Pd(II) and Pt(II) complexes of 2,2′-biimidazole and its N,N′-dimethyl derivative. The crystal structure of [{PtBr(DMSO)}2(Me2bim)] (Me2bim = N,N′-dimethyl-2,2′-biimidazole)

The complexes [PdCl2(LL)] and [PtX2(LL)] [X = Cl, Br or I; LL = 2,2'-biimidazole (H(2)bim) or N,N'-dimethyl-2,2'-biimidazole (Me(2)bim)] were prepared and characterized spectroscopically. The effects of the chloro compounds on plasmid DNA conformation were studied by electrophoresis in agarose gels, and that of [PtCl2(H(2)bim)] on calf thymus DNA by circular dichroism spectroscopy. The observation that these effects were adversely affected by addition of DMSO (originally used with [PtCl2(Me(2)bim)], to improve its solubility) prompted a study of the solvolysis of [PtCl2(H(2)bim)] by this solvent. H-1 and Pt-195 NMR, and electrospray mass spectra, showed the solvolysis of both Pt-Cl and Pt-N bonds, the release of the ligand H2bim, and the formation of several polynuclear species. X-ray diffractometry of the dinuclear Pt(I) compound [{PtBr(DMSO)}(2)(Me(2)bim)] showed the ligand Me(2)bim to bridge through its non-methylated N atoms between two platinum atoms, the coordination spheres of which were each completed by a Br- ligand, the S atom of a DMSO molecule, and the other Pt atom; the Pt-Pt bond is 2.5560(9) Angstrom in length. (C) 2003 Elsevier Science Ltd. All rights reserved.