Probing the hydrogen bond through experimental charge densities

Abstract

Experimental charge density analysis has been carried out by using low-temperature X-ray diffraction data on molecular crystals exhibiting a variety of hydrogen bond interactions. The various types of hydrogen-bonded interactions examined include O-H···O, N-H···O, C-H···O, O-H···N, N-H···N, N-H···S and C-H···S bonds. Static deformation density maps reveal depletion of electron density in the hydrogen-acceptor (H···A) regions. While the total density and the Laplacian at the H···A critical points exhibit an exponential dependence on the H···A distance, the positive curvature of the density, λ₃, closely follows the exponential relation with a considerably better correlation factor. The relation derived based on the data for 218 hydrogen bonds of various types is given by 0.47×10³ exp(−2.5×d_H···A).