Hydrogen-Bonded Ladders formed by Crystalline Diols

Abstract

Certain diol molecules crystallize from solution as unidirectional double-stranded ladders. When these two strands assemble in-phase, a step-ladder arrangement results with the diols linked by (O–H)₄ cycles of hydrogen bonds. Using racemic diol samples, the preferred arrangement has two enantiomerically pure strands of opposite handedness. If the two strands assemble out-of-phase, a staircase-ladder results where the molecules are connected by a hydrogen-bonded (O–H)_n chain. The preferred arrangement contains enantiomerically pure diol molecules surrounding a 2₁ screw axis. If a racemic diol is used then either the crystals contain both (+)- and (–)-ladders or, alternatively, self-resolution occurs to yield a conglomerate. New diols (7)–(9) were synthesized and an X-ray investigation confirmed the prediction that these would produce further double-stranded ladders. These structures revealed new variants of the staircase-ladder where both enantiomers are present, inclusion compounds are formed, or crystallographically independent diol molecules are involved.

Manuscript received: 27 August 2001.

Final version: 5 November 2001.