SYNTHESIS AND CRYSTAL-STRUCTURE OF TERNARY SULFIDES A(3)MS(4) WITH A = NA, RB AND M = NB, TA

The new ternary sulfides Na3MS4 and Rb3MS4 (M = Nb, Ta) were prepared from tantalum nitride or niobium powder in the respective alkali metal polysulfide melt. Both sodium sulfides crystallize in form of yellow( Nb) or yellow-orange (Ta) needles in the orthorhombic space group Fdd2 with Z=32 and a 27.3034(4) Angstrom, b = 28.4662(1) Angstrom, and c = 7.9642(1) Angstrom, R/R-w = 0.024/0.048 for M=Nb and a 27.2322(2) Ang strom, b= 28.4264(2)Angstrom, and c=7.9634(6)Angstrom, R/R-w = 0.066/0 .177 for M = Ta. The rubidium sulfides mere obtained as yellow (Nb) an d orange (Ta) crystals with irregular shape. They crystallize in the o rthorhombic space group Pnma with Z=4 and a= 9.6109(6)Angstrom, 6 = 11 .1013(7) Angstrom, and c = 9.6390(6) Angstrom, R/R-w = 0.030/0.072 for M=Nb and a=9.6084(5) Angstrom, b= 11.1067(6)Angstrom, and c=9.6426(5) Angstrom, R/R-w=0.031/0.070 for M=Ta, The structures of all four compo unds are built by stacking isolated MS43- units with the alkali metal ions. (C) 1998 Academic Press.