Phenol hemihydrate: redetermination of the crystal structure by neutron powder diffraction, Hirshfeld surface analysis and characterization of the thermal expansion.

Phenol hemihydrate, CHOH·0.5HO, crystallizes in the space group , = 8. The previously published crystal structure [CSD refcode PHOLHH; Meuthen & von Stackelberg (1960 ▸). . , 387-390] is shown to be incorrect. Pairs of phenol mol-ecules, related by an inversion centre, are bridged by one water mol-ecule O-H⋯O hydrogen bonds; an extended (8) hydrogen-bonded motif links these inversion dimers into chains parallel to the axis. Packing of the chains is achieved by weaker T-shaped C-H⋯π inter-actions between nearest neighbour phenol mol-ecules in the plane. Analysis of the thermal expansion and parameterization with a Debye model in terms of the linear elastic moduli shows that the axis is ∼3 times stiffer than the two orthogonal directions.