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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.

We discovered superconductivity at 4.8 K in the hexagonal layered compound La2IRu2 comprising a triangular lattice of the La and a honeycomb lattice of the Ru atoms. First-principles calculations reveal a two-dimensional band structure made up of La 5d and Ru 4d electrons and formal oxidation states +1.5 for the La and the uncommon oxidation state −1 for the Ru atoms. The temperature dependence of the specific heat indicates fully gapped superconductivity. Nevertheless, the upper critical field of this compound violates the Pauli limit. We argue that the high upper critical field is ascribed to an antisymmetric spin–orbit coupling in the unique multilayer structure.

(Ba,K)BiO

The air-stable phosphide, Ag6Ge10P12, was synthesized from its elements in gram amounts. As its structure is closely related to high-performance thermoelectric tetrahedrites (Ag6□Ge4Ge6P12 ≡ Cu6SSb4Cu6S12), we studied temperature dependent single-crystal X-ray diffraction experiments, quantum chemical calculations, and thermoelectric transport properties of spark plasma sintered and pristine, single crystalline samples, in order to give a comprehensive picture of its thermoelectric performance and its origin. The semiconducting character of this material is reflected in band structure calculations. Measurements of the thermal diffusivity exhibit a very low thermal conductivity, κ < 1 W m–1 K–1, which is close to a phonon glass-like behavior, and has its origin in a strong local bonding asymmetry, induced by strong bonding of the phosphorus–germanium (Ge4+) covalent framework and weak bonding of lone-pair electrons (Ge2+). This chemical bond hierarchy creates a pronounced anisotropic behavior of the silver...

We discovered superconductivity at 4.8 K in the hexagonal layered compound La

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.

The electronic structure of the intermetallic compound MgZn2, a prototypical Laves phase, was investigated by first-principles calculations based on Kohn-Sham density-functional theory. A variety of six exchange-correlation energy density functionals, from local density approximation to hybrid functionals, was used to fully optimize the crystal structure. Cell parameters and mass density calculated with the density functional parameterization by Perdew, Burke, and Ernzerhof (PBE) were found closest to their corresponding experimental values. The revised version of the functional, PBEsol, recommended for solid state applications, gave inferior results. The electronic structure was analysed in terms of band structure, density of states and electron density.

The electron distributions in position and in momentum space of the hcp metals magnesium and zinc are investigated experimentally and compared to results of quantum-chemical calculations. Furthermore, a survey is given on recent analyses of the bonding properties of zinc and cadmium, using the method of increments. The experimental deformation densities were obtained by refining multipole models to X-ray diffraction data sets measured at 100 K with either Mo-Kα (Mg) or Ag-Kα (Zn) radiation. The final RF values (Valray/Jana2006) are 0.0028/0.0034 (Mg) and 0.0068/0.0068 (Zn). The differences to deformation densities obtained from periodic density functional calculations are discussed. The effect of dynamical electron correlation on the electron density was analyzed, using cluster models. Compton profiles were measured with 88.67 keV synchrotron radiation at beamline ID15B at the ESRF in Grenoble. Varied orientations of the samples allowed for probing the projected momentum distribution along the [100], [423] and [001] directions. Fourier transforms of the computed reciprocal form factor B(r) resulted in the corresponding theoretical Compton profiles. It is suggested that the anomalous hcp structure of zinc is favored by a kinetic balancing of the valence electrons, i.e. correlation mediated 4s-3d interactions.

The structural relations of La2Sb type compounds and their oxygen stuffed variants, like e.g. Eu4Sb2O (anti-K2NiF4 type), are discussed. In the course of these investigations, the crystal structures of La2Sb, Pr2Sb, Sm2Sb, Nd2Bi, and Sm4Bi2O were determined and refined from single crystal data. Band structures have been calculated in the framework of density functional theory, and the bonding properties of the individual compounds are compared on the basis of the Electron Localization Function (ELF). Based on specific geometrical parameters, the La2Sb type compounds are arranged in a structure field map. Three distinct areas arise: insulating K2NiF4 type compounds, semiconducting, oxygen stuffed variants and oxygen-free metallic compounds. La2Sb is found in the latter area, ruling out oxygen content, which is confirmed by high resolution single-crystal X-ray diffraction. The electronic structures of the compounds are related to the valence electron count. Pnictides of tri-valent metals are metallic and feature local multicenter metal–metal bonds, di-valent metals form oxygen stuffed variants. Samarium is the only element which is found in both areas of the structure field map, displaying an oxygen free and a stuffed variant.

