Synthesis and characterization of rigid+2 and+3 heteroleptic dinuclear ruthenium(II) complexes

Synthesis and characterization of the dinuclear ruthenium coordination complexes with heteroleptic ligand sets, [Cl(terpy)Ru(tpphz)Ru(terpy)Cl](PF6)(2) (7) and [(phen)(2)Ru(tpphz)Ru(terpy)Cl](PF6)(3) (8), are reported. Both structures contain a tetrapyrido[3,2-alpha.:2',3'-c:3 '',2 ''-h:2 '',3 ''-j]phenazine (tpphz) (6) ligand bridging the two metal centers. Complex 7 was obtained via ligand exchange between, RuCl2(terpy)DMSO (5) and a tpphz bridge. Complex 8 was obtained via ligand exchange between, [Ru(phen)(2)tpphz](PF6)(2) (4) and RuCl2(terpy)DMSO (5). Metal-to-ligand-charge-transfer (MLCT) absorptions are sensitive to ligand set composition and are significantly red-shifted due to more electron donating ligands. Complexes 7-9 have been characterized by analytical, spectroscopic (IR, NMR, and UV-Vis), and mass spectrometric techniques. The electronic spectral properties of 7, 8, and [(phen)(2)Ru(tpphz)Ru(phen)(2)](PF6)(4) (9), a previously reported +4 analog, are presented together. The different terminal ligands of 7, 8, and 9 shift the energy of the MLCT and the pi-pi* transition of the bridging ligand. These shifts in the spectra are discussed in the context of density functional theory (DFT). A model is proposed suggesting that low-lying orbitals of the bridging ligand accept electron density from the metal center which can facilitate electron transfer to nanoparticles like single walled carbon nanotubes and colloidal gold. (C) 2010 Elsevier Ltd. All rights reserved.