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Funding: This research was carried out in part due to funding from the Max Planck-UBC-UTokyo Centre for Quantum Materials. Part of the research described in this paper was performed at the Canadian Light Source, a national research facility of the University of Saskatchewan, which is supported by the Canada Foundation for Innovation, the Natural Sciences and Engineering Research Council, the National Research Council, the Canadian Institutes of Health Research, the Government of Saskatchewan and the University of Saskatchewan. We thank the Science and Technology Facilities Council ISIS facility for the provision of beamtime. (Ba,K)BiO3 constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature Tc of 30 K arises in proximity to charge density wave order. However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO3 with a positive oxygen–metal charge transfer energy in contrast to (Ba,K)BiO3. The parent compound BaSbO3−δ shows a larger charge density wave gap compared to BaBiO3. As the charge density wave order is suppressed via potassium substitution up to 65%, superconductivity emerges, rising up to Tc = 15 K. This value is lower than the maximum Tc of (Ba,K)BiO3, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO3 indicates that strong oxygen–metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors. Publisher PDF

Where are the excess electrons in Ag16B4O10?

Ag16B4O10 has been obtained as a coarse crystalline material via hydrothermal synthesis, and was characterized by X-ray single crystal and powder diffraction, conductivity and magnetic susceptibility measurements, as well as by DFT based theoretical analyses. Neither composition nor crystal structure nor valence electron counts can be fully rationalized by applying known bonding schemes. While the rare cage anion (B4O10)8− is electron precise, and reflects standard bonding properties, the silver ion substructure necessarily has to accommodate eight excess electrons per formula unit, (Ag+)16(B3+)4(O2−)10 × 8e−, rendering the compound sub-valent with respect to silver. However, the phenomena commonly associated with sub-valence metal (partial) structures are not perceptible in this case. Experimentally, the compound has been found to be semiconducting and diamagnetic, ruling out the presence of itinerant electrons; hence the excess electrons have to localize pairwise. However, no pairwise contractions of silver atoms are realized in the structure, thus excluding formation of 2e–2c bonds. Rather, cluster-like aggregates of an approximately tetrahedral shape exist where the Ag–Ag separations are significantly smaller than in elemental silver. The number of these subunits per formula is four, thus matching the required number of sites for pairwise nesting of eight excess electrons. This scenario has been corroborated by computational analyses of the densities of states and electron localization function (ELF), which clearly indicate the presence of an attractor within the shrunken tetrahedral voids in the silver substructure. However, one bonding electron pair of s and p type skeleton electrons per cluster unit is extremely low, and the significant propensity to form and the thermal stability of the title compound suggest d10–d10 bonding interactions to strengthen the inter-cluster bonding in a synergistic fashion. With the present state of knowledge, such a particular bonding pattern appears to be a singular feature of the oxide chemistry of silver; however, as indicated by analogous findings in related silver oxides, it is evolving as a general one., Ag16B4O10, obtained via hydrothermal synthesis, displays an unprecedented bonding scheme, hosting excess electrons localized pairwise in cluster-like silver subunits.

A thorough systematic study of the Electron Localization Function (ELF) in fcc silver metal, the deficient vacant-type Ag16□4 structure, and the Ag16B4O10 title compound of the Chem. Sci., 2020, 11, 962 edge article leads to a further understanding of the sub-valent characteristics of silver in the silver borate compound. By visualizing the process in three consecutive steps, (fcc)eq-Ag → (fcc)ex-Ag → Ag16□4 → Ag16B4O10, the electron reduction of Ag atoms can be traced to be due to (i) the expansion (ex) of the host metallic array from its equilibrium (eq) geometry and (ii) the vacancy creation and subsequent insertion of guest borate clusters. Our ELF analysis also allows us to identify to what extent metallic features remain in the title compound, providing an alternative explanation of why Ag16B4O10 is not a conductor whereas pure silver is., ELF superbasins (dark-yellow stick and ball circuits) reveal how borate clusters (green and red spheres) play the role of crystal defects interrupting the electric conductivity of metallic silver (grey spheres).

