Search

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 [Ga5] clusters, the isostructural compound Sr3Li5Ga5 (space group R3‾ m, a = 9.6040(5) Å, c = 22.061(1) Å) 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 [Sr6] polycation. [ABSTRACT FROM AUTHOR]

The domain-averaged Fermi hole (DAFH) orbitals provide highly visual representation of bonding in terms of orbital-like functions with attributed occupation numbers. It was successfully applied on many molecular systems including those with non-trivial bonding patterns. This article reports for the first time the extension of the DAFH analysis to the realm of extended periodic systems. Simple analytical model of DAFH orbital for single-band solids is introduced which allows to rationalize typical features that DAFH orbitals for extended systems may possess. In particular, a connection between Wannier and DAFH orbitals has been analyzed. The analysis of DAFH orbitals on the basis of DFT calculations is applied to hydrogen lattices of different dimensions as well as to the solids diamond, graphite, Na, Cu and NaCl. In case of hydrogen lattices, remarkable similarity is found between the DAFH orbitals evaluated with both the analytical approach and DFT. In case of the selected ionic and covalent solids the DAFH orbitals deliver bonding descriptions, which are compatible with classical orbital interpretation. For metals the DAFH analysis shows essential multicenter nature of bonding. [ABSTRACT FROM AUTHOR]

Black and irregularly shaped crystals of the bismuth‐rich bromide Bi5Br4 were obtained as a by‐product of the reaction of CsBr, Bi, and BiBr3. X‐ray diffraction on a single‐crystal revealed its orthorhombic structure with the space group Pmmn (no. 59) and lattice parameters a = 1800.0(2) pm, b = 1476.1(1) pm, and c = 924.5(2) pm at 296 K. The structure is composed of Bi82+ and Bi95+ polycations and bromidobismuthate(III) anions according to the structured formula Bi5Br4 = Bi20Br16 = Bi82+Bi95+[BiBr5]2–[Bi2Br11]5–. Bi5Br4 is the bismuth‐richest among the bismuth subhalides containing isolated polycations. Extensive differential scanning calorimetry studies indicate that Bi5Br4 decomposes at 262 °C, i.e. one degree below the bismuth‐rich eutectic at 263 °C. All attempts towards a rational synthesis yielded predominantly the neighboring phases BiBr and Bi6Br7. [ABSTRACT FROM AUTHOR]

REMo2B5 (RE = Ce, Pr, Nd) and CeW2B5 have been synthesized by arc melting with further annealing at 1300 °C. CeMo2B5 crystallizes in a new structure type with space group Pnma, a = 11.0298(2) Å, b = 3.12080(5) Å, c = 9.9594(2) Å, Z = 4. Its structural arrangement reveals puckered [B6]‐hexagonal rings, trigonal‐prismatic‐ and empty pyramidal‐tetrahedral‐slabs. The structure can be related to the derivatives of AlB2 and CrB prototypes. The boron atoms form a two‐dimensional network of corrugated ribbons, each composed of four edge‐linked [B6] rings infinitely extending along the b‐axis. CeMo2B5 is a Pauli paramagnet. Electrical transport measurements together with the calculated density of states at the Fermi level of 3.81 states eV–1 f.u.–1 indicate CeMo2B5 to be a typical metallic system. Electronic structure calculations reveal significant hybridization of Ce 4f5d states with Mo 4d states. The chemical bonding scenario is dominated by chains of [Ce2Mo2] clusters with multi‐center bonds. These clusters are connected via metallic Mo–Mo bonds. This metal‐framework, in turn, is stabilized by bonding interactions with the boron ribbons to which it donates electrons. [ABSTRACT FROM AUTHOR]

Single crystals of the polytellurides RETe1.8 of gadolinium, terbium, and dysprosium were prepared by chemical vapor transport and alkali metal halide flux reactions. To determine proper synthesis conditions for the desired target composition, the binary phase diagram Gd‐Te was evaluated by CalPhaD methods. The compounds are isostructural to SmTe1.8 and crystallize in space group P4/n (no. 85) with lattice parameters of a = 966.10(4), 960.00(3), and 957.33(2) pm and c = 1794.15(10), 1785.77(6), and 1779.38(5) pm for GdTe1.8, TbTe1.8 and DyTe1.8, respectively. The structures consist of puckered [RETe] double slabs and planar telluride layers composed of Te2 dumbbells and linear Te3 units in accordance with ELI‐D based bonding analyses. The latter can be understood as a Te34– anion. GdTe1.8 is a semiconductor with a bandgap of 0.19 eV/0.17 eV (experimental/calculated). Magnetization data confirm trivalent RE ions and indicate antiferromagnetic order at TN = 12 K for TbTe1.8 and TN = 9.8 K for DyTe1.8, whereas GdTe1.8 remains paramagnetic down to 2 K. [ABSTRACT FROM AUTHOR]

