HIGH-NUCLEARITY RUTHENIUM CARBONYL CLUSTER CHEMISTRY .5. LOCAL-DENSITY FUNCTIONAL, ELECTRONIC SPECTROSCOPY, MAGNETIC-SUSCEPTIBILITY, AND ELECTRON-PARAMAGNETIC-RESONANCE STUDIES ON (CARBIDO)DECARUTHENIUM CARBONYL CLUSTERS

Electronic spectra of ''giant tetrahedral'' decaruthenium cluster anio ns are consistent with a HOMO-LUMO gap of less than or equal to 1.2 eV , with intense transitions assigned to M-M --> CO 2 pi* at high energ y and weak transitions assigned to M-CO pi --> M-CO sigma at low ener gy; the former are relatively insensitive to increasing phosphine subs titution or cluster core charge, whereas the latter show some ligand d ependence. The first diffuse reflectance UV-vis-MR spectra of metal ca rbonyl clusters have been obtained; spectra of )(NC5H5)(2)][Ru-10(mu-H )(mu(6)-C)(Co)(23)(PPh(3))] and [ppn](2)[Ru-10(mu(6)-C)(CO)(24)] conta in broad absorptions extending to a lambda(onset) of 1300 nm with abso rption maxima corresponding to those of the solution spectra superimpo sed. Local density functional (LDF) calculations support the optical s pectra assignments and predict a triply degenerate HOMO approximately 1.3 eV below the LUMO. Magnetic susceptibility data for )(4)(NC5H5)(2) ][Ru-10(mu-H)(mu(6)-C)(CO23(PPh(3))] show a temperature independent su sceptibility chi(m) of +1384 +/- 10 x 10(-6) cm(3) mol(-1) (diamagneti c correction including decaruthenium valence electrons), arising from Van Vleck paramagnetism; unlike related decaosmium clusters and lower nuclearity ruthenium clusters, no temperature dependent component of t he susceptibility exists. Electron paramagnetic resonance (EPR) invest igations on three decaruthenium cluster anions reveal a temperature-in dependent paramagnetic (TIP) signal which does not derive from solid-s tate packing effects, the nature of the cation, the presence of impuri ties such as colloids, particles, or oxides, or incipient metallic cha racter (''mesometallic'' behavior); this EPR signal, the first reporte d TIP resonance from a carbonyl cluster, is assigned to the presence o f radical decaruthenium clusters due to oxidation of the cluster anion s. Unlike high-nuclearity clusters examined previously by EPR, no temp erature-dependent response was found for )(CO)(4)(NC5H5)(2)][Ru-10(mu- H)(mu(6)-C)(CO)(24)]. The electronic spectroscopy, magnetic susceptibi lity data, EPR studies, and LDF calculations are consistent with these high-nuclearity carbonyl clusters having; ''molecular'' rather than ' 'mesometallic'' character.