SYNTHESIS AND STRUCTURE OF THE FIRST CERIUM IODOTHIOSILICATE - CE-3(SIS4)(2)I

The first cerium iodothiosilicate, Ce-3(SiS4)(2)I, has been synthesize d from the reaction at 900 degrees C between cerium sulfide, silicon, iodine and sulfur in a Ce2S3/Si/S/I = 3:6:11:2 ratio. This compound cr ystallises in the monoclinic space group C2/c (Z = 4) with the powder refined cell parameters: a = 15.9634(5) Angstrom, b = 7.8502(2) Angstr om, c = 10.8664(3) Angstrom, beta = 97.931(2)degrees. The structure wa s solved from single crystal X-Ray diffraction analysis (R(%) = 2.17 a nd R-w(%) = 2.60). The Ce-3(SiS4)(2)I structure is quite different fro m those of the other already known rare earth thiosilicates because of the template role of iodine, leading to the occurrence of tunnels. In these tunnels are found the iodide anions which are surrounded by thr ee cerium, so as to form [ICe3] isosceles triangular entities. Around the tunnels is found a three-dimensional network consisting of (CeIS8) polyhedra (trigonal prisms of sulfur tricapped by two sulfur and one iodine atom) linked to (SiS4) tetrahedra. (C) 1998 Elsevier Science S. A.