Synthesis, structures, and spectroscopic, magnetic, and electrochemical properties of (mu-alkoxo)bis(mu-carboxylato)diruthenium complexes, M[Ru-2(dhpta)(mu-O(2)CR)(2)] (M=Na and K, dhptaH(5)=1,3-diamino-2-hydroxypropanetetraacetic acid)

[RuCl2(dmso)(4)] (dmso = dimethyl sulfoxide) was treated with dhptaH(5) (1,3-diamino-2-hydroxypropanetetraacetic acid) and carboxylate ligands in the presence of NaOH or KOH and gave dinuclear ruthenium(III) complexes of dhpta with two bridging carboxylates, M[Ru(dhpta)(mu-O(2)CR)(2)] (1, R = C6H5, M = Na; 1', R = C6H5, M = K; 2, R = p-OHC6H4, M = Na; 3, R = p-NH2C6H4, M = Na; 4, R = CH3, M = Na; 4', R = CH3, M = K), which were characterized by elemental analysis, mass, electronic absorption, and H-1 and C-13 NMR spectroscopies, and X-ray absorption and crystallographic analyses (4, orthorhombic, space group Pca2(1) with a = 21.359(4) Angstrom, b = 7.484(2) Angstrom, c = 12.930(2) Angstrom, Z = 4, R = 0.065, and R(w) = 0.044 for 1116 independent reflections with I > 3 sigma(I); 4'. 1.5H(2)O: monoclinic, P2(1), a = 7.689(2) Angstrom, b = 17.213(2) Angstrom, c = 18.103(2) Angstrom, beta = 94.50(1)degrees, Z = 4; R = 0.041, and R(w) = 0.047 for 4705 independent reflections with I > 3 sigma(I)). The complex anion consists of two ruthenium atoms bridged by the alkoxide of dhpta and the two acetate ligands. The Ru-Ru distances of 3.433(3) Angstrom (4) and 3.421(1) Angstrom (average) (4') are longer than those found in (mu-oxo)bis(mu-carboxylato)diruthenium(III) complexes. EXAFS analysis and H-1 NMR spectra indicated that complexes 1-4 have the identical dinuclear structure in both solid and water solution states. Temperature-dependent magnetic susceptibility of 1-4 showed a strong antiferromagnetic interaction between the two Ru(III) ions with -J = 310-470 cm(-1). Cyclic voltammograms showed two reduction processes at ca. -0.34 and ca. -0.94 V vs Ag/AgCl, corresponding to two stepwise one-electron reductions, (RuRuIII)-Ru-III <-> (RuRuII)-Ru-III <-> (RuRuII)-Ru-II. The most remarkable feature is the large separation between the two redox potentials, implying that the mixed-valence diruthenium(III,II) complexes of dhpta are fairly stable. Potentiostatic electrolysis of 1-4 at a potential in between E(1/2)(1) and E(1/2)(2) consumed 1 F per dimer and afforded a mixed-valence diruthenium species, [(RuRuIII)-Ru-II(dhpta)mu-O(2)CR)(2)](2-), in solution, which showed two weak and broad absorption bands (nu(max) 5.5-5.7 and 11.6-11.9 kcm(-1)) in DMF assignable to intervalence charge transfer (IT) bands. The lower energy IT band was analyzed by Gaussian curve fitting and the electron exchange integral H-ad was estimated as 640-870 cm(-1) on the basis of Hush's theory. The spectroscopic analysis indicated that [(RuRuIII)-Ru-II(dhpta)(O(2)CR)(2)](2-) belongs to Class II type mixed-valence diruthenium complexes.