Synthesis, Structure and Magnetic and Electrochmical Properties of Tetrakis(benzamidato)diruthenium(II,III) Tetrafluoroborate

A lantern-type diruthenium(II,III) complex [Ru2(HNOCPh)4(BF4)(H2O)] was prepared from [Ru2(HNOCPh)4Cl]n by removal of the axial chlorido-bridge using AgBF4 in THF. The room temperature magnetic moment (per Ru25+ unit) of [Ru2(HNOCPh)4(BF4)(H2O)] is 3.84 μB, which is similar to that (4.15 μB) of [Ru2(HNOCPh)4Cl]n, for which magnetic measurement was newly performed in this study. These results indicate that both of the complexes have a spin state of S = 3/2, although temperature-variable (VT) magnetic moments (2–300 K) showed that considerable antiferromagnetic interaction (zJ = −2.8 cm−1) exists through the axial chlorido-bridge for [Ru2(HNOCPh)4Cl]n, but such a large interaction (zJ = −0.08 cm−1) does not exist for [Ru2(HNOCPh)4(BF4)(H2O)], where the large zero-field splitting D = 61 cm−1 is operative for both complexes, like other lantern-type diruthenium(II,III) complexes. The X-ray single-crystal structure analysis of [Ru2(HNOCPh)4(BF4)(H2O)]·2(acetone) showed that the axial positions of the complex were occupied by a fluorine atom of the BF4− ion and an oxygen atom of the water molecule, with distances of Ru-Fax = 2.3265(19) A and Ru-Oax = 2.280(2) A, respectively. The Ru-Ru bond distance was 2.2793(4) A, which is shorter than those (2.295(2) and 2.290(2) A) reported for [Ru2(HNOCPh)4Cl]n. The quartet ground states (S = 3/2) were reasonably interpreted for [Ru2(HNOCPh)4(BF4)(H2O)] and [Ru2(HNOCPh)4Cl]n, as well as the theoretically modeled complex cation [Ru2(HNOCPh)4]+, by DFT calculation results. A Ru26+/Ru25+ redox couple was observed at 1.12 V (vs. SCE) for [Ru2(HNOCPh)4(BF4)(H2O)] in dichloromethane containing Bu4NPF6 as electrolyte.