The general building principle of the commensurate subset of mixed valent sodium cuprates Na1+x CuO2 (0 ≤ x ≤ 1) has been revealed. Starting from parent ­NaCuO2, spin doping of the chain of edge sharing CuO4 plaquettes requires to incorporate further sodium ions for charge compensation. The accessible space needed for this purpose is generated by elongating the NaO6 octahedra present in NaCuO2. In this way, from one octahedron two square pyramidal and two tetrahedral sites result, out of which at best one each tetrahedral and square pyramidal site per original octahedron can be occupied, excluding combinations of electrostatically blocked sites. This general building principle has been employed to predict further structure candidates of this series (x = 1/4, 1/3, 2/3, 5/7, 3/4, 1). Density functional calculations (x = 0, 5/7, 3/4, 1) confirm the predicted charge ordering as well as the related structural features. The structure candidates are identified as local minima on the energy landscape.

Cs22In6(SiO4)4 was synthesized by the reaction of appropriate starting materials at 673 K, followed by slow cooling to room temperature, in arc-welded tantalum ampoules. According to single-crystal X-ray analysis, the compound crystallizes in a new structure type (P21/n(no. 14), a = 14.3533(4), b = 16.1712(4), c = 25.0135(7) A, β = 94.368(1), Z = 4), consisting of [In6]6– clusters with the shape of a distorted octahedron or more appropriately described as a condensate of three face sharing tetrahedra. The cluster is the first example of a “hypoelectronic” isolated [In6]6– indium cluster. The oxosilicate indide can be regarded as a “double salt“, Cs6In6 on one hand and the oxosilicate Cs4SiO4 ( × 4) on the other, which form the quaternary structure by inhomogeneous intergrowth of partial structures. The electronic structure of Cs22In6(SiO4)4 was examined by DFT calculations and compared to the one of Rb2In3, which exhibits linked In6 polyhedra. According to the DOS the title compound is a semiconductor with a band gap of 0.5 eV, which is in agreement with its observed insulating character. [In6]6– is an “isolated” cluster bearing inert electron pairs at each vertex. In contrast, [In6]4– in Rb2In3 only exhibits inert pairs at the apical atoms. The four basal atoms are linked to neighboring clusters by covalent bonds forming a 2D network. These bonding scenarios are supported by the analysis of the projected density of states, the electron localization function and the partitioning of the electron density according to Bader.

Aluminium carbide, Al4C3, was characterised by 13C and 27Al solid-state NMR spectroscopy. The 13C NMR spectra display two resonances with an intensity ratio of 1:2, which is in agreement with the reported crystal structure. The 27Al NMR spectra of Al4C3 under both static and MAS conditions were deconvoluted into two spectral components, belonging to the two aluminium species Al1 and Al2 in the crystal structure of Al4C3. The spectral fit allowed for determination of the relatively large quadrupolar coupling constants (χ ≈ 16 MHz) of both 27Al species. One aluminium species displayed a tendency of having a χ of slightly smaller magnitude compared to the other. By carrying out DFT calculations of the EFG tensor at the 27Al sites using the Wien2k software, we could tentatively assign the smaller χ site to be the crystallographic Al1 species. Also, the isotropic chemical shift for the carbon-coordinated aluminium in Al4C3 could be determined, being in the range of 111 to 120 ppm. This is somewhat larger than those shift values observed for 27Al in nitrogen coordination.

