Taking a closer look for a broader view: combining powder diffraction with electron crystallography for a better understanding of modulated structures

Electron crystallography has made enormous progress over the last decade. It can provide the necessary information that complements powder diffraction data and allows for successful structure analysis of modulated (and unmodulated) structures.

Synergy between transmission electron microscopy and powder diffraction: application to modulated structures

Using examples of anion-deficient perovskites modulated by periodic crystallographic shear planes, it is demonstrated what kind of local structural information can be obtained using various transmission electron microscopy techniques and how this information can be implemented in the crystal structure refinement against the powder diffraction data.

Hydrogen bonding patterns in salts of derivatives of amino­pyrimidine and thiobarbituric acid

Supramolecular interactions in three salts, namely 2-amino-4,6-dimethylpyrimidin-1-ium thiobarbiturate trihydrate (I), 2-amino-4,6-dimethoxypyrimidin-1-ium thiobarbiturate dihydrate (II) and 2,4-diamino-5-(3′,4′,5′-trimethoxybenzyl)pyrimidin-1-ium thiobarbiturate (III), were analysed. The formation of N—H⋯S hydrogen bonds, a water-mediated base pair and water–water interactions in these crystal systems offer scope for these systems to be considered as a model in the study of hydration of nucleobases and water-mediated nucleobase base pairs in macromolecules.

Structure and stability of BaTiSi₂O₇

The crystal structure of BaTiSi₂O₇ (BTS2) has been solved from powder diffraction data. It shows the coexistence of monoclinic and triclinic domains within the same crystals. The confirmed presence of TiO₅ pyramidal units, with one short Ti—O distance involving the apical oxygen, is in agreement with the theories on the photo-luminescent properties of this compound. Considerations on the stability of BTS2 justifies BaTiSi₄O₁₁ (BTS4) as an unavoidable contaminant during synthesis. The reflection list for BTS4 is reported.

A comprehensive classification and nomenclature of carboxyl–carboxyl(ate) supramolecular motifs and related catemers: implications for biomolecular systems

The vast diversity of carboxyl–carboxyl(ate) arrangements is reduced to 17 supramolecular motifs and eight catemers. Examples of each, extracted from the CSD, are presented.

Phosphoramides bearing isoxazole derivative: spectroscopic and structural characterization, study of hydrogen-bonding interactions and two lanthanide complexes (Ln^III = Ce and Eu)

The synthesis, spectral and structural study of new phosphoramides containing isoxazole, and two lanthanide complexes are reported. Hydrogen bonding and metal–ligand interactions are studied theoretically.

Structure of fluorite-like compound based on Nd₅Mo₃O₁₆ with lead partly substituting for neodymium

A single crystal of the Nd₅Mo₃O₁₆ structure type with lead partly substituting for neodymium was studied by precision X-ray diffraction and high-resolution transmission microscopy. Partial substitutions of Mo cations for the Nd position and of Nd for the Mo position in crystals of the Ln₅Mo₃O₁₆ oxide family are corroborated by X-ray diffraction for the first time.

Structure of the mixed-metal carbonate KAgCO₃ revisited: order–disorder (OD) polytypism and allotwinning

KAgCO₃ is polytypic and crystallizes as allotwins (oriented associations of non-equivalent polytypes) with highly ordered domains.

Lack of a threefold rotation axis in α-Fe₂O₃ and α-Cr₂O₃ crystals

The symmetry of the magnetic ordering of α-Fe₂O₃ and α-Cr₂O₃ is found to be monoclinic and not trigonal, so the symmetry of their crystal structures should also be monoclinic. This conclusion is supported both by experimental X-ray powder diffraction studies as well as by theoretical arguments.

Cocrystals of 6-chlorouracil and 6-chloro-3-methyl­uracil: exploring their hydrogen-bond-based synthon motifs with several triazine and pyrimidine derivatives

Two chlorine-containing uracil derivatives have been cocrystallized with several triazine and pyrimidine derivatives. Six cocrystals and two (pseudo-) polymorphs were obtained with two-dimensional layers mainly promoted by hydrogen bonds.

Synthesis and structural elucidation of new complexes of 2,4- and 3,5-di­methyl di­phenyldi­thiophosphates with cobalt(II)

New cobalt(II) complexes of disubstituted diphenyldithiophosphates with donor ligands have been synthesized and structurally characterized by elemental analyses, IR and single-crystal X-ray analyses. Single-crystal X-ray diffraction analysis reveals a six-coordinated distorted octahedral geometry for the CoS₄N₂ chromophore, defined by two chelating dithio anions and two N-donor ligands.

Resonance-stabilized partial proton transfer in hydrogen bonds of incommensurate phenazine–chloranilic acid

Correlated variations of chemical bonds demonstrate stabilization by the resonance of the chloranilic acid anion. Proton transfer in some of the intermolecular hydrogen bonds is responsible for the ferroelectic properties.

Predicting the lattice constants of the ternary pyrochlores A₂B₂O₆O′

Statistical models to predict lattice constants of ternary pyrochlores A₂B₂O₆O′ have been derived using multiple linear regression analysis.

First experimental charge density study using a Bruker CMOS-type PHOTON 100 detector: the case of ammonium tetraoxalate dihydrate. Addendum

Addendum to Jarzembska et al. [Acta Cryst. (2014), B70, 847–855].

Introduction to Nanofiber Materials