Hydrogen bonds in solid hydroxides, a bond valence approach

The bond valences SOH due to the O-H bonds of OH- ions in solids have been calculated indirectly from intermolecular (HO)-O-... distances, viz. those within the Wigner Seitz cell around the respective hydrogen atom, by using the equation SOH 1 - Sigmas(H)...(O). The bond valences thus derived are an excellent measure of the strength of O-H bonds [J. Mol. Struct. 351 (1995) 205]. This is shown by their almost linear correlation with the wave numbers of the stretching modes of matrix isolated OD- ions observed with IR or Raman experiments. In the case of very weak or lacking hydrogen bonds, this correlation fails because then other interionic bonding phenomena than hydrogen bonds as metal-oxygen interactions and hydrogen-hydrogen repulsion etc. gain in importance or dominate finally and, hence, partly or fully determine the wave numbers of the OD stretching modes, which, however, still remain a measure of the respective bond strengths. The relation of the distances r(OH), the bond valences SOH, and the stretching modes v(OD) of both free, gaseous OH- ions and H2O molecules and those embedded in crystalline matrices is discussed. (C) 2003 Elsevier Science B.V. All rights reserved.