NEW QUATERNARY THIOSTANNATES AND THIOGERMANATES A(2)HG(3)M(2)S(8) (A = CS, RB, M = SN, GE) THROUGH MOLTEN A(2)S(X) - REVERSIBLE GLASS-FORMATION IN CS2HG3M2S8

Cs2Hg3M2S8 (M = Ge, Sn) were synthesized in 70% and 65% yields by reac ting HgS, and Sn or Ge, in molten Cs2Sx at 520 degrees C. Rb2Hg3Sn2S8 aad Rb2Hg3Ge2S8 were synthesized in 42% and 73% yield by reacting the same reagents in molten Rb2Sx at 350 degrees C. Cs2Hg3M2S8 crystallize in the triclinic space group P (1) over bar. Cs2Hg3Sn2S8: a = 7.878(2 ) Angstrom, b = 9.157(3) Angstrom, c = 6.803(2) Angstrom, alpha = 92.9 6(2)degrees, beta = 109.45(2)degrees, gamma = 107.81(2)degrees, V = 43 4.1(2) Angstrom(3), and D-calc = 5.207 g/cm(3). The unit cell of isost ructural Cs2Hg3Ge2S8 is a = 7.808(2) Angstrom, b = 9.164(2) Angstrom, c = 6.612(2) Angstrom, alpha = 92.02(2)degrees, beta = 108.65(2)degree s g, gamma = 108.10(2)degrees, and V = 419.9(2) Angstrom(3). Rb2Hg3M2S 8 crystallize in the monoclinic space group P2(1)/c, Rb2Hg3Sn2S8: a = 10.132(2) Angstrom, b = 6.540(2) Angstrom, c = 13.434(2) Angstrom, bet a = 97.93(1)degrees, V = 881.7(6) Angstrom(3), and D-calc = 4.770 g/cm (3). The unit cell of isostructural Rb2Hg3Ge2S8 is a = 9.938(3) Angstr om, b = 6.352(2) Angstrom, c = 13.117(3) Angstrom, beta = 97.33(2)degr ees, and V = 821.3(4) Angstrom(3). The structure of Cs2Hg3M2S8 consist s of [Hg3M2S8](2-) layers separated by Cs+ cations. The layers contain tetrahedral Sn4+ or Ge4+ centers and two types of Hg2+, two coordinat e linear and three-coordinate pseudotrigonal centers. The structure of Rb2Hg3M2S8 consists of a 3-dimensional [Hg3M2S8](2-) framework with R b+ cations located within channels of the structure. This structure al so contains tetrahedral Sn4+ or Ge4+ centers and two types of Hg2+, th e two-coordinate linear type and a four-coordinate ''seesaw'' geometry . Optical band gaps, determined from single-crystal UV/vis spectroscop y, range from 2.52 eV in the tin-based compounds to 2.89 eV in the ger manium-based analogues. Cs2Hg3M2S8 become glasses upon melting. Infrar ed and Raman spectroscopic characterization of the glasses are reporte d.