Emission spectroscopy of metal-to-ligand-charge-transfer states of HRe(CO)_3(H-dab),model system for alphadiimine rhenium tricarbonyl complexes

摘要

The emission and absorption theoretical spectra of HRe(CO)_3(H-dab)(H-dab=1,4-diaza-1,3-butadiene),model system for a broad class of transition metal carbonyls alphadiimine compounds,have been obtained by means of wave packet propagations on the V(q)(q=[Re-H])CASSCF/MRCI potentials calculated for the electronic ground state and the'MLCT(metal-to-ligand charge-transfer)absorbing state corresponding mainly to a 5d_(Re)->pi_(H-dab)~* excitation.The simulated spectra reproduce the main features of the experimental spectra of this class of complexes,namely one intense absorption band between 20 000 and 25 000 cm~(-1)assigned to this MLCT state and one strong emission band shifted to the red.The contribution of the low-lying bound MLCT triplet states or dissociative sigma-bond-to-ligand-charge-transfer(SBLCT)state is not taken into account in these preliminary simulations.Indeed the main goal is to understand the contribution of the absorbing MLCT state to the radiative process which may compete with the homolytic cleavage of the rhenium-hydrogen bond via the ~3SBLCT state coupled to the absorbing state by spin-orbit(SO).The theoretical time-resolved emission spectrum simulated by wave packet propagation on the same potentials(absorbing ~1'MLCT state and electronic ground state)is also presented.