Alternative hydrogen bonding modes employed by a helical tubuland diol host molecule

Abstract

The racemic alicyclic diol 3 yields different types of hydrogen bonded inclusion structures depending on the recrystallisation solvent used. Non-protic guests are enclosed within parallel tubes through formation of the helical tubuland structure in chiral space group P3₁21 (or P3₂21). This arrangement contains the molecules of 3 surrounding threefold screw axes. Racemic hydrogen bonded 1 ∶ 1 co-crystalline adducts are formed in space group P2₁/c on crystallisation of 3 from mono-functional alcohols or carboxylic acids. In these, the alcohol molecules contribute one hydroxy group to an intermolecular pseudo-threefold screw arrangement with a ⋯O–H⋯O–H⋯O–H⋯ hydrogen bonded repeat unit, while the carboxylic acid groups participate in the closely-related ⋯O–H⋯OC(R)–O–H⋯O–H⋯ repeat unit. The carboxylic acid functionality thus behaves like an extended alcohol hydroxy group in these compounds. In contrast, crystallisation of 3 from ethane-1,2-diol yields a novel 4 ∶ 3 network compound in space group P. This material assembles using hydroxy group hydrogen bonded ladders and (O–H)₆ cycles. The X-ray structures of these various materials are described and compared in crystal engineering terms.