We present the electronic and structural properties of monolayer ${\mathrm{WSe}}_{2}$ grown by pulsed-laser deposition on monolayer graphene (MLG) on SiC. The spin splitting in the ${\mathrm{WSe}}_{2}$ valence band at $\overline{\mathrm{K}}$ was ${\mathrm{\ensuremath{\Delta}}}_{\mathrm{SO}}=0.469\ifmmode\pm\else\textpm\fi{}0.008$ eV, as determined by angle-resolved photoemission spectroscopy. Synchrotron-based grazing-incidence in-plane x-ray diffraction (XRD) revealed the in-plane lattice constant of monolayer ${\mathrm{WSe}}_{2}$ to be ${a}_{{\mathrm{WSe}}_{2}}=3.2757\ifmmode\pm\else\textpm\fi{}0.0008$ \AA{}. This indicates a lattice compression of $\ensuremath{-}0.19$% relative to bulk ${\mathrm{WSe}}_{2}$. By using the experimentally determined graphene lattice constant (${a}_{\mathrm{MLG}}=2.4575\ifmmode\pm\else\textpm\fi{}0.0007$ \AA{}), we found that a $3\ifmmode\times\else\texttimes\fi{}3$ unit cell of the slightly compressed ${\mathrm{WSe}}_{2}$ is perfectly commensurate with a $4\ifmmode\times\else\texttimes\fi{}4$ graphene lattice with a mismatch below 0.03%, which could explain why the monolayer ${\mathrm{WSe}}_{2}$ is compressed on MLG. From XRD and first-principles calculations, we conclude that the observed size of strain will affect ${\mathrm{\ensuremath{\Delta}}}_{\mathrm{SO}}$ only on the order of a few meV. In addition, angle-resolved, ultraviolet, and x-ray photoelectron spectroscopies shed light on the band alignment between ${\mathrm{WSe}}_{2}$ and MLG/SiC and indicate electron transfer from graphene to the ${\mathrm{WSe}}_{2}$ monolayer. As further revealed by atomic force microscopy, the ${\mathrm{WSe}}_{2}$ island size depends on the number of carbon layers on top of the SiC substrate. This suggests that the epitaxy of ${\mathrm{WSe}}_{2}$ favors the weak van der Waals interactions with graphene, while it is perturbed by the influence of the SiC substrate and its carbon buffer layer.

Scandium dysprosium antimonide ScDySb was synthesized from scandium metal and DySb in an all-solid state reaction at 1770 K. According to X-ray analysis of the crystal structure [P4/nmm, Z = 4, a = 430.78(1) pm, c = 816.43(4) pm, R1 = 0.0238, wR(all) = 0.0688, 268 independent reflections], ScDySb adopts the anti-PbFCl type of structure, but with pronounced deviations in structural details, which are related to specific bonding interactions between the atoms involved. ScDySb shows antiferromagnetic ordering below 35.4 K, which was verified by susceptibility, heat capacity, and resistivity measurements. X-ray structure determination, performed at 30 K, showed no significant structural changes to occur during the magnetic phase transition. The band structure was calculated in the framework of Density Functional Theory. The bonding properties are comparable to those of Sc2Sb. Pronounced basins of the Electron Localization Function (ELF) appear in the tetragonal pyramidal Sc4Dy voids.

Ba3Pt2 has been synthesized by reaction of a 3 : 2 mixture of Ba and Pt at 1223 K in argon, and characterized by single-crystal X-ray structure determination and electrical resistivity measurements. Ba3Pt2 crystallizes in the Er3Ni2 structure type (space group R3̅ with a = 962.40(6), c = 1860.6(1) pm, Z = 9, R(F)N′ = 0.063, N′(hkl) = 777), and is isotypic to Ca3Pt2 and Sr3Pt2. The Pt atoms occur in pairs at a distance of 303 pm. According to the analysis of the Electron Localization Function and the Crystal Orbital Hamilton Population obtained from DFT band structure calculations, covalent bonding can be assumed in the Pt-dumbbells, although it is weaker in Ba3Pt2 than in Ca3Pt2. The peculiarities of the platinum compounds due to relativistic effects are elaborated by a comparison with theoretical results for Ca3Pd2. Ba3Pt2 exhibits metallic conductivity (ρ270 = 0.7 mΩ · cm), which is in accordance with band structure calculations.