Relativistic spherically averaged numerical all-electron densities ρ were computed for the atoms Be–Ba, B–Tl, C–Pb, Cu–Au, and Zn–Hg. The Laplacian of these densities is not able to resolve the valence shell from the inner shells in case of heavy atoms, starting with the fourth row. The distribution of the local kinetic energy Ekin shows a valence maximum even for these heavy atoms, unfortunately, in a region of negative kinetic energy; i.e., nonclassically allowed. The quantity -|∇ρ|/ρ was also investigated. For all computed atoms, the -|∇ρ|/ρ diagrams are capable of describing the complete shell structure. -|∇ρ|/ρ is sensitive to basis set quality: poor Gaussian basis sets exhibit spurious oscillations and a premature onset of the linear decay. For the atoms B–Tl, Ba, Au, Hg, and Pb, nonrelativistic numerical calculations were performed to examine the effect of the relativity on the aforementioned quantities. Tests with pseudopotential densities reveal that for pseudopotential calculations, it is advisable to use at least two outermost shells in order to reproduce the all-electron values of ∇ 2ρ, Ekin, and -|∇ρ|/ρ in the valence region. [ABSTRACT FROM AUTHOR]

Abstract: Several quantum chemical topology indicators (bond paths, electron density values at bond critical points, delocalization indices, interaction energies, electron localizability indicator) are used to describe the change in the bonding situation during the pressure‐induced cd → β‐Sn phase transition for the group IV elements C, Si, Ge and Sn. To understand the absence of the cd → β‐Sn transition for carbon, we utilize the criteria of structural stability based on the electron density and electron localizability indicator. [ABSTRACT FROM AUTHOR]

ThPt3+xBe (x = 0.08) is synthesized by arc melting of a mixture of the elements. It crystallizes with its own type of structure [space group I4/mmm (No. 139), a = 7.7370(4), c = 11.4990(6) Å], which can be related to the cubic Ru3Sn7 and W2Cr21C6 types. Measurements of magnetic susceptibility, electrical resistivity and specific heat indicate ThPt3+xBe (x = 0.08) to be a diamagnet [χ0 = -9.0(3) × 10-6 emu mol-1] with metallic electrical resistivity, in good agreement with the calculated electronic structure [N(EF) = 3.2 states eV-1 f.u.-1]. A chemical bonding analysis was performed by the QTAIM and ELI-D approaches. [ABSTRACT FROM AUTHOR]

The electron density logarithm is closely connected to the Shannon information entropy characterising the spread of the electron density. It can be seen as the uncertainty to predict the position of an electron. The position uncertainty curvature, defined as the negative of the Laplacian of the electron density logarithm, describes regions of space where the uncertainty of the electron position is higher, respectively lower, than the average in the surrounding. The atomic shells can be located in regions of high-position uncertainty curvature, thus resolving the atomic shell structure of the atoms Li to Xe. The shell boundaries are given as minima of the uncertainty curvature. This indicator, based alone on the electron density, is suitable to describe the bonding situation in molecules and solids. [ABSTRACT FROM PUBLISHER]

The bonding in the ground state of C2is examined using a combined approach based on the analysis of domain-averaged Fermi holes and of the contributions to covalent bond orders that can be associated with individual localised natural orbitals. The σ system in this molecule turns out to be particularly sensitive, evolving from a description that includes a fairly traditional shared electron pair σ bond, for a range of intermediate nuclear separations, to a somewhat different situation near equilibrium geometry, where non-classical repulsive interactions are particularly important. The various results provide further support for the view that the electronic structure of this molecule sufficiently exceeds the scope of traditional bonding paradigms that attempts to classify the bonding in terms of a classical bond multiplicity are highly questionable. [ABSTRACT FROM PUBLISHER]