Ideal bond lengths and angles in nucleic acid structures: an update for the 2020s

A valuable addition to the toolkit for analysis of nucleic acid structures described by Gilski et al. [Acta Cryst. (2019), B75, 235–245] is discussed.

Electronic criterion for categorizing the chalcogen and halogen bonds: sulfur–iodine interactions in crystals

The electronic criterion for categorizing chalcogen or halogen bonds in complicated cases of S⋯I interactions in crystals is proposed. It is based on the dispositions of minima of electron density and electrostatic potential along the interatomic line.

Room-temperature synthesis of a new stable (N₂H₄)WO₃ compound: a route for hydrazine trapping

A new (N₂H₄)WO₃ compound has been obtained by mixing WO₃ and aqueous hydrazine solution at room temperature for 24 h. The material crystallizes in the trigonal space group P3₂21 and is stable up to 220°C, greatly beyond the boiling point of N₂H₄ (114°C).

Crystal defects responsible for mechanical behaviors of a WC–Co composite at room and high temperatures – a simulation study

Evolutions of microstructure and crystal defects in the nanocrystalline WC–Co composite during room- and high-temperature deformations were studied using molecular dynamics simulations.

A large anisotropic plasticity of L-leucinium hydrogen maleate preserved at cryogenic temperatures

Unusually large plasticity of an organic crystal at liquid nitro­gen temperature is described and rationalized using variable-temperature single-crystal X-ray diffraction data.

Investigation of the changes in hydrogen bonding accompanying the structural reorganization at 103 K in ammonium iodate

Variable-temperature neutron powder diffraction has been used to study the structure of ammonium iodate from 4.2 K to 290 K, in particular the hydrogen bonding between the ND₄⁺ and IO₃⁻ ions. No phase transition is observed at 103 K, but at low temperatures the ammonium ion is firmly locked in place.

Using powder XRD and pair distribution function to determine anisotropic atomic displacement parameters of orthorhombic tridymite and tetragonal cristobalite

Anisotropic atomic displacement parameters of orthorhombic tridymite and tetragonal cristobalite can be determined accurately using the combined methods of powder XRD and pair distribution function analysis.

Li₂₀Mg₆Cu₁₃Al₄₂: a new ordered quaternary superstructure to the icosahedral T-Mg₃₂(Zn,Al)₄₉ phase with fullerene-like Al₆₀ cluster

The new quaternary aluminide Li₂₀Mg₆Cu₁₃Al₄₂ was studied by the single-crystal method: cI162, , a = 13.8451 (2), R[F² > 2σ(F²)] = 0.023. The Li₂₀Mg₆Cu₁₃Al₄₂ structure can also be described as three-shell icosahedral clusters of [CuAl12@Li20Cu12@Al60] which can be enclosed inside a truncated octahedron of magnesium atoms in which all hexagonal faces are centered by lithium atoms. The electronic structure calculations confirm the concept of core–shell packing of clusters.

Taxifolin tubes: crystal engineering and characteristics

Microtubes of taxifolin were synthesized by crystal engineering. They were characterized using physicochemical, microscopic, spectral and computational methods of analysis.

Thermal, spectroscopic and structural analysis of a thermosalient phase transformation in ta­pentadol hydro­chloride

A first-order phase transformation in tapentadol hydrochloride, taking place at ca 318 (1) K (on heating) and 300 (1) K (on cooling), is described and the changes in crystal structure relating the high-temperature and low-temperature forms are analyzed. The crystals present an ostensible thermosalient behaviour during the transformation, explainable through some abrupt unit-cell changes taking place.

The formation of the salt and neutral molecule cocrystal from equimolar solution of heli­amine and bi­cyclo­[2.2.1]hept-5-ene-endo-2,3-di­carb­oxy­lic acid

An unusual cocrystal of salt and neutral molecule was formed from the equimolar solution of 6,7-di­meth­oxy-1,2,3,4-tetra­hydro­iso­quinoline (heli­amine) and bi­cyclo­[2.2.1]hept-5-ene-endo-2,3-di­carb­oxy­lic acid due to peculiarities of crystal packing formation.

Quantum pressure focusing in solids: a reconstruction from experimental electron density

The indicator of quantum pressure focusing (IQPF) displays the inner-crystal regions where the electronic pressure is concentrated or depleted due to the quantum kinetic, exchange and correlation effects. It reveals the chemical bond features in crystals, using orbital-free formalism of the density functional theory in combination with experimental electron density.

Developing new SrI₂ and β-D-fructo­pyran­ose-based metal–organic frameworks with nonlinear optical properties

This article describes novel strontium iodide–fructose-based metal–organic frameworks with nonlinear optical properties, with a high potential for theragnostic applications in cancer radiotherapy.

Acid–ammonium heterodimer and N_(ammonium)–H⋯N_(pyridine) synthon preference in three salts of nicotinic acid with (1R,2R)-1,2-di­phenyl­ethyl­enedi­amine

The crystal structures and solubilities of three nicotinic acid salts with (1R,2R)-1,2-di­phenyl­ethyl­enedi­amine are discussed and an analysis of synthon preference is provided.

Crystal structure solution for the A₆B₂O₁₇ (A = Zr, Hf; B = Nb, Ta) superstructure

The crystal structure solutions for Zr₆Ta₂O₁₇, Hf₆Nb₂O₁₇ and Hf₆Ta₂O₁₇ have been solved using synchrotron X-ray and neutron powder diffraction. These structures have been shown to be isomorphous with each other and Zr₆Nb₂O₁₇, leading to the classification of the A₆B₂O₁₇ orthorhombic compound family with symmetry Ima2 (No. 46).

Accurate geometrical restraints for Watson–Crick base pairs

Revised geometrical parameters are proposed for the Watson–Crick pairs of nucleobases, for use as restraints in modeling and refinement of the structures of nucleic acids. Accurate values of these parameters were derived (and compared) from small-molecule Cambridge Structural Database structures, from super accurate ultrahigh-resolution nucleic acid structures in the Protein Data Bank, and from quantum mechanical calculations. The effect of base pairing on the molecular geometry of the nucleobases is also investigated.

New insights on the GeSe_xTe_1−x phase diagram from theory and experiment

The high-pressure and low-temperature behaviour of the GeSe_xTe_1−x system was studied using in situ diffraction and DFT calculations. The high-pressure phase of GeTe-III was determined.

Structural evolution of La₂Ti₂O₇ at elevated temperatures

Crystals of La₂Ti₂O₇ undergo successive phase transitions between the low-temperature monoclinic phase and the high-temperature orthorhombic phase with an intermediate incommensurately modulated phase at around 1000 K.

Crystal structure and XANES investigation of petzite, Ag₃AuTe₂

A single-crystal X-ray diffraction and XANES investigation of the mineral petzite is reported.

Chemical and structural variability in cubic spinel oxides

The empirical relations between cubic spinel oxides with different compositions were investigated using data from 349 refined crystal structures. The results show that the spinel structure is able to tolerate many constituents and the structure distortion can be explained in terms of variation in ionic potential (= charge/size) at the cation sites.

Hydrogen Storage Alloys with RE–Mg–Ni Based Negative Electrodes