New phosphate langbeinites, K₂MTi(PO₄)₃ (M = Er, Yb or Y), and an alternative description of the langbeinite framework

Three new synthetic langbeinite structures, K₂ErTi(PO₄)₃, K₂YbTi(PO₄)₃ and K₂YTi(PO₄)₃, are presented as well as a reinvestigation of K₂CrTi(PO₄)₃. An alternative approach for the description of cation cages in the langbeinite framework is given using [M₅X₆O₃₉] building units.

Structural study of the low-temperature phase of TlH₂PO₄ at 180 K

The structure of TlH₂PO₄ at 180 K has been determined by X-ray diffraction in the space group P. A comparison with the room-temperature antiferroelectric structure of TlD₂PO₄ shows that the structural distortions they undergo with respect to the common high-temperature phase are not analogous.

Location of the H atoms in ammonium persulphate by deuteron NMR. Verification by X-ray diffraction

The equilibrium positions of the H atoms in (NH₄)₂S₂O₈ are determined using deuteron NMR spectroscopy, mainly at T = 17 K. The results are verified by X-ray diffraction and constitute the background for a discussion of the complex tunnelling and stochastic jump dynamics of the ammoniuum ions.

Relation between interatomic distances and sizes of ions in molecules and crystals

Bond lengths have been compared in molecules and crystals of alkali halides and alkaline earth metal fluorides and oxides. It was concluded that in alkali halide crystals the counterions considered as compressible spheres do not have common boundaries.

Analyzing experimental electron density with the localized-orbital locator

The approximate determination of the localized-orbital locator for detecting the features of chemical bonds in terms of the local kinetic energy is described. Characterization of the covalent, ionic and van der Waals bonds is possible using this approach.

Ferrocene-1,1′-di­carboxylic acid as a building block in supramolecular chemistry: supramolecular structures in one, two and three dimensions

Ferrocene-1,1′-dicarboxylic acid forms adducts with a wide range of organic amines: the structures of nine examples show that most are salts and that hydrogen bonds of O—H⋯O, O—H⋯N and N—H⋯O types can link the components into one-, two- or three-dimensional arrays.

Synthesis, properties and X-ray crystal structure of a new heteropolyacid supermolecular charge-transfer complex [(VB₁)₂DMFHPMo₁₂O₄₀·5DMF]

Crystal structure analysis of [(VB₁)₂DMFHPMo₁₂O₄₀·5DMF] [VB₁ = vitamin B₁ (thiamine chloride), DMF = N,N-dimethylformamide] indicates that two sets of PO₄ tetrahedra are formed around the central P atom. The PO₄ tetrahedra and MoO₆ octahedra are disordered in the heteropolyanion.

Synthesis and characterization of the barium oxalates BaC₂O₄·0.5H₂O, α-BaC₂O₄ and β-BaC₂O₄

X-ray single-crystal and powder diffraction and neutron powder diffraction analysis were used to study the structure of BaC₂O₄·0.5H₂O and in situ X-ray powder diffraction was used to study the thermal decomposition of BaC₂O₄·0.5H₂O to α-BaC₂O₄.

Terephthalate salts of dipositive cations

The structure of a series of divalent metal terephthalate salts was determined by applying Monte Carlo simulated annealing techniques to X-ray powder data. The hydrogen bonding was characterized using quantum calculations.

Structures of three substituted arenesulfonamides from X-ray powder diffraction data using the differential evolution technique

The crystal structures of three substituted arenesulfonamides have been solved from X-ray powder diffraction data using a new direct-space structure solution method based on a differential evolution algorithm: N—H⋯O hydrogen bonding leads to supramolecular aggregates in three, two or one dimensions, modified in some cases by C—H⋯O hydrogen bonds and aromatic π⋯π stacking interactions.

The use of restraints in Rietveld refinement of molecular compounds; a case study using the crystal structure determination of tryptamine free base

The crystal structure determination of tryptamine free base from powder X-ray diffraction data is described, including an investigation into the effect of the weight of restraints during Rietveld refinement.

Aminoguanidinium(1+) penta­fluorozirconate: multiple redetermination and comparisons

Crystals of CH₇N₄,ZrF₅ subjected to X-radiation exhibit significant variation in axial lengths and decreased standard reflection intensities. Analysis of the variation in atomic coordinates determined on four separate crystals reveals the presence of small but highly significant radiation-induced structural changes.

An exceptionally stable peptide nanotube system with flexible pores

Channels in the structure of L-alanyl-L-valine act as supramolecular hosts for organic solvent molecules. The crystals are stable after the complete removal of small guests. Irreversible absorption of alcohols larger than methanol induces a doubling of two axes' lengths and a change of the shape and size of the pores.

Predictable close-packing similarities between cis- and trans-2-hy­droxy-1-cyclo­octane­carboxylic acids and trans-2-hy­droxy-1-cyclo­octanecarboxamide

Racemic crystals of three optically active molecules, containing a saturated eight-membered ring bearing two vicinal (either cis or trans) hydrogen-bond donor/acceptor groups, were found to represent two novel forms of supramolecular close packing. The crystals of trans isomers (carboxylic acid and carboxamide) are isostructural, while the cis isomer (carboxylic acid) exhibits only one-dimensional isostructurality with them.

Nine isomeric nitro­benzyl­idene-iodoanilines: interplay of C—H⋯O hydrogen bonds, iodo⋯nitro interactions and aromatic π⋯π stacking interactions

In crystalline nitrobenzylidene-iodoanilines, isolated molecules may occur, or the molecules may be linked by some combination of C—H⋯O hydrogen bonds, iodo⋯nitro interactions and aromatic π⋯π stacking interactions, so giving overall supramolecular structures in zero, one, two or three dimensions.

Bond angles and bond lengths in monosubstituted benzene and ethene derivatives: a comparison of computational and crystallographic results

Bond angles and bond lengths in monosubstituted derivatives of benzene and ethene were calculated using the density functional theory. They agree reasonably with available values derived statistically from crystallographic data but correlate poorly with the reactivity parameters.

Some errors from the crystallographic literature, some amplifications and a questionable result

Correction of space-group errors for some crystals leads to clarification of relationships among chemically similar but apparently crystallographically different crystal structures. There are new examples of the `centrosymmetric–non-centrosymmetric' ambiguity and also straightforward revisions of space groups. Finally, a questionable structure presents evidence either for a new type of N—H⋯Cl hydrogen bonding or for an error.

The space groups of point group C₃: some corrections, some comments

A survey of the October 2001 release of the Cambridge Structural Database has uncovered approximately 675 separate apparently reliable entries under space groups , , and ; in approximately 100 of these entries, the space-group assignment appears to be incorrect. Other features of these space groups are also discussed.

Conformational study of S-alkylated iso­thiosemicarbazones

Ab initio calculations on S-alkylated isothiosemicarbazones were performed in order to investigate the role of intra- and intermolecular effects in determining the molecular conformation.