Herein, Fe‐doped graphitic carbon nitride is rationally prepared by a simple adsorption method and is used as template to construct isolated FeN4 sites through a confined pyrolysis strategy, which avoids the agglomeration of metal atoms to particles during the synthesis process and thus provides abundant active sites for the CO2 reduction reaction. The isolated FeN4 sites lower the energy barrier for the key intermediate in the CO2 reduction process, leading to the enhanced selectivity for CO production with a faradaic efficiency of up to 93%.The construction of isolated metal sites represents a promising approach for electrocatalyst design toward the efficient electrochemical conversion of carbon dioxide (CO 4 sites in carbon substrate are constructed through a confined pyrolysis strategy with graphitic carbon nitride as the template. The isolated FeN4 sites show lower free energy change for the key intermediate in the CO2 reduction process, leading to enhanced selectivity for CO production with a faradaic efficiency of up to 93%.Isolated FeN Electrocatalytic CO2 reduction offers a promising approach to mitigate CO2 levels and convert it to value‐added fuels. Many efforts have been dedicated to developing efficient electrocatalysts for CO2 reduction. Nevertheless, the low selectivity of the reduction products is still a key obstacle which restricts the further development of CO2 conversion technologies. Homogeneous catalysts could possess excellent selectivity due to its homogeneously distributed and well‐defined active sites, while its inferior stability and difficulty of separation hinder the further development toward industrial applications. In contrast, heterogeneous catalysts could provide stable catalytic performance, while the diverse nature of active sites restricts the selectivity. Thus the development of catalysts that combine the advantages of both heterogeneous and homogeneous catalysts is urgently imperative for the efficient conversion of CO2.The accumulation of COconcerns.1 Elec Apart from the maximum atom efficiency, single‐atom catalysts afford the isolated and well‐defined active sites confined in the support of inorganic solid material, offering high selectivity and stability toward catalytic reaction. Benefiting from the unique structure, the single‐atom catalysts present comparable catalytic activity to that of homogeneous catalysts, meanwhile possessing high recyclability and stability arising from heterogenization. Among the single‐atom catalysts, the isolated metal atoms coordinated with nitrogen (MNx) in carbon substrates have shown excellent performance in electrocatalysis, providing a promising way for electrocatalytic CO2 reduction. However, construction of MNx sites is still a challenge since isolated active sites are easily agglomerated to particles during the synthesis process, leading to loss of catalytic performance. Recently, isolated NiN4 sites have been successfully constructed via a confined pyrolysis strategy, in which Ni‐doped graphitic carbon nitride (g‐C3N4) acts as the template and nitrogen source during the confined pyrolysis process. Considering the synthesis of metal‐doped g‐C3N4 by pyrolyzing the precursor of g‐C3N4 and metal salts is uncontrollable, a more simple and universal design of metal‐doped g‐C3N4, which is the pivotal step in the confined pyrolysis strategy, is still much desirable but remains challenging for the construction of MNx sites.Single‐atom‐based catalysts provide a great potential to bridge the gap between heterogeneous and homogeneous catalysts.6 Apar4 sites in carbon substrates (denoted as FeN4/C) by the rational design of Fe‐doped g‐C3N4. A simple adsorption method was adopted for g‐C3N4 to trap Fe atoms, making it an excellent template for the formation of FeN4 sites. Then the formation of a carbon layer on the surface of Fe‐doped g‐C3N4 would provide a confined environment to suppress the agglomeration of Fe atoms to particles during the pyrolysis process, thus effectively constructing the isolated active sites. Benefiting from the unique structure and coordination environment, the isolated FeN4 sites show high selectivity for the electrocatalytic conversion of CO2 to CO, with the highest faradaic efficiency of 93% at −0.6 V versus RHE. The isolated configuration was revealed by spherical aberration correction electron microscopy and extended X‐ray absorption fine structure analysis. The theoretical calculation demonstrates that isolated FeN4 sites lower the energy barrier for the formation of COOH*, leading to the enhanced activity for CO production. We believe this study would pave a new avenue for rational design of highly efficient single atom catalysts with abundant active sites.Herein, we report the construction of isolated FeNFigure 4/C, which presents a sheet‐like structure, similar to that of bare N‐doped carbon (denoted as N/C) and g‐C3N4, as seen in Figure S1 (Supporting Information). No particles are observed from the high‐magnification TEM image for FeN4/C, as shown in Figure 4/C in Figure 4/C. Energy‐dispersive X‐ray spectroscopy (EDX) mapping analysis in Figure The morphology of the catalysts was confirmed by transmission electron microscopy (TEM). 4/C and N/C in Figure S2 (Supporting Information) shows two distinct peaks at about 1570 and 1330 cm−1, which could be assigned to graphitic sp2 carbon (G‐band) and disordered sp3 carbon (D‐band). The ratio of the relative intensity of the D band to the G band presents no much difference for FeN4/C and N/C, with an ID/IG value of 1.38 and 1.31, respectively, indicating the similar extent of graphitization and disorder in the catalysts. The X‐ray diffraction (XRD) patterns of FeN4/C and N/C in Figure S3 (Supporting Information) both show two typical broad peaks at about 24° and 44°, which could be ascribed to (0 0 2) and (1 0 1) lattice plane of graphite. Apparently there is no new crystal phase present in the FeN4/C. While without the confinement of the carbon layer during pyrolysis, Fe3C and Fe particles would appear in the synthesized catalyst (denoted as Fe/C). As shown in the TEM images in Figure S4 (Supporting Information), the catalyst shows a morphology of particles wrapped with outer carbon layer. XRD pattern of Fe/C in Figure S5 (Supporting Information) presents the distinct peaks corresponding to Fe3C (JCPDS Card No. 350772) and Fe (JCPDS Card No. 060696), demonstrating the dominant species in Fe/C are Fe3C and metallic Fe. Note that the further additional loading of Fe will also result in the formation of Fe nanoparticles in FeN4/C . As seen in Figure S6a (Suppoerting Information), the XRD pattern of Fe NPs/C shows a distinct peaks at 44.6°, corresponding to the (1 1 0) lattice planes of metallic Fe (JCPDS Card No. 060696). The TEM image in Figure S6b (Supporting Information) shows the presence of small particles on the Fe NPs/C. The EDX mapping clearly shows the aggregation of Fe atoms to particles, as shown in Figure S6c (Supporting Information). The high resolution TEM (HRTEM) image of Fe NPs/C in Figure S6d (Supporting Information) presents a lattice distance of 0.20 nm, which could be ascribed to the (1 1 0) plane of Fe particles (JCPDS Card No. 060696), agreed well with the XRD result.The Raman spectrum for FeN(D‐band).10 TheFigure 4/C, in comparison to Fe NPs/C and Fe foil. It is clearly seen that the absorption‐edge of FeN4/C shifts toward higher energy compared with Fe NPs/C and Fe foil, suggesting Fe in FeN4/C is in an oxidation state. As a comparison, the absorption‐edge of Fe NPs/C is located between the FeN4/C and Fe foil, which could be ascribed to the coexistence of oxidized Fe single atoms and metallic Fe particles. The Fe 2p X‐ray photoelectron spectroscopy (XPS) of FeN4/C is shown in Figure S7 (Supporting Information), in which the characteristic Fe 2p3/2 peak is located at about 710 eV, indicating the existence of Fe2+ species in FeN4/C. The Fourier‐transformed (FT) k3‐weighted extended X‐ray absorption fine structure (EXAFS) spectra are shown in Figure 4/C, its FT curve only displays a prominent peak at 1.5 Å, which is generally attributed to the Fe—N first coordination shell. Beyond this distance, no obvious FT peaks are observed, especially at the distance of Fe–Fe interaction, indicating that the Fe atoms in FeN4/C are atomically dispersed. For Fe NPs/C, a distinct peak corresponding to Fe—Fe bond appears, demonstrating the existence of metallic Fe particles. The quantitative simulation for the EXAFS of FeN4/C was performed to obtain the precise chemical configuration around Fe atoms. Figure 4/C has been perfectly reproduced. The fitting results reveal isolated Fe atoms are coordinated with four N atoms at a distance of 1.97 Å. The FeN4 structure has been also demonstrated as a more reasonable configuration after the high‐temperature pyrolysis process. The relevant fitting parameters are given in Table S1 (Supporting Information). To further determine the chemical bond for FeN4 sites, N 1s XPS was performed, as shown in Figure  For FeN4/C, the peak assigned to pyridinic N clearly shifts to the higher energy side compared with that of N/C, indicating the pyridinic N bonds with the Fe atoms. Thus the local structure of FeN4 sites is revealed that the isolated Fe atoms coordinated with four pyridinic N atoms.Synchrotron‐based X‐ray absorption spectroscopy was further adopted to determine the precise local chemical configuration around isolated Fe sites. on state.12 As 2 reduction measurement demonstrates the introduction of isolated FeN4 sites in carbon substrate greatly enhances the catalytic performance. The linear sweep voltammetry (LSV) curves  toward CO was measured and presented in Figure 4/C exhibited high conversion efficiency to CO and greatly suppressed the competitive H2 evolution reaction , achieving a maximum FE of 93% for CO at −0.6 V. This performance could be comparable with the state‐of‐the‐art catalysts for CO2 reduction . In contrast, the N/C and Fe/C only give a maximum FE of 46% and 23%, respectively. The partial current density for CO production of the catalysts is presented in Figure 4/C shows a much higher catalytic current density of 2.5 mA cm−2 at −0.8 V, which is 35 times and 17 times of that for N/C and Fe/C, respectively. This agrees with the electrochemical impedance spectroscopy (EIS) measurement. As presented by the Nyquist plots in Figure 4/C has the much smaller charge transfer resistance than that of N/C and Fe/C, correlating to a faster charge‐transfer process for the CO2 reduction reaction. Good stability of FeN4/C is also demonstrated in the 24 h stability test .The electrocatalytic COs Figure 3a show treaction.17 Goo4/C is shown in Figure S10 (Supporting Information). As seen in the LSV curves, the initial increase of Fe loading leads to a better catalytic activity of CO2 reduction, while a further increase of loading to 2.5 wt% (Fe NPs/C) will decrease the catalytic performance. Apparently, the appearance of Fe particles is detrimental to CO2 reduction. The FE results in Figure S11 (Supporting Information) also show that the existence of Fe particles suppresses the selectivity for CO2 reduction to CO. To compare the intrinsic activity of FeN4/C and Fe NPs/C, their electrochemical active surface area (ECSA) was determined by performing cyclic voltammetry test  to get the double‐layer capacitance . Fe NPs/C shows a lower ECSA compared with that of FeN4/C, indicating a decreased ability for affording the active sites. The intrinsic activity after normalization by the ECSA for the FeN4/C and Fe NPs/C is shown in Figure S12d (Supporting Information), in which FeN4/C presents an enhanced current density for CO production than that of Fe NPs/C. Based on the catalytic performance, we could see the unique structure and coordination environment endow the isolated FeN4 sites with excellent catalytic performance for CO2 conversion.The influence of the Fe loading on the catalytic activity of FeNrmation).18 Fe 4/C for CO2 conversion to CO, density functional theory (DFT) calculations were performed. Considering the formation of COOH* is the initial step for the reduction of CO2 to CO, we first explored the electronic structure of FeN4 and N/C sites with adsorbed COOH*. Figure 4/C and N/C with COOH* adsorption from the section  and three‐dimensional view. For FeN4 sites, it could be seen that the depletion of electron density appears at Fe site and the electron density accumulation occurs on the C atom of adsorbed COOH*, indicating a charge transfer happens from the Fe site to C atom. While there is no obvious electron interaction between N/C and COOH*. This charge transfer for FeN4 sites results in the effective binding strength for the adsorbed intermediate, thereby effectively modulating the energy barrier in CO2 reduction process. As shown in Figure 4/C, the formation of COOH* is the rate‐limiting step for CO2 reduction reaction . Benefiting from the charge transfer, the introduction of FeN4 sites greatly decreases the barrier for the formation of COOH* compared with that of N/C, thus facilitating the subsequent reduction process, eventually resulting in the enhanced activity for CO production. Different from FeN4 structure, Fe nanoparticle shows much strong adsorption for CO*, as shown in Figure S13 (Supporting Information), which restricts the further desorption of CO, and thus leads to relative low selectivity.To ravel the high activity of FeNO2 to CO,19 we 2 evolution is the competitive reaction, the difference between thermodynamic limiting potentials for CO2 reduction and H2 evolution (UL(CO2) – UL(H2)) was also calculated as a reference for the selectivity in CO2 reduction reaction. A more positive value would indicate a better selectivity for CO2 conversion. As shown in Figure 4/C presents a more positive value than that of N/C, demonstrating a higher selectivity for CO2 reduction. Based on the DFT analysis, FeN4 sites endow the catalyst with a lowered energy barrier for CO2 reduction, thus leading to the enhanced activity for CO production.Considering that H4 sites on carbon substrate through a confined pyrolysis strategy using Fe doped g‐C3N4 as a template. The isolated and well‐defined FeN4 sites endow the catalyst with the advantages of both heterogeneous and homogeneous catalysts, showing high activity toward electrocatalytic CO2 reduction. Benefiting from the unique structure and coordination environment, the intermediate could be easily formed on the FeN4 sites during CO2 reduction process, resulting in the greatly improved selectivity for CO production. We anticipate our work will provide valuable guidance for the design of isolated active sites and would inject new vitality to the related electrocatalytic field.In conclusion, we have constructed isolated FeNThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.


