Photoactivity and UV absorption spectroscopy of RCo(CO)4 (R = H, CH3) organometallic complexes

The photoactivity of RCo(CO)4 (R = H, CH3) complexes has been investigated and compared by means of state correlation diagrams connecting the low-lying singlet (1)E (d(Co) --> sigma*(Co-R) and d(Co) --> pi*(CO)) and (1)A1 (d(Co) --> pi*(CO)) electronic states accessible through UV irradiation, and the low-lying triplet states ((3)E and (3)A1), to the corresponding states of the primary products R + Co(CO)4 and CO(ax) + RCo(CO)3. The electronic absorption spectra have been calculated by time-dependent wave packet propagations on two-dimensional potential energy surfaces describing both channels of dissociation, namely the homolysis of the R-Co and the CO(ax)-Co bonds. It is shown that the absorption spectrum of HCo(CO)4 is characterized by two peaks; the most intense peaks for each set are located respectively at 42,659 and 45,001 cm(-1). The CH(3)Co(CO)4 absorption spectrum also gives two sets of signals with maximum intensities found at 42,581 and 51,515 cm(-1). These bands for both molecules are assigned to the two metal-to-ligand-charge-transfer (MLCT; d(Co) --> pi*(CO)) states. Three photoactive states have been determined in both molecules, namely the singlet metal-to-sigma-bond-charge-transfer (MSBCT) states (a(1)E and b(1)E), simultaneously dissociative for both the homolysis of CO and the R-Co bond, and the (3)A1 (sigma(Co-R) --> sigma*(Co-R)), dissociative along the R-Co bond.