Bonding properties of a novel inorganometallic complex, Ru(SnPh(3))(2)(CO)(2)(iPr-DAB) (iPr-DAB=N,N'-diisopropyl-1,4-diaza-1,3-butadiene), and its stable radical-anion, studied by UV-Vis, IR, and EPR spectroscopy, (spectro-) electrochemistry, and density functional calculations

Ru(SnPh(3))(2)(CO)(2)(iPr-DAB) was synthesized and characterized by UV-vis, IR, H-1 NMR, C-13 NMR, Sn-119 NMR, and mass (FAB(+)) spectroscopies and by single-crystal X-ray diffraction, which proved the presence of a nearly linear Sn-Ru-Sn unit. Crystals of Ru(SnPh(3))(2)(CO)(2)(iPr-DAB). 3.5C(6)H(6) form in the triclinic space group P1 in a unit cell of dimensions a = 11.662(6) Angstrom, b = 13.902(3) Angstrom, c = 19.643(2) Angstrom, alpha = 71.24(2)degrees, beta = 86.91(4)degrees, gamma = 77.89(3)degrees, and V = 2946(3) Angstrom(3). One-electron reduction of Ru(SnPh(3))(2)(CO)(2)(iPr-DAB) produces the stable radical-anion [Ru(SnPh(3))(2)(CO)(2)(iPr-DAB)](.-) that was characterized by IR, and UV-vis spectroelectrochemistry. Its EPR spectrum shows a signal at g = 1.9960 with well resolved Sn, Ru, and iPr-DAB (H, N) hyperfine couplings. DFT-MO calculations on the model compound Ru(SnH3)(2)(CO)(2)(H-DAB) reveal that the HOMO is mainly of sigma(Sn-Ru-Sn) character mixed strongly with the lowest pi* orbital of the H-DAB ligand. The LUMO (SOMO in the reduced complex) should be viewed as predominantly pi*(H-DAB) with an admixture of the sigma(Sn-Ru-Sn) orbital. Accordingly, the lowest-energy absorption band of the neutral species will mainly belong to the sigma(Sn-Ru-Sn)-->pi*(iPr-DAB) charge transfer transition. The intrinsic strength of the Ru-Sn bond and the delocalized character of the three-center four-electron Sn-Ru-Sn sigma-bond account for the inherent stability of the radical anion.