Electronic Structures of Ligand Bridged Ruthenium and Cobalt Binuclear Complexes

Bridged superoxo and peroxodecaamminedicobalt complexes have been investigated using electronic room and low temperature spectroscopy. Assignments for these spectra have been proposed. The most important feature in the superoxo spectra is a low energy metal ligand, Co → O2-, charge transfer transition of moderate intensity. Both the superoxide and peroxide ions have been assigned positions in the spectrochemical series. The Dq of superoxide is very close to ammonia, while the Dq of peroxied is between NCS- and H2O. These results have been used to eliminate Fe(III) - O2- as possible model for oxyhemoglobin. Cyano bridged dicobalt and mixed iron-cobalt dimers have been looked at, and their spectra assigned as simple super-positions of their component parts. A series of 4+, 5+ and 6+ µ-pyrazinedecaamminediruthenium compounds have been investigated. Magnetic susceptibilities of the 5+ and 6+ compounds were measured and analyzed, assuming a tetragonally distorted d5 ion. Values for the tetragonal field, delocalization, and spin-orbit coupling parameters have been obtained. The 5+ compound gives an ESR signal at room temperature, a result not usually obtained for d5 Ru(III) salts. Electronic spectra were looked at for the ruthenium pyrazine dimers. The interesting 1570 nm band was found to be temperature independent, indicating an orbitally allowed transition. The origin of this band is discussed. A molecular orbital description of these compounds is suggested. The near IR transition is explained as a b3u (xz + xz) → b2g (xz - xz) d-d transition. The applicability of the Marcus Hush theory of electron transfer to the 5+ cation is discussed. The crystal structure of µ-nitrogendecaamminediruthemium(II) was determined. The Ru-N-N-Ru linkage is linear, and the N-N distance was found to be 1.124 Å, - only slightly longer than that in free nitrogen. An approximate molecular orbital scheme is given which assumes back donation of electrons from ruthenium d orbitals to the π*N2 orbital.