Cs4Tl2O was synthesized by reaction of the binary compounds CsTl and Cs2O at 573 K, followed by slow cooling to room temperature. According to single-crystal X-ray analysis, the title compound crystallizes in a new structure type (trigonal, space group Rm (no. 166), a = 11.986(1), c = 20.370(2) A, Z = 9). It consists of isolated [Tl6]6– octahedra, being regular with respect to the equality of all three main diagonals (4.546(5) A), and of [Cs12O3]6+ triple octahedra extending along the c direction.The electronic structure of Cs4Tl2O was examined by relativistic density functional calculations including spin–orbit coupling and compared to the one of Rb10Tl6O2, which exhibits a highly distorted [Tl6]6– octahedra. In the latter case the closed-shell electronic structure is the result of a Jahn–Teller distortion. In contrast, the regular one in Cs4Tl2O corresponds to a closed-shell configuration, in accordance with diamagnetic properties, only if spin–orbit coupling is considered.

Cs(18)Tl(8)O(6) was synthesized reacting the binary compounds CsTl and Cs(2)O. According to single crystal X-ray analysis, the title compound crystallizes as a novel structure type in the cubic space group I23 and is diamagnetic. The electronic structure of the extended solid and of excised Cs(6)Tl(8) clusters has been examined by relativistic density functional calculations including spin-orbit coupling. Cs(18)Tl(8)O(6) comprises a clusteranion [Tl(8)](6-) in the shape of a tetrahedral star. An isoelectronic cluster was found previously in Cs(8)Tl(8)O, however, with the shape of a parallelepiped. Both clusteranions can be derived from a homocubane unit by displacive distortions. It has been shown by quantum mechanical analyses that the closed-shell electronic structure of the parallelepiped is the result of a Jahn-Teller distortion, while in contrast the tetrahedral star in Cs(18)Tl(8)O(6) would still exhibit an open-shell degenerate HOMO within a scalar relativistic approximation. Only if spin-orbit coupling is considered, a closed-shell electronic system is obtained in accordance with the diamagnetic behavior of Cs(18)Tl(8)O(6).

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.

The crystal structure of elemental zinc deviates from the ideal hexagonal close packing by a significantly increased c/a ratio. We determined the evolution of the lattice constants and thermal displacement parameters in the temperature range of 40 to 500 K by accurate single-crystal X-ray diffraction. The c axis varies linearly within the whole temperature range, whereas the a lattice constant stays constant below ≈ 160 K, which indicates that at lower temperatures the Zn–Zn distances are no longer thermally contractible in the ab plane. As a further significant observation, the thermal expansion coefficient along the c direction exceeds the one in a direction by a factor of ~10, and consequently the c/a ratio slightly reduces, but stays unusually high (c/a = 1.826, extrapolated for T = 0 K). The thermal motion of zinc shows a striking anisotropy as expressed by a ratio U33/U11 of ≈ 2.6 at 500 K. This ratio decreases significantly towards lower temperatures and reaches almost 1.6 at 40 K. The thermal behavior as observed is thus reflecting the structural and bonding anisotropy of zinc at ambient conditions, but thermal motion turns isotropic at cooling, in contrast to the atomic equilibrium structure.

Cadmium crystallises 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 with an embedding scheme for metals were performed to explore the potential energy surface of cadmium with respect to the hexagonal lattice parameters. This potential energy surface is compared to density functional theory based surfaces, as calculated with various functionals. The overall flatness of the potential energy surface over a wide range of values of the lattice parameter c is analogous for both treatments, however only within the method of increments do we quantitatively describe the cohesion. The overall behaviour of the method of increments for cadmium is consistent with previous results for zinc, emphasising the dominant role of electronic correlation in achieving a sufficiently accurate description of bonding properties for the two elements; however, a detailed analysis shows differences. We discuss this in detail in terms of the correlation contributions of the s- and d-electrons.

The new barium nitridoosmate oxide (Ba(6)O)(OsN(3))(2) was prepared by reacting elemental barium and osmium (3:1) in nitrogen at 815-830 degrees C. The crystal structure of (Ba(6)O)(OsN(3))(2) as determined by laboratory powder X-ray diffraction (R3, No 148: a = b = 8.112(1) A, c = 17.390(1) A, V = 991.0(1) A(3), Z = 3), consists of sheets of trigonal OsN(3) units and trigonal-antiprismatic Ba(6)O groups, and is structurally related to the "313 nitrides" AE(3)MN(3) (AE = Ca, Sr, Ba, M = V-Co, Ga). Density functional calculations, using a hybrid functional, likewise indicate the existence of oxygen in the Ba(6) polyhedra. The oxidation state 4+ of osmium is confirmed, both by the calculations and by XPS measurements. The bonding properties of the OsN(3)(5-) units are analyzed and compared to the Raman spectrum. The compound is paramagnetic from room temperature down to T = 10 K. Between room temperature and 100 K it obeys the Curie-Weiss law (mu = 1.68 mu(B)). (Ba(6)O)(OsN(3))(2) is semiconducting with a good electronic conductivity at room temperature (8.74x10(-2) ohms(-1) cm(-1)). Below 142 K the temperature dependence of the conductivity resembles that of a variable-range hopping mechanism.

