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A hexagonal phase in the ternary Ge-Se-Te system with an approximate composition of GeSe0.75Te0.25 has been known since the 1960s but its structure has remained unknown. We have succeeded in growing single crystals by chemical transport as a prerequisite to solve and refine the Ge4Se3Te structure. It consists of layers that are held together by van der Waals type weak chalcogenide-chalcogenide interactions but also display unexpected Ge-Ge contacts, as confirmed by electron microscopy analysis. The nature of the electronic structure of Ge4Se3Te was characterized by chemical bonding analysis, in particular by the newly introduced density of energy (DOE) function. The Ge-Ge bonding interactions serve to hold electrons that would otherwise go into antibonding Ge-Te contacts. [ABSTRACT FROM AUTHOR]

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A well-defined spatial orientation of atomic basis functions is essential for the correct analysis of quantum-mechanical calculations in terms of chemical (bonding) concepts. Here, we present the implementation of a straightforward, convenient algorithm to rotate basis functions using real spherical harmonics within a linear combination of atomic orbitals (LCAO) framework. The highly efficient technique only relies on overlap integrals of the basis functions and Wigner's rotation matrices. To do so, a previously known and simple way to calculate the latter (defined by a rotation axis and angle) for real spherical harmonics is modified to enable chemical-bonding interpretation. The method's usefulness is illustrated by an application to carbon crystallizing in the diamond structure. [ABSTRACT FROM AUTHOR]

An unexpected polymorph of the highly energetic phase CuN3 has been synthesized and crystallizes in the orthorhombic space group Cmcm with a=3.3635(7), b=10.669(2), c=5.5547(11) Å and V=199.34(7) Å3. The layered structure resembles graphite with an interlayer distance of 2.777(1) Å (=1/2 c). Within a single layer, considering N3− as one structural unit, there are 10-membered almost hexagonal rings with a heterographene-like motif. Copper and nitrogen atoms are covalently bonded with CuN bonds lengths of 1.91 and 2.00 Å, and the N3− group is linear but with NN 1.14 and 1.20 Å. Electronic-structure calculations and experimental thermochemistry show that the new polymorph termed β-CuN3 is more stable than the established α-CuN3 phase. Also, β-CuN3 is dynamically, and thus thermochemically, metastable according to the calculated phonon density of states. In addition, β-CuN3 exhibits negative thermal expansion within the graphene-like layer. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A hexagonal phase in the ternary Ge-Se-Te system with an approximate composition of GeSe 0.75 Te 0.25 has been known since the 1960s but its structure has remained unknown. We have succeeded in growing single crystals by chemical transport as a prerequisite to solve and refine the Ge 4 Se 3 Te structure. It consists of layers that are held together by van der Waals type weak chalcogenide-chalcogenide interactions but also display unexpected Ge-Ge contacts, as confirmed by electron microscopy analysis. The nature of the electronic structure of Ge 4 Se 3 Te was characterized by chemical bonding analysis, in particular by the newly introduced density of energy (DOE) function. The Ge-Ge bonding interactions serve to hold electrons that would otherwise go into antibonding Ge-Te contacts., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An unexpected polymorph of the highly energetic phase CuN3 has been synthesized and crystallizes in the orthorhombic space group Cmcm with a=3.3635(7), b=10.669(2), c=5.5547(11) Å and V=199.34(7) Å(3). The layered structure resembles graphite with an interlayer distance of 2.777(1) Å (=1/2 c). Within a single layer, considering N3(-) as one structural unit, there are 10-membered almost hexagonal rings with a heterographene-like motif. Copper and nitrogen atoms are covalently bonded with Cu-N bonds lengths of 1.91 and 2.00 Å, and the N3(-) group is linear but with N-N 1.14 and 1.20 Å. Electronic-structure calculations and experimental thermochemistry show that the new polymorph termed β-CuN3 is more stable than the established α-CuN3 phase. Also, β-CuN3 is dynamically, and thus thermochemically, metastable according to the calculated phonon density of states. In addition, β-CuN3 exhibits negative thermal expansion within the graphene-like layer., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Despite its simple chemical constitution and unparalleled technological importance, the phase-change material germanium telluride (GeTe) still poses fundamental questions. In particular, the bonding mechanisms in amorphous GeTe have remained elusive to date, owing to the lack of suitable bond-analysis tools. Herein, we introduce a bonding indicator for amorphous structures, dubbed "bond-weighted distribution function" (BWDF), and we apply this method to amorphous GeTe. The results underline a peculiar role of homopolar Ge-Ge bonds, which locally stabilize tetrahedral fragments but not the global network. This atom-resolved (i.e., chemical) perspective has implications for the stability of amorphous "zero bits" and thus for the technologically relevant resistance-drift phenomenon., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)