Flux Synthesis of the Noncentrosymmetric Cluster Compounds (Cs)2Sn(As)2(Q)9 (Q = S, Se) Containing Two Different Polychalcoarsenite (beta)-[As(Q)4]^(3-) and [As(Q)5]^(3-) Ligands

Two noncentrosymmetric quaternary tin chalcoarsenates, Cs2SnAs2Sg (1) and Cs2SnAs2Seg (2), were synthesized by the polychalcoarsenate flux method. Compound 1 crystallizes in the orthorhombic space group Pmc2i with a = 7.386(3) A, b = 14.614(5) A, c = 14.417(5) A, and Z= 4. Compound 2 crystallizes in the monoclinic space group P2i with a = 7.715(5) A, b = 17.56(1) A, c = 7.663(5) A, ft = 115.86(1) and Z = 2. Both structures contain the same tin-centered molecular cluster anions {Sn[AsQ2(Q2)][AsQ(Q2)2]} (Q = S, Se) separated by Cs cations. The Sn ion is in a distorted octahedral environment coordinated by two different pyramidal-shaped tridentate ligands, [AsQ(Q)] and [AsQ(QP". These compounds absorb visible light at energies above 1.98 and 1.45 eV for 1 and 2, respectively. Differential thermal analysis revealed that 1 melts at 350 °C and on cooling gives a glass. The glass recrystallizes at 268 °C upon subsequent heating. Compound 2 melts at 258 °C.