Structural and electronic properties of Ag2NiO2 and AgNiO2 were investigated and compared. Single crystal X-ray diffraction experiments on Ag2NiO2 at 100 K provide evidence for a ferrodistortive phase below 260 K. Ni K-edge and Ag LIII-edge XANES spectra, both measured and simulated, as well as core level and valence band photoelectron spectra are analysed. They agree well with the results of bandstructure calculations, where pure DFT and mixed Hartree–Fock/DFT (hybrid) functionals were applied and spin-polarisation was considered. The electronic structure of the [NiO2] − layers with Ni 3+ in a low spin state, forming a spin-1/2 triangular lattice, is very similar in both compounds. A ferrimagnetic alignment of the spins within the [NiO2] − layers and their antiferromagnetic coupling via the intermediate silver layers is suggested.

A new low temperature modification of TaTe2 is reported (structural data at T = 150 K: C2/m (no. 12), Z = 18, a = 14.792(1) A, b = 10.8829(9) A, c = 9.3005(7) A, β = 110.693(1)°). Temperature dependent single crystal X-ray diffraction , magnetic susceptibility , resistivity, specific heat capacity and differential scanning calorimetry measurements all show a phase transition at TPT ≈ 170 K. The structural change is mainly reflected by a shift of only 2/9 of the Ta atoms by 0.283 A, which leads to clustering of the Ta atoms. The bonding patterns were derived from the Crystal Orbital Hamiltonian Population and from the Electron Localization Function based on Density Functional Theory calculations, respectively. Differences to the room temperature modification and to the hypothetical 1T-TaTe2 structure are elaborated. It is suggested, that the room temperature structure might show a dynamic type of disorder, with the X-ray structure analysis reflecting the time averaged structure.

The structural relations of the intermetallic compounds Cu2Sb, Mn2Sb, Fe2As, Mn2As, Cr2As, Sc2Sb as well as of YTiSi and ZrSiS, all adopting the PbFCl structure, are discussed. In the course of these investigations, the crystal structures of Mn2Sb, Mn2As and Fe2As have been redetermined and refined from single crystal data. Bandstructures have been calculated in the framework of Density Functional Theory. The bonding properties are compared on the basis of partial densities of states, of the Crystal Orbital Hamilton Population (COHP) and of the Electron Localization Function (ELF). The trend of thedelectrons to become more localized with increasing number leads to different bonding conditions in the compounds discussed.

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 compound has been produced by using the radio frequency (RF) method. Barium and carbon were evaporated simultaneously under dynamic flow of helium at different temperatures. About 0.5 mg of pure Ba@C(74) was isolated via a three-step high-pressure liquid chromatography separation. For the first time, the structure of a monometallofullerene has been analyzed by means of single-crystal synchrotron diffraction on microcrystals of Ba@C(74).Co(OEP).2C(6)H(6) (Co(II)(OEP): cobalt(II) octaethylporphyrin) at 100 K. The monometallofullerene exhibits a high degree of localization of the endohedral metal ion, with just two split positions for Ba and two orientations of the C(74)-cage. The barium atom is localized inside the C(74)-cage and displaced off-center, toward the Co(OEP) molecule (d approximately 127 pm). The shortest Ba-C distance is 265 pm. The Co(OEP) molecules form dimers in which the coordination of the cobalt is (4 + 1). Due to the all-syn conformation of the ethyl groups, each Co(OEP) molecule of the dimer coordinates one C(74)-fullerene. The units (Ba@C(74))[Co(OEP)](2)(Ba@C(74)) are arranged in a distorted primitive hexagonal packing. The free space between these complex units is filled by benzene molecules of crystallization. The Ba L(III) XANES spectrum of a thin film sample of Ba@C(74) exhibits a pronounced double maximum structure at about E = 5275 eV. The comparison of the shape resonances of the experimental data with simulated XANES spectra, based on different exo- and endohedral structure models, confirm that the Ba atom is located inside the C(74)-cage (D(3)(h)()) in an off-center position. The Ba atom is shifted by about 130-150 pm from the geometric center of the C(74)-cage. This is in good agreement with quantum chemical results. Thus, despite the disorder still present, a consistent and conclusive structure model for the title compound has been derived by employing a combination of X-ray diffraction, XANES spectroscopy, and quantum chemical calculations.

