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

Abstract

The complexes [PdCl 2(LL)] and [PtX 2(LL)] [X=Cl, Br or I; LL=2,2′-biimidazole (H 2bim) or N, N′-dimethyl-2,2′-biimidazole (Me 2bim)] 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 [PtCl 2(H 2bim)] on calf thymus DNA by circular dichroism spectroscopy. The observation that these effects were adversely affected by addition of DMSO (originally used with [PtCl 2(Me 2bim)], to improve its solubility) prompted a study of the solvolysis of [PtCl 2(H 2bim)] by this solvent. 1H and 195Pt NMR, and electrospray mass spectra, showed the solvolysis of both PtCl and PtN bonds, the release of the ligand H 2bim, and the formation of several polynuclear species. X-ray diffractometry of the dinuclear Pt(I) compound [{PtBr(DMSO)} 2(Me 2bim)] showed the ligand Me 2bim 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) Å in length.