A re­interpretation of the phase transitions in Na₂CO₃

The interactions between C atoms and Na ions can be directly associated with the phase transitions in sodium carbonate, Na₂CO₃. By lowering the temperature, the coordination number of the C atoms increases from 3 to 7 in the second coordination sphere. The behavior of the carbonate ion is influenced by the neighbouring Na ions.

X-ray diffraction study for one-dimensional ionic conductors K_x(Ga_1 − yAl_y)_2 + xTi_2 − xO₇ (x ≃ 0.14, y ≃ 0.10, 0.23, 0.39)

Probability density distributions of the K ion in the title compounds were examined by single-crystal X-ray diffraction. A Gram–Charlier expansion was used for the atomic displacement parameters.

Tilt and acoustic instabilities in ABX₄, A₂BX₄ and ABX₃ perovskite structure types: their role in the incommensurate phases of the organic–inorganic perovskites

An examination of tilts and their relationships to acoustic modes is made for simple perovskite structure types. The origin of the incommensurate phases in the organic–inorganic perovskites is shown to be due to the coupling of low-frequency buckling modes which are intrinsic to the inorganic layer with the onset of orientational ordering of the amine cations.

Second-degree twinning and dynamic disorder in the crystal structure of deca-dodecasil 3R

Twinning in the structure of deca-dodecasil 3R has been resolved and a new structure determination is presented. Ab initio molecular dynamics calculations show that disorder in deca-dodecasil 3R is dynamic rather than static in nature.

Geometrical parameterization of the crystal chemistry of P6₃/m apatites: comparison with experimental data and ab initio results

A geometrical crystal-chemical model of P6₃/m apatite based on a specific set of bond-length and bond-angle parameters is derived. The model is used to compare the experimental results of apatite materials studied by single-crystal and Rietveld analysis with computed results of ab initio simulations, which are also used to predict the structures of hypothetical compounds which have not yet been studied.

Incommensurately modulated ordering of tetra­hedral chains in Ca₂Fe₂O₅ at elevated temperatures

Single-crystal XRD experiments at 1100 K show that the compound Ca₂Fe₂O₅ forms an incommensurately modulated structure. The modulation can be explained with aperiodic alternation of enantiomorphic tetrahedral chains.

Structures of Na₉[SO₄]₄X·2H₂O₂, where X = Cl or Br, in which the halide anions orchestrate extended orientation sequences of H₂O₂ solvate molecules

Both Na₉[SO₄]₄Cl·2H₂O₂ and its newly discovered bromide analogue are extremely stable and can be used as sources of anhydrous H₂O₂ or, in the presence of H⁺, dihalogen. Despite being composed of small, inorganic molecules and ions, long H₂O₂ orientation sequences require the chloride unit-cell dimensions to be exceptionally large. The extended patterns of H₂O₂ orientations can be linked to displacements of the eight sodium cations that coordinate each halide anion.

Structural characterization of Cd₃(O₃PC₂H₄CO₂)₂·2H₂O from in-house X-ray powder data and NMR

The crystal structure of Cd₃(O₃PC₂H₄CO₂)₂·2H₂O has been determined from in-house powder data. This compound crystallizes in the monoclinic system and shows a layered-type structure in which the layers are connected by the ligand into a three-dimensional array.

Three modulation patterns in four related [M(H₂O)₂(15-crown-5)](NO₃)₂ structures

The modulated structures of [M(H₂O)₂(15-crown-5)](NO₃)₂, M = Cu, Zn, Mg and Co, have been redetermined at 294 and 90 K. Significant problems in the original determinations have been fixed, the relationships between the structures have been identified and a reason for the modulations has been proposed.

The unusual phases of anhydrous and hydrated pinacol

The structure of highly twinned pinacol monohydrate has been determined, and the structures of anhydrous pinacol and its two other known hydrates have been reinvestigated.

Isostructural phase transition in m-carboxyphenyl­ammonium mono­hydrogenphosphite

The isostructural phase transition of the title compound and its 3.6 K hysteresis (T_c = 246 K on cooling and 249.6 K on heating) have been characterized by X-ray diffraction and differential scanning calorimetry.

Structure and intermolecular interactions of glipizide from laboratory X-ray powder diffraction

The crystal structure of the major diabetes treatment glipizide (glucotrol) has been determined. Intermolecular forces have been quantitatively evaluated from analysis of the thermal expansion of the lattice.

Pressure-induced polymorphism in cyclo­propyl­amine

The crystal structure of cyclopropylamine has been determined at 1.2 GPa using high-pressure single-crystal X-ray diffraction techniques. The structure of this previously unobserved phase is orthorhombic.

Variable-temperature neutron diffraction studies of the short, strong hydrogen bonds in the crystal structure of pyridine-3,5-di­carboxylic acid

Temperature-dependent proton migration has been observed in pyridine-3,5-dicarboxylic acid and also in pyridine-3,5-dicarboxylic acid in which the carboxylic acid protons have been replaced by deuterons.