Synthesis and crystal structures of urea and thiourea derivatives of diruthenium(II,III) tetraacetate

Diadduct complexes of the mixed-valent form of diruthenium tetraacetate, [Ru-2(mu-O2CCH3)(4)L-2](PF6), with L = urea (1), 1,1,3,3-tetramethylurea (tmu) (2) and 1,1,3,3-tetramethyl-2-thiourea (tmtu) (3) have been synthesized and characterized by elemental analysis, IR and UV-Vis spectroscopy, magnetic susceptibility, cyclic voltammetry and X-ray crystallography. Compound 1 crystallizes as a co-diadduct system from 1-propanol in which both [Ru-2(mu-O2CCH3)(4)(urea)(2)](+) and [Ru-2(mu-O2CCH3)(4)(1-propanol)(2)](+) cations are present in the unit cell. Complex 3 displays a very long Ru-S bond of 2.610(2) Angstrom and is only the second example of a sulfur-donor adduct of a diruthenium tetracarboxylate that has been structurally characterized. Electrochemical measurements on 2 and 3 show them to have reduction potentials of -487 and -541 mV (vs. Fc/Fc(+)), respectively, which is in the range of moderate to strong axial donor adducts despite the long Ru-S bond in 3. Reaction of [Ru-2(mu-O2CCH3)(4)(H2O)(2)](PF6) with thiourea yields a 1:1 complex, [Ru-2(mu-O2CCH3)(4)(thiourea)](PF6), which from solubility and infrared evidence appears to be a polymer in which the thiourea bridges through the sulfur and one of the amine nitrogens