Characterization of intra-framework and guest/host interactions in the AlPO₄-15 molecular sieve by charge-density analysis

An accurate charge-density analysis of the title compound is presented and compared with the procrystal topological properties.

Structural refinements of high-pressure phases in germanium dioxide

Rietveld refinements of the high-pressure polymorphs of GeO₂ synthesized in the laboratory have been performed. The structure refinements confirm that the high-pressure phases have the α-PbO₂- and pyrite-type (modified-fluorite-type) structures.

Two-dimensionally modulated structure of the rare-earth polysulfide GdS_2−x (x = 0.18 ≃ 13/72)

GdS forms a 144-fold superstructure that is shown to result from an ordering of vacancies in the layers of S atoms. Charge balance is maintained by the presence of both S dimers and S ions in these layers.

Structure of δ₁-CoZn_7.8, an example of a phason pinning–unpinning transformation?

The incommensurately (3 + 1)-dimensional modulated structure of δ₁-CoZn_7.8 was solved and refined from single-crystal X-ray diffraction data. The linking of double icosahedra along the b axis is considered to be both a consequence of geometric demands and the cause of the incommensurate modulation.

Single-crystal structure refinement of NaTiSi₂O₆ clinopyroxene at low temperatures (298 < T < 100 K)

The alkali-metal clinopyroxene compound NaTiSi₂O₆ (sodium titanium silicate) shows a crystallographic phase transition at 197 K. The structure of the low-temperature phase was determined and the temperature-induced structural changes were investigated in detail by X-ray diffraction experiments on a single crystal between 100 and 298 K.

Low-temperature structure of V₆O₁₃

The low-temperature structure of V₆O₁₃ has been re-investigated using single-crystal X-ray diffraction. The transition temperature and heat of transition have been determined using differential scanning calorimetry.

Structures of potassium, sodium and lithium bis­(oxalato)borate salts from powder diffraction data

The ab initio determinations of the crystal structures of three alkali-metal salts A[B(C₂O₄)₂] (A = K, Na, Li) from conventional powder diffraction data are reported.

Diffuse X-ray scattering from 4,4′-di­methoxybenzil, C₁₆H₁₄O₄: analysis via automatic refinement of a Monte Carlo model

A recently developed method for fitting a Monte Carlo computer-simulation model to observed single-crystal diffuse X-ray scattering has been used to study diffuse scattering in 4,4′-dimethoxybenzil, C₁₆H₁₄O₄. The analysis has shown that the most prominent features of the diffraction patterns, diffuse steaks that occur normal to the direction, are due to longitudinal displacement correlations along chains of molecules extending in this direction.

Molecular and crystal properties of E-1,2-bis­(3-meth­oxy-2-thienyl)ethene: static disorder in the crystal

Static disorder in the crystal structure of E-1,2-bis(3-methoxy-2-thienyl)ethene is described and attributed to a high-energy conformer of the compound.

Monitoring structural transformations in crystals. 6. The [4 + 4] photodimerization of 9-methyl­anthracene

The structural changes in a crystal of 9-methylanthracene during the [4 + 4] photodimerization were monitored step-by-step by means of X-ray structure analysis. The results were compared with data for the [2 + 2] photodimerization.

Protonation site and hydrogen bonding in anhydrous and hydrated crystalline forms of doxazosin mesylate from powder data

The protonation site and hydrogen bonding in an anhydrous and in a hydrated crystalline form of doxazosin mesylate, a commonly used antihypertensive medication, have been determined as a result of crystal structure solution from synchrotron X-ray powder diffraction data.

Variable-temperature neutron diffraction studies of the short, strong N⋯O hydrogen bonds in the 1:2 co-crystal of benzene-1,2,4,5-tetra­carboxylic acid and 4,4'-bi­pyridyl

The 1:2 adduct of benzene-1,2,4,5-tetracarboxylic acid and 4,4'-bipyridyl has been studied by single-crystal neutron diffraction at 20, 200 and 296 K. The structure contains two short N⋯O hydrogen bonds; the H atom in the shortest is observed to migrate across the hydrogen bond between 20 and 296 K.

New electron diffraction method to identify the chirality of enantiomorphic crystals

A new CBED (convergent-beam electron diffraction) method is proposed for the identification of the chirality of enantiomorphic crystals, in which asymmetry in the intensities of the reflections of Bijvoet pairs in an experimental symmetrical zone-axis CBED pattern is compared with that of a computer-simulated CBED pattern. With the present method, a single CBED pattern is sufficient and chiral identification can be made for all the possible enantiomorphic crystals that are allowed to exist in crystallography.

Systematic prediction of new ferroelectrics in space groups P3₁ and P3₂. Erratum

An erratum to the paper by Abrahams (2003). Acta Cryst. B59, 541–556.