The results obtained showed that DNRA occurred to a similar extent to denitrification and appeared to be enhanced by a nitrate limitation relative to organic carbon. We also demonstrated that different microbial taxa were responsible for these distinct processes. Based on these results and previous field observations, nitrate produced by nitrification within the surface oxidized layer may be reduced not only to gaseous N2 via denitrification, but also to NH4+ via DNRA, within the reduced layer. The present results also indicate that DNRA reduces N loss through denitrification and nitrate leaching and provides ammonium to rice roots in rice paddy fields.Nitrification–denitrification processes in the nitrogen cycle have been extensively examined in rice paddy soils. Nitrate is generally depleted in the reduced soil layer below the thin oxidized layer at the surface, and this may be attributed to high denitrification activity. In the present study, we investigated dissimilatory nitrate reduction to ammonium (DNRA), which competes with denitrification for nitrate, in order to challenge the conventional view of nitrogen cycling in paddy soils. We performed paddy soil microcosm experiments using  The supply of nitrogen (N) to rice roots generally limits production. Various biochemical processes involved in N cycling occur in paddy soils. As initially discovered in the 1930s, nitrification  challenges our current knowledge of the N cycle in paddy soils. DNRA competes with denitrification for NO3– and has a similar energy yield. Theoretically, DNRA yields more free energy per molecule of NO3– reduced than complete denitrification, while denitrification yields more free energy for every electron or carbon oxidized, as shown by the equations below  has been cultivated in the field since 2003. The soil is classified as grey lowland soil. We sampled soil at a depth of 0–20 cm, removed the oxidized layer (1 cm from the top), then sieved (<4 mm) and mixed the soil. The biogeochemical conditions of the field were previously described by 4+ in the sample collected on June 12, 2015 were 25.9±0.3 μg C (g soil)–1 (n=5), as measured by a TOC meter , and 1.4±0.1 μg N (g soil)–1 (n=5), as measured by the indophenol spectrophotometric method with a 2 M KCl extract  in Niigata Prefecture, the richest rice-producing area in Japan. Rice (3– was completely depleted. We then added 14NH415NO3 solution enriched with 99% 15N (SI Science) (1.6 μmol 15N [g soil]–1) and glucose  using a syringe with a fine needle after the headspace was replaced by pure helium gas. The addition of 14NH4+ prevents underestimations of DNRA because it inhibits the microbial assimilation of 15NO3– and DNRA-generating 15NH4+. We incubated the vial for 10 min and 4, 8, 12, and 24 h and then measured 15NO3–, 15NO2–, 15NH4+, 15N2O, and 15N2 (n=2 for each incubation time). We initially measured 15N2O and 15N2 in the headspace with gas chromatography mass spectrometry (GCMS) according to the method described by 15N2O and 15N2 were calculated based on the Bunsen coefficient , which catalyzes the last step of DNRA (NO2–→NH4+), were amplified using a polymerase chain reaction (PCR) with the primers nrfAF2aw and nrfAR1  ranged from 0, 1, 3, 5, and 7 to 9 by changing the concentration of added glucose , while maintaining that of 14NH415NO3 (1.6 μmol 15N [g soil]–1). We then incubated the soil microcosms for 12 h and measured 15NO3–, 15NO2–, 15NH4+, 15N2O, and 15N2 (n=2 for each org-C/NO3–) as in the first experiment. We also investigated whether NH4+ oxidation to NO2– or NO3– occurred by adding the 15NH414NO3 solution and measuring changes in 15NO3– and 15NO2–. The DNRA rate was calculated from 15NH4+ production during 10 min and 12 h, whereas the denitrification rate was calculated from the production of 15N of N2 and N2O during 10 min and 12 h.Our second objective was to examine the effects of the NO3–=3 (see below) used in the second experiment. The nrfA gene transcripts were amplified by PCR using the primers nrfAF2aw and nrfAR1. The gene transcripts of copper-containing nitrite reductase (NirK) and cytochrome cd1-containing nitrite reductase (NirS), which catalyze the step of denitrification (NO2––>NO), were also amplified using the following primers: nirKC1F and nirKC1R (nirK Cluster I), nirKC2F and nirKC2R (nirK Cluster II), and nirSC1F and nirSC1R (nirS Cluster I). Denitrifiers may be phylogenetically grouped based on their nirK and nirS sequences into several clusters. We previously demonstrated that denitrifiers with nirK Cluster I and Cluster II and nirS Cluster I were dominant in the soils tested  GENOME database . nrfA expression was also less evident in soils without glucose. These results indicate that DNRA occurred in rice paddy soils and was driven by nrfA-possessing microbial populations.The results obtained from our first experiment confirmed that DNRA occurred in rice paddy soils at a similar rate to denitrification A. NO3– west rate B. Conver3– (org-C/NO3–) affected the partitioning of NO3– reduction processes; higher org-C/NO3– enhanced DNRA over denitrification  environments. The ratios of DNRA to denitrification differed between the first and second experiments: the ratios of soil samples with org-C/NO3– of 0 and 9 were larger and smaller in the second experiment, respectively. Although the reason for this result currently remains unclear, it may depend on the sampling period (see above).The results from our second experiment showed that the ratio of organic carbon to NOfication A and B. 3– of 3, we analyzed the microbial populations responsible for these processes based on the sequences of nrfA transcripts for DNRA and those of nirK and nirS transcripts for denitrification. We obtained 57, 43, 45, and 46 clones for nrfA, nirK in Cluster I, nirK in Cluster II, and nirS in Cluster I, respectively. The taxonomic composition of DNRA and denitrifying microbes appeared to differ (nrfA sequences showed the highest similarity to those from the genera Anaeromyxobacter and Geobacter (class Deltaproteobacteria), while many others showed the highest similarity to those from the taxa of which genus-level taxonomy is unknown. In contrast, nirK sequences in Cluster I showed the highest similarity to those from the genera Bradyrhizobium and Afipia in the Bradyrhizobiaceae family (class Alphaproteobacteria). nirK sequences in Cluster II showed the highest similarity to those from the genera Rhodanobacter (class Gammaproteobacteria) and Ralstonia (class Betaproteobacteria). nirS sequences showed the highest similarity with the genera Thiothrix, Rhodanobacter, and Marinobacter (class Gammaproteobacteria) and the genus Burkholderiaceae (class Betaproteobacteria). Although the majority of nrfA, nirS, and nirK sequences were assigned to the reference sequences with high similarity, they did not form distinct phylogenetic clades with these reference sequences with a bootstrap support of >80%, except for the clones assigned to the genus Geobacter or Pseudogulbenkiania  anaerobic paddy soils and that Anaeromyxobacter-like and Geobacter-like nrfA expression enhanced DNRA activity. Based on these results, the paddy field may form more closed N-cycling than the nitrification-denitrification centric understanding; that is, NO3– produced by nitrification at the surface oxidized layer is reduced not only to gaseous N2 via denitrification, but also to NH4+ via DNRA, below the oxidized layer.The results obtained herein and previous field observations in the same location suggest that DNRA is a substantial N cycling process in on-site paddy soil under practical management conditions. A previous field observation study reported that soil NO15NO3–). The contribution of DNRA to the depletion of NO3– may be larger in an anaerobic environment with a large influx of readily degradable organic matter, but with a small influx of NO3–, leading to high org-C/NO3–. An anaerobic environment around the rhizosphere, in which a large amount of root secretions is supplied  Dissimilatory Nitrate Reduction to Ammonium and Responsible Microbes in Japanese Rice Paddy Soil. https://doi.org/10.1264/jsme2.ME20069Supplementary Material


By analyzing the computational results, a concept was developed to predict which of the yet missing anions should be synthesizable and why. Additionally, the results of an electrophilic attack by protons or trimethylsilyl groups or a nucleophilic attack by transition metal complex fragments are described. The latter yields butterfly‐like structures that can be viewed as a new form of adaptable tridentate chelating ligands.Binary pseudo‐tetrahedral Zintl anions composed of (semi)metal atoms of the p‐block elements have proven to be excellent starting materials for the synthesis of a variety of heterometallic and intermetalloid transition metal–main group metal cluster anions. However, only ten of the theoretically possible 48 anions have been experimentally accessed to date as isolable salts. This brings up the question whether the other species are generally not achievable, or whether synthetic chemists just have not succeeded in their preparation so far. To contribute to a possible answer to this question, global minimum structures were calculated for all anions of the type metals of periods 3–6, with 20 valence electrons and pseudo‐tetrahedral shape suggest that more than the known ten species should be generally accessible experimentally. Furthermore, the investigations illustrate the impact of the respective elemental combinations on substitution with electrophiles or nucleophiles, in comparison with isoelectronic P4, As4, or Si44−. One century after the discoveryDuring the past two decades, it was shown that Zintl anions and their respective salts are excellent starting materials for the generation and isolation of compounds with heterometallic and intermetalloid cluster anions. While the use of homoatomic Zintl anions yields bimetallic clusters, reactions of binary Zintl anions, several of which have been known to exist with atoms of groups 13 and 14, 13 and 15, or 14 and 15, usually lead to the formation of trimetallic clusters. It was shown that the larger degree of freedom upon using binary anions as precursors is reflected in a large variety of new cluster structures and bonding modes.4 or As4 are of particular interest. They show a high reactivity in cluster synthesis, but exhibit a lower overall charge than homoatomic Zintl anions Tt44−  for elemental combinations involving groups 13 and 15 or 14 and 15 in the anions (TrPn3)2− and (Tt2Pn2)2− . However, not all of these elemental combinations could be experimentally accessed to date. Some of them, like the combination of Ge and Bi, yielded other anions like (Ge4Bi14)4−,3)5−, (TrPn3)2−, and (Tt2Pn2)2−.In this context, binary pseudo‐tetrahedral anions that are isoelectronic with Pvide infra) to simultaneously optimize geometric and electronic structures.Another contribution to contemporary Zintl anion chemistry is charge reduction by (element‐)organic ligand decoration, as an alternative or addition to the admixture of neutral atoms.4 in white phosphorous and As4 in yellow arsenic, these species can either be described by the pseudo‐element concept, also referred