O. Ga´lveza) and P. C. Go´mezb) Departamento de Quı´mica Fı´sica I, Facultad de Quı´mica, Universidad Complutense de Madrid, 28040 Madrid, Spain L. F. Paciosc) Departmento de Quı´mica y Bioquı´mica, E. T. S. I. Montes, Universidad Polite´cnica de Madrid, 28040 Madrid, Spain ~Received 27 July 2001; accepted 3 October 2001
The variation with the intermolecular distance of features in hydrogen bond ~HB! dimers dependent on the electron density r~r! are studied in four complexes representative of weak/medium HB interactions. Topological properties, energy densities and integrated atomic properties are obtained with r~r! of dimers at B3LYP/6-31111G(d,p) optimized structures obtained upon fully relaxing the geometry of monomers. The dependence of A–H¯B bond properties on intermolecular R(H¯B) distances allows to characterize the nature of the interaction as monomers move nearer from infinite separation. At long distances the interaction is only electrostatic while for separations about 1 Å larger than the equilibrium distance Req , quantum effects arising from r~r! begin to dominate. In the immediate neighborhood of Req the interaction is mainly led by the stabilization of the H-donor due in turn to energy lowering in A and B atoms associated to polarization effects. The mutual penetration of electron densities of donor and acceptor monomers provokes a considerable reduction of atomic volumes for H and B atoms which reveals in the form of redistribution rather than transfer of charge. This range of distances exhibits noncovalent bond features but shortly after, when monomers approximate a few tenths of Å below Req , characteristics typical of covalent interactions begin to appear while the rate of change of all the r~r!-dependent properties increases rapidly. © 2001 American Institute of Physics. @DOI: 10.1063/1.1420749
EFS Comments: Appears to speak to the effect of charge density affecting bond lengths.
