An analysis of electron donor-acceptor complexes: H2O center dot F-2, H2O center dot Cl-2, and H2O center dot ClF

An extended geminal model has been applied to study the electron donor-acceptor complexes H2O . F-2, H2O . Cl-2 and H2O . ClF. By adopting a [9s, 6p, 4d, 2f/8s, 5p, 4d, 2f/4s, 3p, 1d] contracted Gaussian-type basis set, the equilibrium O-X (X nearest halogen atom) distances are predicted to be 2.69, 2.84, and 2.60 Angstrom, and the binding energies to be 5.86, 12.51, and 20.24 kJ/mol for the complexes H2O . F-2, H2O . Cl-2, and H2O . ClF, respectively. The halogen molecule is situated in the plane of the H2O molecule in the H2O . F-2 complex, whereas it points approximately toward a lone pair of the O atom in the H2O . Cl-2 and H2O . ClF complexes. The charge centroid of the corresponding lone pair geminal is moved considerably toward the halogen molecule as a result of the complex formation in the two latter complexes. Two slightly different decomposition schemes for the potential are considered, For the equilibrium structures the Coulombic interaction between the distorted monomers has the largest magnitude within the primary decomposition scheme, and the potential is not very different from the intermolecular correlation energy.