Characterization of Ce3(SiS4)2I, a compound with a new structure type

The first cerium iodothiosilicate, Ce-3(SiS4)(2)I, has been synthesized from the reaction of cerium sulfide with silicon, iodine and sulfur at high temperature. This compound crystallizes in the monoclinic symmetry (space group C2/c and Z=4)with the powder refined cell parameters: a = 15.9634(5), b = 7.8502(2), c = 10.8664(3) Angstrom, beta = 97.931(2)degrees. The crystal structure was refined to R(%)= 2.17 and R-W(%)= 2.60 from single crystal X-ray diffraction data. Ce(SiS4)(2)I presents tunnels in which are located the iodide anions surrounded by three ceriums, in [ICe3] isosceles triangular entities. The tunnels are constituted of a three dimensional network made of (CeIS8) polyhedra (trigonal prisms of sulfur tricapped by two sulfur and one iodine atom) linked to (SIS,) tetrahedra. Magnetic susceptibility measurements and UV-VIS diffuse reflectance spectroscopy are consistent with the occurrence of Ce-III ions, whereas band structure calculations indicate that the phase is a semiconductor. The charge balance in the material can be written as : (Ce3Si2I8-I -II)-Si-III-I-IV.