Theoretical studies on the optimal X (OH)3–H2O (X = N, P, Sb) complexes: Interaction energies and topological analysis of the electronic density

We study the interaction of N (OH)3, P (OH)3 and Sb (OH)3 with a water molecule for which triply hydrogen-bonded complexes have been found. We obtain interaction energies and analyze the electronic density through Atoms-in-Molecules approach. Including the recent result for As (OH)3, MP2 CBS extrapolated interaction energies are 9.37, 10.06, 10.67 and 10.72 kcal/mol for N (OH)3, P (OH)3, As (OH)3 and Sb (OH)3, respectively. CASSCF (6,6)+CASPT2 calculations reveal a multireference character for the complexes yielding interaction energies from 6.4 to 14 kcal/mol. AIM analysis shows three intermolecular bond critical points confirming the hydrogen bonds. NBO atomic charges show reveal the dominant dipole–dipole nature of the intermolecular interactions.