SUCCESSIVE BINDING-ENERGIES OF FE(CO)(5)(+)

The Fe(CO)(n)(+) geometries are optimized using second-order Moller-Plesset (MP2) perturbation theory, the modified coupled-pair functional (MCPF) approach, and density functional theory (DMT) The Becke-Lee-Yang-Parr (BLYP) functional yields very poor results, while a semiempirical exchange-correlation functional works very well. Fe(CO)(5)(+) has a doubler ground state, while Fe(CO)(n)(+) for n = 1-3 have quartet ground states. For Fe(CO)(4)(+) the doublet and quartet states are too close in energy to definitively determine the ground state. The calculations show that the small third CO binding energy is not due to a change in spin state from a quarter for Fe(CO)(2)(+) to a doublet for Fe(CO)(3)(+), but instead is due to the loss of sdo hybridization when the third CO is added. The theoretical successive CO binding energies agree best with the revised values of Distefano.