STRUCTURES, ELECTROCHEMICAL AND SPECTROSCOPIC PROPERTIES OF TERNARY RUTHENIUM(II)-POLYPYRIDYL COMPLEXES WITH ADDITIONAL CARBOXYLATE, BIGUANIDE OR SULFONAMIDE DONORS

The following complexes have been prepared: [Ru(bipy)(2)(pic)][PF6] (b ipy = 2,2'-bipyridine; Hpic = picolinic acid); [Ru(terpy)(dipic)] (ter py =2,2':6',2''-terpyridine; H(2)dipic=dipicolinic acid); [Ru(bipy)(2) (Hbig)][PF6](2) (Hbig=biguanide); and [Ru(bipy)(2)(apps)][PF6] [where Happs is the p-tolylsulfonamide of 2-(2-aminophenyl)-pyridine]. The l atter three have been characterised by X-ray crystallography and are a ll mononuclear pseudo-octachedral complexes. Electrochemical studies r eveal the relationship between the potential of the metal-based Ru(II) /Ru(III) couple, with the potential values being clearly related to th e sigma-donor or pi-acceptor capabilities of the ligands. The energies of the lowest-energy m.l.c.t. maxima in the electronic spectra also c orrelate with ligand properties. [Ru(bipy)(2)(Hbig)][PF6](2), which ha s a dissociable proton on the biguanide ligand, undergoes deprotonatio n in strongly basic conditions (pK(a) = 12.3 +/- 0.2), which results i n a red-shift of the m.l.c.t. transition consistent with weakening of the ligand field due to the increased pi-donor capability of the depro tonated ligand. (C) 1998 Elsevier Science Ltd. All rights reserved.