Synthesis, spectroscopic and a ZINDO study of cis- and trans-(X-2)bis(4,4 '-dicarboxylic acid-2,2 '-bipyridine)ruthenium(II) complexes (X = Cl-, H2O,NCS-)

Ruthenium complexes of the type trans-[Ru(dcbpyH(2))(2)(Cl)(2)], trans-[Ru( dcbpyH(2))(2)(H2O)(2)] and trans-[Ru(dcbpyH(2))(2)(NCS)(2)] (dcbpyH(2) = 4, 4'-dicarboxylic acid-2,2'-bipyridine) were synthesized and characterized by NMR, UV-vis absorption and emission spectroscopy. The proton NMR spectra o f the trans isomers, in the aromatic region, show only three peaks correspo nding to the two dcbpy ligands in which all the pyridine rings are trans to each other and magnetically equivalent. The C-13-NMR spectrum of the trans isomer is characterized by a relatively simple pattern of resonances from the four equivalent pyridine rings. The lowest energy metal-to-ligand charg e-transfer transition maximum of the trans-[Ru(dcbpyH(2))(2)(Cl)(2)] comple x is at 14500 cm(-1) in DMF solution and shows onset of weak and broad emis sion signals above 11100 cm(-1), This is a significantly larger red shift c ompared with any of the trans ruthenium(II) polypyridyl complexes reported to date. The absorption and emission maxima of the trans complexes are red shifted compared with the cis analogues, which is due to the CO2H contribut ion in the trans isomer that stabilizes the LUMO relative to the LUMO of th e cis isomer. The enhanced red response of the trans complexes renders them as suitable dyes for dye-sensitized titanium dioxide mesoporous electrodes . The electronic spectra of cis- and trans-[Ru(dcbpyH(2))(2)(Cl)(2)] comple xes were calculated by ZINDO/S and compared with the experimental data. (C) 2000 Elsevier Science S.A. All rights reserved.