Dodekaeder und Archimedisches Antiprisma als Molekülstrukturen bei Oktacyanokomplexen des Molybdän(IV) und Wolfram(IV)

Abstract

Infrared spectra (300—4000 cm-1) have been measured on the octacyanide complexes K4Mo (CN)8·2H2O and K4W (CN)8·2 H2O in aqueous solution, in the solid dihydrates, and in the solid anhydrous compounds. Comparison with relevent Raman data, particularly in the 2100 cm-1 region, provides conclusive evidence for the effective molecular symmetry of the M (CN)8 4- group in the different surroundings. In aqueous solution, the ions [Mo (CN)8]4- and [W (CN) 8] 4- assume the symmetry of an Archimedean antiprism, D4d . In the dihydrate crystals, the groups Mo (CN)8 4- and W (CN)8 4- approach the full D2d symmetry of a dodecahedron with triangular faces, possibly slightly distorted by packing effects. In the anhydrous compounds, the symmetry of these groups is considerably lower, very likely C8. Reasonable assignments for all normal frequencies in the 2100 cm-1 region are proposed, both in D4d and D2d symmetry.