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Among the known planar pentacoordinate atoms, chlorine is missing due to its large radius and high electronegativity. Herein, we report the first star-like superhalogen anion D5h Cl©Li5Cl5− (1), which contains a planar pentacoordinate chlorine (ppCl) at the center. Computer structural searches and high-level calculations reveal that 1 is a true global minimum (GM) on the potential energy surfaces. Molecular dynamics simulations indicate it is kinetically stable against isomerization or decomposition. Although detailed chemical bonding analyses reveal one delocalized 6c-2e σ bond over the Cl©Li5 central unit and five delocalized 3c-2e σ bonds along the periphery, while aromaticity has very little beneficial effect on stability, instead, ionic interaction dominates the stability of the system. More encouragingly, with the large HOMO–LUMO energy gap of 7.66 eV and vertical detachment energy of 7.87 eV, the highly chemically inert 1 can be viewed as a typical superhalogen anion and is possible to be synthesized and characterized in future experiments. [ABSTRACT FROM AUTHOR]

Using the experimentally known aromatic icosahedral superatoms Ih B12H122− and D5d 1,12-C2B10H12 as building blocks and based on extensive density functional theory calculations, we predict herein a series of core–shell superpolyhedral boranes and carboranes in a bottom-up approach, including the high-symmetry Th B12@B152H722− (2), C2h C2B10@B152H72 (3), D3d B12@B144H66 (4), Ih B12@C24B120H722− (6), and D5d C2B10@C24B120H72 (7). More interestingly, the superatom-assembled linear D2h B36H322− (8), close-packed planar D3dB84H602− (10), and nearly close-packed core–shell D3d B12@B144H66 (4) can be extended periodically to form the one-dimensional (1D) α-rhombohedral borane nanowire B12H10 (Pmmm) (9), two-dimensional (2D) α-rhombohedral monolayer borophane B12H6 (P 3 ¯ m 1 ) (11), and the experimentally known three-dimensional (3D) α-rhombohedral boron (R 3 ¯ m ) (12) which can be viewed as an assembly of the monolayer B12H6 (11) staggered in vertical direction, setting up a bottom-up strategy to form low-dimensional boron-based nanomaterials from their borane "seeds" via partial or complete dehydrogenations. Detailed bonding analyses indicate that the high stability of these nanostructures originates from the spherical aromaticity of their icosahedral B12 or C2B10 structural units which possess the universal skeleton electronic configuration of 1S21P61D101F8 following the Wade's n+1 rule. The infrared (IR) and Raman spectra of the most-concerned neutral B12@B144H66 (4) and C2B10@C24B120H72 (7) are computationally simulated to facilitate their experimental characterizations. [ABSTRACT FROM AUTHOR]

Based on extensive global minimum searches augmented with first-principles theory calculations, we predict herein the first boron-based perfect tetrahedral clusters Td B16P4 (2) and Td B16As4 (3) which, as aromatic non-metal analogs of the experimentally observed Td Au20 (2003, Science299, 864), all contain a truncated Td B16 (1) cage at the center effectively stabilized by four trivalent non-metal atoms (P, As) at the corners. Detailed natural bonding orbital (NBO) and adaptive natural density partitioning (AdNDP) bonding analyses indicate that the valences of all the trivalent component atoms in these tetrahedral clusters are fully satisfied, rendering spherical aromaticity and extra stability to the systems. The IR, Raman, and photoelectron spectra (PES) of the concerned species are theoretically simulated to facilitate their characterizations in future experiments. [ABSTRACT FROM AUTHOR]

Boron has been found to be able to form multiple bonds with lead. To probe Pb–B bonding, here we report an investigation of three Pb-doped boron clusters, PbB2−, PbB3O−, and PbB4O2−, which are produced by a laser ablation cluster source and characterized by photoelectron spectroscopy and ab initio calculations. The most stable structures of PbB2−, PbB3O−, and PbB4O2− are found to follow the formula, [PbB2(BO)n]− (n = 0–2), with zero, one, and two boronyl ligands coordinated to a triangular and aromatic PbB2 core, respectively. The PbB2− cluster contains a B＝B double bond and two Pb–B single bonds. The coordination of BO is observed to weaken Pb–B bonding but strengthen the B＝B bond in [PbB2(BO)n]− (n = 1, 2). The anionic [PbB2(BO)2]− and its corresponding neutral closed-shell [PbB2(BO)2] contain a B≡B triple bond. A low-lying Y-shaped isomer is also observed for PbB4O2−, consisting of a central sp2 hybridized B atom bonded to two boronyl ligands and a PbB unit. [ABSTRACT FROM AUTHOR]

Understanding the fluxional bonding nature of hydrogen bonds (HBs) and their networks in small water clusters and bulk water remains a huge challenge in both chemistry and physics. Detailed natural bonding orbital (NBO) and non-covalent interactions-reduced density gradient (NCI-RDG) analyses performed in this work at ab initio theoretical level unveil the existence of fluxional hydrogen bonds (FHBs) in small neutral water clusters (H2O)n (n = 2–6). The fluxional mechanisms of linear water dimer (H2O)2 and cyclic water trimer (H2O)3, tetramer (H2O)4, and pentamer (H2O)5 from their transition states (TSs) to ground states (GSs) mainly involve one 3c-2e FHB which fluctuates backward and forward through a weak 4c-2e van der Waals interaction in the TS, while that of the triangular prism water hexamer (H2O)6 involves two 3c-2e FHBs on two neighboring edges perpendicular to each other in a concerted mechanism. It is the FHBs that facilitate the structural fluxionalities of water clusters and their assemblies. [ABSTRACT FROM AUTHOR]

