CALCULATED THERMODYNAMICS OF REACTIONS INVOLVING NO2-DOT-X COMPLEXES (WHERE X=H2O, N-2, AND CO2)(CENTER)

Ab initio molecular orbital calculations have been performed on the NO 2+. X complexes (X=H2O, N-2, and CO2). Optimized geometries and vibrat ional frequencies, as well as computed total energies have been used t o calculate standard enthalpies, entropies, and free energies for the complexing reactions, and ligand-switching reactions between the three molecular complexes. The results obtained have been compared with exp erimental values where available. The following thermodynamic values a re recommended for the association reaction NO2++X-->NO2+. X: Delta H- 298 = -16.8, -4.7, and -7.9 kcal mol(-1) and Delta S-298 = -23.1, -20. 2, and -20.8 cal mol(-1) K-1, for X=H2O, N-2, CO2, respectively. Corre sponding thermodynamic values for the ligand-switching reactions have also been calculated. Minimum energy geometries calculated for NO2+. H 2O and NO2+. N-2 are found to be in agreement with those obtained in p revious theoretical studies. The NO2+. CO2 complex has been studied fo r the first time, and the minimum energy geometry has been shown to be planar and of C-2v geometry. (C) 1997 American Institute of Physics.