Flux Synthesis of the Noncentrosymmetric Cluster Compounds Cs<sub>2</sub>SnAs<sub>2</sub>Q<sub>9</sub> (Q = S, Se) Containing Two Different Polychalcoarsenite β-[AsQ<sub>4</sub>]<sup>3-</sup> and [AsQ<sub>5</sub>]<sup>3-</sup> Ligands
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Two noncentrosymmetric quaternary tin chalcoarsenates, Cs2SnAs2S9 (1) and Cs2SnAs2Se9 (2), were synthesized by the polychalcoarsenate flux method. Compound 1 crystallizes in the orthorhombic space group Pmc21 with a = 7.386(3) Å, b = 14.614(5) Å, c = 14.417(5) Å, and Z = 4. Compound 2 crystallizes in the monoclinic space group P21 with a = 7.715(5) Å, b = 17.56(1) Å, c = 7.663(5) Å, β = 115.86(1)°, and Z = 2. Both structures contain the same tin-centered molecular cluster anions {Sn[AsQ2(Q2)][AsQ(Q2)2]}2- (Q = S, Se) separated by Cs cations. The Sn4+ ion is in a distorted octahedral environment coordinated by two different pyramidal-shaped tridentate ligands, [AsQ2(Q2)]3- and [AsQ(Q2)2]3-. 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.
