Controlling Lewis Basicity in Polythioarsenate Fluxes:  Stabilization of KSnAsS5 and K2SnAs2S6. Extended Chains and Slabs Based on Pyramidal β-[AsS4]3- and [AsS3]3- Units

Two low-dimensional compounds, KSnAsS5 and K2SnAs2S6, were prepared using liquid polythioarsenate salts, and the results differ from those obtained with the well studied thiophosphate flux. KSnAsS5 crystallizes in the orthorhombic space group Pbam with cell parameters of a = 8.136(2) Å, b = 13.784(4) Å, c = 7.428(2) Å. KSnAsS5 features the unusual pyramidal species [AsS2(S2)]3-. K2SnAs2S6 crystallizes in the trigonal space group P3̄ with cell parameters a = 6.717(5) Å, b = 7.204(8) Å, γ = 120°. The compounds were obtained by controlling the Lewis basicity of the K2S/As2S3/S flux. The optical, thermal, and spectroscopic properties of the compounds are reported.