CSSMGES4 - A NOVEL LAYERED MIXED-METAL SULFIDE CRYSTALLIZING IN THE NONCENTROSYMMETRIC SPACE GROUP P2(1)2(1)2(1)

A novel mixed-metal sulfide compound CsSmGeS4 was isolated from a reac tion intended to grow single crystals of AgSm3GeS7 via the CsCl molten flux. The title compound possesses an unusual structural feature, a h elix made of CsS8 units, which is likely responsible for the formation of the noncentrosymmetric lattice. This compound crystallizes in an o rthorhombic unit cell with a = 6.768 (2) Angstrom, b = 17.752 (2) Angs trom, c = 6.488 (1) Angstrom, V = 779.5 (3) Angstrom(3); P2(1)2(1)2(1) (No. 19); Z = 4. The structural and thermal parameters were refined b y full-matrix least-squares methods to R = 0.057, R(w) = 0.071 and GOF = 2.18 based on F with 64 variables. The structure of this quaternary chalcogenide can be considered as a layered type in that the [SmGeS4] (-) slabs are stacked along the crystallographic b axis with cesium ca tions in the van der Waals gap between sulfur layers. The coordination of the CsS8 unit is characterized by a planar pentagonal arrangement of sulfurs at a slight angle to the ab plane, with the three other sul furs in the coordination sphere above the plane in a staggered orienta tion. The CsS8 polyhedra are interconnected about a 2(1) screw axis to form a helix along the c direction. The differential thermal analysis (DTA) and preliminary infrared absorption spectroscopy :studies sugge st that the CsSmGeS4 compound melts congruently at similar to 1086 deg rees C and is likely IR transparent, respectively. The comparison of t he title compound with the structurally related chalcogenides KLaGeS4 (P2(1)) and CaYbInS4 (Pnma) is discussed.