to as Zintl–Klemm–Busmann concept,The results presented herein provide a deeper understanding of binary pseudo‐tetrahedral Zintl anions. Being valence isoelectronic to P3)5−, (TrPn3)2−, and (Tt2Pn2)2− have been isolated to date, which is why we focused our studies on these species. In theory, 48 element combinations should be possible. However, only ten anions have been reported, namely, (TlSn3)5−, (GaBi3)2−, (InBi3)2−, (TlBi3)2−, (Ge2P2)2−, (Ge2As2)2−, (Sn2Sb2)2−, (Sn2Bi2)2−, (Pb2Sb2)2−, and (Pb2Bi2)2−.Of the herein studied pseudo‐tetrahedral Zintl anions with said elemental combinations, only examples with the general formulae , but to “experimental feasibility” or “experimental accessibility” throughout. We note in addition that, compared to the experimental data, most bond lengths were elongated by a few pm on average during the geometry optimization, as typical and expected for the applied methods. Nevertheless, we were able to accurately reproduce the experimental data within the error of the method (Table S12 in the Supporting Information). We therefore used the selected methods to further study all unknown binary pseudo‐tetrahedral Zintl anions. We were indeed able to find a stable minimum structure for every possible group 13/14, 13/15, and 14/15 elemental combination 5− and (TrPn3)2− exhibit C3v symmetry, although originally calculated without any symmetry restrictions. These anions can hence be viewed as distorted tetrahedra with the triel atom sitting on an apex over a triangular base consisting of tetrel or pnictogen atoms, respectively. The bond lengths within the bases are in the range of bond lengths that were reported for the known homoatomic tetrahedra of (Tt4)4− or Pn4, respectively.2Pn2)2− can be viewed as being composed of two homoatomic dumbbells. As expected, the deviation from an ideal tetrahedral shape is most obvious for elemental combinations with extreme differences in atomic sizes, like (Si2Bi2)2− or (Pb2P2)2−. The heteroatomic bonds again increase as the radii of the involved atoms become larger. Tt−Tt and Pn−Pn bond lengths are in the same range as calculated for (TrTt3)5− or (TrPn3)2−. This indicates that the ring strain in the trigonal bases does not play a significant role compared to the overall strain of the pseudo‐tetrahedral architecture.As shown in Figure 3)2−, (TlP3)2−, or (Pb2P2)2−. Still, the highest partial charges, and thus the highest electron densities, are located at the more electronegative sites, indicating that the formalism of the pseudo‐element concept is oversimplifying the matter, while the trend is still correct. The results of the population analyses also showed that the distribution of the partial charges plays no significant role for the stabilities of these anions.Mulliken analyses,3)5− and (TrPn3)2− look qualitatively the same, which is due to their common 1:3 element ratio. That is except for a few group 13/14 anions, where the HOMO−1 and the HOMO−2, as well as the LUMO and the LUMO+1, are interchanged . The latter has, however, only a minor influence on the observed substitution patterns (vide infra). The lowest unoccupied molecular orbital (LUMO) of the (TrTt3)5− type anions is always located at the triangular tetrel base. The highest occupied molecular orbital (HOMO) is doubly degenerate and extends along the heteroatomic bonds. The main contribution to HOMO−1 stems from the group 13 atom, hence essentially representing its lone pair. The doubly degenerate HOMO−2 only shows contributions of the three group 14 or group 15 atoms. As an alternative, the HOMO−2 and the LUMO may be viewed as representing the bonding (occupied) e and antibonding (unoccupied) a1 combination of the in‐plane tangential p‐type atomic orbitals (p‐AOs) of a hypothetical “Tt32−” anion, hence the 3‐center‐4‐electron (3c4e) σ‐type bond of this species, which is isoelectronic with the (C3H3)+ cation). HOMO−1 and HOMO are based on the bonding (and occupied) a1 and the antibonding (and unoccupied) e representation of the orthogonal p‐AOs, hence the 2π aromatic system of the said species. The latter overlap effectively with the p‐AOs of a hypothetical “Tr3−” anion, which adds another 4 p‐electrons to the 10 electrons in 5 highest occupied MOs of the resulting anion. As a consequence of the combination of “Tt32−” and “Tr3−”, the binary anions become electron‐precise with only minor multi‐center bonding (vide infra). For the C2v‐symmetric (Tt2Pn2)2− type anions, the LUMO extends along the Pn−Pn bond, the HOMO along the Tt−Tt bond and the HOMO−1, as well as the HOMO−2, along the heteroatomic bonds.Figure 3)2− and (Sn2As2)2−. Since we were able to localize the MOs, the overall bonding in this polyhedra can be viewed as being based on regular 2‐center‐2‐electron (2c2e) bonds , with the main contributions coming from the p‐AOs. This is in good agreement with earlier studies.To further investigate the bonding situation within these clusters, we calculated localized molecular orbitals (LMOs) according to Boys’ method.4]4− or [Si9]4− and their analogues,5Sb3]2−}2,We would like to note here that our findings are in agreement with the alternative way of discussing such clusters as superatoms2Bi2)2− has been synthesized for the first time 35 years ago and in several different salts since then,2Bi2)2−” remains unknown to date. Another example is (GaBi3)2−, which can be synthesized,0 and Binq− polyanions.4Bi14)4−, with strictly separated element types.From the results discussed so far, one cannot deduce why some of the binary pseudo‐tetrahedral Zintl anions could be synthesized and some could not, or why some of the anions seem to be more stable than others. While (Sncr) between 0.8 and 1.1, e.g., Qcr(Ga:Bi)=0.82, Qcr(Tl:Bi)=0.98 or Qcr(Ge:P)=1.12 (vide infra). Given that the different atomic sizes are critical, Qcr should have an effect on the strength of the respective heteroatomic bonds within the pseudo‐tetrahedral architecture. To corroborate this, we calculated shared electron numbers (SEN) of the heteroatomic bonds, relative to the homoatomic Tt−Tt bonds in (TrTt3)5− and relative to the Pn−Pn bonds in (TrPn3)2− and (Tt2Pn2)2−, respectively, (SENrel). The results that may be taken as a measure of the relative stability of the binary anions are given in Table All of the anions that have been known to date exhibit ratios of the covalent radii (Q3)5− and (TrPn3)2− type anions: (a) The heteroatomic bonds become weaker for heavier triel atoms, as expected. (b) The opposite is the case as the tetrel or pnictogen atoms become heavier, that is, the Ga−Bi bond is stronger than the Tl−Bi bond, despite a seemingly unfavorable value of Qcr. At first glance, this seems to contradict the conclusions drawn above, according to which the difference of the covalent radii should be as small as possible. An explanation for this discrepancy can be derived from the molecular structures. Longer Tt−Tt or Pn−Pn bonds allow a closer approach of the triel atoms towards the center of the trigonal bases, similar to a close‐packed lattice: a Ga atom fits better in the space between three Bi atoms, than the Tl atom does, leading to a better overlap of the involved orbitals and to the formation of stronger bonds 2− is actually less stable than (InBi3)2− according to the experiments, while it should be more stable according to the data in Table cr=1.00 becomes too large. In addition, charge distribution and the size of the anions in comparison to that of the cation of choice will definitely play a role in affecting the lattice energy and thus the formation of a respective isolable salt. As a result, anions of the type (TrTt3)5− and (TrPn3)2− with Qcr close to 1.00 should be most stable, whereby deviations towards larger values are less tolerable than deviations towards smaller values.This, however, does not explain why (GaBi2Pn2)2− type anions can formally be viewed as being composed of two homoatomic dumbbells. The lack of a similar stabilizing effect as for the (TrTt3)5− and (TrPn3)2− type anions results in these anions being much more sensitive to deviations from Qcr=1.00 towards smaller values. This is shown by the fact that (GaBi3)2− with Qcr=0.82 was successfully synthesized, whereas (Ge2Bi2)2− with Qcr=0.81 is unknown and seems to be systematically inaccessible. In contrast, deviations towards larger ratios (Qcr>1.00) seem to be less problematic, cf. the experimentally observed (Ge2P2)2− anion (Qcr=1.12); still, the anion undergoes a re‐organization in solution to form a larger Zintl anion in the course of several days, indicating its metastability.As mentioned above, the , (Tt2Pn2R2), as well as anionic (TrTt3R2)3− and (Tt2Pn2R2)2− .Because of the high anionic charges of −2 and −5, respectively, salts of the pseudo‐tetrahedral binary anions are more difficult to handle in common (organic) solvents than species with lower or no charge. We therefore performed extensive studies on possible electrophilic substitution with protons and trimethylsilyl (TMS) groups, and on possible nucleophilic substitutions with organometallic substituents, in order to reduce the cluster charge, and thereby modify properties like solubility and reactivity. As none of these attempts proved possible for the herein discussed binary anions in experimental work so far, we aimed at examining the effects of substituents on the molecular structures by theoretical work. We limited our efforts to structures with two substituents, neutral ]+[24a] and [Si4(μ‐H)]3−,2 in [(μ‐H)(η2‐Ge4)ZnPh2]3−.5R4)2−. This anion can be interpreted as an Si44− tetrahedron with two substituents  and an additional SiR2 moiety acting as an electrophile and bridging one of the Si−Si bonds of the underlying tetrahedral structure motif.3)2− and (Tt2Pn2)2− species), and explored all possible protonation sites of the resulting species.While first theoretical studies of a singly protonated P3)5− and (TrPn3)2− show the same preferred protonation pattern. As expected, the hydrogen atoms bridge two heteroatomic bonds by involving the doubly degenerate HOMO 3− and (AlP3H2), where the H atoms are much closer to the Al atoms.Anions of the type (TrTt2Pn2)2− type anions, bridging of the Tt−Tt bond and one of the heteroatomic bonds is most favorable, which is realized by involvement of HOMO and HOMO−1. In all cases, the (μ‐H)‐bridged bonds are significantly elongated, by 8–10 % for all three cluster types  and (Sn2As2H2) as examples). This is in perfect agreement with the recent experimental findings for the isoelectronic species mentioned above.For the (Ttcr close to 1.00. They are hence the weakest (on average) for clusters (TrPn3H2). Table 3H2) and (Sn2As2H2) as examples.The presence of 3‐center‐2‐electron (3c2e) bonds upon μ‐H‐bridging is supported by corresponding SEN values, and the 3c2e bonds become stronger for values of Q3H2)3−, the negative charge is delocalized over all atoms. Yet, the largest electron density is also localized at the H atoms and the (unsubstituted) tetrel atom.NPA and Mulliken analyses illustrate the impact of the protonation on the electronic structures. While the negative charge was relatively evenly distributed over all four atoms in the naked anions, the three atoms that are involved in the bonds to the