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

Abstract

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(μ-L)]⁺ (3⁺) which was isolated as its hexafluorophosphate salt; in this complex a {Ru(bipy)₂}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 s. ferrocene/ferrocenium, which means that the complex is part of a four-membered redox chain spanning the oxidation states 3⁺ to 3⁴⁺. A spectroelectrochemical study in MeCN at −30°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.