Crystal packing in vicinal diols CnHm(OH)2

The O-H...O bonds in vic-diols CnHm(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-2(2)(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.