two hydrogen atoms  with Pn: P, As, Sb, Bi. The energy differences with respect to the global minimum decreases in the order Pn: P>As>Sb>Bi. Hence, the stabilization of the edge‐bridged isomer is more significant for underlying pseudo‐tetrahedra with larger size differences of the (semi)metal atoms, thus larger Qcr in the given series.Geometry optimizations with the H atoms being forced into a position over the trigonal faces were done to study stability trends. The molecular structures relaxed into local minima that were significantly higher in energy than the structures exhibiting edge‐bridging, as illustrated in Figure 2Pn2H2), HOMO−2 contributes to the bond, which has a stabilizing effect. Nevertheless, the difference between the global and the local minimum is still large, e.g., 97 kJ mol−1 for (Sn2As2H2).In case of the clusters (Tt3(SiMe3)2}3−, {TrPn3(SiMe3)2} and {Tt2Pn2(SiMe3)2}, respectively. These follow a continuous trend from a preference of edge‐bridging to a preference of terminal bonding, which can be put down to the anions’ different tendency to form efficient 3c2e bonds.While protonating the binary pseudo‐tetrahedral anions always yields clusters with bridged edges, the picture becomes more complex for the  addition of trimethylsilyl (TMS) groups. After the geometry optimizations, we find three different (dominant) substitution patterns for clusters {TrTt4(C{SiMe3})4}, for instance, the alkylsilyl groups are tilted sideways.The derivatization of homoatomic, tetrahedral main group compounds with four alkylsilyl groups yielding tetrahedrane‐like structures was previously reported.3(SiMe3)2}3− prefer edge‐bridging under formation of two 3c2e bonds. Notably, only here, the above mentioned interchanging of HOMO−1 and HOMO−2 in anions of the type (TrTt3)5− plays a role: in cases, in which these MOs are interchanged, the bridging involves one heteroatomic bond and one of the opposing homoatomic bonds 2}3− as an example), with the exception of {InGe3(SiMe3)2}3−, in which two homoatomic bonds are bridged. The other order of MOs, however, leads to bridging of two heteroatomic bonds instead . The relative energy difference between both isomer types is smallest for anions comprising heaviest atoms, such as {TlPb3(SiMe3)2}3−. In all cases, addition of TMS groups causes elongation of the involved bonds, by 4–10 %. This elongation becomes less prominent for values of Qcr≈1.00, irrespective of the observed substitution pattern.Anions of the type {TrTt3(SiMe3)2} tend the least to forming 3c2e bonds, like discussed for the protonated species. Here, the preferred substitution pattern includes two terminal bonds, with one TMS group bonded to the triel atom, and the other one bonded to one of the pnictogen atoms 2} as an example). The heteroatomic bonds in the 4‐vertex units are elongated by up to 10 % . In this conformation, the two TMS groups are the furthest apart of all examples discussed herein. We recognize an exception from this pattern only for {InP3(SiMe3)2} and for the sub‐series including the heaviest triel thallium, {TlPn3(SiMe3)2} , where the TMS groups are bonded to two pnictogen atoms. We ascribe this to the fact that both In−Si and Tl−Si bonds are significantly disfavored in comparison with Pn−Si bonds, owing to the larger differences in covalent radii.Due to the larger differences of the electronegativity of the involved atoms, clusters of the type {TrPn2Pn2(SiMe3)2} finally represents a combination of the aforementioned cases: Here, we find the Tt−Tt bond to be bridged, thereby involving the HOMO of the naked anion under formation of a 3c2e bond. The Tt−Tt bond lengths are again elongated by up to 10 %, depending on the respective Pn atoms, with the largest effect observed for the heaviest Pn atoms, again. The second TMS group is bonded as a terminal substituent to one of the Tt atoms, or to one of the Pn atoms, depending on the similarity of the covalent radii of the respective Tt or Pn atoms and the Si atoms of the terminal TMS group 2} as an example). In the two heaviest homologues, {Pb2Sb2(SiMe3)2} and {Pb2Bi2(SiMe3)2}, an additional bond is formed between one of the Pb atoms and the SiTMS atom . For this class of clusters, silicon atoms cause differences again: all species of the sub‐series {Si2Pn2(SiMe3)2}  prefer another substitution pattern. Here, both TMS groups are bonded to the two Si atoms of the former pseudo‐tetrahedron, thereby forming a chain‐like Si4 moiety .The silylation pattern for clusters of the type {TtIn summary, the attachment of two protons to pseudo‐tetrahedral, binary anions of p‐block (semi)metals leads to mostly hydridic substituents. The substitution patterns for substitutions with TMS groups are different but at the same time characteristic for the chosen combination of main group elements, with some exceptions for subseries involving the lightest (Si) or heaviest (Tl) congener(s) of the involved group(s).44− to form [Si4(μ2‐H)]3− was reported,+ as an electrophile, and a corresponding result remains elusive for any other tetrahedral Zintl anions. The attachment of electrophilic transition metal complex fragments like (MesCu)+, (ZnPh)+, or Zn2+ to a 4‐vertex anion has also been unknown for binary anions involving atoms from different main groups, but it was reported for tetrahedral anions of the type Tt44− (including Si/Ge mixtures).The calculations discussed so far addressed the electrophilic attack of binary anions. While the mono‐protonation of Si4 or As4 can be activated via nucleophilic attack by transition metal complexes to form butterfly‐like moieties. The first compound reported to emerge from such reactions was [{Cp’’Fe(CO)2}2(μ:η2:2‐P4)] (Cp’’: η5‐C5H3tBu2).2}2(μ:η2:2‐Pn4)]  to show that such moieties can subsequently act as chelating ligands for Lewis acidic species, like the cationic complex fragment [Cu(NCMe)]+.To the best of our knowledge, a nucleophilic attack towards any Zintl anion has not yet been reported until today,2}2(μ:η2:2‐Tt2Pn2)]2− , hence based on pseudo‐tetrahedral species, in which two of the P or As atoms were replaced with tetrel atoms. To reduce the computational effort, we used the smaller Fp substituent (Fp: CpFe(CO)2⋅; Cp: η5‐C5H5) and performed geometry optimizations for the resulting molecules.Inspired by this work, and beyond the background that the binary Zintl anions possess the same electron count and very similar frontier orbitals, we tried to expand this concept to (hypothetic) species with binary cluster cores, 2−, as an example of the resulting type of anionic molecules, is shown in Figure The optimized structure of [{CpFe(CO)2}2(P4)] and [{CpFe(CO)2}2(As4)], the partial charge distribution is exactly the opposite . The negative partial charge at the bridgehead sites increases as the difference in electronegativity between the two main group elements gets larger. Hence, also the softness of the respective pnictogen (donor) atom, according to the Pearson concept, increases. Therefore, these anions should be less suitable as ligands for electrophiles than the homoatomic reference clusters, which may explain the lack of experimental evidence so far.The Pn⋅⋅⋅Pn distances become larger with increasing atomic number of the tetrel atoms. This is accompanied by smaller SEN values, which can be viewed as a very rough approximation of the trend of the remaining electron density between the two P or As atoms. The dihedral angles stay relatively constant, between 88° and 90° on average. NPA and Mulliken analyses further showed that the pnictogen atoms are partially negatively charged, while the tetrel atoms exhibit a positive partial charge. In the homoatomic analogues, − . Indeed, the results are slightly different from the experimental findings for the homoatomic phosphorous or arsenic analogues, where the [Cu(NCMe)]+ fragment is pointing away from the P4 or As4 unit in an orientation perpendicular to two of the Pn–Pn edges. Here, we always find the [Cu(NCMe)]+ fragment to be tilted sideways, thus forming an additional Tt−Cu bond. Population analyses showed the strength of these bonds to be roughly of the same order of magnitude as for the other Pn−Fe and the Pn−Cu bonds, thus corroborating the Lewis‐basic character of the respective chelating ligand. Further back‐donation from the transition metal complex fragment into the LUMO of the ligand was not observed. The calculated minimum structure of [Cu(NCMe)(Ge2P2{CpFe(CO)2}2)]−, as an example of the whole series, is displayed in Figure z2atomic orbital with HOMO−4 of the chelating [{CpFe(CO)2}2(Ge2P2)]2− moiety. This HOMO−4 is mainly located at the tetrel atoms and between them , thus rendering the formation of said Tt−Cu bond energetically favorable.To check this hypothesis, we added a [Cu(NCMe)]+ fragment are highly exoenergetic (see Table S13). Furthermore, we found the P‐containing species slightly favored compared to the As‐containing analogues. This can again be explained by the Pearson concept and is in agreement with our previous results.A comparison of the absolute energies shows that the hypothetical reactions of the respective butterfly‐like anions with a [Cu(NCMe)]+ fragment into a perpendicular position by symmetry (C2v), and calculated the absolute energies of the corresponding isomers for all elemental combinations studied in this section. We found these structures to be local minima on the potential hypersurface within the given symmetry restrictions. Their total energies are between 22 kJ mol−1 and 82 kJ mol−1 above the total energies of the isomers with tilted [Cu(NCMe)]+ moieties, depending on the elemental combination of the underlying binary “butterfly” core. In the global minimum structures, the coordination sphere around the Cu atom is thus not trigonal planar as in the P4‐based and As4‐based structures, but strongly distorted “tetrahedral”. Hence, the [{CpFe(CO)2}2(μ:η2:2‐Tt2Pn2)]2− type anions do not only act as bidentate, but as tridentate chelating ligands. This and the increased softness of the respective pnictogen atoms, due to their higher negative partial charge, suggest that these anions are more suitable as ligands for softer Lewis acids that tend to tetra‐coordination, such as Hg2+, Pt2+ or Ag+, which will be studied in future work.To verify the observed conformation to be preferred, we forced the [Cu(NCMe)]3)5−, (TrPn3)2−, and (Tt2Pn2)2−, composed of p‐block (semi)metals. We described structural trends, and found possible answers to the question, why some of these cluster anions seem to be systematically elusive in experimental work. At the same time, our findings allow to predict that some of the yet not isolated species should be generally accessible.In summary, we presented calculated global minimum structures for all binary pseudo‐tetrahedral Zintl anions of the type  chelating ligands for Lewis‐acidic transition metal cations.The findings presented herein might be of help for synthetic chemists (including ourselves) and their approaches towards more of these fascinating compounds.Computational details: All calculations were undertaken by means of the program system TURBOMOLE,ϵ=∞). Localized molecular orbitals were obtained via Boys’ method.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.


