The cage compound BaIr 2 Si 9 adopts the BaRh 2 Si 9 structure type with space group C 2/ c (Pearson symbol mC 48, a = 6.230(1) Å, b = 21.409(3) Å, c = 6.232(1) Å, β = 90.30(1)°). The atomic arrangement features fragmented sodalite cages that are interrupted along [010] by puckered Ir–Si layers showing the pentagonal Cairo‐Tiling motif. The compound melts incongruently at 1180°C and is obtained as a single‐phase after annealing at 800°C for 3 days. Electric transport measurements reveal that BaIr 2 Si 9 is a p ‐type semiconductor, consistent with band structure calculations indicating a bandgap of 0.5 eV. Quantum chemical calculation confirms positively charged Ba atoms accompanied by Ir atoms with negative charges. The charge distribution of silicon is heterogeneous as Si atoms bonded to Ir exhibit positive charges while those forming merely Si–Si contacts are negatively charged.

Li2ZnSi is a layered Zintl phase composed of heterographene-like Zn-Si sheets separated by Li atoms. Although the intrinsic crystal structure is fully ordered, mechanical handling readily introduces stacking faults of the Zn-Si layers. These defects significantly broaden the 7Li and 29Si NMR signals and are described by statistically disordered structure models in single-crystal X-ray diffraction. Upon moderate heating to only 310-370 K, the 7Li NMR spectra sharpen, while single-crystal X-ray diffraction reveals a fully ordered structure model. The heat-capacity data exhibit a broad endothermic feature during heating, characteristic of a stress-relief annealing process rather than a thermodynamic phase transition. Mechanical treatment strongly affects physical properties, and the transport response in impedance measurements is dominated by grain-boundary effects. Density-functional calculations show that the stacking-fault formation is energetically unfavorable but localized, explaining why the defects are readily introduced mechanically and can be healed at unexpectedly low temperatures.

The new binary silicide Pr2Si7 is prepared by high-pressure high-temperature techniques at 9.5 GPa and 1100 K (600 min). The crystal structure is solved and refined using synchrotron X-ray diffraction data. It belongs to the structure type of Ce2Si7 (space group Cmmm, a = 7.1513(2) angstrom, b = 10.0033(2) angstrom, c = 4.5417(1) angstrom, and Z = 2). The characteristic feature of the atomic arrangement is the 3D-polyanion formed by silicon atoms with (highest weight) topological coordination numbers of 4, 5, and 6. Analysis of chemical bonding within the electron-localizability approach reveals six electron localizability indicator (ELI-D) attractors around each of the three symmetrically independent silicon atoms. The bonding picture in the polyanion is characterized by the appearance of lone-pair-like arrangements at silicon species and two types of two-atomic Si-Si bonds. The total of six attractors for each silicon atom documents hypervalent configurations within the polyanionic framework. Magnetic susceptibility measurements indicate an oxidation state +3 for praseodymium (f 2 configuration) with the degenerate states of the free ion being split by crystalline electric fields.

The layered Zintl phase Li 2 ZnSi is a structural analog of intercalated graphite with hexagonal layers of Zn and Si atoms separated by Li atoms (space group P 6 3 / mmc , a = 4.2458(2) Å, c = 8.224(1) Å). Single‐crystal X‐ray diffraction reveals Zn relocation into the center of the Zn 3 Si 3 rings in 4% of the hexagonal layers. The Zn relocation is coupled with Li migration. The resulting 2D defects can be modeled either as 60° slab rotations or, alternatively, as layer translations by k = 1/3 [1,−1,0]. Li 2 ZnSi shows metal‐type electrical resistivity (ρ = 1.18 μΩ m at 300 K) and exhibits significantly enhanced diamagnetism, suggesting orbital contributions akin to those in graphite. This study demonstrates transition‐metal mobility in a layered Zintl phase, generating localized 2D defects that leave the local coordination of each atom unchanged. This mechanism is relevant for understanding defect tolerance in structurally related electrode materials.

