Theoretical study of HmGaPNn. Characteristics of gallium-phosphorus multiple bonds

Equilibrium structures, harmonic vibrational frequencies, and relative ener gies of 12 neutral or ionic gallium phosphorus hydrides are reported and an alyzed. Hartree-Fock (HF), Becke's three-parameter exchange with Lee, Yang, and Parr correlation DFT (B3LYP), and second-order Moller-Plesset (MP2) ca lculations using the 6-311++G(d,p) basis set were performed on all molecule s. Gallium-phosphorus bond energies were determined based on the MP2/6-311+G(d,p) calculations of the equilibrium structures and of their decompositi on products. We find that the gallium-phosphorus double bond is, perhaps, s urprisingly strong (i.e., 93 +/- 2 kcal/mol) and short (2.128 +/- 0.018 Ang strom); CCSD(T)/6-311 ++G(3df,3dp) single-point calculations on HGaPH corro borate the prediction of a strong double bond. Bond order analysis of some of the neutral species revealed that these compounds satisfy a Pauling rela tion between bond length and bond order, and also bond energy and bond orde r. CASSCF(8\8) calculations on H2PGa show that the surprising weakness of t he phosphorus-gallium bond in this compound can be understood in terms of a n occupied antibonding a orbital. Comparisons of the B3LYP method to NF and MP2 methods reveal that the B3LYP DFT method, in most cases, gives relativ e energies and equilibrium structures in substantial agreement with the MP2 method for these types of compounds.