CRYSTAL-STRUCTURE AND VIBRATIONAL-SPECTRUM OF DIPOTASSIUM MANGANESE (II) HEXATHIODIPHOSPHATE(IV), K2MN[P2S6]

K2Mn[P2S6] was synthesized from the elements in sealed quartz ampoules at 1173 K. The compound forms transparent light brown crystals, stabl e against air and moisture. The crystal structure (monoclinic; space g roup P2(1)/n, No. 14; a = 6.1966(9), b = 12.133(2), c = 7.424(1) angst rom, beta = 101.52(1)-degrees, Z = 2; Pearson code mP22) consists of c olumns of face-sharing S6 polyhedra (distorted octahedra and trigonal antiprisms) parallel to the a axis, interconnected by inserted K+ (CN 10; d(K-S) = 3.23-3.92 angstrom). The S6 polyhedra of the columns are centered alternately by Mn (in octahedra with d(Mn-S) = 2.647 angstrom ) and P2 pairs (in trigonal antiprisms) which are inclined to the a ax is by 73.1-degrees. The bond lengths in the resulting hexathiodiphosph ate(IV) anions, [P2S6]4-, with approximate 3BAR 2/m - D3d symmetry, ar e d(P-P) = 2.211 angstrom and dBAR(P-S) = 2.018 angstrom. K2Mn[P2S6] i s isotypic to K2Fe[P2S6], being the second member of this structure ty pe. The internal modes of the observed Raman and FIR/IR spectra of K2M n[P2S6] are in accord with the factor group analysis, and the fundamen tals are assigned on the basis of [P2S6]4- units, taking into account the deviation of the D3d symmetry.