Synthesis, electrochemistry, UV/VIS/NIR spectroelectrochemistry and ZINDO calculations of a dinuclear ruthenium complex of the tetraoxolene bridging ligand 9-phenyl-2,3,7-trihydroxy-6-fluorone

Reaction of 9-phenyl-2,3,7-trihydroxy-6-fluorone (H3L) with [Ru(bipy)(2)(H2O)(2)](2)(+) affords the complex [{Ru(bipy)(2)}(2)(mu-L)](+) (3(+)) which was isolated as its hexafluorophosphate salt; in this complex a (Ru(bipy),)2+ fragment is coordinated to each dioxolene-like terminus of the bridging ligand [L](3-). Voltammetric experiments in MeCN show the presence of three reversible one-electron redox couples at -0.36, 0.00 and +0.53 V ns. ferrocene/ferrocenium, which means that the complex is part of a four-membered redox chain spanning the oxidation states 3(+) to 3(4+). A spectroelectrochemical study in MeCN at -30 degrees C reveals a complicated series of electronic spectra in the different oxidation states which include some intense transitions in the near-IR region of the spectrum. The spectra could be partly assigned with the assistance of ZINDO calculations, which show that extensive mixing between the metal-centred and bridging-ligand-centred orbitals occurs; metal-to-ligand charge-transfer, ligand-to-ligand charge-transfer and intra-ligand transitions, amongst others, could be identified.