New Hexachalcogeno–Hypodiphosphates of the Alkali Metals: Synthesis, Crystal Structure and Vibrational Spectra of the Hexathiodiphosphate(IV) Hydrates K4[P2S6] · 4 H2O, Rb4[P2S6] · 6 H2O, and Cs4[P2S6] · 6 H2O

Abstract

AbstractThe new hexathiodiphosphate(IV) hydrates K4[P2S6] · 4 H2O (1), Rb4[P2S6] · 6 H2O (2), and Cs4[P2S6] · 6 H2O (3) were synthesized by soft chemistry reactions from aqueous solutions of Na4[P2S6] · 6 H2O and the corresponding heavy alkali‐metal hydroxides. Their crystal structures were determined by single crystal X‐ray diffraction. K4[P2S6] · 4 H2O (1) crystallizes in the monoclinic space group P 21/n with a = 803.7(1), b = 1129.2(1), c = 896.6(1) pm, β = 94.09(1)°, Z = 2. Rb4[P2S6] · 6 H2O (2) crystallizes in the monoclinic space group P 21/c with a = 909.4(2), b = 1276.6(2), c = 914.9(2) pm, β = 114.34(2)°, Z = 2. Cs4[P2S6] · 6 H2O (3) crystallizes in the triclinic space group $P {\bar 1}$ with a = 742.9(2), b = 929.8(2), c = 936.8(2) pm, α = 95.65(2), β = 112.87(2), γ = 112.77(2)°, Z = 1. The structures are built up by discrete [P2S6]4− anions in staggered conformation, the corresponding alkali‐metal cations and water molecules. O ··· S and O ··· O hydrogen bonds between the [P2S6]4− anions and the water molecules consolidate the structures into a three‐dimensional network. The different water‐content compositions result by the corresponding alkali‐metal coordination polyhedra and by the prefered number of water molecules in their coordination sphere, respectively. The FT‐Raman and FT‐IR/FIR spectra of the title compounds have been recorded and interpreted, especially with respect to the [P2S6]4− group. The thermogravimetric analysis showed that K4[P2S6] · 4 H2O converted to K4[P2S6] as it was heated at 100 °C.