The crystal structure of the α form of quinol

Abstract

The α form of quinol crystallises in the rhombohedral space group R with 54 molecules in each unit cell of hexagonal dimensions a=b= 38.46(2), c= 5.650(3)Å, i.e. three times larger than the cell originally described by Caspari. There are therefore 3 molecules in each asymmetric unit. Two of these are involved in forming two interpenetrating, open, hydrogen-bonded cageworks similar to those found in the structure of β-quinol and capable of clathrating small molecules such as CO₂, N₂, and Ar, whereas the third forms double helices consisting of hydrogen-bonded chains of quinol molecules round three-fold screw axes. The cageworks and helices are hydrogen-bonded together in such a way that the interpenetrating cageworks are connected (unlike the β structure) and the two strands of the double helix are connected. The overall α structure is more dense than the β structure and is the stable form at room temperature.