The polycationic main group element clusters (As3S5)(+) and (As3Se4)(+) - Syntheses from chloroaluminate melts, crystal structures, and vibrational spectra

The reaction of arsenic, arsenic trichloride and AICl(3) with sulfur or selenium, respectively, in closed glass ampoules at 80 degrees C leads to melts from which on slow cooling to 50 degrees C (As3S5)[AlCl4] and (As3Se4)[AlCl4] can be obtained in the form of yellow and red crystals. The crystal structures ((As3S5)[AlCl4]: monoclinic, P2(1)/m, a = 640.48(4), b = 977.54(7), c = 1146.39(8) pm, beta = 104.003(3)degrees; (As3Se4)[AlCl4]: monoclinic, C2/c,a = 2080.57(2), b = 1251.41 (1), c = 1367.68(l) pm, beta = 127.969(1)degrees) consist of nearly regular tetrahedral [AlCl4](-) ions and of arsenic-chalcogen polycations. The structures of the cations can be derived from As3E tetrahedra (E = S, Se) with three edges bridged by Se atoms for (As3Se4)(+) and with four edges bridged by S atoms for the Cs symmetric (As3S5)(+). In both structures the ions are arranged in the motif of the CsCl structure type. Infrared und Raman spectra of both compounds show the vibration modes of both kinds of ions in the region 50 - 500 cm(-1). Symmetry analysis and normal mode calculations of the vibrational spectra of (As3Se4)[AICl(4)] confirm the presence of the (As3Se4) clusters and the [AlCl4] groups.