Structures and Bond Energies of the Transition-Metal Carbonyls M(CO)₅ (M = Fe, Ru, Os) and M(CO)₄ (M = Ni, Pd, Pt)

The equilibrium geometries of the transition-metal carbonyls M(CO)_n (M = Fe, Ru, Os; n = 4, 5) and M(CO)_n (M = Ni, Pd, Pt; n = 3, 4) are calculated at the MP2 level using effective core potentials for the metals and 6-31G(d) basis sets for C and O. The first ligand dissociation energies of the saturated metal carbonyls are theoretically predicted using the coupled cluster theory (CCSD(T)) approach. The calculated dissociation energies ΔH²⁹⁸ (Fe-(CO)₅, 46.5 kcal/mol; Ru(CO)₅, 30.9 kcal/mol; Os(CO)₅, 42.4 kcal/mol; Ni(CO)₄, 24.4 kcal/ mol; Pd(CO)₄, 9.6 kcal/mol; Pt(CO)₄, 13.0 kcal/mol) indicate that the second-row transition elements have the weakest carbonyl bond.