MN-2)(N) AND ZN+(H-2)(N) CLUSTERS - INFLUENCE OF 3D AND 4S ORBITALS ON METAL-LIGAND BONDING((H)

Equilibrium methods were used to measure Delta G(T) degrees as a funct ion of temperature for the sequential clustering of up to six H-2 liga nds to the Mn+(3d(5)4s(1 7)S) and Zn+(3d(10)4s(1 2)S) core ions. The r esulting binding energies are by far the lowest in the first-row trans ition metal series, ranging from 3.75 kcal/mol for Zn+(H-2) and 1.9 fo r Mn+(H-2) down to 1-1.5 kcal/mol for the highly ligated clusters. Den sity functional theory calculations using the B3-LYP parametrization w ere performed to provide information on structures, vibrational freque ncies, and orbital populations, which, together with the experimental data, give insight into the types of bonding that are present. It was found that the repulsion between the singly occupied 4s orbital and th e H-2 sigma orbital accounts for the low binding energies and that the 4p orbitals play a key role in reducing this repulsion.