This approach can control the geometry and orientation of the photosensitizing dye on the TiO2 surface. In this study, a density functional theory (DFT) and time-dependent DFT (TD-DFT) investigation was carried out on cresyl violet (CV) covalently attached to SCAs with a terminal oxirane group (OTES–Cn) to reveal the influence of OTES–Cn on the geometry of the photosensitizing dyes. The potential of CV covalently attached to OTES–Cn (CV–OTES–Cn) to act as a photosensitizing dye was also analyzed. The hydroxyl group formed by the epoxy-opening reaction between CV and OTES–Cn strongly influenced the geometry of CV–OTES–Cn, which was attributed to a CH–O interaction. Additionally, TD-DFT, frontier molecular orbital and molecular electrostatic potential calculations revealed that CV–OTES–Cn has excellent optical properties and electron injection ability. In particular, the characteristics of the unbent conformation of CV–OTES–Cn are expected to contribute significantly to the photocurrent in TiO2-based photocatalysts and DSSCs. These findings enhance the understanding of the covalent attachment strategy using SCAs and contribute to improving TiO2-based photocatalysts and DSSCs.The covalent attachment of photosensitizing dyes to TiO Therefo2-based photocatalysts and the PCEs of DSSCs [λmax) of CV0 and CViso were observed at 491 and 432 nm, respectively (f) at λmax were calculated to be 0.513 and 0.5968, respectively. Good light-harvesting efficiency (LHE) is important for obtaining high photocurrent in TiO2-based photocatalysts and DSSCs; this parameter can be calculated from the f values using the following equation [Next, the UV-visible absorption spectra of CV in the gas phase were simulated . It was expected that the solvent effect would result in a shift in the UV-visible absorption spectra and changes in the LHE values. The simulated UV-visible absorption spectra of CV0 and CViso using CPCM in EtOH showed a red-shift, and their LHE values increased .Like CV in EtOH B. The λm species . Additio ~525 nm . On the  ~585 nm ,29,30. T2-based photocatalysts and DSSCs [2 is the first process in TiO2-based photocatalysis and DSSCs. The HOMO level is related to the reduction of the oxidized dye formed by electron injection. Therefore, FMO calculations of CV using CPCM in EtOH were performed. The FMOs and energy diagrams of CV are shown in In addition to the UV-visible absorption spectra, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of photosensitizing dyes play important roles in TiOnd DSSCs . Electro0 and CViso, the LUMOs, in particular, are delocalized around the aromatic rings with the imino moiety. This result suggests electron transfer from the aromatic ring with the amino group to the region near the imino moiety, i.e., the amino group acts as a donor. The LUMO levels of CV0 and CViso were calculated to be −2.55 eV and −2.42 eV, respectively. These values are much higher than the CB level of TiO2 (−4.0 eV) [0 and/or CViso to the CB of TiO2. Additionally, the HOMO levels of CV0 and CViso were calculated to be −5.14 eV and −5.33 eV, respectively. These values are lower than the redox potential of the iodide ion/triiodide ion , which is a common redox couple in the electrolyte solution in DSSCs [0 and CViso formed by electron injection can be regenerated in the electrolyte. In conclusion, CV was confirmed to act as a photosensitizing dye in TiO2-based photocatalysts and DSSCs.According to the TD-DFT calculations, the UV-visible absorption spectra of CV are dominated by the transition from the ground state to the singlet excited state attributed to the HOMO–LUMO transition. The HOMO and LUMO of CV are distributed over the whole molecule due to its extended π-conjugation. In the cases of CV−4.0 eV) ,11,12,27in DSSCs ,11,12,27+ results calculated at the B3LYP/6-31+G** level  suggested the possibility of electron injection and regeneration in the electrolyte. However, the LUMO level calculated at the SVWN/6-31+G** level of theory was lower than the CB level of TiO2. These results suggested that the accuracy of both the optical properties and FMO levels of CV+ could not be guaranteed. Therefore, CV+ was excluded from further study, and only the details of CV0 and CViso were investigated.The CV0 and/or CViso attached to OTES–C2 in the gas phase was performed  [The hydroxyl group and secondary amine moieties on the alkyl chain resulted from the epoxy-ring-opening reaction between CV(2.72 Å) . This re0–OTES–C2 and CViso–OTES–C2 were performed with different torsional angles for the secondary amine moieties and the dihedral angles of the secondary amine moieties  was 152.5°, which represented a remarkable distortion compared to that in the other conformations. Since this distortion of the dihedral angle may result in energy differences  between the different geometries, frequency analysis was then performed. The ΔE between the different optimized geometries of CV0–OTES–C2 (conformations A1 and A2) was 13.2 kJ/mol, with a bias toward A2. On the other hand, the two conformations of CViso–OTES–C2 (conformation B1 and B2) were competitive, as ΔE was 1.4 kJ/mol. The ΔE between the conformations of CV–OTES–C2 was clearly due to the condensed aromatic rings of CV and the CH–O interaction. Based on the above results, it was concluded that the CH–O interaction influences the conformation of CV–OTES–C2.The CH–O interaction was expected to affect the geometry of CV–OTES–C2. In particular, a dihedral angle distortion was expected due to the steric hindrance of the condensed aromatic ring. To confirm this, geometry optimizations of CV0–OTES–C2 and CViso–OTES–C2 using CPCM in EtOH. The λmax of CV–OTES–C2 was red-shifted by 12–22 nm compared with that of isolated CV. Additionally, the LHE increased slightly. These results indicated that CV–OTES–C2 was more promising as a photosensitizing dye than isolated CV.λmax was attributed to this result. The LUMOs of CV–OTES–C2 are delocalized around the aromatic ring with the imino moiety, similar to isolated CV. The LUMO levels of CV–OTES–C2 were in the range of −2.36 eV to −2.61 eV, which are higher than the CB level of TiO2 (−4.0 eV). Additionally, the calculated HOMO levels (−4.99 eV to −5.17 eV) of CV–OTES–C2 are lower than the redox potential of I−/I3− (−4.8 eV) in an electrolyte solution. These results confirm that CV–OTES–C2 could act as a photosensitizing dye in TiO2-based photocatalysts and DSSCs. However, the distribution of the LUMOs around the aromatic ring with the imino moiety may be unfavorable in terms of electron injection, because the LUMOs are located relatively distant from the TiO2 surface.FMO calculations of CV–OTES–C2  were per0–OTES–C4, CV0–OTES–C8, CViso–OTES–C4 and CViso–OTES–C8 were investigated. The geometries of these molecules are illustrated in 0–OTES–C2; however, CV0–OTES–C2 adsorbed on the TiO2 surface may adopt the unbent molecular configuration (A1) due to the large steric hindrance between adjacent CV moieties and/or between the SAM surface and CV moieties (see below for further details). Therefore, the details of the unbent molecular configurations of CV0–OTES–Cn and CViso–OTES–Cn (A1 and B1) were investigated. The simulated UV-visible absorption spectra of the dyes did not exhibit significant differences. The alkyl chain length of OTES–Cn did not affect the optical properties of CV–OTES–Cn  surface model was selected because anatase is known to exhibit higher photocatalytic activity than rutile and the (101) surface has the lowest surface energy [6O15H6 was employed, and the cluster optimized at the B3LYP/6-31G*/LanL2DZ level of theory to compromise between computational costs and accuracy . The calculated bond lengths between the alkoxysilane oxygen atoms and connected titanium atoms were ~1.86 Å, comparable to the Ti–O bond lengths in the Ti6O15H6 cluster (1.80–1.84 Å). These bond lengths indicated strong chemical adsorption of CV–OTES–C2 onto the TiO2 (101) surface.2 surface. The long axes  of CV0–OTES–C2 and CViso–OTES–C2 in the unbent conformations (A1 and B1) were 15.9 Å  of the bent conformations were 9.5 Å and 9.6 Å, respectively. If a SAMs based on OTES–Cn was present on the TiO2 surface, the bent molecular geometry would be unlikely due to the steric hindrance between adjacent CV moieties and/or between the SAMs surface and CV moieties. Therefore, it was expected that the unbent conformation of CV–OTES–C2 would predominate on the TiO2 surface.The molecular length provided information related to the conformation of CV–OTES–C2 adsorbed on the TiOe 15.9 Å . In comp2 cluster were calculated to investigate the electron injection from CV–OTES–C2 to TiO2  adsorbed on the TiO to TiO2 . As in t2. In particular, the downshift of the LUMO level was remarkable and suggested degeneracy between the CB level of TiO2 and the LUMO level of CV–OTES–C2. This bandgap reduction may induce efficient visible light absorption and electron injection.According to the DOS spectra, the HOMO and LUMO levels of CV–OTES–C2 were downshifted by adsorption onto TiO2 cluster were calculated to complement the FMO calculations and DOS spectra , Φinject and ηcollect are the LHE at a given wavelength, the electron injection efficiency and the charge collection efficiency, respectively. It was assumed that all the components of the DSSC were constant except for the photosensitizing dye. Hence, ηcollect can be assumed to be constant. Φinject is related to the injection driving force (∆Ginject) of the electrons injected from the excited dyes to the TiO2. ∆Ginject can be estimated using the following equation [Here, equation ,11,27:Jsequation ,11,27:∆GEdye*, Edye, ECB and ES1 are the oxidation potential of the photosensitizing dye in the excited state, the redox potential of the photosensitizing dye in the ground state, the reduction potential of the CB level of TiO2 (4.0 eV) and the energy of the singlet excited state. Edye can be estimated as the negative of the HOMO level [ES1 is the vertical transition energy associated with the λmax value obtained from the UV-visible absorption spectra and is listed in Edye, Edye* and ∆Ginject values of isolated CV–OTES–C2 are listed in MO level . ES1 is Ginject values for the A1, A2, B1 and B2 conformations were −1.17 eV, −1.35 eV, −1.36 eV and −1.38 eV; these values were more negative than that of ECB. This result indicates that the excited state of CV–OTES–C2 lies above the CB edge of TiO2, i.e., that electron injection