CRYSTAL-STRUCTURE OF SYNTHETIC PB4.32SB3.68S8.68CL2.32 - A CHLORINE-BEARING ALTERNATIVE TO PB4SB4S11

A new synthetic chlorine sulphosalt, Pb4.32Sb3.68S8.68Cl2.32 was prepa red at 500 degrees C by gas-transport reaction. Microprobe analyses gi ve: Pb - 50.7, Sb - 27.3, S - 17.0, Cl - 4.5 wt%; total 99.5 wt%. An X -ray single-crystal investigation including site-occupancy refinement and application of the bond-valence method, shows that the chlorine su lphosalt is isopointal to Pb4Sb4S11. Crystal data: space group Pbam, a = 15.04(4), b = 15.51(3), c = 4.09(1) Angstrom, V = 954.1(7) Angstrom (3), Z = 2, F.W. = 1675.24, D-X = 5.83 g.cm(-3), and R = 0.039 for 101 2 reflections with I > 3 sigma (I). The special position 0, 0, 1/2 is recognized as being entirely occupied by chlorine. Other chlorine atom s partially substitute on specific sulphur positions, in connection wi th mixed (Pb, Sb) sites according to the heterovalent substitution sch eme Pb2+ + Cl- --> Sb3+ + S2-. It is possible that the planar Pb4Cl gr oup plays a key structural-determining role in the formation of high c hlorine-bearing lead-antimony sulphosalts.