Synthesis and crystal structure of La4S3Si2O7

In an attempt to grow 'LaNaGeS4' single crystals by using NaBr as flux in a sealed evacuated carbon-coated quartz tube, transparent yellow crystals of La4S3Si2O7 were isolated. La4S3Si2O7 crystallizes in a tetragonal system, space group I4(1)/and (No. 141), with a=12.098(3) Angstrom, c=14.379(5) Ang strom and Z=8. The new compound belongs to the family of compounds with com position RE(4)Q(3)Si(2)O(7) (RE=rare earth; Q=S, Se). The structure of La4S 3Si2O7 contains two crystallographically independent La3+ cations that are interconnected by S2- anions and isolated [Si2O7](6-) units. La(1) is coord inated by three O atoms and three S atoms to form a trigonal prismatic geom etry, while La(2) is coordinated by six O atoms and three S atoms to form a tri-capped trigonal prismatic geometry. The Si,O, double tetrahedra are in the eclipsed configuration with nonlinear Si-O-Si bridges (angle: 131.4(6) degrees). (C) 1999 Elsevier Science S.A. All rights reserved.