TY - JOUR
T1 - The unusual phases of anhydrous and hydrated pinacol
AU - Hao, Xiang
AU - Parkin, Sean
AU - Brock, Carolyn Pratt
PY - 2005/12
Y1 - 2005/12
N2 - The structure of highly twinned pinacol (2,3-dimethyl-2,3-butanediol) monohydrate, the existence of which has been known since 1922, has been determined, and the structures of anhydrous pinacol and its two other known hydrates have been reinvestigated. All the phases are unusual. The anhydrous phase [Jeffrey & Robbins (1978). Acta Cryst. B34, 3817-3820] is exceptional among molecular crystals in having molecules located on three different symmetry sites (1, and 2). A hexagonal form of pinacol originally described as a second polymorph [Dahlqvist & Sillanpää (2000). J. Mol. Struct.524, 141-149] has been shown to be a solvate of uncertain composition that is very loosely packed. Pinacol hexahydrate, which was originally reported as tetragonal and highly disordered [Kim & Jeffrey (1970). J. Chem. Phys.53, 3610-3615], appears to be described better as having an orthorhombic structure that is both disordered and twinned; the diffraction pattern at 90 K shows structured diffuse scattering that suggests short-range correlations of disordered molecules. The occurrence of this unusual set of structures is attributed to the combination of the hydrogen-bonding requirements of the pinacol molecule with its small size and limited conformational flexibility.
AB - The structure of highly twinned pinacol (2,3-dimethyl-2,3-butanediol) monohydrate, the existence of which has been known since 1922, has been determined, and the structures of anhydrous pinacol and its two other known hydrates have been reinvestigated. All the phases are unusual. The anhydrous phase [Jeffrey & Robbins (1978). Acta Cryst. B34, 3817-3820] is exceptional among molecular crystals in having molecules located on three different symmetry sites (1, and 2). A hexagonal form of pinacol originally described as a second polymorph [Dahlqvist & Sillanpää (2000). J. Mol. Struct.524, 141-149] has been shown to be a solvate of uncertain composition that is very loosely packed. Pinacol hexahydrate, which was originally reported as tetragonal and highly disordered [Kim & Jeffrey (1970). J. Chem. Phys.53, 3610-3615], appears to be described better as having an orthorhombic structure that is both disordered and twinned; the diffraction pattern at 90 K shows structured diffuse scattering that suggests short-range correlations of disordered molecules. The occurrence of this unusual set of structures is attributed to the combination of the hydrogen-bonding requirements of the pinacol molecule with its small size and limited conformational flexibility.
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U2 - 10.1107/S0108768105031356
DO - 10.1107/S0108768105031356
M3 - Article
C2 - 16306676
AN - SCOPUS:33745283946
SN - 0108-7681
VL - 61
SP - 689
EP - 699
JO - Acta Crystallographica Section B: Structural Science
JF - Acta Crystallographica Section B: Structural Science
IS - 6
ER -