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Metal-ligand electron transfer occurs as a fundamental step in redox processes of complexed metal ions, but only in rare cases has it been studied directly. Intramolecular charge separation induced photochemically contributes to the activity of photocatalysts where oxidative and reductive centers result from transfer of charge between localized metal and ligand electronic levels. Ruthenium bipyridine and diimine complexes have been of particular interest in this context5 and recent studies on o-quinone complexes indicate even more facile electron-transfer properties.6 Quinone ligands7 chelated to metal ions as either semiquinone or catecholate form complexes with quinone * electronic levels and metal d-orbitals close in energy yet discrete in the molecular orbital structure of the complex.8 This has permitted studies on parameters which direct charge distribution within the metal-quinone chelate ring.9Air oxidation of Ru(bpy)2(DBCat) yields the Ru"(bpy)2-(DBSq)+ cation with oxidation occuring at the catecholate ligand.10 This charge distribution has been determined from the structural features of the cation11 and from electronic spectroscopic considerations.10 Complexes containing two quinone ligands bonded to ruthenium were prepared by treating Ru2(OAc)4C1 with DBCat.

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Heats of mixing and densities of very dilute aqueous solutions (mol fraction concentration << 2 x of cyclic ether derivatives have been measured at several temperatures. The solutions studied included tetrahydrofuran, tetrahydropyran, 1,6dioxan, tetrahydrofurfuryl alcohol, and tetrahydropyran-2-carbinol. Limiting partial heats, heat capacities, volumes and expansibilities are discussed in terms of current ideas on polar and apolar hydration.

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