Electron densities in hydrogen bonds: lizardite-1T
European Journal of Mineralogy Volume 9 Number 4 (1997), p. 811 - 820
published: Jul 23, 1997
manuscript accepted: Feb 10, 1997
manuscript received: Apr 4, 1996
ArtNo. ESP147050904012, Price: 29.00 €
Abstract Charge densities within hydrogen bonds (HB) of the l: l sheet silicate lizardite (Mg3Si2O5(OH)4) were investigated by the periodic Hartree-Fock method using a large basis set. The difference electron density map (DEDM) provides a good understanding of the nature of the bonding, displaying a picture characteristic of the HB which can be used in general to identify effective HBs fingerprints in any structure. Based on the DEDM pattern, an improvement of the existing definition of the hydrogen bond is proposed, describing the rearrangement of the electron density, viz.: An effective hydrogen bond is created when a partial positive charge on the hydrogen atom, raised by its bonding towards an electronegative atom, makes contact with a partical negative charge accumulated by another electronegative atom. The comparison of electron densities within HBs in lizardite and brucite shows that the former represents a simple dipole-to-ion interaction, while the latter shows dipole-to-dipole interaction in a head-to-tail arrangement. The total energy of the HB is 28.121 kJ mol-1 and 4.203-5.728 kJ/mol-1 for lizardite and brucite, respectively. The evaluation of the deformation of the electron density due to the interlayer bonding qualitatively accounts for shifts in OH stretching frequencies in IR spectra.