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](PF 6)2 (7) and [(phen)2Ru(tpphz)Ru(terpy)Cl] (PF6)3 (8), are reported. Both structures contain a tetrapyrido[3,2-α: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)2tpphz](PF6)2 (4) and RuCl 2(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) 2Ru(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 π-π* 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. © 2010 Elsevier Ltd. All rights reserved.