Neutron and electron diffraction studies of La(Zn_1/2Ti_1/2)O₃ perovskite

The structure of the perovskite compound La(Zn_1/2Ti_1/2)O₃ is monoclinic, space group P2₁/n. The B site is ordered on {110}, but the presence of the pseudocubic (111) reflection is insufficient by itself to indicate the existence of such order.

Classification of stacking faults and their stepwise elimination during the disorder → order transformation of nickel hydroxide

Stacking faults in nickel hydroxide are classified by comparing their local structures with the structures of different theoretically possible polytypic modifications. The stacking faults are eliminated by a two-step process on hydrothermal treatment to yield ordered β-nickel hydroxide.

Structures and phase transitions in the ordered double perovskites Ba₂Bi^IIIBi^VO₆ and Ba₂Bi^IIISb^VO₆

High-resolution neutron powder diffraction has been used to investigate structures and phase transitions in the title compounds over a range of temperatures. The charge-ordered BaBiO₃ and chemically ordered Ba₂BiSbO₆ compounds show closely similar behaviour, except that the former shows a transition to a low-temperature phase that does not occur in the latter. The structure of this low-temperature phase has been determined for the first time.

Structure and phase transitions in Ca₂CoSi₂O₇–Ca₂ZnSi₂O₇ solid-solution crystals

Experimental studies are reported of the structure and phase transitional behavior of synthetic Co/Zn melilite single crystals using X-ray and electron diffraction as well as calorimetry. The commensurate lock-in phase was refined as a pseudomerohedral twin in the space group P2₁2₁2.

The incommensurately and commensurately modulated crystal structures of chromium(II) diphosphate

The structure of chromium(II) diphosphate is incommensurately modulated at room temperature and locks into a commensurately modulated structure at 285 K. The superspace structure model is found to also apply to other members of the thortveitite structure family.

Searching the Cambridge Structural Database for the `best' representative of each unique polymorph

A computer program is described that eliminates problem entries from the Cambridge Structural Database, clusters the remaining entries per unique polymorph and selects the best representative based on four criteria.

Structural characterization of selenium and selenium-diiodine analogues of the antithyroid drug 6-n-propyl-2-thiouracil and its alkyl derivatives

The structures of selenium analogues of the antithyroid drug 6-n-propyl-2-thiouracil, the charge-transfer complex 6-n-propyl-2-selenouracil·I₂, two diselenides and the deselenation product 6-n-propyl-2-uracil all show extended architectures. These are based on hydrogen-bonding and, in the case of 6-n-propyl-2-selenouracil·I₂, on Se⋯I interactions.

The low-temperature phase III structure and phase transition behaviour of cyclo­hexanone

The crystal structure of phase III of perdeuterocyclohexanone, C₆D₁₀O, has been determined at 5 K using high-resolution neutron powder diffraction. The structure is monoclinic in the space group P2₁/n and crystallizes from the face-centred cubic plastic phase I structure below 225 K. Details of the orthorhombic phase II structure, thought previously to exist only at high pressure, are also reported, and isotope effects on the phase behaviour are discussed.

Hexamer formation in tertiary butyl alcohol (2-methyl-2-propanol, C₄H₁₀O)

The crystal structure of phase II of tertiary butyl alcohol (2-methyl-2-propanol) has been solved using a combination of single-crystal X-ray diffraction techniques and ab initio density functional calculations. The calculations indicate that the trigonal P phase II structure is slightly more stable at elevated pressure than that of the triclinic phase IV.

Structures of (S)-(−)-4-oxo-2-azetidine­carboxylic acid and 3-azetidine­carboxylic acid from powder synchrotron diffraction data

The crystal structures of the four-membered heterocycles (S)-(−)-4-oxo-2-azetidinecarboxylic acid and 3-azetidinecarboxylic acid were solved by direct methods using powder synchrotron X-ray diffraction data.

Intra- and intermolecular interactions in small bioactive molecules: cooperative features from experimental and theoretical charge-density analysis

The intra- and intermolecular interactions based on the experimental and theoretical topological features of the charge densities of three bioactive molecules, 2-thiouracil, cytosine monohydrate and salicylic acid, have been analyzed on a quantum basis.

Synchrotron and neutron diffraction study of 4-methylpyridine-N-oxide at low temperature

A structural investigation of 4-methylpyridine-N-oxide between 300 K and 10 K by synchrotron and neutron powder diffraction is reported.

Role of strong intramolecular N—H⋯N hydrogen bonds in determining the conformation of adenosine-receptor antagonists

The crystal structures of four adenosine antagonists containing the —N=C—NH—C(=X)—NH— fragment and forming a strong intramolecular N—H⋯N hydrogen bond have been determined. A CSD search and DFT calculations have been performed in order to review the occurrence of this strong interaction in similar molecules and to evaluate the energy associated with its formation.

Blind crystal structure prediction of a novel second polymorph of 1-hy­droxy-7-azabenzotriazole

The crystal structure of a novel conformational polymorph of 1-hydroxy-7-azabenzotriazole has been independently predicted in an informal blind test.

Nine N-aryl-2-chloronicotinamides: supramolecular structures in one, two and three dimensions

Substituted N-aryl-2-chloronicotinamides, 2-ClC₅H₃NCONHC₆H₄X-4′, can have supramolecular structures which are one-, two- or three-dimensional, and are all built from different combinations of direction-specific intermolecular interactions.

Isomers and polymorphs of (E,E)-1,4-bis­(nitro­phenyl)-2,3-di­aza-1,3-butadienes

Five isomeric (E,E)-1,4-bis(nitrophenyl)-2,3-diaza-1,3-butadienes all display different direction-specific intermolecular interactions and all give different supramolecular structures.

Molecular and crystal properties of ethyl 4,6-di­methyl-2-thioxo-1,2,3,4-tetra­hydro­pyrimidine-5-carboxylate from experimental and theoretical electron densities

The electron-density and electronic energy-density features in ethyl 4,6-dimethyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate derived from accurate X-ray diffraction measurements at 110 K and theoretical calculations have been analyzed to estimate their reproducibility in molecules and crystals.

Further errors in polymorph identification: furosemide and finasteride

Reassessment of the reported single-crystal X-ray diffraction characterization of polymorphs of furosemide and finasteride shows that, in each case, incomplete data collections have resulted in the mistaken identification of two forms that are, in fact, identical.

On measuring the size of distortions in coordination polyhedra

The increase in average bond length is a useful measure of the distortion in a coordination polyhedron.