Looking deeper into molecular structures with Z′ > 1

A commentary is given on the article by Carolyn Pratt Brock and Robin Taylor [Acta Cryst. (2020), B76, 630–642] in this issue.

Complex minerals preserve natural geochemically important nanoscale metal oxide clusters

The rapidly emerging family of polyoxometalate-based minerals is unusually complex owing to inclusion of nanoscale metal oxide clusters

Variations of quantum electronic pressure under the external compression in crystals with halogen bonds assembled in Cl₃-, Br₃-, I₃-synthons

Changes in quantum electronic pressure in crystals under external compression reveal spatial areas of relatively higher compressibility. The halogen bonds assembled in Hal₃-synthons create the `stiff framework' in hexahalo­benzene crystals.

Crystal forms and phase transformation of 1,5-pentanedi­amine-terephthalate: a bio-based nylon 5T monomer

Monohydrate and anhydrate forms of PDA-TPA crystal structures are determined and analysed, and the monohydrate shows favourable stability. The phase transition between the monohydrate and the anhydrate depends strongly on the temperature and water activity, and the larger the value of water activity is, the higher is the transition temperature.

New cubic cluster phases in the Mg–Ni–Ga system

The crystal structures of two new Mg₉Ni₆Ga₁₄ and Mg₃Ni₂Ga phases were determined using X-ray diffraction and their chemical compositions were confirmed by electron probe microanalysis. The main common feature for both phases, besides being of cubic symmetry (), is that they form three-shell clusters which close pack in crystal space.

Investigation of thermal behavior of mixed-valent iron borates vonsenite and hulsite containing [OM₄]ⁿ⁺ and [OM₅]ⁿ⁺ oxocentred polyhedra by in situ high-temperature Mössbauer spectroscopy, X-ray diffraction and thermal analysis

The Fe²⁺ to Fe³⁺ oxidation in oxoborates vonsenite and hulsite leads to a decrease of values of unit-cell volumes, volumetric thermal expansion coefficients and subsequent solid-phase decomposition. A partial magnetic ordering in hulsite is observed for the first time with T_c ∼383 K, which is accompanied with unusual changes of thermal expansion coefficients.

Variation of cation distribution with temperature and its consequences on thermal expansion for Ca₃Eu₂(BO₃)₄

The structural behavior of Ca₃Eu₂(BO₃)₄ at high temperature was investigated. A change in thermal expansion anisotropy was found at around 923 K, connected to a variation of Ca/Eu distribution over the three cationic sites.

Low-temperature martensite relaxation in Co–Ni–Ga shape memory alloy monocrystal revealed using in situ cooling, transmission electron microscopy and low rate calorimetry

A Co₄₉Ni₂₁Ga₃₀ magnetic shape memory single crystal was studied using in situ imaging and low-temperature calorimetry. Both methods confirmed the occurrence of local reconstruction of the crystal lattice at temperatures below 190 K.

Analysis of charge density in nona­aqua­gadolinium(III) tri­fluoro­methane­sulfonate – insight into Gd^III—OH₂ bonding

Results of experimental multipole refinement and theoretical density functional theory calculations show that donation of electron density from lone pairs of water molecules to 5d and 6s orbitals of Gd³⁺ produces a covalent admixture to predominantly ionic Gd—O(H₂) bonds.

New insights into the structural properties of κ-(BEDT-TTF)₂Ag₂(CN)₃ spin liquid

The first accurate study of the room-temperature and 100 K structures of one of the first organic spin liquids, κ-(BEDT-TTF)₂Ag₂(CN)₃, is presented.

Crystal and molecular structure of [Ni{2-H₂NC(=O)C₅H₄N}₂(H₂O)₂][Ni{2,6-(O₂C)₂C₅H₃N}₂]·4.67H₂O; DFT studies on hydrogen bonding energies in the crystal

Computational studies of the network packing of the title compound by high level DFT-D/B3LYP calculations indicate stabilization of the networks with conventional and non-conventional intermolecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds (HBs) along with π-stacking contacts.

Evaluation of fluorine-mediated intermolecular interactions in tetrafluorinated tetra­hydro­iso­quinoline derivatives: synthesis and computational studies

The importance of fluorine-mediated interactions in the crystal structures of a series of tetra-fluorinated tetra­hydro­iso­quinoline derivatives through structural and computational analysis is presented.

Polyoxometalate clusters in minerals: review and complexity analysis

This article reviews current progress in the investigations of polyoxometalate clusters in minerals.

Identifying and characterizing translationally modulated molecular crystal structures

A program to identify and characterize approximate translations has been written. Running it for the structures archived in the Cambridge Structural Database showed that the frequency of pseudotranslations increases with Z′ and is approximately 50% for Z′ > 4.

Zero-obliquity twin lattice quasi-symmetry threefold twinning in 1-{(R)-1-[(3-oxo-2-isoindolinoyl)methyl]-2-propenyl}-5-methyl-2,3-indolinedione

Threefold twinning in the title compound is described in detail.

The effective volumes of waters of crystallization: general organic solids

The effective volumes of waters of crystallization have been determined for 163 hydrate/parent systems, yielding a mean value of 24 ų. A generic value of 147 ± 56 × 10⁻⁶ K⁻¹ has been established for the volumetric coefficient of thermal expansion of organic solids. These results may be helpful in assessing and predicting hydrate crystal structures and volume-related thermodynamic properties.

Monoclinic SmAl₃(BO₃)₄: synthesis, structural and spectroscopic properties

Monoclinic SmAl₃(BO₃)₄ borate was successfully synthesized by the group growth on seed method and the structural and spectroscopic properties were investigated in detail.

A positive to negative uniaxial thermal expansion crossover in an organic benzothienobenzo­thio­phene structure

A rare transition from positive to negative thermal expansion in an organic herringbone-stacked structure is reported and related to an isosymmetric phase transition.

Mechanical behavior and phase change of alkali-silica reaction products under hydro­static compression

The anisotropic deformation and pressure-induced phase change of nano-crystalline alkali-silica reaction (ASR) products are studied by high-pressure X-ray diffraction, providing the first molecular-scale input for mechanical modeling of the micro-degradation of concrete that suffers from ASR damage.

ChemEnv: a fast and robust coordination environment identification tool

A new tool called ChemEnv, which can identify coordination environments in a fast and robust manner, is presented.

Melting points of one- and two-component molecular crystals as effective characteristics for rational design of pharmaceutical systems

A database containing the fusion temperatures of two-component molecular crystals (1947 co-crystals) and individual components thereof has been created and analysed. The approach based on an efficacy parameter allowing the prediction of co-crystals with melting points lower than those of individual compounds was developed.

σ-Hole interactions in small-molecule compounds containing divalent sulfur groups R₁—S—R₂

The occurrence of non-covalent σ-hole interactions at divalent sulfur has been shown by Cambridge Structural Database searches and their strength and interaction geometries investigated in exemplar systems with quantum mechanical calculations.

Crystal Structures. Patterns and Symmetry. By Michael O'Keeffe and Bruce G. Hyde. Dover, 2020. Paperback, pp. xvi+461. Price USD 39.95. ISBN 978-0-486-83654-6