BaPt has been synthesized by reaction of a 1:1 mixture of Ba and Pt at 1223 K in argon and characterized by single-crystal X-ray structure determination and electrical resistivity and magnetic susceptibility measurements. The compound crystallizes in the NiAs structure type with an extremely low value for the c/a ratio (hexagonal space group P63/mmc with a = 5.057(2) A, c = 5.420(3) A, c/a = 1.072, R1 = 0.0297, Nhkl = 93). This c/a ratio reflects structural features that are unusual for the NiAs type: Pt is coordinated linearly by two other Pt atoms at a distance as short as 2.71 A, thus forming a chain along [001] of homonuclearly bonded platinum. Band structure calculations and electron localization function analyses reveal a covalent character of Pt−Pt interactions along the c axis and two-dimensional metallic conductivity parallel to the ab plane. In terms of the Zintl−Klemm concept, in its most general sense, BaPt can be formulated as (Ba2+) , and it can be considered a new example of platinide anio...

The reduction of C70 with strontium, dissolved in liquid ammonia, in a molar ratio of 2:3 and crystallisation under solvothermal pressure at room-temperature results in the formation of crystalline [Sr(NH3)8]3(C70)2·19NH3. The crystal structure ( P 1 , a=1594.7(1) pm, b=1656.3(1) pm, c=2409.5(2) pm, α=79.664(1)°, β=75.207(1)°, γ=80.460(1)°, Z=2, R1=0.082, 14301 reflections) is built up of polymeric chains 1 ∞ [C703−] arranged in a distorted hexagonal close packing of rods parallel [ 1 2 1 ] intersected by layers of [Sr(NH3)8]-polyhedra extending parallel (111). Quantum chemical results on the model systems [C70(CH3)2]n− (n=2, 3, 4) are discussed in comparison to the accurate crystal structure data in order to analyse the total charge, charge distribution and the bonding character due to the structural response of the C70 fullerene units upon reduction.

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.

