Theoretical determination of δ in 18+δ organometallic complexes

The 19-electron organometallic complexes [Co(CO)3(L2)] (L2=2,3-bis phosphino maleic anhydride), [Co(CO)2(PH3)(L2)], [Fe(CO)3(L2)]− and [ReBr(CO)3(L2)]− were studied theoretically at the B3LYP level. The SBKJC effective core potentials and their associated basis sets were used for metals and the 6-31G(d) basis set was used for all other elements. The theoretically calculated geometries are compared with experiment, where known. The results reveal that the 19th electron is predominantly distributed over the chelating ligand, although partially localized onto the metal fragment, showing 18+δ character. Two different methods, calculated IR-frequencies and natural atomic charges, were used to determine the value of δ. The computed δ values are compared with the available experimental data.