Electron density and electrostatic potential of KMnF₃: a phase-transition study

Three accurate X-ray diffraction experiments were carried out to determine the temperature dependence of the electron density in cubic perovskite KMnF₃, from room temperature to just above that of the phase transition to the tetragonal structure (186 K), and to correlate the parameters of the critical points with the phase-transition mechanism.

Variation of large-scale regularity in modulated structures of Ca₂CoSi₂O₇ studied by a simulation method

Simulation studies on changes in structure with a variation in q revealed that various large-scale regularities larger than the modulation wavelengths are formed in the incommensurate structures of Ca₂CoSi₂O₇.

Structure of a high-pressure phase of vanadium pentoxide, β-V₂O₅

The structure of a high-pressure phase of vanadium pentoxide, β-V₂O₅, has been studied by X-ray and neutron powder diffraction and HRTEM. Structural relationships between α- and β-V₂O₅, and between β-V₂O₅- and B-Ta₂O₅-type structures are discussed.

Li_3+δV₆O₁₃: a short-range-ordered lithium insertion mechanism

The structures of Li₃V₆O₁₃ and Li_3+δV₆O₁₃, δ ≃ 0.3, have been determined by single-crystal X-ray diffraction. A mechanism is proposed for lithium insertion in the composition range Li₃V₆O₁₃–Li₆V₆O₁₃.

Synchrotron X-ray and ab initio studies of β-Si₃N₄

The redistribution of bonding electron density in SiN was studied by means of three synchrotron X-ray experiments and a theoretical plane-wave study.

Structural manifestations of proton transfer in complexes of 2,6-di­chlorophenols with pyridines

The experimental results on X-ray structure determination in complexes of 2,6-dichlorophenols with different pyridines are analyzed in relation to the degree of proton transfer. Theoretical trends are described on the basis of B2LYP/6-31G(d,p) calculations.

Bis(1-chloro-2,2,4,4-tetra­methyl-3-oxo­cyclobutan-1-yl)pentasulfane: an occupancy modulated structure

The title compound crystallizes in the space group P2₁/n and may be described by a partial ordering of a 1:1 disordered P2₁/a parent structure with the c axis halved. The structure can be redescribed as 0.732 (1) of an ordered P2₁/n structure and 0.268 (1) of a 1:1 disordered P2₁/a structure with atom positions in the asymmetric unit that are significantly non-identical.

Analysis of the less common hydrogen bonds involving ester oxygen sp³ atoms as acceptors in the crystal structures of small organic molecules

Experimental evidence of the Osp³ ester acceptor function in hydrogen bonds extracted from the Cambridge Structural Database is shown. Geometrical data are analysed in view of known hydrogen-bond criteria. The observed data revealing the acceptor function of the Osp³ ester are in agreement with the ab initio-based energy calculations performed by Lommerse et al. [(1997>), J. Comput. Chem. 18, 757–774].

Rigid backbone moiety of KNI-272, a highly selective HIV protease inhibitor: methanol, acetone and di­methylsulfoxide solvated forms of 3-[3-benzyl-2-hy­droxy-9-(isoquinolin-5-yl­oxy)-6-methylsulfanylmethyl-5,8-dioxo-4,7-di­azanonanoyl]-N-tert-butyl-1,3-thiazolidine-4-carboxamide

Crystals of KNI-272, a highly selective HIV protease inhibitor, were grown in three different solvent systems. The local conformations around the hydroxymethylcarbonyl moiety were similar in all three forms with a remarkable similarity in the C-terminal region. Their conformational characteristics of the uncomplexed forms resembled those of the inhibitor within the KNI-272–HIV protease complex. This suggests that the structure of the C-terminal region of KNI-272 is rigid or very stable.

2-Hydroxyisophthalic acid: hydrogen-bonding patterns in the monohydrate and the tetra­phenylphosphonium salt. An instance of dramatic acidity enhancement by symmetric, internally hydrogen-bonded anion stabilization

The title phenolic diacid presents an elaborate two-dimensional hydrogen-bonding pattern, in which its water of monohydration is intimately involved. The title compound's high phenol acidity is reflected in its monoanionic tetraphenylphosphonium salt, where charge is stabilized on the phenol oxygen by symmetrical hydrogen-bond donation from both ortho groups.

Sizes of molecules in organic crystals: the Voronoi–Dirichlet approach

The volumes of more than 100 000 molecules in organic crystals have been calculated using the Voronoi–Dirichlet procedure. It is shown in this report that the average volumes are nearly equal to the corresponding values in homomolecular crystals and the reasons for the variations in molecular sizes are discussed.

Ab initio structure determination of the hygroscopic anhydrous form of α-lactose by powder X-ray diffraction

The crystal structure of the hygroscopic anhydrous form of α-lactose is solved ab initio at 293 K from powder X-ray diffraction data. A real-space method (Monte Carlo simulated annealing), Rietveld refinements with geometric soft restraints, and energy minimization calculations have been used.

Supramolecular structures of substituted α,α′-trehalose derivatives

Hard and soft hydrogen bonds in substituted trehalose derivatives generate supramolecular structures in one, two and three dimensions.

Isomeric iodo-N-(nitro­benzyl)anilines: interplay of hard and soft hydrogen bonds, iodo⋯nitro interactions and aromatic π⋯π stacking interactions

Iodo-N-(nitrobenzyl)anilines, O₂NC₆H₄CH₂NHC₆H₄I, can exhibit hydrogen bonds of four types, N—H⋯O, C—H⋯O, N—H⋯π(arene) and C—H⋯π(arene), as well as iodo⋯nitro and aromatic π⋯π stacking interactions. The resulting supramolecular structures can be one-, two- or three-dimensional.

Structural features controlling the binding of β-carbolines to the benzodiazepine receptor

A structural comparison study by superimposition techniques, integrated by the analysis of affinity data, is presented in this paper in order to obtain a deeper insight into the structure–activity relationships in β-carbolines.

New bond-valence parameters for lanthanides. Addendum

An addendum to the paper by Trzesowska et al. (2004>). Acta Cryst. B60, 174–178.