Stochastic polarity formation in molecular crystals, composite materials and natural tissues

Investigation of an Unusual Crystal Habit of Hydrochlorothiazide Reveals Large Polar Enantiopure Domains and a Possible Crystal Nucleation Mechanism

The observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro-XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit-cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.

Vapour growth, morphology, absolute structure and pyroelectric coefficient of meta-nitroaniline single crystals

The growth speed of (hkl) faces in the vapour phase, the absolute structure obtained by X-ray crystallography, and the value and the sign of the pyroelectric coefficient of meta-nitroaniline (mNA) were analysed in detail. The in situ observation of morphologically well developed faces of several mNA crystals growing in evacuated ampoules reveals no pronounced growth speed anisotropy for polar faces defining the unique axis 2 of the mm2 group. Scanning pyroelectric microscopy confirms mono-domain mNA crystals. X-ray measurements in the space group Pca21 show that the molecular planes coincide with the {\bar 211} and {\bar 2\bar 1\bar 1} faces, and the nitro groups cover the {201} face in the opposite direction to the crystal tip, characterizing the polar habitus studied here. At room temperature, the sign of the pyroelectric coefficient is positive for a measured effective value of 6.3 µC m−2 K−1, in good agreement with values reported by other authors. From previous elastic and piezoelectric published data, the secondary pyroelectric effect was calculated to be positive and far greater than the effective one, yielding a negative value for the primary pyroelectric coefficient.

Seventy years of publications

The IUCr, which was established 70 years ago, will be celebrating 70 years of peer-reviewed publications in 2018. Three of its journals, including IUCrJ, are ranked in the top 10% of all journals, with the remainder striving to be in the top quartile in the next five years.