Nitrogen trifluoride as a bifunctional Lewis base: implication for the adsorption of NF3 on solid surfaces

The structure, stability, and thermochemistry of isomeric adducts between NF3 and the Lewis acids BH3.nFn (n = 0.3) have been investigated at the coupled-cluster and at the Gaussian-3 (G3) level of theory. At the CCD/cc-pVDZ level both the nitrogen- and the fluorine-coordinated structures of all BH3.nFn.(NF3) (n = 0.3) adducts were characterized as true minima on the potential energy surface, thus providing the first theoretical evidence for the behavior of NF3 as a bifunctional Lewis base when interacting with neutral Lewis acids. At the G3 level, and 298.15 K, including the contribution of the entropy term, the H3B.NF3 adduct is predicted to be more stable than H3B.F.NF2 by 4.3 kcal mol.1; this free energy difference is 3.7 kcal mol.1 at the CCSD(T)/ccpVTZ// CCD/cc-pVDZ level of theory. Conversely, at the lat- ter computational level, the fluorine-coordinated isomers of the BH2F.(NF3), BHF2.(NF3), and BF3.(NF3) adducts are practically degenerate with the nitrogen-coordinated ones. BH3.nFn.(NF3) (n = 0.3) complexes feature typical bond dissociation energies of ca. 1.2 kcal mol.1, and are predicted to be thermodynamically stable only at low temperatures. However, the appreciable influence of the basis set superposition error (BSSE) prevents a quantitative assessment of these small computed dissociation energies. Finally, we briefly discuss the implications of our calculations for the adsorption of NF3 on solid surfaces.