Crystal and molecular structures of di-µ-bromo-dibromo-trans-bis-(dimethyl sulphide)-dipalladium(II), Pd2Br4(SMe2)2, and tetrabromo-µ-bis(diethyl sulphide)-diplatinum(II), Pt2Br4(SEt2)2

Abstract

The crystal structures of Pd2Br4(SMe2)2 and Pt2Br4(SEt2)2 have been determined by single-crystal X-ray analysis. Both crystals are monoclinic, space-group P21/n which, with Z= 2, requires both molecules to posses a centre of symmetry. In fact both molecules have a planar skeleton comprising two metal atoms held apart by bridging groups, but whereas in Pd2Br4(SMe2)2 the bridging groups are halogen, with the sulphur atoms in a trans terminal configuration, in Pt2Br4(SEt2)2 the metal atoms are symmetrically bridged by the sulphur atoms, and all the halogens are terminal. These structures were determined to corroborate evidence from infrared spectral studies that, despite similar modes of preparation, these crystals possess fundamentally different structures.In Pd2Br4(SMe2)2, a= 6·00, b= 10·49, c= 11·47 A, β= 107° 35′ . The Pd–Br terminal distance is 2·404(4) significantly shorter than the (weighted mean) Pd–Br bridging distance of 2·440(10)A. The Pd–S terminal distance is 2·30(2), significantly longer than the (weighted mean) Pt–S bridging distance in Pt2Br4(SEt2)2 of 2·22(1)A. The carbon atoms of the methyl groups attached to the sulphur atoms are not symmetrically related to the plane of the molecule; one S–C bond lies close to the plane, the other nearly perpendicular to it.In Pt2Br4(SEt2)2, a= 7·36, b= 13·45, c= 9·20 A, β= 104° 05′ . The (weighted mean) Pt–Br terminal distance of 2·385(8)A is closely similar to the Pd–Br distance in Pd2Br4(SMe2)2, while the Pt–S distance is significantly shorter. The sulphur-carbon bonds are here symmetrically related to the plane of the molecule.