The compound Li2[ZnSi] is known to crystallize in the Li2CuAs structure type featuring graphite-like [ZnSi] layers separated by Li atoms, thus supporting the view of a Zintl phase (Li+)2[ZnSi]2-. The comparative band structure (PBE + U technique) and chemical bonding analysis with insulating h-BN using the electron localizability indicator ELI-D and the electron density reveal unexpected crystal structure-band structure effects. They lead to partial valence band depletion and the metallic conductivity of Li2[ZnSi]. As a result, the conventional polar diatomic bonds of h-BN become polar 4-atomic ones in Li2[ZnSi].

The (electro)-chemical behavior of intermetallic compounds Mo2 TMB2 (TM = Fe, Co, Ni) under OER conditions has been investigated using electrochemical data combined with extensive bulk- and surface-sensitive material characterization. In situ formation of TM-rich amorphous layers, composed of oxides and hydroxides, accompanied by partial dissolution of molybdenum and boron, was observed for all three compounds. The degree of molybdenum and boron dissolution also influences the electronic state of TMs in their oxides/hydroxides formed on the surface of Mo2 TMB2. The in situ-formed Fe2O3 and Ni-(OH)2 on the surface of Mo2FeB2 and Mo2NiB2, respectively, are the origin of surface passivation and their OER inactivity. At the same time, the simultaneous presence of Co3O4 and Co-(OH)2 on the surface of an OER-exposed Mo2CoB2 electrode allows for the start of OER at a lower overpotential (ca. 290 mV) compared to elemental Co (ca. 370 mV), revealing better electrocatalytic activity. Extensive characterization of these materials as well as variation of the experimental conditions extends our understanding of the chemical properties of intermetallic compounds, which are of clear importance for their possible application as efficient electrocatalysts.

New metastable SmSi3-x (x=0-0.05) is obtained by high-pressure high-temperature synthesis (9.5 GPa, 870-1270 K). Powder diffraction data refinements reveal that the crystal structure of SmSi3 is isotypic to that of YbSi3 (space group I4/mmm, a=7.23634(5) angstrom, c=11.0854(1) angstrom). In the crystal structure, two types of Si2 dumbbells agglomerate into layers, which embed the samarium atoms. At ambient pressure, SmSi3 decomposes exothermally upon heating into Si and SmSi2-x. Single-crystal structure refinements of a specimen SmSi3-x (x=0.05) reveal considerable electron density, which is not accounted for by the YbSi3-type model. The additional maxima can be assigned to disorder which affects the samarium positions and induces silicon vacancies. Scanning transmission electron microscopy experiments evidence that the disorder can be attributed to extended defects. Magnetic measurements on SmSi3-x reveal van Vleck paramagnetic behavior and antiferromagnetic ordering at low temperatures. Computations within the local spin density approximation (LSDA and LSDA+U) on the crystal structure of SmSi3 reproduce the antiferromagnetic coupling as the favored long-range order. Quantum chemical analysis of the chemical bonding in SmSi3 reveals two-center two-electron bonds within the Si-2 dumbbells plus a total of a little less than four electrons in lone pairs at each silicon atom.

The Zintl phase CaSi2 is a layered compound with stacking variants known as 1P, 3R, and 6R. We extend the series by the 21R polytype formed by rapid cooling of the melt. The crystal structure of 21R-CaSi2 (space group R3̅m) was derived from HRTEM images, and the atomic positions were optimized by using the FPLO code (a = 3.868 Å, c = 107.276 Å). We explore polytype transformations by powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron backscattering diffraction (EBSD), and thermal analysis. While 6R-CaSi2 is thermodynamically stable at ambient conditions, nanosized impurities of silicon stabilize 3R-CaSi2 as a bulk phase.

