Prediction of the crystal structures of perovskites using the software program SPuDS

The software program SPuDS has been developed to calculate the crystal structures of distorted perovskites. Calculated structures are compared with known crystal structures in order to verify the accuracy of this approach. Further calculations are presented to demonstrate the possible application of this program for synthesizing new materials.

Five-dimensional structure refinement of natural melilite, (Ca_1.89Sr_0.01Na_0.08K_0.02)(Mg_0.92Al_0.08)(Si_1.98Al_0.02)O₇

The incommensurately modulated structure of the natural melilite (Ca_1.89Sr_0.01Na_0.08K_0.02)(Mg_0.92Al_0.08)(Si_1.98Al_0.02)O₇ has been refined from single-crystal X-ray diffraction data. The refinement program Jana2000 has been modified to account for a severe overlap of satellite reflections m × n = ±1.

Temperature-dependent neutron powder diffraction study of the Ba(OD)₂ polymorphs: a new low-temperature phase

The investigation of the structural behaviour of Ba(OD)₂ with varying temperature reveals a new low-temperature polymorph. The phase transition is caused by an order–disorder mechanism, since a D atom, which on average occupies a special position on a mirror plane, is frozen at a general position at low temperature.

Superlattice formation in the li­thiated vanadium oxide phases Li_0.67V₆O₁₃ and LiV₆O₁₃

As a small amount of lithium is inserted into the host material V₆O₁₃ two new superlattice structures Li_2/3V₆O₁₃ and LiV₆O₁₃ are formed. The insertion of lithium causes the superlattice formation as well as a charge reduction of specific V atoms in the structure.

Systematic generation of all nonequivalent closest-packed stacking sequences of length N using group theory

An algorithm using group theory has been developed that generates all of the nonequivalent closest-packed stacking sequences of length N.

Bis(hfac)-copper(II) complexes bridged by pyrimidines showing magnetic interactions

Crystal structures of [Cu(hfac)₂(pm)]_n (pm = pyrimidine), [Cu(hfac)₂(4-Me-pm)]_n, [Cu(hfac)₂(qz)]_n (qz = quinazoline) and Cu₃(hfac)₆(4-Me-pm)₂ were determined and relations between structures and magnetic interactions were discussed.

Influence of aromatic sulfonation on the geometry of [2.2]para­cyclophane: crystal structures of one sulfonate, one di­sulfonic anhydride and five disulfonimides

The direction of the rotation of the para-phenylene rings in sulfonated [2.2]paracyclophanes depends on the degree of sulfonation.

Irreversible single-crystal to polycrystal and reversible single-crystal to single-crystal phase transformations in cyanurates

Two examples of phase transformations in cyanurates are compared. One of them describes single-crystal to polycrystalline transitions from stacking to herringbone packing modes. The other is a single-crystal to single-crystal phase transformation involved with a very small atomic displacement. The DSC thermographs, structures and thermal motion analysis are discussed.

Use of software to search for higher symmetry: space group C2

With the help of software designed to detect cases of missed higher symmetry, we have searched the Cambridge Structural Database for entries in space group No. 5 and identified 50 cases in which the structure should be described in space groups of higher symmetry. The most common revision is to space group C2/m, which entails adding a center of inversion and usually results in important changes in bond lengths and angles.

X-ray investigations of sulfur-containing fungicides. III. Intramolecular forces governing the conformation of a novel orthorhombic polymorph of benzoylmethyl phenyl sulfone, benzoylmethyl 4-chloro­phenyl sulfone and benzoylphenylmethyl phenyl sulfone

The crystal and molecular structures of three β-ketosulfones have been investigated using X-ray analysis and density functional theory supplemented by ab initio Hartree–Fock calculations. At room temperature and in daylight the pale yellow, orthorhombic polymorph of the benzoylmethyl phenyl sulfone undergoes a transformation to a stable, colourless, monoclinic crystal form.

Rules governing the crystal packing of mono- and dialcohols

Hydrogen-bonding patterns in mono- and dialcohols are strongly correlated with steric effects. Empirical rules governing the packing of these compounds can be discerned, but they are not transferable to even closely related systems.

Synthesis, structure, thermal and non-linear optical properties of L-argininium hydrogen selenite

The synthesis, structure and non-linear optical properties of L-argininium hydrogen selenite hydrate are reported. It crystallizes in the non-centrosymmetric space group C2 with four formula units per cell. This compound shows a second-harmonic generation power about twice that of urea, as measured on polycrystalline samples by the Kurtz method.

Hydrogen-bond network in cyclodecaamylose hydrate at 20 K; neutron diffraction study of novel structural motifs band-flip and kink in α-(1→4)-D-glucoside oligosaccharides

The neutron diffraction study at 20 K on a single crystal of cyclodecaamylose·27.18H₂O permitted the characterization of the hydrogen-bond network in the novel structural motifs band-flip and kink which occur in larger α-(1→4)-D-glucoside oligosaccharides with 10 or more glucoside units.

X-ray studies on crystalline complexes involving amino acids and peptides. XXXVIII. Crystal structures of the complexes of L-arginine and L-histidine with glutaric acid and a comparative study of amino acid–glutaric acid complexes

Amino acid complexes of glutaric acid and other dicarboxylic acids exhibit a variety of ionization states and stoichiometry. While some complexes contain already characterized aggregation patterns, new patterns are observed in others.

Amino and cyano N atoms in competitive situations: which is the best hydrogen-bond acceptor? A crystallographic database investigation

Statistical analyses of data retrieved from the Cambridge Structural Database, and density functional theory calculations on model molecules, are used to investigate the relative hydrogen-bond acceptor abilities of amino and cyano N atoms in N—T—C≡N (T is a transmitter of resonance effects) and N—(Csp²)₃—C≡N molecular fragments. The nitrile nitrogen is almost always the preferred hydrogen-bond acceptor, since in push–pull systems the amino nitrogen lone pair is delocalized through the π system of the transmitter towards the nitrile nitrogen, whereas in aliphatic aminonitriles the amino nitrogen is shown to be sensitive to steric hindrance.

Associations of squaric acid and its anions as multiform building blocks of hydrogen-bonded molecular crystals

Squaric acid (SQ) is a strong diprotic acid that can crystallize as pure H₂SQ, as well as hydrogen squarate (HSQ⁻) or squarate (SQ²⁻) anions interacting with a variety of hydrogen-bond donors. The HSQ⁻ ions easily form a number of supramolecular architectures connected by strong O—H⋯O bonds. A rationalization of the observed structural motifs is attempted in terms of the formation of HSQ⁻ polyanions and of their ability to pack with aromatic bases protonated by the dissociation of the squaric acid itself.