should occur from the excited CV–OTES–C2 to the CB of TiO2.The ∆Ginject of CV0–OTES–C2 (A1) is the lowest, suggesting that conformation A1 would exhibit slower electron injection and a lower JSC than the other geometries. However, the bent molecular conformations of CV–OTES–C2 (A2 and B2) may not form on the TiO2 surface (see above for further details). The UV-visible absorption spectrum of conformation A1 also has a broader absorption band than geometry B1 (0–OTES–C2 (A1) would contribute significantly to enhancing the photocurrent in TiO2-based photocatalysts and DSSCs.The ∆metry B1 . The LHE2-based photocatalysts and DSSCs. Additionally, the results of FMO calculations, DOS spectra and MEP calculations indicated that electron injection proceeds from CV–OTES–Cn to TiO2. In particular, the characteristics of the unbent molecular geometry of CV–OTES–Cn (conformation A1) should contribute significantly to enhancing photocurrent in TiO2-based photocatalysts and DSSCs. Overall, the following conclusions were drawn: (i) SAMs based on the OTES–Cn on the TiO2 surface can control CV conformation covalently attached to the terminal functional group of OTES–Cn (CV–OTES–Cn); (ii) CV–OTES–Cn has potential as a promising photosensitizer for TiO2-based photocatalysts and DSSCs. This article’s findings should enhance covalent attachment strategies between photosensitizing dyes and TiO2 and improve TiO2-based photocatalysts and DSSCs.This article reported a DFT and TD-DFT study of CV–OTES–Cn to determine the influence of OTES–Cn on photosensitizing dyes’ geometry. The potential of CV–OTES–Cn to act as a photosensitizing dye was also evaluated. The hydroxyl group formed by the epoxy-opening reaction resulted in a CH–O interaction between CV and the covalently attached OTES–Cn. This CH–O interaction significantly influenced the conformation of CV–OTES–Cn and distorted the C–C–N–C dihedral angle due to the steric hindrance of the condensed aromatic ring of CV. According to TD-DFT calculations (simulated UV-visible absorption spectra), CV–OTES–Cn has excellent optical properties and should act as a promising photosensitizer for TiO


Ca2+ oscillations and egg activation can be triggered in mature mouse eggs by incubation in Sr2+ containing medium, but this does not appear to be effective in human eggs. Here, we have investigated the reason for this apparent difference using mouse eggs, and human eggs that failed to fertilize after IVF or ICSI. Mouse eggs incubated in Ca2+-free, Sr2+-containing medium immediately underwent Ca2+ oscillations but human eggs consistently failed to undergo Ca2+ oscillations in the same Sr2+ medium. We tested the InsP3-receptor (IP3R) sensitivity directly by photo-release of caged InsP3 and found that mouse eggs were about 10 times more sensitive to InsP3 than human eggs. There were no major differences in the Ca2+ store content between mouse and human eggs. However, we found that the ATP concentration was consistently higher in mouse compared to human eggs. When ATP levels were lowered in mouse eggs by incubation in pyruvate-free medium, Sr2+ failed to cause Ca2+ oscillations. When pyruvate was added back to these eggs, the ATP levels increased and Ca2+ oscillations were induced. This suggests that ATP modulates the ability of Sr2+ to stimulate IP3R-induced Ca2+ release in eggs. We suggest that human eggs may be unresponsive to Sr2+ medium because they have a lower level of cytosolic ATP.At fertilization in mice and humans, the activation of the egg is caused by a series of repetitive Ca These aocytosis  The sper species .2+ increase that fails to mimic the Ca2+ oscillations seen at fertilization (2+ increase is less effective at activating development than causing multiple Ca2+ increases (2+ free) Sr2+ containing medium   were super-ovulated by serial i.p. injections of pregnant mare’s serum gonadotropin and HCG, about 48 h apart. The CD1 female mice (8–12 weeks old) were super-ovulated by serial i.p. injections of PG600, about 48 h apart . All procedures were carried out under a UK Home Office Project Licence held by KS. Mice were housed in conventional cages with environmental enrichment on a 12 h dark light cycle. For either mouse strain, 15 h after the second hormone injection the mice were culled by cervical dislocation. The oviducts were dissected and then the cumulus-oocyte masses were transferred to M2 medium  containing hyaluronidase (2 (±3.16 SD). Unfertilized eggs were identified 16–18 h after insemination or sperm injection and transferred from the clinic to the research laboratory in a heated transporter within 3 h, so that experiments were initiated within 24 h of egg recovery. Eggs from each patient were processed on a different experimental day that covered a period of up to 3 years. Only eggs that showed no sign of activation (neither 2nd polar bodies nor a pronucleus) from failed IVF or ICSI were used. Eggs that contained any obvious vacuoles in the cytoplasm were not used for research. The eggs were maintained in the research laboratory in the M2 medium at 37°C under the same conditions as mouse eggs.Human eggs that had failed to fertilize were obtained from patients attending the Wales Fertility Institute for IVF treatment. All patients providing such eggs gave written informed consent to the research. The project was approved by the South East Wales Ethics Committee 2 and is licenced by the Human Fertilisation and Embryology Authority (R0161). Patients donating eggs used in this study had a mean age of 33.59 years  and mean BMI of 24.27 kg/m2+ dye that has a similar Ca2+ affinity and spectral properties to OGBD. In either case the dextran tag ensures that the dye is retained within the cytosolic compartment of the egg. For experiments on the IP3R sensitivity we microinjected eggs with a mixture of 0.5 mM NPE-Caged InsP3  plus 0.5 mM OGBD. With both mouse and human eggs, the volume injected was about ∼¼ diameter (∼2% of the egg volume) in order to make the relative amount of caged InsP3 and OGBD similar for the differently sized human and mouse egg.Mouse or human eggs were microinjected using pressure pulses applied to the back of a micropipette that was inserted into the egg using electrical oscillation, as described in detail elsewhere . In some2+ in different media. Sr2+ containing HKSOM consisted of 95 mM NaCl, 2.5 mM KCl, 0.35 mM KH2PO4, 0.2 mM MgSO4, 4 mM NaHCO3, 0.01 mM EDTA, 0.2 mM Na pyruvate, 10 mM Na lactate, 1 mM glutamine, 0.2 mM glucose, 0.1 mg/l phenol red and 20 mM HEPES at pH 7.4 to which SrCl2 was added at the concentrations indicated. In some cases, a Mg2+ and Ca2+ free M2 was used that consisted of 10 mM SrCl2 plus 94.7 mM NaCl, 4.78 mM KCl, 1.19 mM KH2PO4, 4 mM NaHCO3, 0.33 mM pyruvate, 23.3 mM Na lactate, 5.56 mM glucose, 1 mg/l phenol red and 21 mM Na HEPES at pH 7.4. Other experiments used a HEPES-buffered saline solution (HS) that consisted of 10 mM SrCl2 plus 137 mM NaCl, 5.5 mM KCl, 1.2 mM MgCl2, 5.6 mM glucose, and 7.5 mM Na HEPES at pH 7.4 (Mouse or human eggs were tested for responses to Srt pH 7.4 . All med2+-sensitive dyes was sampled and imaged intermittently (every 10 s) with CCD cameras , or else we used continuous very low light imaging with an intensified CCD (ICCD) camera . Micromanager Software (https://micro-manager.org/) was used to control the shutters and collect data except for the ICCD, which used specific software . The dyes used are single wavelength indicators and so the fluorescence traces for most experiments have been normalized by plotting the fluorescence as a ratio of each point divided by the starting fluorescence value (hence F/F0), as described previously  in a heated dish (35–37°C) on the stage of an epifluorescence microscope . Excitation light was at 490 nm from a halogen lamp or LED , and emission was at 520–550 nm. The fluorescent light from eggs injected with Caeviously . The tim3 uncaging experiments, eggs were microinjected under red light and transferred within ∼15 min to a heated microscope stage containing HKSOM medium  with a current to voltage convertor sampled at 10 Hz by an AD convertor connected to a computer. During application of the UV pulse there was a large flux of light that caused an artifactual signal from the photomultiplier tube and so this part of the recording was removed from the traces.For InsP2+ by injecting firefly luciferase along with OGBD, as described previously . The light signals were taken as the steady state values. Light was recorded using a custom made luminometer consisting of a cooled photomultiplier tube in photon counting mode . Signals from single eggs were typically 1000 times the background count. The signals were calibrated with a series of dilutions of ATP. In other experiments on live eggs the dynamic changes in (relative) cytosolic ATP levels were measured at the same time as cytosolic Caeviously . Lumineseviously .https://imagej.nih.gov/ij/index.html) and SigmaPlot software . The error bars used in all cases are SDs. The ‘n’ numbers refer to the number of eggs and were compiled from at least two experimental runs for mouse eggs and involved as many experimental runs as patients’ donations for human eggs. Statistical tests used and P-value inequalities refer to Student ‘t’ tests when the data passed the Shapiro–Wilk normality test, and the Mann–Whitney rank sum test when data failed the Shapiro–Wilk test. A P-value of less than 0.05 was considered to be significant. The effect size (Cohen’s d) for two sets of data was calculated by dividing the differences in the means by the averaged SD.Data sets were analyzed using ImageJ (2+ in Ca2+ free (HKSOM) medium was shown to cause Ca2+ oscillations and activate MF1 mouse eggs  containing Sr2+  that were aged in vitro (∼24 h) also showed Ca2+ increases in 5 mM Sr2+ containing medium (2+ increase was more variable. A large proportion of eggs (12/28) showed a very prolonged Ca2+ increase before oscillating  underwent Ca2+ oscillations for at least 3 h . We also tested the effect of using a 10 mM Sr2+ medium that is both devoid of added Ca2+ or Mg2+ ions on eggs (2+ increase and cell lysis in CD-1 mouse eggs (data not shown). However, when this medium was used for human eggs, we failed to observe any Ca2+ distinctive oscillations in 10 human eggs in up to 10 h of recording. Out of 10 such eggs, eight showed no oscillations, but many eggs displayed a gradual rise in Ca2+ levels . This difference between mouse and human eggs was not likely due to the in vitro ageing of human eggs because when we tested CD1 mouse eggs that had been aged in vitro for 24 h, we found that they also responded to UV pulses of much shorter duration than that of human eggs  and human eggs . These data suggest that human eggs have a more variable Ca2+ store content than mouse eggs. However, there is a considerable overlap in the responses between mouse and human eggs, which makes it unlikely that differences in Ca2+ store content can provide an explanation for marked differences in response to Sr2+, and in IP3R sensitivity.The differences in the response of mouse and human eggs to both Srman eggs . However2+ medium failed to trigger Ca2+ oscillations in mouse eggs. A HEPES-buffered saline medium has previously been used to study the mechanism of Ca2+ influx in hamster eggs (2+ (with no added Ca2+) none of 32 eggs showed any Ca2+ oscillations or signs of activation  underwent Ca2+ oscillations and activated (2+. We then incubated mouse eggs in Sr2+ HS (with no pyruvate) from the start of the recording  for 30 min before adding them to the same substrate-free HKSOM containing 5 mM Sr2+. 