Archan Dey

The development of morphology and structure in hexagonal vaterite

Inspired by the remarkable shapes and properties of CaCO(3) biominerals, many studies have investigated biomimetic routes aiming at synthetic equivalents with similar morphological and structural complexity. Control over the morphology of CaCO(3) crystals has been demonstrated, among other methods, by the use of additives that selectively allow the development of specific crystal faces, while inhibiting others. Both for biogenic and biomimetic CaCO(3), the crystalline state is often preceded by an amorphous precursor phase, but still limited information is available on the details of the amorphous-to-crystalline transition. By using a combination of cryoTEM techniques (bright field imaging, cryo-tomography, low dose electron diffraction and cryo-darkfield imaging), we show for the first time the details of this transition during the formation of hexagonal vaterite crystals grown in the presence of NH(4)(+) ions. The formation of hexagonal plate-like vaterite occurs via an amorphous precursor phase. This amorphous phase converts into the crystalline state through a solid state transformation in which order and morphology develop simultaneously. The mineral initially develops as polycrystalline vaterite which transforms into a single crystal directed by an NH(4)(+)-induced crystal plane that acts as a templating surface.

Supramolecular equivalence of halogen, ethynyl and hydroxy groups. A comparison of the crystal structures of some 4-substituted anilines

Chloro, bromo and ethynyl substituents play exactly the same role in the crystal structures of the corresponding 4-substituted anilines and this is related to their similar polarisations. The iodo derivative is, however, distinct and this may be related to its greater size.

Supramolecular equivalence of ethynyl, chloro, bromo and iodo groups. A comparison of the crystal structures of some 4-phenoxyanilines

4-(4′-Iodo)phenoxyaniline is isostructural to the corresponding bromo, chloro and ethynyl derivatives in contrast to 4-iodoaniline which is not isostructural to its bromo, chloro and ethynyl counterparts. This difference is rationalised in terms of conditional isomorphism.

Crystal structure prediction with the supramolecular synthon approach: Experimental structures of 2-amino-4-ethylphenol and 3-amino-2-naphthol and comparison with prediction

Two earlier crystal structure predictions (CSP) of aminophenol compounds are checked against experimental structure determinations. One of the predictions classified originally as “good” is verified and is now seen to be somewhat correct. The other prediction, which was classified earlier as “unclear”, is incorrect. The two experimental crystal structures are characterized by small and large synthons both of which contain O–H⋯N and N–H⋯O hydrogen bonds. The evolving nature of the CSP exercise is noted.

Dimorphs of 4′-amino-4-hydroxy-2′-methylbiphenyl: Assessment of likelihood of polymorphism in flexible molecules

The less stable polymorph of the title compound has the better synthon while the more stable polymorph the better packing. The possibility of polymorphism in a closely related isomer is examined computationally.

Crystal engineering in the aminophenols. Novel carborundum network in a supramolecular homologous series

Molecular complexes of 4-(4-aminophenoxy)aniline with a series of diphenols are structurally homologous and adopt the carborundum III topology, which is an unprecedented network for organic solids.

Correlation between molecular dipole moment and centrosymmetry in some crystalline diphenyl ethers

The presence of a large molecular dipole moment in diphenyl ethers leads unequivocally to a centrosymmetric crystal structure.