Coordination Polyhedra IrX-n (X = O, S, Se, Te) in Crystal Structures

摘要

The Voronoi-Dirichlet partition and the intersecting spheres method were used for the crystal-chemical analysis of compounds with structures containing coordination polyhedra IrX_n (X = O, S, Se, Te). It was found that iridium atoms, which occur in oxidation states from III to VI, commonly exhibit an octahedral coordination with chalcogen atoms. In oxygen-containing compounds, Ir(IV) atoms exhibit unique stereochemistry and, along with the coordination number (CN) 6, can have CN =4 (square IrO_4 fragments), as well as CN = 6 + 1 or 6 + 2 due to one or two Ir-Ir bonds between the central atoms of face-sharing IrO_6 octahedra. In addition, iridium atoms of Ir~(IV)O_4 squares and Ir~(IV)O_6, Ir~VO_6, and Ir~(III)Te_6 octahedra can form additional Ir-M bonds (M = Li, Na, K, Cs, Ca, Sr, Cu, Ta), whereas direct Ir-M interactions are completely absent in the structures of oxygen-containing compounds of Ir(III) and Ir(VI). The effect of site symmetry and the valence state of Ir atoms on the characteristics of their Voronoi-Dirichlet polyhedra and the character of the distortion of IrO_6 octahedra are considered. The reasons for the existence of the square coordination of Ir(IV) atoms atypical of d~5 coordination centers are discussed.