein ISCU2 by a high molecular weight complex (HMW complex hereafter), composed of five proteins  –135. On karyotes –144. Onckaryotes , 145–147E. coli cells. Due to its very high molecular mass, X-ray crystallography and cryo-EM are the most appropriate techniques to structurally characterize the complex at the atomic level and have, indeed, successfully generated structural models of the complex or sub-complex forms [In the de novo formation of a [2Fe–2S] cluster, the majority of the proteins of the human ISC assembly machinery forms permanent interactions featuring tight binding affinities –135, 148ex forms –135. In ex forms , 150. Asex forms , 152, thex forms , 132. InSolution NMR largely contributed to investigate the subsequent steps of the ISC assembly machinery, being able to provide a detailed model of how the [2Fe–2S] clusters, de novo synthetized in the multi-component complex, couple with each other to form a [4Fe–4S] cluster. This process involves four interacting proteins as mentioned above, i.e., GLRX5, ISCA1, ISCA2 and IBA57.1H–15N HSQC and 1H–15N IR-HSQC-AP NMR experiments allowed the identification of the residues affected by [2Fe–2S] cluster binding  GLRX5 in solution adopts essentially the same structural arrangement as observed for the dimer in the crystal structure. However, 1H–15N IR-HSQC-AP and 1D 13C NMR experiments tailored to paramagnetic systems also showed that dimeric [2Fe–2S] GLRX5 exists in solution as a mixture of two species in equilibrium each other (GLRX5a and GLRX5b), as two sets of signals for the Fe–S ligand Cys 67, and for Ser 70 were identified  GLRX5, we observed that they are all around the iron-bound GSH molecule. Among these eight residues, the two charged ones, Lys 101 and Asp 123, are particularly important to establish electrostatic interactions with the glycine carboxylate and the glutamate amine groups of GSH, respectively. All the available NMR data indicate that two dimeric species of [2Fe–2S] GLRX5 exist in solution, differing in the binding mode of the GSH molecule , where two [2Fe–2S] clusters are coordinated by four protein subunits and four GSH molecules and buried in the tetramer . In such binding . By mapp binding , we founperiment . Their 1entified . Also in15N NMR relaxation data showed a global rigidity of the α–β domain, but also identified a certain degree of backbone flexibility in the loop containing the Fe–S ligand Cys 79, located in the first position of the conserved CXnCGC motif. Also, the C-terminal tail of ISCA2, encompassing residues 141–154, and containing the other two conserved Fe–S binding Cys residues (Cys 144 and Cys 146), was found to be highly flexible. Therefore, NMR analysis indicated that all the regions containing the conserved Cys residues can easily undergo structural rearrangements to bind the cluster. Severe line broadening of a few backbone NH signals observed in the 1H–15N HSQC map of apo ISCA2 indicates that dynamic processes also occur at the dimer interface, suggesting an intrinsic propensity for the subunits to be swapped with other protein partners. This is, indeed, what occurs by mixing apo ISCA2 with apo ISCA1. This process has been characterized by solution NMR, performing 1H–15N HSQC NMR titrations of 15N-labeled apo ISCA1 or ISCA2, with, respectively, unlabeled apo ISCA2 or ISCA1 2+ cluster binding [1H spectrum is consistent with the presence of a mixture of [4Fe–4S]+ cluster-bound dimeric species and a minor [2Fe–2S]2+ cluster-bound species [15N relaxation data indicated that [2Fe–2S] or [4Fe–4S] cluster binding does not alter the quaternary structure of ISCA2 [1H NMR experiments have been perfomed to identify the two pairs of [2Fe–2S] cluster ligands. The [2Fe–2S] cluster binding properties of Cys-to-Ser single mutants for each conserved cysteine were compared with those of the wild-type protein and their 1H NMR spectra analyzed  cluster  GLRX5a [15N NMR relaxation data showed that ISCA1 and ISCA2 receive the [2Fe–2S] cluster from [2Fe–2S] GLRX5 in their dimeric state. NMR data also showed that cluster transfer occurs via the formation of a low-populated protein–protein complex, with an interacting surface involving the GLRX5 region