Studies of some octathiocyanate complexes of thorium(IV) and uranium(IV). I. Infrared spectra in the v(CN) region

Abstract

Infrared spectra have been recorded for compounds of formula A₄^IM^IV(NCS)₈,_- xH₂O (M = Th, U; A = Cs, Rb, NH₄) in the region 2200-265 cm-1. The band splittings in the v(CN) region, both in solution and in the solid state, have been examined in detail and compared with the number of active modes predicted for eight-coordinate ions with D_2d (dodecahedral), D_4d (square-antiprism), and O_h (cubic) symmetry. The results suggest that both the [Th(NCS)₈]^4- and [U(NCS)₈]^4- complexes adopt the configuration of an Archimedean antiprism in solution, but in the solid state the symmetry is lowered to dodecahedral.