Chemical reduction of B9X9 (X = Cl, Br, I) with gaseous HI proceeds stepwise to give the neutral paramagnetic clusters HB9X9·, and the corresponding diamagnetic clusters H2B9X9. Together they comprise the first neutral derivatives in the series BnHn+1 and BnHn+2 with n = 9. The EPR spectra of the paramagnetic HB9X9· (X = Cl, Br, I) in glassy frozen CH2Cl2 solutions showed increasing g anisotropy for the heavier halogen derivatives, illustrating significant halogen participation at the singly occupied MO due to the larger spin-orbit coupling contributions. Temperature dependent 1H NMR spectra of H2B9X9 (in CD3CN, X = Cl, Br) indicate the presence of H2B9X9, [HB9X9]–, and [CD3CNH]+ with H2B9X9 acting as a Bronsted acid. The corresponding 11B NMR spectra (in CD3CN) show the presence of the dianions [B9X9]2– as a result of the protonation of CD3CN. The 11B resonances of the species H2B9X9 and [HB9X9]– are obscured by superimposition of the two resonance lines of the dianions [B9X9]2–. Temperature dependent 11B{1H} MAS-NMR spectra of H2B9Br9 show coalescence at 410 K and hence dynamic behaviour of the neutral B9-cluster in the solid. Cyclic voltammetry experiments of H2B9Br9 in CH3CN solvent) are compatible with the redox sequence [B9Br9]2––[B9Br9]· ––B9Br9. Quantum chemical calculations with the electron localization function (ELF) are described. HB9X9˙ und H2B9X9 (X = Cl, Br, I): Neutrale closo-Nonaborane aus der neuartigen Reihe BnHn+1 und BnHn+2 – Synthesen, ab initio Rechnungen und elektronische Strukturen Die chemische Reduktion von B9X9 (X = Cl, Br, I) mit gasformigem HI verlauft stufenweise, wobei die neutralen paramagnetischen Cluster HB9X9· sowie die diamagnetischen Cluster H2B9X9 gebildet werden. Beide Verbindungstypen sind die ersten neutralen Vertreter der Serien BnHn+1 und BnHn+2 mit n = 9. Die EPR-Spektren der paramagnetischen Verbindungen HB9X9· (X = Cl, Br, I) in glasartig gefrorenen CH2Cl2-Losungen zeigen fur die schwereren Halogenide zunehmende g-Anisotropie, was auf signifikante Halogen-Beteiligung am einfach besetzten MO hinweist, (zunehmende Spin-Bahn-Kopplungsbeitrage). Temperaturabhangige 1H-NMR-Spektren von H2B9X9 (in CD3CN, X = Cl, Br) zeigen die Anwesenheit von H2B9X9, [HB9X9]– neben [CD3CNH]+, die H2B9X9 als Bronsted-Saure ausweisen. Die entsprechenden 11B-NMR-Spektren zeigen die Anwesenheit der Dianionen [B9X9]2– als Resultat der Protonierung von CD3CN. Die 11B-NMR-Resonanzlinien von H2B9X9 und [HB9X9]– sind von den beiden Linien des Dianions [B9X9]2– uberlagert und somit nicht nachweisbar. Temperaturabhangige 11B{1H}-MAS-NMR-Spektren von H2B9Br9 zeigen bei 410 K Koaleszenz und beweisen damit das dynamische Verhalten des H2B9Br9-Clusters im festen Zustand. Cyclovoltammetrische Untersuchungen von H2B9Br9 in CH3CN sind in Ubereinstimmung mit der Redox-Sequenz [B9Br9]2–[B9Br9]· ––B9Br9. Quantenmechanische Rechnungen sowie Elektronen-Lokalisierungs-Funktionen (ELF) werden beschrieben.

