Solvent effect on hydrogen bonded ammonia-hydrogen halide complexes: continuum medium versus cluster models

The influence of water and dinitrogen environment on the structures of hydrogen bonded XH-NH3 (X = F, Cl, and Br) complexes has been investigated using the self-consistent isodensity polarizable continuum solvent model (SCI-PCM) with two values of dielectric constants, 1.5 and 78.0, respectively. The geometrical parameters, along with the interaction energies as well as harmonic frequencies were calculated at the B3M-LYP/6-311 + + G(d,p) level of theory. The results from dielectric continuum model were compared with those obtained by traditional supermolecule approach. In order to model the proton transfer in M-NH3 systems by supermolecular approach, one should add from two to four explicit water or dinitrogen molecules to the calculations. The dielectric continuum model provides similar effect using less effort. As our results shown, the SCI-PCM model, where a solvent is treated as a continuum medium, reproduces quite accurately the molecular properties of investigated medium strong hydrogen bonded systems both with dinitrogen and water environment. In order to represent solvent effects on hydrogen-bonded complexes with less acidic HX subunit it is necessary to take explicit solvent molecules into account. (C) 2000 Elsevier Science Ltd. All rights reserved.