LiCa8[(CrN3)-N-IV](2)N2F (Pnnm (#58), a = 17.5230(13) & Aring;, b = 7.3379(5) & Aring;, c = 4.9433(4) & Aring;) is an example of a multinary nitridochromate fluoride, that provides additional information on almost elusive tetravalent nitridochromates. Shorter Cr-N bond lengths compared to those in the previously reported nitridochromates(III), as well as diamagnetic behavior and vibrational spectroscopy data suggest Cr(IV), which is in good agreement with the charge balance and crystal structure refinement. According to band structure calculations, LiCa8[(CrN3)-N-IV](2)N2F is a semiconductor with a band gap of 1.1 eV. The compound features trigonal planar [CrN3](5-) units of C-s symmetry, and lithium, calcium, nitrogen and fluorine atoms arranged in a fragment of the rock salt type structure.

Samples of the pseudo-binary system Na2-xLixGa7 (x <= 1) were synthesized from the elements at 300 degrees C in sealed Ta ampoules or by the reaction of Na2Ga7 with LiCl. The peritectic formation temperature decreases with increasing Li content from 501(2) degrees C (x = 0) to 489(2) degrees C (x = 1). The boundary compositions Na2Ga7 and Na1Li1Ga7 crystallize with different structure types related by a group-subgroup relation. While the Na-rich compositions (x <= 0.5) represent a substitutional solid solution (space group Pnma), the Li-rich compositions feature an unconventional replacement mechanism in which Li atoms occupying interstitial positions induce vancancies at the Na positions (space group Cmce). The crystal structure of Na1Li1Ga7 (a = 8.562(1) & Aring;, b = 14.822(2) & Aring;, c = 11.454(2) & Aring;; Z = 8) was determined from X-ray single-crystal diffraction data, and reveals an anionic framework comprising 12-bonded Ga-12 icosahedra and 4-bonded Ga atoms, with alkali-metal atoms occupying channels and cavities. The arrangement of cations makes NaLiGa7 a new structure type within the MgB12Si2 structure family. Band structure calculations for the composition NaLiGa7 predict semiconducting behavior consistent with the balance [Na+](2)[Li+](2)[(Ga-12)(2-)][Ga-](2), considering closo Wade clusters [(12b)Ga-12](2-) and Zintl anions [(4b)Ga](-). Susceptibility measurements indicate temperature-independent diamagnetic behavior.

Intermetallic compounds in the Al-Pt system were systematically studied via hard X-ray photoelectron spectroscopy, focusing on the positions of Pt 4f and Al 2s core levels and valence band features. On one hand, with increasing Al content, the Pt 4f core levels shift towards higher binding energies (BE), revealing the influence of the atomic interactions (chemical bonding) on the electronic state of Pt. On the other hand, the charge transfer from Al to Pt increases with increasing Al content in Al-Pt compounds. These two facts cannot be combined using the standard "chemical shift" approach. Computational analysis reveals that higher negative effective charges of Pt atoms are accompanied by reduced occupancy of Pt 5d orbitals, leading to the limited availability of these electrons for the screening of the 4f core hole and this in turn explains the experimentally observed shift of 4f core levels to higher BE.

The quaternary nitridochromate(IV) LiSr2[CrN3] crystallizes in a new structure type with the non-centrosymmetric space group P21 (no. 4) with a = 5.5685(7) Å, b = 5.3828(8) Å, c = 7.5381(1) Å, and β = 92.291(8)°. Predominant structural features of the compound are slightly nonplanar trigonal units [CrN3]5-, which are connected by three-fold coordinated lithium to form slabs in the (001) plane. Shorter Cr-N bond lengths in comparison with reported nitridochromates(III), as well as diamagnetic behavior and vibrational spectroscopy data indicate Cr(IV), which is in a good agreement with the charge balance. According to electronic structure calculations, the compound is a semiconductor with a band gap of 1.19 eV.