Halogenation of nido-B10H14 with C2H2Cl4, C2Cl6, Br2, or I2, produces by cluster degradation the (2 n)-closo-clusters B9X9 (X = Cl, Br, I). The synthesis of salts of the perhalogenated radical anions of the type (2 n + 1)-closo-[B9X9]· – and of the corresponding dianions (2 n + 2)-closo-[B9X9]2– from neutral B9X9 is described [n is the number of cluster atoms; (2 n), (2 n + 1), and (2 n + 2) is the number of cluster electrons]. Molecular and crystal structures of B9Cl9, B9Br9, [(C6H5)4P][B9Br9] · CH2Cl2, and [(C4H9)4N]2[B9Br9] · CH2Cl2 have been determined via X-ray diffraction. All three oxidation states of the cluster retain the tricapped trigonal prism. The reduction of the clusters B9X9 was shown by cyclic voltammetry in CH2Cl2 to proceed via two successive one-electron reversible steps, separated by at least 0.4 V. The paramagnetic radical anions [B9X9]· – (X = Cl, Br) were further characterized by magnetic susceptibility measurements of [Cp2Fe][B9X9] and [Cp2Co][B9X9], respectively. The EPR spectra of [B9X9]· – (X = Cl, Br, I) in glassy frozen CH2Cl2 solutions showed increasing g anisotropy for the heavier halogen derivatives, illustrating significant halogen participation at the singly occupied MO. The 11B NMR spectra of CD2Cl2 solutions of the neutral clusters B9X9 exhibit only one sharp resonance, indicating that the boron atoms are highly fluxional in solution. In contrast, two different boron resonances as expected for a rigid tricapped trigonal prism are clearly observed for the [B9X9]2– dianions in solutions and for solid B9Br9 in the 11B MAS NMR spectra. Temperature dependent 11B MAS NMR experiments on B9Br9 and [B9Br9]2– in the solid state show a reversible coalescence of the two resonances at higher temperature. 11B MAS NMR spectra and DTA measurements of [B9Br9]2– showed a phase transition. Die closo-Cluster-Triade: B9X9, [B9X9]· – und [B9X9]2– mit dreifach uberkappten trigonalen Prismen (X = Cl, Br, I). Synthesen, Kristall- und Elektronenstrukturen Bei der Halogenierung von nido-B10H14 mit C2H2Cl4, C2Cl6, Br2 oder I2 entstehen unter Clusterabbau die (2 n)-closo-Cluster B9X9 (X = Cl, Br, I). Die Synthese der Salze der perhalogenierten Radikal-Anionen des Typs (2 n + 1)-closo-[B9X9]· – sowie der entsprechenden Dianionen des Typs (2 n + 2)-closo-[B9X9]2– wird beschrieben [n = Anzahl der Clusteratome; (2 n), (2 n + 1) bzw. (2 n + 2) = Zahl der Clusterelektronen]. Die Molekul- und Kristallstrukturen von B9Cl9, B9Br9, [(C6H5)4P][B9Br9] · CH2Cl2 und [(C4H9)4N]2[B9X9] · CH2Cl2 wurden durch Rontgenstrukturanalysen bestimmt. In allen drei Oxidationsstufen bleibt die dreifach uberkappte trigonal prismatische Struktur des Clusters erhalten. Cyclovoltammetrische Untersuchungen ergaben, das die Reduktion der B9X9-Cluster uber zwei sukzessive, reversible Ein-Elektronen-Schritte verlauft, die sich um wenigstens 0.4 V unterscheiden. Die paramagnetischen Radikal-Anionen [B9X9]· – (X = Cl, Br) wurden ferner durch magnetische Suszeptibilitatsmessungen an [Cp2Fe][B9X9] und [Cp2Co][B9X9] charakterisiert. Die EPR-Spektren von [B9X9]· – (X = Cl, Br, I) der glasartigen, gefrorenen CH2Cl2-Losungen zeigen fur die schwereren Halogenide zunehmende g-Anisotropie, was auf signifikante Halogenbeteiligung am einfach besetzten MO hinweist. Die neutralen B9X9-Cluster zeigen im 11B-NMR-Spektrum in CD2Cl2-Losung nur ein scharfes Resonanzsignal, was durch eine Dynamik der Cluster-B-Atome verursacht wird. Im Gegensatz dazu sind die B-Atome der Dianionen [B9X9]2– statisch und zeigen im 11B-NMR-Spektrum erwartungsgemas fur ein dreifach uberkapptes trigonales Prisma zwei getrennte Resonanzlinien; ebenso findet man im 11B-MAS-NMR-Spektrum von B9Br9 zwei getrennte Resonanzlinien, die die statische Natur im Festkorper beweisen. Temperaturabhangige 11B-MAS-NMR-Spektren von B9Br9 und [B9Br9]2– zeigen im festen Zustand bei hoheren Temperaturen reversible Koaleszenz. Das Anion [B9Br9]2– zeigt auserdem bei 127 °C im 11B-MAS-NMR-Spektrum eine displacive Phasenumwandlung, die durch DTA-Messungen bestatigt wird.

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.

The chemical bonding schemes of thallium cluster anions commonly comply with neither Wade-Mingos's rules nor the Zintl-Klemm concept and thus far have escaped a fully consistent description. In general, the number of electrons available for the cluster skeleton bonding fall below those required according to the qualitative concepts mentioned and the clusters were labeled "hypoelectronic". Based on fully relativistic band structure calculations on respective complete extended solids and electronic structure calculations on excised, charge compensated, and geometrically optimized clusters, we have identified two mechanisms that are suited to lift the degeneracy of partially filled electronic states and to open a HOMO-LUMO gap, the Jahn-Teller effect and relativistic spin-orbit coupling. Treatment on this level of theory shows that, in accordance with experiment, the thallium cluster anions known are electronically saturated and not deficient in valence electrons. We provide qualitative group theoretical procedures for analyzing the Jahn-Teller effect and spin-orbit coupling in lifting the degeneracy of frontier orbitals in highly symmetric thallium cluster anions.

