Molecular solids formed by the self-organisation of dialcohols into hydrogen-bonded ladders

The ability of certain dialcohols to form solid-state structures containing unidirectional hydrogen-bonded ladders has been investigated. Two double-s tranded structures, staircase-ladders and step-ladders, have been identifie d. In each, dialcohol molecules are hydrogen-bonded into linear strands wit h two parallel strands cross-linked through additional hydrogen bonding. St aircase-ladders are made up of (O-H)(n) chains of hydrogen bonds, with the molecules in the two strands out of phase with each other. Step-ladders are formed from (O-H)(4) cycles of hydrogen bonds, with the molecules of the t wo strands in phase. Sixteen examples of staircase-ladder structures and tw elve cases of step-ladder structures were identified by use of the Cambridg e Structural Database. A further three examples, all shown to be staircase- ladders by single-crystal X-ray analysis, were synthesised. Distinct struc tural preferences in ladder formation can be identified. Nearly all stairca se-ladders contain only one type of enantiomer, with the dialcohol building blocks arranged around a twofold screw axis. This type of ladder is thus f avoured for enantiomerically pure compounds. The preferred step-ladder cons truction contains (+)-enantiomers in one strand and (-)-enantiomers in the other, giving two repeating centres of symmetry along the ladder axis. Ther e are, however, many exceptions to this norm. These two ladder types are co mpared with each other and with those formed by organic molecules containin g other hydrogen-bonding functionalities.