2+ levels in CD1 mouse eggs in substrate-free medium containing 5 mM Sr2+, with the luciferase trace indicating the relative level of ATP. There were no Ca2+ oscillations in any of the 18 eggs tested and the ATP level continued to decline. However, when pyruvate was added to the medium there was rapid increase in ATP levels and a series of Ca2+ oscillations was observed in all eggs. These data support experiments on MF1 mouse eggs and show that a reduction in ATP leads to a reversible loss of sensitivity to Sr2+ induced Ca2+ oscillations. This implies that the ATP level plays a significant role in determining whether an egg undergoes Ca2+ oscillations in response to Sr2+ medium.We repeated these experiments with medium deficient in pyruvate on CD1 mouse eggs, but also measured the dynamics of ATP changes by monitoring the luminescence of firefly luciferase, which indicates ATP levels . There was no significant decline in ATP during in vitro ageing of mouse eggs, and mouse eggs aged for ∼24 h post collection still had a higher ATP than that of human eggs  do not display Ca2+ oscillations or activate in response to Sr2+ medium that is otherwise effective at inducing immediate Ca2+ oscillations in mouse eggs. Mammalian eggs that are aged in vitro show a number of biochemical changes that are not seen in freshly ovulated eggs  that have downregulated the level of IP3Rs by several fold in response to InsP3 production (2+ induced oscillations are associated with a marked increase in the sensitivity of mouse eggs to InsP3 (3 receptor (ITPR1) cerebellar microsomes where Sr2+ directly promotes InsP3 induced Ca2+ release  is known to promote Ca2+ release via the ITPR1, which is the predominant IP3R subtype found in mammalian eggs (4− produced by mitochondria has a localized action on the ITPR1 because the membranes of mitochondria and the endoplasmic reticulum in cells can be located c. 20–40 nm apart (It would have been useful to investigate the effect of ATP on IP3Rs in eggs by increasing cytosolic ATP levels in human eggs. However, it is not clear how this can be achieved because supplying more substrate, such as pyruvate, is not effective at increasing ATP . In conteviously . This sunm apart .2+ medium, which is more effective than Ca2+ ionophores (2+ medium was as effective as recombinant PLCζ in activating development to the blastocyst stage (2+ medium is the most effective means of activating mouse eggs and it causes the highest rates of artificially induced pre-implantation development (2+ induced mouse egg activation is simple, cost effective and easily modulated by changing concentrations and incubation times. Our work suggests that Sr2+ medium, as currently used in mouse eggs, will fail to activate human eggs because they have a lower ATP level. However, methods for promoting mitochondrial ATP production may enable human eggs to undergo Ca2+ oscillations and activate in response to Sr2+ medium.Parthenogenetic activation of mouse eggs routinely involves using SrMolecular Human Reproduction online.The datasets underlying this article will be shared on reasonable request to the corresponding author.gaaa086_Supplementary_DataClick here for additional data file.


Structure predictions reveal two energetically stable NH3–He compounds with stoichiometries (NH3)2He and NH3He at high pressures. At low temperatures, (NH3)2He is ionic with NH3 molecules partially dissociating into (NH2)− and (NH4)+ ions. Simulations show that (NH3)2He transforms into intermediate phase at 100 GPa and 1000 K with H atoms slightly vibrate around N atoms, and then to a superionic phase at  ~2000 K with H and He exhibiting liquid behavior within the fixed N sublattice. Finally, (NH3)2He becomes a fluid phase at temperatures of 3000 K. The stability of (NH3)2He at high pressure and temperature could contribute to update models of the interiors of Uranus and Neptune.Uranus and Neptune are generally assumed to have helium only in their gaseous atmospheres. Here, we report the possibility of helium being fixed in the upper mantles of these planets in the form of NH Helium is generally considered too inert to be present in giant ice planet mantles. The authors, by first-principles calculations and crystal structure searches, find stable ammonia–helium compounds at the conditions of Uranus and Neptune’s upper mantles, with possible implications in the planet composition models. Uranus and Neptune are generally assumed to have a three-layer structure: a rocky core, an ice mantle (contains an upper mantle and a lower mantle), and a gas atmosphere6. Although many studies have focused on the interiors of Uranus and Neptune, their internal compositions remain to be fully understood12. A widely accepted model for each of these planets is that the upper mantle comprises a mixture of ionized H2O, NH3, and CH411, whereas the lower mantle consists of metallic H2O, NH36 Much effort has been devoted to determine the ratio of the components in the interior of the ice planets11, however, no consensus were reached.Knowledge of the interior compositions of planets is crucial to understanding the processes of their formation and evolution. Various methods have been used to investigate the Earth’s interior, while studies of the composition and structure of the solar system’s ice giants, Uranus and Neptune, are limited by using only global observable properties such as gravitational and magnetic moments3 and H2O, and mixtures of the two15. Cavazzoni et al16. performed molecular dynamic simulations to estimate the phase diagram of water and ammonia at pressures and temperatures in the range of 30– 300 GPa and 300–7000 K. They found that water and ammonia exhibited a superionic phase  between the ionic solid phase and ionic fluid phase. However, for the component CH4, the results of equation of state have shown that it would dissociate into hydrocarbons at the extreme conditions17. A computational search undertaken by Pickard and Needs in 2008 found that ammonia transformed into an ionic phase consisting of (NH2)− and (NH4)+ ions at pressures above 90 GPa13; the transformation was subsequently confirmed by experiment15. By combining empirical and theoretical results, Ninet et al18. found that a novel superionic conductive phase of ammonia becomes stable at about 70 GPa and 8500 K. Using Raman spectroscopy and synchrotron X-ray diffraction, Laniel et al19. found two unusual ionic N–H stoichiometries, (N2)6(H2)7 and N2(H2)2, which are stable at about 50–GPa. While for water, it has a rich phase diagram, with at least 17 solid phases identified experimentally22, and seven other high-pressure phases predicted by theoretical studies26. Ninet et al18. and Millot et al27. proposed that superionic water ice can exist in the mantles of the ice giants as a result of shock compression. Recently, Huang et al28. found that H2O can react with H2 and form a novel superionic compound of H3O under high pressure and high temperature.To understand realistic compositions of Uranus and Neptune, researchers have focused on high-pressure and high-temperature phases of NH3 and H2O, Robinson et al29. predicted a novel ionic compound, O2−(NH4+)2, to form at pressures above 65 GPa. Recent theoretical and experimental studies have shown that NH3H2O decomposes into ammonia and water at 120 GPa31. Bethkenhagen et al32. used an evolutionary random structure search code to propose a superionic phase of NH3H2O at 800 GPa and high temperature (1000–6000 K). An unusual layered ionic phase of NH3(H2O)2 was predicted for a 1:2 mixture of NH3 and H2O; it was then modeled to transform into a superionic phase at high pressure and high temperature (41 GPa and 600 K)33. These findings contribute to our understanding of the interiors of the giant ice planets.For a 2:1 mixture of NH11. have proposed a three-layer structure model, in which the considering of small amount of He/H in the outer core of the planets reproducing well the gravitational moments of the ice giants. Recent studies have indicated that high pressure can induce He to form compounds such as HeN434,Na2He35, FeHe36, MgOHe37, H2OHe39, and FeO2He40. Specially, the compound of H2OHe2 exhibited a superionic property under high pressure and high temperature and then transformed into fluid39. These results inspired us to explore whether some of the abundant elemental He from the planets’ atmospheres could be trapped inside the mantles of Uranus and Neptune. Therefore, we carried out calculations to search for stable compounds in NH3–He systems at high pressure and high temperature. Our results show that He can react with NH3 to form (NH3)2He under extreme conditions, to a certain extent corresponding to the upper mantles of Uranus and Neptune, thereby providing information essential to the understanding of the interior models of these planets.The above results have led to the assumption that the elements  in the ice giants’ gaseous atmospheres except He appear in their solid mantles. Helium is generally considered likely to remain only in the atmosphere and not form solid compounds in the mantle, because it is the most chemically inert element due to its stable closed-shell electronic configuration. In fact, Nettelmann et al3)xHey  as compared to mixtures of NH3 and He at