In situ high-pressure x-ray and neutron powder diffraction experiments on the recently reported metastable high-pressure polymorph of Bi${}_{2}$O${}_{3}$ (HP-Bi${}_{2}$O${}_{3}$) at ambient temperature has revealed a first-order translationengleiche subgroup-supergroup phase transition at a pressure of $~$2.1 GPa from $P31c$ toward space group $P{6}_{3}\mathit{mc}$ (No. 186). Density functional theory calculations were performed to rationalize the experimental observation and to gain further insight into the mechanism of the phase transition. The transition is caused by a torsion of Bi-O polyhedra and the appearance of a mirror plane. It is accompanied by a contraction of the trigonal c axis and reorientation of localized Bi related electron lone pairs, which leads to a volume drop of $~$3.3%. Both modifications were treated independently in terms of common equations of state evaluation. Bulk moduli were determined to be 32.8 GPa for HP-Bi${}_{2}$O${}_{3}$ and 60.3 GPa for the polymorph past phase transition. It was found that the observed phase transition represents a thermally triggered discontinuity in a continuous evolution of the crystal structure of HP-Bi${}_{2}$O${}_{3}$ with pressure, shifting the phase transition from ideally the second order to the observed first order.

Cs4Tl2O is synthesized by reaction of CsTl and Cs2O in the molar ratio 1:0.95 (Ta tube, 573 K, 7 d).

One of the key methods in quantum chemistry, the Hartree-Fock SCF method, is performing poorly on typical vector supercomputers. A significant acceleration of calculations of this type requires the development and implementation of a parallel SCF algorithm. In this paper various parallelization strategies are discussed comparing local and global communication management as well as sequential and distributed Fock-matrix updates. Programs based on these algorithms are bench marked on transputer networks and two IBM MIMD prototypes. The portability of the code is demonstrated with the portation of the initial Helios version to other operating systems like Parallel VM/SP and PARIX. Based on the PVM libraries, a platform-independent version has been developed for heterogeneous workstation clusters as well as for massively parallel computers.

Die Struktur und die Elektronendichte der closo-Bor-Cluster B4X4 (X = Br, I), B6X62− (X = H, Cl, Br, I) und B12H122− wurden mittels Pseudopotential-Hartree-Fock-Rechnungen bestimmt. Die Interpretation der Bindungsverhaltnisse erfolgte durch Auswertung der Elektronen-Lokalisierungs-Funktion (ELF). Die Bereiche hohen ELF-Wertes besitzen in allen Fallen die Form des zum Bor-Gerust dualen Polyders. Sie lassen die 3-Zentren-2-Elektronen-Bindungen besonders gut erkennen. Der Vergleich zwischen Hartree-Fock- und Extended-Huckel-Rechnungen zeigt, das auch semiempirische Verfahren eine gute Grundlage fur eine ELF-Interpretation sein konnen.

Cs18TI8O6 is prepared by reaction of an equimolar mixture of CsTl and Cs2O (Ta tube, 573 K, 7 d) and characterized by single crystal XRD, magnetization measurements, and relativistic DFT calculations.

High-pressure and high-temperature experiments with ${\text{Bi}}_{2}{\text{O}}_{3}$ using a 6--8 type multianvil device led to the formation of a metastable polymorph $({\text{HP-Bi}}_{2}{\text{O}}_{3})$ with noncentrosymmetric trigonal symmetry. This phase relaxes during the course of several months at ambient temperature or more rapidly via annealing, to a second intermediate modification $({\text{R-Bi}}_{2}{\text{O}}_{3})$. Upon further annealing finally the transformation back to the known ambient phase $(\ensuremath{\alpha}{\text{-Bi}}_{2}{\text{O}}_{3})$ takes place. Both crystal structures were solved from high-resolution x-ray and neutron powder-diffraction data. The orientation and stereochemical activity of the ${\text{Bi}}^{3+}$ lone pairs (or inert pairs) is discussed in terms of crystal-chemical considerations and density-functional theory calculations. Whenever suitable, results were verified by experimental determination of the respective properties. The results of the theoretical analyses show that within the structure type of ${\text{HP-Bi}}_{2}{\text{O}}_{3}$, bismuth oxide exhibits a pronounced polarization and can be considered as ferroelectric.