Structure Determination from Powder X-ray Diffraction Data of a New Polymorph of a High-Density Organic Hydrate Material, with an Assessment of Hydrogen-Bond Disorder by Rietveld Refinement

The structural properties of a new polymorph of a material distributed commercially as “hexaketocyclohexane octahydrate” have been determined directly from powder X-ray diffraction data, employing the direct-space genetic algorithm technique for structure solution followed by Rietveld refinement. It is shown that the molecule actually present in the crystal structure is dodecahydroxycyclohexane (C6(OH)12) rather than hexaketocyclohexane (C6O6). This assignment is also confirmed from high-resolution solid-state 13C NMR data. The crystal structure contains two molecules of water per molecule of C6(OH)12. In the asymmetric unit, there are 16 hydrogen-bond donor groups (O–H bonds) and 14 hydrogen-bond acceptors (oxygen atoms), leading to multiple permutations for intermolecular hydrogen-bonding arrangements. Detailed analysis of the results from Rietveld refinement suggests that a disordered model provides the most appropriate description of the hydrogen-bonding arrangement, in which the hydrogen atom of each OH group of C6(OH)12 and the hydrogen atoms of each water molecule are distributed among several different intermolecular O–H···O hydrogen bonds. The density of this material (1.926 g cm–3 at ambient temperature) is one of the highest ever reported densities among organic materials that contain no elements heavier than oxygen.