Using full configuration interaction (FCI) and multi‐reference configuration interaction methods (MRCI), reliable geometrical and energetic references for Bn (n = 1–4) clusters were established. The accuracy of the computed results was confirmed by comparison with available experimental data. Benchmark calculations indicated that B97D3, B97D, VSXC, HCTH407, BP86 and CCSD(T) methods provided reasonable results for structural parameters, with mean absolute error (MAEs) within 0.020 Å. Among the tested density functional theory (DFT) methods, the VSXC functional showed the best performance in predicting the relative energies of B1B4 with a MAE of 12.8 kJ mol−1. Besides, B1B95, B971, TPSS, B3LYP, and BLYP functionals exhibited reasonable performance with MAE values of less than 15.0 kJ mol−1. T1 diagnostic values between 0.035 and 0.109 at the CCSD(T) level revealed strong correlations in B2B4 clusters, highlighting the need for caution in using CCSD(T) as an energy reference for small boron clusters. The methods of CCSDT, CCSDT(Q) and CCSDT[Q], which incorporate three‐electron and four‐electron excitations, effectively improved the accuracy of the energy calculations. [ABSTRACT FROM AUTHOR]

The development of electrochemical nitrogen reduction reaction (NRR) catalysts with high catalytic activity and high stability is a significant challenge. In this work, a LaCu0.1Fe0.9O3−δ (LCuF) electrocatalyst for NRR was developed based on B-site Cu doping in the LaFeO3 (LF) perovskite. Good NRR catalytic performance and long-term stability were achieved when this catalyst was used as the cathode material for a protonic ceramic electrolysis cell (PCEC). Experimental results demonstrate that the synergistic effect between Cu and Fe enhances the NRR activity of this electrocatalyst. Electrons are transferred through the Fe–O2−δ–Cu chain, resulting in the formation of more Fe4+ at Fe sites and more Cu+ at Cu sites. This accelerates the electron transfer rate and thus increases the NRR rate. At the same time, more oxygen vacancies (OVs) are generated around Cu+. Fe4+ and OVs are both electron-deficient species, which are helpful for activating N2 by trapping metastable electrons in the anti-bonding orbitals of adsorbed nitrogen molecules. This work provides a viable strategy for developing a highly efficient NRR electrocatalyst. [ABSTRACT FROM AUTHOR]

Efficient bifunctional catalysts for oxygen evolution and reduction reactions (OERs/ORRs) are of great importance for sustainable and renewable clean energy, especially for metal–air batteries. Herein, we investigated β12-borophene with double-hole sites capped with 3d transition metal atoms to explore its catalyst performance for hydrogen evolution reactions (HERs), OERs and ORRs. It was found that the borophene is a good platform for diatomic site catalysts (DASCs) due to their advantage of stability over the corresponding single-atom catalysts (SACs) or clusters. The HER performance of DASCs on β12-BM was further improved compared to the SAC case. Furthermore, the supported FeNi DASC exhibited good catalytic performance for both OERs and ORRs, the overpotentials for which were 0.43 and 0.55 V, respectively, better than those of the corresponding supported Ni or Fe SAC due to synergistic effects. We herein propose a novel descriptor involving the Bader charges of coordinated atoms explicitly, behaving much better than the d-band center and integrated crystal orbital Hamilton population (-ICOHP) for DASCs. The synergistic effect of Fe–Ni pairs balanced the too strong binding of OH and further activated OH to achieve better catalytic performance. The results of this study can provide theoretical guidance for the design of efficient bifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

Pr0.5Sr0.5Cr0.1Fe0.9−xNixO3−δ (PSCFNx, x = 0.1, 0.2) catalysts are prepared and utilized as electrodes in symmetric solid oxide fuel cells (SOFCs) for the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). Although the PSCFNx cathode retains its perovskite phase during operation in SOFCs, the anode is totally decomposed and decorated with an exsolved metallic Ni–Fe alloy (denoted as re-PSCFNx) in a reducing atmosphere. Electrochemical impedance spectroscopy (EIS) combined with distribution of relaxation times (DRT) analysis reveals that the rate-limiting step for the HOR at the anode is the hydrogen adsorption–dissociation process, while the charge transfer process is found to dominate the ORR at the cathode. As the doping of Ni is increased, the cathode polarization resistance for the ORR decreases from 0.19 Ω cm2 for PSCFN0.1 to 0.09 Ω cm2 for PSCFN0.2 at 800 °C in air. A similar trend is observed for the anode polarization resistance for the HOR, which exhibits a reduction from 2.46 Ω cm2 of re-PSCFN0.1 to 1.28 Ω cm2 of re-PSCFN0.2 at 800 °C in H2. When fueled with hydrogen, a single cell based on the PSCFN0.2/La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM)(240 μm)/re-PSCFN0.2 configuration delivers a maximum power density of 623 mW cm−2 and slight performance degradation when operated for 220 h at 800 °C. Ni doping results in the charge redistribution of B-site ions. Increasing the doping level of Ni results in additional electron transfer channels and oxygen vacancies that adsorb more oxygen species, which facilitates the ORR performance. Furthermore, an increase in the number of Ni–Fe nanoparticles and creation of abundant interfaces in the anode promote the HOR. This work suggests that PSCFN0.2 has the potential to be an excellent electrode material for a symmetric SOFC. [ABSTRACT FROM AUTHOR]