selected pressures are summarized in Fig. 3)2He at 10 and 300 GPa, NH3He at 50, 100, and 150 GPa, and NH3He2 at 300 GPa 2He and NH3He2, i.e., (NH3)2He becomes energetically stable also at 150 and 300 GPa, while NH3He2 turns to be unstable at all pressures.The formation enthalpies of the energetically most-stable structures of (NH3)2He with space group I4, labeled here as I4–(NH3)2He, becomes energetically stable with respect to NH3 and He at pressures as low as 9 GPa 2He consists of isolated NH3 molecules and He atoms. Figure 3 layers of this structure in the a–b planes, with He atoms located in the pockets formed by neighboring NH3 molecules. Interestingly, the I4 structure displays unique channels formed by NH3 molecules that are arranged parallel to the c-axis, and linear He chains localize within the interstices formed by four neighboring channels 2He remains energetically stable up to 40 GPa, above which it decomposes into a mixture of NH3 and He. However, (NH3)2He re-emerges as energetically stable phase at 110 GPa with the formation of an orthorhombic Fmm2 structure. A similar combination-decomposition-recombination pattern has previously been reported for CaLi244. Partial dissociation of NH3 molecules into (NH2)− and (NH4)+ ions is found to accompany the formation of Fmm2–(NH3)2He. Bader analysis demonstrates the strongly ionic nature of the species, with Bader charges of −0.57 e− and 0.53 e− for (NH2)− and (NH4)+, respectively, similar to those observed in the ionic phase of pure NH313. The Fmm2 phase is also layered, consisting of layers formed by NH3, (NH2)−, and (NH4)+ units in the a–c planes. The spacing between neighboring layers is 2.07 Å. Viewing the structure along the a-axis reveals unique channels formed by NH3, (NH2)−, and (NH4)+ units, with He atoms located in the interstices.−, (NH4)+) and He atoms, given the absence of any ELF local maxima between them 2He as  ~ -0.02 e− at 10 GPa, which increases to -0.03 e− when the Fmm2 structure is adopted at 120 GPa. Similar to that in (NH3)2He, each He atom in NH3He and NH3He2 gains nearly 0.03 e− from the NH3 molecules. The Bader charge of a He atom in the three NH3–He compounds is similar to the charges predicted for H2O–He, MgF2He, MgOHe, and FeO2He (between −0.02 e− and -0.07 e−)40. The current results indicate the three compounds have an ionic nature and that He atoms could serve as a Coulomb shield in stabilizing them at high pressure. Electronic band structures show that all three compounds are insulators 2He is calculated to be 6.0 eV at 10 GPa, which increases to 7.5 eV at 180 GPa. For NH3He, the band gaps is calculated to be 7.2 eV at 35 GPa.To examine the interactions among N, H, and He atoms in the two compounds, we calculate electronic properties including the electronic localization function (ELF) and Bader charges. The ELF is a quantum chemistry tool to visualize covalent bonds; values close to 1 corresponding to strong covalent bonding. The ELF results rule out covalent bonds between N–H units (NHNH2)−, NH+) and HeFmm2–(NH3)2He cover the geotherms in the upper mantle of Neptune and Uranus. We, therefore, performed ab initio molecular dynamics simulations at the pressure of 100 GPa, 200 GPa, and 300 GPa, respectively, to examine the formation of Fmm2–NH3)2He inside Neptune and Uranus. The calculated mean squared displacement (MSD) of the atomic positions and the behaviors of three different atoms of Fmm2–(NH3)2He are shown in the Fig. P = 100 GPa and T = 200 K, Fmm2–(NH3)2He is a solid phase with all atoms vibrating around their lattice positions and with diffusion coefficients (DH = DHe = DN = 0). When the temperature increasing to 1000 K, the H atoms seems diffusive with DH = 1.4 × 10−6 cm2 s−1. However, from the atomic trajectories shown in Fig. 3 become diffuse while H atoms in (NH2)− and (NH4)+ keep vibrating around their lattice positions. This means that the H atoms in NH3 units become considerable vibrate with a fixed N position at this condition. With the temperature further increased to 2000 K, Fmm2–(NH3)2He transforms into a real superionic phase with fully diffusive H atoms (DH = 2.0 × 10−4 cm2 s−1) within the fixed N and He framework. With the temperature increased to 3000 K, all atoms including N, He, and H are diffusive with high diffusion coefficients . This result reveals that at this conditions the superionic Fmm2–(NH3)2He phase transformed into a fluid phase. Here, we found the diffusion of H atoms occurs prior to that of He atom, which is opposite to that found for He2(H2O)39, where He atoms diffuse firstly. Generally, lighter atoms are easier to diffuse. The abnormal diffusive behavior in He2(H2O) was explained by that the H atoms has higher diffusion barrier than He atoms because of the strong covalent H-O bonds39. In fact, He atoms in He2(H2O) share large space that allows the free diffusion, as shown in Supplementary Fig. 2(H2O), although form weak interaction with N–H units, He atoms are trapped in cages formed by NH3, (NH2)− and (NH4)+ units, this makes helium atoms are more difficult to diffuse.The stable pressure and temperature regions of P = 200 GPa and T = 300 K, Fmm2–(NH3)2He keeps its solid property. With the temperature increasing to 1000 K and up to 4000 K, Fmm2–(NH3)2He becomes to a superionic phase and then turns in to a fluid when the temperature is above 4200 K, as shown in Supplementary Fig. 3 and He, showing the (NH3)2He and NH3He phases. Temperature has a significant effect on the system: I4–(NH3)2He and NH3He decompose at high temperature 2He (which decomposes fully to NH3 and He),  >1000 K for NH3He (for full decomposition to NH3 and He at P < 100 GPa and decomposition into Fmm2–(NH3)2He and He at P > 100 GPa). In contrast, Fmm2–(NH3)2He has a large stability field and thermodynamically stable in pressure range of 80–300 GPa and at any temperature in the tested range (0–5000 K). Figure Fmm2–(NH3)2He in the Fig. Fmm2–(NH3)2He phase presents superionic and fluid properties at the condition which is close to the geotherms in the upper mantle of Neptune and Uranus. This suggests that He could be trapped as superionic (NH3)2He inside the upper mantles of these planets with the mixture of superionic and fluid forms during their formation.While for  range 0–000 K. Fi range 0–000 K. Fi3, CH4, H2O, and H2 inside the giant ice planets. Our predicted stability of superionic (NH3)2He as well as the recent reported superionic H2OHe239 under the P–T conditions corresponding to the ice giants’ upper mantles indicate that helium could be remained inside the planets during their formation. Coincidently, the stability of NH3–He and H2O–He compounds provide an evidence to support the new three-layer model suggested by Nettelmann11, in which helium was considered as a small component in outer core of the planets. Therefore, the current results are essential to the understanding of the interior models of these planets. Moreover, CH4 and H2 are another two main components in upper mantle of these planets, therefore, there is a high possibility that helium could react with CH4 or H2 at high pressures to form new compounds, which deserves further investigation.Previous studies have assumed the presence of NH46 predicting plastic and superionic helium-ammonia compounds at extreme condition. They predicted three stable stoichiometries and eight new stable phases of He–NH3 compounds under pressures up to 500 GPa and found that the predicted He–NH3 compounds exhibit superionic behavior at high pressure and high temperature. These similar results further provide knowledge for our understanding of the composition of the planet’s interior.In our submission process, we were aware of the work by Liu et al.3–He systems under high-P–T conditions. Calculations at 0 K revealed two compounds ((NH3)2He and NH3He) that are energetically stable relative to the equivalent mixture of solid NH3 and He at high pressures. Specially, (NH3)2He remains energetically stable under the extreme conditions corresponding to the upper mantles of Uranus and Neptune. The current results provide evidence that He could be trapped inside these planets as NH3–He compounds with the mixture of superionic and fluid properties, in contrast to the current view that He occurs only in their atmospheres. Molecule dynamic simulations results show that the Fmm2-(NH3)2He phase will transform into a superionic solid and then to a fluid with the increasing temperature.In summary, a combination of first-principles calculations and crystal structure predictions was carried out to search for stable compounds in the NH3–He compounds were performed using a particle-swarm optimization algorithm implemented in calypso code48. This method is unbiased, not using any known structural information, and has successfully been used to predict various systems under high pressure57. We performed structural searches on (NH3)xHey  at 0–300 GPa with maximum simulation cells up to four formula units. Each generation of structures was evolved by selecting the 60% lowest-enthalpy structures in the last step and randomly producing the remaining 40%. The structure searches were considered converged when  ~1000 successive structures were generated without finding a new lowest-enthalpy structure.Structure predictions for NHvasp code58 combined with the generalized gradient approximation (GGA)59 for the exchange-correlation potential in the form of the Perdew–Burke-–Ernzerhof60 (PBE) functional. The electronic wave functions were expanded in a plane wave basis set with a cutoff energy of 1000 eV. The electronic interaction was described by means of projector augmented wave 61 pseudopotentials with valence electrons of 1s1, 2s22p3 and 1s2 for H, N, and He atoms, respectively. Monkhorst-Pack k-point62 meshes with a grid density of 0.03 Å−1 were chosen to achieve a total energy convergence of better than 1 meV per atom. The phonon dispersion curves were computed by direct supercell calculation63, as implemented in the phonopy program64.Density functional theory calculations were performed using 3)2He compound at high pressures and high temperatures. The simulation supercells contain 32 NH3 molecules and 16 helium atoms and the Brillouin zone was sampled by Γ point. Each simulation consists of 10,000 time steps with a time step of 0.5 fs.The molecular dynamics simulations were also carried out to explore the superionic property of (NHSupplementary InformationPeer Review File