Al-Pt compounds have been systematically studied as electrocatalysts for the oxygen evolution reaction (OER). Considering the harsh oxidative conditions of the OER, all Al-Pt compounds undergo modifications during electrochemical experiments. However, the degree of changes strongly depends on the composition and crystal structure of a compound. In contrast to Al-rich compounds (Al4Pt and Al21Pt8), which reveal strong leaching of aluminum, changes in other compounds (Al2Pt, Al3Pt2, rt-AlPt, Al3Pt5, and rt-AlPt3) take place only on the surface or in the near-surface region. Furthermore, surface modification leads to a change in the electronic structure of Pt, giving rise to the in situ formation of catalytically more active surfaces, which are composed of intermetallic compounds, Pt-rich AlxPt1-x phases and Pt oxides. Forming a compromise between sufficient OER activity and stability, Al2Pt and Al3Pt2 can be considered as precursors for OER electrocatalysts.

The binary Be2Fe, which crystallizes in the C14-structure type hexagonal Laves phase, can dissolve a large amount of Os as a third element, without changing the crystal structure (about 3/4 of Fe can be replaced by Os). A study of the homogeneity range for the Be2Fe1-xOsx Laves phase, shows an increase of the lattice parameters with an increase of the Os content. When Ru substitutes Fe in Be2Fe, a temperature- and composition-dependent transformation from the C14 to the cubic C15 Laves phase is observed, with a narrow homogeneity range. Formation energy calculations revealed that the C14-structure type is energetically favored when Os substitutes Fe in Be2Fe, while a structural phase transition is observed between Be2Fe (C14) and Be2Fe0.5Ru0.5 (C15), all in good agreement with the experimental results. A strong charge transfer from Be to Os or Ru is observed from the analysis of electron density within the Quantum Theory of Atoms in Molecules (QTAIM) framework. A formation of multiatomic bonds is found from the electron localizability approach. Be2Fe1-xOsx undergoes a transition to a disordered ferromagnetic state at T-C = 350 K and behaves like a ferromagnet with a non-collinear magnetic structure (not all domains polarized along field). Be2Fe1-xRux orders ferromagnetically below T-C = 340 K and the very narrow hysteresis curves show that Be2Fe1-xRux is a soft ferromagnet.

Na2Ga7 crystallizes with the orthorhombic space group Pnma (no. 62; a = 14.8580(6) Å, b = 8.6766(6) Å, and c = 11.6105(5) Å; Z = 8) and constitutes a filled variant of the Li2B12Si2 structure type. The crystal structure consists of a network of icosahedral Ga12 units with 12 exohedral bonds and four-bonded Ga atoms in which the Na atoms occupy the channels and cavities. The atomic arrangement is consistent with the Zintl [(4b)Ga]- and Wade [(12b)Ga12]2- electron counting approach. The compound forms peritectically from Na7Ga13 and the melt at 501 °C and does not show a homogeneity range. The band structure calculations predict semiconducting behavior consistent with the electron balance [Na+]4[(Ga12)2-][Ga-]2. Magnetic susceptibility measurements show that Na2Ga7 is diamagnetic.

The structural features of the hexagonal layered crystal structure of Be2 Ru (a=5.7508(3) Å, c=3.0044(2) Å, space group P 6 ‾ ${\bar{6}}$ 2m) were investigated by single crystal X-ray diffraction and transmission electron microscopy (TEM). The residual electron density and high-resolution TEM images show that the real structure can be described as an intergrowth of the main hexagonal matrix of the Fe2 P type with minor orthorhombic inclusions of its stacking variants. Such atomic arrangement is stabilized by the charge transfer from Be to Ru and by a system of polar three- and four-atomic bonds involving both components. The calculated electronic density of states (DOS) of Be2 Ru revealed, contrarily to typical intermetallic compounds, a pseudo gap (dip) in the vicinity of the Fermi level. The temperature dependence of the electrical resistivity of Be2 Ru shows metal behaviour in agreement with the non-zero DOS at the Fermi level.

