An analysis of electron donor-acceptor complexes: BH 3CO and BH 3NH 3

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An extended geminal model has been applied to study the electron donor-acceptor (EDA) complexes BH 3·CO and BH 3·NH 3. By adopting a [7s,4p,2d/4s,2p] contracted Gaussian type basis set and the numerical model EXRHF3, a complete geometry optimization of the complexes is performed for C 3v geometries. The calculated binding energies are 90.5 and 118.1 kJ/mol for BH 3·CO and BH 3·NH 3, respectively. The calculated equilibrium distance B-C distance is 1.558 Å (1.54 Å) and the B-N distance is. 1.666 Å (1.657 Å/1.672 Å), experimental values in parenthesis. The changes in the one-electron density during the formation of the complexes are analyzed in terms of charge centroids and charge ellipsoids of the (localized) geminal densities. The intermolecular potential is decomposed into a sum of distortion energies for the subsystems and the interaction energy between the distorted subsystems. The latter term is decomposed into a Coulombic, exchange and correlation part. The Coulombic component is further partitioned into an electrostatic and induction component. The strongly bonded EDA complexes BH 3·CO and BH 3·NH 3 are compared with the hydrogen bonded systems (HF) 2, H 2O·HF and (H 2O) 2, and the weakly bonded EDA complexes F 2·NH 3, Cl 2·NH 3 and ClF·NH 3. For all complexes the Coulombic term is the dominanting attractive term. The partitioning of the Coulombic term shows that the induction component is larger in magnitude than the electrostatic one for all the systems.