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

The Fe(CO)(n)(+) geometries are optimized using second-order Moller-Pl esset (MP2) perturbation theory, the modified coupled-pair functional (MCPF) approach, and density functional theory (DMT) The Becke-Lee-Yan g-Parr (BLYP) functional yields very poor results, while a semiempiric al exchange-correlation functional works very well. Fe(CO)(5)(+) has a doubler ground state, while Fe(CO)(n)(+) for n = 1-3 have quartet gro und states. For Fe(CO)(4)(+) the doublet and quartet states are too cl ose in energy to definitively determine the ground state. The calculat ions show that the small third CO binding energy is not due to a chang e 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 agre e best with the revised values of Distefano.