ELECTRONIC-STRUCTURE AND DISSOCIATION-ENERGY OF THE MOLYBDENUM-TO-MOLYBDENUM TRIPLE BOND
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Generalized molecular orbital (GMO) and configuration interaction (CI) calculations are reported for the series N2, P2, As2, Sb2, and Mo2H6 in a large Gaussian basis set. Similar calculations are reported for Mo2H6 and Mo2(NH2)6 in a smaller Gaussian basis set. The potential energy curve for Mo2H6 at the GMO-CI level has a minimum at 2.194 in excellent agreement with the Mo-Mo distance in a range of systems: Mo2(OCH2CMe3)6 at 2.222 , Mo2(NMe2)6 at 2.214 , and Mo(CH2SiMe2)6 at 2.167. By comparing the calculated dissociation energies of the triply bonded diatomics and Mo2H6, we predict a dissociation energy for the molybdenum-to-molybdenum triple bond of 284 kJ mol-1. The results indicate the importance of including the differential correlation energy, which in Mo2H6 contributes 70 kJ mol-1 to the dissociation energy. We find that the larger basis set increases the calculated dissociation energy by 40 kJ mol-1. When we change the hydride ligand of Mo2H6 to an amino ligand in Mo2(NH2)6, the dissociation energy increases 117 kJ mol-1. A significant fraction of this increase is due to the -donating ability of the NH2 ligand, which results in an expansion of the Mo orbitals and a stronger bond. The relationship between the donor strength of the ligand and the expansion of the Mo orbitals may be responsible for much of the variation in the Mo-Mo triple-bond lengths. 1983, American Chemical Society. All rights reserved.
