Rb-8[B-12(BS3)(6)] and Cs-8[B-12(BS3)(6)]: the first thioborato-closo-dodecaborates

Systematic studies on chalcogenoborates containing a B-12 cluster entity and alkali metal cations led to the new crystalline phases Rb-8[B-12(BS3)(6)] and Cs-8[B-12(BS3)(6)] which consist of a icosahedral B-12 cluster completely saturated with trigonal-planar BS3 Units and rubidium (cesium) counter-ions. The new chalcogenoborates were prepared in solid state reactions from rubidium (cesium) sulfide, amorphous boron and sulfur in evacuated carbon coated silica tubes at a temperature of 923 K (873 K). From single crystal X-ray analyses the lattice parameters of both compounds (space group P (1) over bar) were determined to be: a = 10.085(2) Angstrom, b = 10.036(2) Angstrom, c = 10.598(2) Angstrom, a = 104.74(2)degrees, beta = 91.56(2)degrees, gamma = 109.08(2)degrees for Rb-8 [B-12(BS3)(6)] and a = 10.330(2) Angstrom, b = -10.369(2) Angstrom, c = 10.833(2) Angstrom, alpha = 103.64(3)degrees, beta = 91.91(3)degrees, gamma = 109.51(3)degrees for Cs-8[B-12(BS3)(6)]. The [B-12(BS3)(6)](8-) ions in the structure obey Wade's rules and are composed of B-12 icosahedra with six of their edges bridged by trigonal-planar BS3 groups. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.