Crystal packing in vicinal diols C n H m (OH)2

Abstract

The O—H...O bonds in vic-diols C n H m (OH)2 have been studied using data retrieved from the Cambridge Structural Database. About half of these diols form complete, or almost complete, sets of intermolecular O—H...O bonds (i.e. two satisfied donors per molecule). For this half of the structures the frequencies of high-symmetry space groups and of structures with Z′ > 1 (more than one molecule in the asymmetric unit) are substantially elevated. The most common motif among fully bonded structures is an R_{\rm{2}}^{\rm{2}} {\rm{(10)}} dimer, which can be linked in a variety of ways to form one-, two- or even three-dimensional patterns. Most of the other half of the vic-diols form simple O—H...O chains in which each OH group participates in only one intermolecular hydrogen bond. The space-group frequencies for this second group of structures are unexceptional. The most important factor determining the extent of O—H...O bond formation is the degree of substitution of the vic-diol. The spatial segregation of OH groups that is necessary for the formation of O—H...O bonds is found to make the dense filling of space more difficult because the intermolecular spacings that are appropriate for the O—H...O bonds may be inappropriate for the rest of the molecule.