surrounding Cys 67 [a and [2Fe–2S] GLRX5b; (2) dimeric [2Fe–2S] GLRX5 specifically transfers the [2Fe–2S]2+ cluster to apo ISCA1 and apo ISCA2 via an associative process that involves a weak transient protein–protein intermediate; and (3) [2Fe–2S] GLRX5b is more reactive than [2Fe–2S] GLRX5a to donate the cluster to apo ISCA1 and apo ISCA2. In conclusion, the equilibrium between [2Fe–2S] GLRX5a and [2Fe–2S] GLRX5b species is the trigging factor specifically driving cluster transfer to ISCAs proteins, and thus plays a functional role in the cluster transfer mechanism , we were able to define the different roles of the cysteines in the cluster transfer process  cluster bound species can be isolated once Cys 79 is absent, i.e., upon chemical reconstitution of the C79S ISCA2 mutant  or [4Fe–4S] clusters, and presumably also in the heterodimeric ISCA1–ISCA2 complex. This mechanism would also make two of the C-terminal cysteines (Cys 146 of ISCA2 and Cys 121 of ISCA1) available for the coordination of a second cluster which can be extracted from GLRX5, upon the formation of another GLRX5-ISCA intermediate. This transient intermediate, which contains two [2Fe–2S]2+ clusters, might be the species that, by accepting two electrons from a still unknown physiological electron donor  domain with no Trx enzymatic activity, but functionally indispensable , 175, anAnamorsin is the appropriate protein partner to investigate the functional role of GLRX3 in transferring [2Fe–2S] clusters for these reasons: (1) it interacts with GLRX3 in vivo ; (2) it 2+ cluster-bound forms of GLRX3  ctively)  were firractions . This stractions . Moleculractions . These tractions .1H–15N-HSQC and 1H–15N-IR-HSQC-AP NMR experiments, combined with UV–Vis and EPR spectroscopy, showed that [2Fe–2S]2 GLRX32 forms a 1:1 hetero-dimeric complex with anamorsin, the same formed by the apo proteins, in which both clusters of GLRX3 have been unidirectionally transferred to the two cluster binding sites of the CIAPIN1 domain of anamorsin 4 complex, via a membrane transporter; then, the [2Fe–2S] cluster is believed to be uptaken by the cytosolic form of ISCU2, which delivers it to cytosolic form of NFU1, which finally transfers the cluster to GLRX3 [2 have been defined. NMR data showed that the [2Fe–2S]2 GLRX3–BOLA22 complex in vitro transfers both its [2Fe–2S]2+ clusters to apo anamorsin producing its mature holo state, through the same protein–protein recognition mechanism operative in the GLRX3-anamorsin interaction, that specifically occurs between the N-terminal domains of the two proteins  to the final target, and then to be disrupted once the cluster has been transferred, thus producing a matured final target. Second, solution NMR is the optimal technique to investigate, at near-physiological conditions and at an atomic level, protein–protein interaction events that are transient and weak. Solution NMR will be able to clearly define the molecular function of these interactions, and thus open up new horizons on how to deal with the human diseases related to defects in Fe–S protein biogenesis processes, which have been growing rapidly. In this respect, we believe that a crucial breakthrough in the Fe–S protein field might be determined by the development and the application of paramagnetic NMR methods to characterize protein–protein complexes directly in mammalian cells. Indeed, it will be possible to study at atomic resolution the interactions responsible for maturing Fe–S proteins in living cells and to investigate physiological cluster-binding properties and cluster redox states.


After publication of this article , the folFigure 2E follistatin and GAPDH panels contain background irregularities such that lane 1 appears to have a different background to lanes 2–6;Figure 3B Magic-F1 and HGF panels contain background irregularities such that lanes 1–3 appear to have a different background to lanes 4–6;Regarding The authors have provided the original images used in Figures 2E and 3B. The original images do not contain background irregularities and the source of the image artifact is unclear.With this correction, the authors provide an updated S1 File(ZIP)Click here for additional data file.