Structure of KNbOB₂O₅ – a commensurately modulated structure

Using the superspace approach allowed a plausible model for the commensurate modulated structure of KNbOB₂O₅ to be determined, which was then refined as a superstructure.

Structure of the clinopyroxene-type compound CaCuGe₂O₆ between 15 and 800 K

The crystal structure of CaCuGe₂O₆, which is closely related to the clinopyroxene structure type, was studied between 15 and 800 K to elucidate the temperature-dependent variation of structural parameters. A phase transition from P2₁/c to C2/c was found at 650 K.

Structure of strontium hydroxide octahydrate, Sr(OH)₂·8H₂O, at 20, 100 and 200 K from neutron diffraction

The crystal structure of Sr(OH)₂·8H₂O has been determined at 20, 100 and 200 K from neutron diffraction data. The structure consists of double layers of H₂O and OH⁻ ions separated by Sr²⁺ along the c axis.

Electron diffraction of tilted perovskites

Simulations of electron diffraction patterns have been performed for each of the known perovskite tilt systems. Full details of the allowed reflections for each system are presented along with examples showing how simple selected-area diffraction patterns can be used to identify tilt systems.

The role of second coordination-sphere interactions in incommensurately modulated structures, using β-K₅Yb(MoO₄)₄ as an example

The complementary character of the first and second coordination-sphere interactions is illustrated with the incommensurately modulated structure β-K₅Yb(MoO₄)₄. It is also shown that even the third coordination sphere should not be neglected in the studies of modulated structures.

Structure refinement of a twinned pseudo-symmetric crystal of [Mn(C₁₀H₂₄N₄)(NCO)₂]⁺·ClO

Pseudo-symmetry operations were used to identify the major and minor components of the reflection intensities. This suggested constraints and restraints to optimize the refinement pathway by minimizing the noise in the minor components, and allowed the successful refinement of the near 1:1 twinned pseudo-symmetric crystal of the title compound.

Atomic interactions in ethylenebis(1-indenyl)zirconium dichloride as derived by experimental electron density analysis

A topological analysis of the experimental electron density in racemic ethylenebis(1-indenyl)zirconium dichloride has been performed. All the atomic interactions and a charge transfer from the Zr atom to the ligands were quantitatively characterized and the `ligand-opposed' charge concentrations around Zr were revealed using the Laplacian of the electron density and a one-particle potential.

New lanthanide–nitrogen bond-valence parameters

Lanthanide–nitrogen bond-valence parameters are presented as they have been calculated for coordination compounds.

Powder diffraction crystal structure analysis using derivative difference minimization: example of the potassium salt of 1-(tetrazol-5-yl)-2-nitroguanidine

The crystal structure of the potassium salt of 1-(tetrazol-5-yl)-2-nitroguanidine was solved and refined from X-ray powder diffraction data by applying the derivative difference minimization (DDM) method. All the atomic positions, including those of the H atoms, were located and refined without restraints. The reproducibility and precision of the results obtained by DDM and Rietveld methods are compared.

Submolecular partitioning of morphine hydrate based on its experimental charge density at 25 K

The electron density distribution of morphine hydrate has been derived from high-resolution single-crystal X-ray diffractions measurements at 25 K and was compared with the theoretical calculated fragment molecules from which the morphine molecule can be reconstructed.

The low-temperature and high-pressure crystal structures of cyclo­butanol (C₄H₇OH)

The low-temperature and high-pressure crystal structures of cyclobutanol have been determined using single-crystal X-ray diffraction techniques. At temperatures below 493 K, cyclobutanol crystallizes in the Aba2 space group (Z′ = 2) and its crystal structure is composed of pseudo-threefold hydrogen-bonded molecular catemers. At a pressure of 1.3 GPa, the crystal symmetry changes to Pna2₁ (Z′ =1) and the molecular catemers adopt a pseudo-twofold arrangement.

Structure determination of the 1/1 α/β mixed lactose by X-ray powder diffraction

The stoichiometry of 1/1 α/β mixed lactose was determined by NMR. Its structure was solved by X-ray powder diffraction and from the minimization of the crystalline energy. The simulated annealing method, followed by Rietveld refinements with soft constraints on bond lengths and angles was used.

A variable-temperature study of a phase transition in barbituric acid dihydrate

Barbituric acid dihydrate undergoes a reversible orthorhombic-to-monoclinic phase transition when cooled below 200 K. This second phase is stable down to 100 K. There are clear differences in the crystal packing of the two phases, although the hydrogen-bonding motifs do not change.