ABINITIO STUDIES OF MOLECULAR-STRUCTURES AND ENERGETICS .4. HEXACOORDINATED NF6- AND CF62- ANIONS

Quantum theoretical computations predicted the structural stabilities of two unique hexacoordinated species, NF6-and CF62-. Both were found to be of Ohsymmetry with six distinct linkages to the central atom. The energies, equilibrium molecular structures, and vibrational frequencies of both species were computed employing the second-order perturbation approximation (MP2) for the energy. These properties were also determined for F2, F3-, CF3-, NF3, CF4, NF4+, and NF5in order to ascertain the thermodynamic stabilities of the hexacoordinate anions and to compare their geometric and electronic structures. CF62-exhibits a free energy about 150 kcal/mol higher than CF4+ 2F-but essentially the same as CF3-+ F2+ F-. NF6-is of lower free energy than NF5+ F-, although nearly the same as NF3+ F2+ F-. Analyses of the distributions of energy and charge in all CFnand NFnspecies showed them to be quite similar. The results were contrasted to the neutral hexalithium compound CLi6, which was shown to exhibit an electronic structure much different from that of NF6-and CF62-. © 1990, American Chemical Society. All rights reserved.