Large black single crystals with a metallic luster of Li16Sr6Ge6N and several other representatives of the series Li(16)Ae(6)Tt(6)N and Li(16)Ae(6)Tt(6.5) (Ae=Ca, Sr; Tt=Si, Ge, Sn, Pb) were grown from mixtures of the respective elements with addition of binary alkaline-earth metal nitrides or lithium nitride in the case of the nitrides. For the synthesis a modified high-temperature centrifugation-aided filtration (HTCAF) technique using reactive lithium melts was employed. These metallic phases crystallize in an ordered defect-variant of the Sc11Ir4 type with selective occupation of the smaller octahedral voids in the origin (000) with N and the larger rhombic dodecahedral voids in (001/2 ) with Tt. Charge balance assuming the presence of exclusively closed shell ions for all examples accounts for an electronic excess. Diamagnetism despite metallic properties is consistent with results from electronic structure calculations.

Abstract The underlying reasons for the catalytic activity of Ga1‐x Sn x Pd2 (0 ≤ x ≤ 1) in the semi‐hydrogenation of acetylene are analyzed considering electronic structure and chemical bonding. Analysis of the chemical bonding shows pronounced charge transfer from the p elements to palladium and an unusual appearance of the Pd core basins at the surface of the QTAIM (quantum theory of atoms in molecules) atoms. The charge transfer supports the formation of the negatively charged palladium catalytic centers. Gallium‐only‐coordinated palladium atoms reveal a smaller effective charge in comparison with palladium species having tin in their coordination sphere. Within the empirical tight‐binding approach, different influence of the E‐Pd distances on the calculation matrix for the energy eigenvalues and the electronic density of states (DOS) leads to an S‐like shape of the plot of the energy position of the 4d band center of gravity versus substitution level x. The latter correlates strongly with the catalytic activity and with the varying charge transfer to palladium. The optimal value of negative palladium charge and the closest position of Pd d‐states gravity center towards the Fermi level correlates well with the catalytically most active composition x. Combination of all features of the chemical bonding and electronic structure allows more insight into the intrinsic reasons for the catalytic activity variation in the platform material Ga1‐x Sn x Pd2 (0 ≤ x ≤ 1).

During the search for a possible replacement of the europium in the structure Eu3Li5+xGa5-x (x = 0.15) in order to facilitate the analysis of the chemical bonding in the bell-like [Ga-5] clusters, the isostructural compound Sr3Li5Ga5 (space group R3? m, a = 9.6040(5) angstrom, c = 22.061(1) angstrom) was discovered. A detailed investigation of the bonding situation in the first five-membered nonconvex Ga cluster utilizing the electron localizability approach became possible, revealing not only first signs of a transition from a Zintl to a Wade cluster, but also the presence of a [Sr-6] polycation.

Unconventional superconductivity in non-centrosymmetric superconductors has attracted a considerable amount of attention. While several lanthanide-based materials have been reported previously, the number of actinide-based systems remains small. In this work, we present the discovery of a novel cubic complex non-centrosymmetric superconductor Th_4Be_33Pt_16 ( I4̅3d space group). This intermetallic cage compound displays superconductivity below T_c = 0.90 ± 0.04 K, as evidenced by specific heat and resistivity data. Th_4Be_33Pt_16 is a type-II superconductor, which has an upper critical field H_c2 = 0.27 T and a moderate Sommerfeld coefficient γ _n = 16.3 ± 0.8 mJ mol^-1_Th K^-2 . A non-zero density of states at the Fermi level is evident from metallic behavior in the normal state, as well as from electronic band structure calculations. The isostructural U_4Be_33Pt_16 compound is a paramagnet with a moderately enhanced electronic mass, as indicated by the electronic specific heat coefficient γ _n = 200 mJ mol^-1_U K^-2 and Kadowaki–Woods ratio A/γ ^2 = 1.1 × 10^-5 Ω cm K^2 mol_U^2 (mJ) ^-2 . Both Th_4Be_33Pt_16 and U_4Be_33Pt_16 are crystallographically complex, each hosting 212 atoms per unit cell.