Oxidation of linear trinuclear ruthenium complexes [Ru3(dpa)4Cl2] and [Ru3(dpa)4(CN)2]:: Synthesis, structures, electrochemical and magnetic properties

The neutral, monocationic, and dicationic linear trinuclear ruthenium compounds [Ru-3(dpa)(4)(CN)(2)], [Ru-3(dpa)(4)(CN)(2)][BF4], [Ru-3(dpa)(4)Cl-2]- [BF4], and [Ru-3(dpa)(4)Cl-2][BF4](2) (dpa = the anion of dipyridylamine) have been synthesized and characterized by various spectroscopic techniques. Cyclic voltammetric and spectroelectrochemical studies on the neutral and oxidized compounds are reported. These compounds undergo three successive metal-centered one-electron-transfer processes. X-ray structural studies reveal a symmetrical Ru-3 unit for these compounds. While the metal-metal bond lengths change only slightly, the metal-axial ligand lengths exhibit a significant decrease upon oxidation of the neutral complex. The electronic configuration of the Ru-3 unit changes as the axial chloride ligands are replaced by the stronger "pi-acid" cyanide axial ligands. Magnetic measurements and H-1 NMR spectra indicate that [Ru-3(dpa)(4)Cl-2] and [Ru-3(dpa)(4)Cl-2][BF4](2) are in a spin state of S = 0 and [Ru-3-(dpa)(4)Cl-2][BF4], [Ru-3(dpa)(4)(CN)(2)], and [Ru-3(dpa)(4)(CN)(2)][BF4] are in spin states of S=1/2, 1, and 3/2, respectively. These results are consistent with molecular orbital (MO) calculations.