EXPERIMENTAL AND THEORETICAL INVESTIGATION OF THE ELECTRONIC-STRUCTURE OF 2 ISOELECTRONIC BINUCLEAR CLUSTERS - UV-PES AND DV-X-ALPHA STUDY OF RU2(CO)6[MU,MU'-N(R)CH2CH2N(R)] AND FERU(CO)6[MU,MU'-N(R)CH2CH2N(R)]

The electronic structure of two novel binuclear complexes, containing the diradical 6e-bonded mu,mu'-1,2-ethanediyldiamido [mu,-mu'-N(i-Pr)CH2CH2N(i-Pr), hereafter R-EDA] ligand, is discussed by using SCF first-principle discrete variational (DV) X-alpha calculations and gas-phase UV-photoelectron (PE) spectroscopy. The nitrogen-metal interaction has been compared with that computed, within the same theoretical framework, for different isoelectronic complexes where the unsaturated 1,4-diaza-1,3-butadiene [N(i-Pr) = CHCH = N(i-Pr), hereafter R-DAB] ligand acts either as an 8e (sigma-N, sigma-N', eta-2-CN, eta-2-CN') or a 4e (sigma-N, sigma-N' chelating) donor. Such a comparison indicates that different coordinative situations correspond to significantly different bonding schemes, pointing out that the versatile coordination behavior of the saturated (R-EDA)/unsaturated (R-DAB) ligand is a consequence of its "electronic flexibility". In particular, two interesting and unexpected points come out from the analysis of theoretical data. First of all, in both Ru2(CO)6[mu,mu'-N(R)CH2CH2N(R)] and FeRu(CO)6[mu,mu'-N(R)CH2CH2N(R)] complexes, the main source of the M-N bonding is pi in nature, while sigma contributions are very poor. Second, in the former compound, a metal-based t2g-like level actively participates in the Ru-N interaction. Transition-state ionization energies reproduce excellently the experimental PE pattern of the homobinuclear complex while some discrepancy is present between computed and experimental ionization energies in the heterobinuclear one.