A DENSITY-FUNCTIONAL STUDY ON THE STRENGTH OF THE METAL BONDS IN CO2(CO)8 AND MN2(CO)10 AND THE METAL HYDROGEN AND METAL-CARBON BONDS IN R-MN(CO)5 AND R-CO(CO)4

Density functional studies have been carried out on the binuclear complexes (CO)4Co-Co(CO)4 and (CO)5Mn-Mn(CO)5 as well as the derivatives R-Mn(CO)5 [R = H, CH3, CH2F, CHF2, CF3, C(O)CH3, and C(O)H] and R-CO(CO)4 [R = H, CH3]. The density functional calculations were based on the local density approximation (LDA) with nonlocal corrections for exchange and correlation included self-consistently (LDA/NL). The geometries optimized by LDA/NL agrees well with experimental structures. The deviations are 0.015 angstrom for M-M and M-ligand distances and 2-degrees for ligand-metal-ligand bond angles. The calculated Mn-Mn bond energy of 173 kJ/mol is in good agreement with recent experimental values. The theoretical Co-Co bond energy is 148 kJ/mol, and it is suggested that older experimental estimates (64-88 kJ/mol) for the Co-Co bond enthalpy are too low. The calculated metal-ligand bond energies are in kJ/mol: D(Mn-H) = 288; D(Mn-CH3) = 208; D(Mn-CH2F) = 208; D(Mn-CF2H) = 203; D(Mn-CF3) = 224; D(Mn-C(O)H = 196; D(Mn-C(O)CH3) = 189; D(Co-H) = 283; D(Co-CH3) = 198. The calculated D(Mn-H) and D(Co-H) values agree within 4 kJ mol with the most recent experimental estimates. The D(Mn-R) enthalpies are on the average 20 kJ/mol higher than experiment for R=CH3, CF3, CF3, and C(O)CH3. It is suggested that the experimental estimates for D(Mn-CFH3) and D(Mn-CF2H) are too low.