Band 235, Heft 12

A topological analysis of the crystal structures of Li, Li–Sn compounds, Li 8 Sn 3− x Sb x and metastable c-Li 3 Sb showed that these structures can be described by a hierarchical scheme of building blocks based on atom blocks and polyhedra blocks, respectively. These blocks are linked in distinct ways to form the individual 3D atom arrangement. A common model was established for the construction of the mentioned structures from bespoke building blocks, for which bcc-Li is the aristotype. This latter structure can be described on the basis of hexa-capped cubes from which variants are derived through substitution of Li by Sn (or Sb). These are then combined into polyhedra blocks that are in turn assembled into polyhedra sequences. These latter are repeated and linked in three dimensions to form the whole crystal structure. At x Sn ≥ 0.5, this mechanism changes and structural elements from bcc-Li and β-Sn can be observed in LiSn and Li 2 Sn 5 . In this work, we present the similarities and differences between the various crystal structures, the topological model with its construction rules and its limitations.

γ-Brass type phases in Cu–Zn–In ternary system were synthesized from the highly pure elements by conventional solid-state synthesis and characterized by X-ray diffraction and EDX analysis. Diffraction analysis confirmed the existence of cubic γ-brass type phases with I- and P -cell having a significant homogeneity range in the ternary Cu–Zn–In system. The phase homogeneity is connected with structural disorder based on mixed site occupancies. Site specific In substitution was observed during single-crystal structure analysis. The γ-brass structures with body-centered cubic lattice ( I 4‾$‾{4}$3 m ) are viewed as 26-atom γ-clusters. Like Cu 5 Zn 8 , the inner tetrahedron (IT), outer tetrahedron (OT) and octahedron (OH) sites in the 26-atom clusters of γ-brass structures with I -cell are occupied by Zn, Cu, Cu, respectively. Indium substitution is restricted to the cuboctahedral (CO) site and the CO site is assumed to be mixed with In, Cu and Zn throughout the homogeneity range. The structures of cubic γ-brass type ( P 4‾$‾{4}$3 m ) phases with P -cell are built up with two independent 26‐atom γ‐clusters and centered at the special positions A (0, 0, 0) and B (½, ½, ½) of the unit cell. According to the single‐crystal X‐ray analyses, In substitutions are largely restricted to the cuboctahedral sited B clusters. In the cubic γ-phases with P -cell, site occupancy pattern of cluster positioned at A is similar to the γ-cluster in Cu 5 Zn 8 , whereas cluster B bears a close resemblance to Cu-poor γ-cluster (Cu 14 In 12 ) of Cu 9 In 4 ( P 4‾$‾{4}$3 m ). The vec values for cubic γ-brass type phases in the Cu–Zn–In ternary system ranges between 1.57 and 1.64.

1,2-trans-diiodo-ethene (C 2 H 2 I 2 ) – is an overlooked halogen bond donor, which demonstrate the distinct similarity of the geometry and directionality of I···I halogen bonds around the iodine atoms in its native and CpMn(CO) 2 (C 2 H 2 I 2 ) π -complex crystals. Distortion of the planar geometry of C 2 H 2 I 2 upon the π -coordination result the distortion of the native planar layered geometry of C 2 H 2 I 2 , so that [CpMn(CO) 2 ]( π -C 2 H 2 I 2 ) features more complex I···I XB assisted 3D network. Unusual structural parallels between the native C 2 H 2 I 2 crystals and solid iodine are discussed.

We propose a new method to calculate topological densities of periodic graphs based on the concept of layer-by-layer growth. Topological density is expressed in terms of metric characteristics: the volume of the fundamental domain and the volume of the growth polytope of the graph. Our method is universal (works for all d- periodic graphs) and is easily automated. As examples, we calculate topological densities of all 20 plane 2-uniform graphs and 14 carbon allotrope modifications.