The title compounds Rb 5 Au 3 O 2 , Rb 7 Au 5 O 2 , and Cs 7 Au 5 O 2 are the first examples of mixed valent phases containing gold in the oxidation states +1 and −1. Their crystal structures (Rb 5 Au 3 O 2 , Pbam , a =736.4(1) pm, b =1430.8(2) pm, c =567.9(1) pm, Z =2, R ( F )=0.053, 647 reflections; Rb 7 Au 5 O 2 , Immm , a =567.1(2) pm, b =930.1(1) pm, C =1659.4(3) pm, Z =2, R ( F )=0.066, 409 reflections; Cs 7 Au 5 O 2 , Immm , a =599.4(1) pm, b =960.6(3) pm, c =1720.8(12) pm, Z =2, R ( F )=0.039, 386 reflections) are characterized by the combination of distinctive structural features of gold(I) oxides and aurides: for Au(+1) a typical linear coordination by oxygen is found and the surroundings of Au(−1) bear a close resemblance to the binary 1:1 aurides. In consequence the overall structures of Rb 5 Au 3 O 2 and M 7 Au 5 O 2 can be described as intergrowths of M 3 AuO 2 and M Au ( M =Rb, Cs), constituting members of a homologous series [ M Au] n [ M 3 AuO 2 ] with n =2 and 4, respectively. The crystal chemical evidence for the valence states assumed, also confirmed by Mosbauer spectroscopy, is supported by various band structure calculations (Hartee–Fock and density functional) clearly indicating the coexistence of two different oxidation states. The compounds have been synthesized by reacting binary aurides M Au and alkali monoxides M 2 O ( M =Rb, Cs) with elemental gold in the required stochiometric amounts. Hereby, a further astonishing parallel to the chemistry of halogens is revealed. Like these, gold disproportionates upon interaction with bases.

The crystal structures of B 9 Cl 9 and B 9 Br 9 have been determined with X-ray single crystal structure analysis (subcell: R3m (166); Z = 6; a = 1259.6(5) pm, c = 1700.1(5) pm (B 9 Cl 9 ); a= 1317.5(3) pm, c =1777.6(3) pm (B 9 Br 9 )). Both compounds are isotypic and consist of a tricapped trigonal B 9 prism (C 3v ) with different bond lengths for the triangles (180.0 pm; 176.5 pm), edges (205.7 pm; 201.0 pm), and caps (174.0 pm; 173.5 pm). For better understanding of the bonding in these clusters the electronic structures of the nonaboranes(9), the dianion B 9 Br 9 2- , B 8 Cl 8 2- , H 2 B 9 Br 9 (three types), and B 10 H 14 have been calculated and compared with respect to their bond distances and configurations together with the experimental results. The calculation of the Electron Localization Function (ELF) of these molecules and anions shows that the 2e-3c bonds play a dominant role in these polyhedral cages. The changes in bonding going from the non-Wade cluster B 9 Br 9 with 18 cluster electrons to the Wade cluster B 9 Br 9 2- with 20 cluster electrons can be visualized by the ELF.

The structure of PdGa 5 is characterized by a framework of condensed bicapped tetragonal antiprisms [PdGa 10 ]. The appropriate symmetry governed periodic nodal surface (PNS) divides the space into two labyrinths. The atoms of the coordination polyhedra are located in one labyrinth or are close to the surface. The second labyrinth seems to be “empty”. The electron localization function (ELF) calculated by the TB-LMTO method, shows that the “empty” labyrinth contains the regions with high ELF values. These regions are related to inter-polyhedral GaGa bonds forming Ga 4 squares. The vertices of eight covalently bonded Ga 4 squares build tetragonal antiprisms which are centered by Pd atoms. High electron density but low ELF values inside these coordination polyhedra of Pd represent regions of delocalized (metal-like) electrons. Thus, the PNS separates the regions of different bonding character. Some relations to stuffed derivatives of the PdGa 5 structure are discussed.

Zinc crystallizes in the hcp structure, but with an anomalously large c/a ratio, indicating a strong distortion away from ideal packing. Coupled cluster calculations within the framework of the method of increments, improved by an embedding scheme for metals, were performed to explore the potential energy surface of zinc with respect to the hexagonal lattice parameters. The inclusion of the filled d shell in the correlation treatment proved to be essential. From the exceptional shape of the potential energy surface the existence of a zinc modification with a nearly ideal c/a ratio can be deduced.