Electronic, magnetic, and spectroscopic properties of binuclear diruthenium tetracarboxylates: A theoretical and experimental study

The electronic structure of binuclear diruthenium tetracarboxylates, in bot h the divalent Ru-2(II,II)(O2CR)(4) and the mixed-valent Ru-2(II,III)(O2CR) (4)X (X = anion) states is studied by means of ZINDO/S-MRCI and DFT calcula tions. Both methods predict a (pi*)(2)(delta*)(2) ground-state configuratio n for the divalent species, contrary to the (pi*)(3)(delta(*))(1) previousl y predicted by SCF-Xa calculations, but in agreement with magnetic measurem ents that show a strong Zero Field Splitting. Our ZINDO/S-MRCI calculations on compounds containing axial Ligands with different degree of pi bonding to the bimetallic center (water, chloride, carboxylate, pyridine, pyrazine) , for both (II,II) and (II,III) ruthenium cores, show the important role pl ayed by the ligands. These theoretical calculations allow us to explain the differences observed in the UV/vis and resonance Raman spectra, both in so lution and in the solid state, when varying the axial ligands. The ZINDO/S- MRCI calculations are also capable of solving some controversies found in t he Literature, related to the assignment of the main electronic bands for b oth kinds of compounds. The electronic structures predicted by the DET meth odology are in agreement with both the experimental evidence and the ZINDO/ S calculations. Moreover, our DFT calculations provide an interpretation of the intermolecular magnetic interactions in the mixed-valent species, expl aining the dependence of the antiferromagnetic coupling on the intermolecul ar Ru-X-Ru angle.