Crystal structure of K6[Zn(CO3)4]

The crystal structure of K6[Zn(CO3)4], hexa-potassium tetra-carbonato-zincate(II), comprises four unique potassium cations (two located on a general position, and two on the twofold rotation axis of the space group C2/c) and a [Zn(CO3)4]6- anion. The ZnII atom of the latter is located on the twofold rotation axis and is surrounded in a slightly distorted tetra-hedral manner by two pairs of monodentately binding carbonate groups, with Zn-O distances of 1.9554 (18) and 1.9839 (18) Å. Both carbonate groups exhibit a slight deviation from planarity, with the C atom being shifted by 0.008 (2) and 0.006 (3) Å, respectively, from the plane of the three O atoms. The coordination numbers of the potassium cations range from 6 to 8, using a threshold of 3.0 Å for K-O bonding inter-actions being significant. In the crystal structure, [KOx] polyhedra and [Zn(CO3)4]6- groups share O atoms to build up the framework structure.

Symmetry Analysis of the Complex Polytypism of Layered Rare-Earth Tellurites and Related Selenites: The Case of Introducing Transition Metals

Our systematic explorations of the complex rare earth tellurite halide family have added several new [Ln12(TeO3)12][M6X24] (M = Cd, Mn, Co) representatives containing strongly deficient and disordered metal-halide layers based on transition metal cations. The degree of disorder increases sharply with decrease of M2+ radius and the size disagreements between the cationic [Ln12(TeO3)12]+12 and anionic [M6Cl24]−12 layers. From the crystal chemical viewpoint, this indicates that the families of both rare-earth selenites and tellurites can be further extended; one can expect formation of some more complex structure types, particularly among selenites. Analysis of the polytypism of compounds have been performed using the approach of OD (“order–disorder”) theory.