Understanding exceptional polymorphs

Detailed analysis by Brock [Acta Cryst. (2016), B72, 807–821] of the details of the crystal packing and chemical functionality in 284 organic crystal structures with Z′ > 4 reveals organizing principles in the vast majority of cases.

High-Z′ structures of organic molecules: their diversity and organizing principles

An in-depth investigation of the Z′ > 4 structures of organic molecules archived in the Cambridge Structural Database has shown that the group is very diverse but that most structures are the result of a simple modulation and/or of a hydrogen-bonded aggregate that has at most approximate symmetry.

Vacancy pairing and superstructure in the high-pressure silicate K_1.5Mg₂Si₂O₇H_0.5: a new potential host for potassium in the deep Earth

The superstructure of a novel high-pressure hydrous silicate K_1.5Mg₂Si₂O₇H_0.5 relevant to the water budget of the Earth's mantle has been determined and its crystal chemistry discussed in relation to its stabilization at mantle conditions.

Cu^II and Zn^II β-diketonate coordination polymers based on pyrimidin-2-amine, pyrazine and 1,2-bis­(4-pyridyl)­ethane

The potential of pyrimidin-2-amine as a building block to construct extended supramolecular structures has been evaluated in comparison to the well established bridging ligands pyrazine and 1,2-bis­(4-pyridyl)­ethane on the 4,4,4-trifluoro-1-phenylbutane-1,3-dionato copper(II) and zinc(II) moieties.

Solvates of selected fenamic acids with substituted pyridines: structure, thermal stability and desolvation

Mefenamic acid and tolfenamic acid form solvates with selected substituted pyridines. The crystal structures, thermal stability, desolvation studies and other modes of preparation were also determined.

Two cubic phases in kimzeyite garnet from the type locality Magnet Cove, Arkansas

Two cubic phases in a kimzeyite crystal create optical anisotropy that results from strain originating from structural mismatch. Two different mechanisms, namely epitaxial growth and exsolution on cooling, give rise to the two phases.

Neutron and high-pressure X-ray diffraction study of hydrogen-bonded ferroelectric rubidium hydrogen sulfate

The hydrogen-bonded ferroelectric material rubidium hydrogen sulfate has been investigated through a combination of high-pressure X-ray diffraction and neutron Laue diffraction. This study confirms the order–disorder origin of the ferroelectric transition as well as fully characterizing the high-pressure phase transition.

Accurate and efficient representation of intra­molecular energy in ab initio generation of crystal structures. I. Adaptive local approximate models

This article describes an important improvement in the CrystalPredictor II code: adaptive Local Approximate Models (LAMs). This improvement allows the most efficient use of computational effort to cover a flexible molecule's conformational space, and is illustrated with a crystal structure prediction (CSP) investigation into the sixth blind test molecule 26.

Hydrogen-substituted β-tricalcium phosphate synthesized in organic media

A hydrogen substitution mechanism, previously unknown in pure β-tricalcium phosphate, was discovered in crystals precipitated from ethylene glycol solutions. The structure was described by means of Rietveld refinement of powder X-ray diffraction data and corroborated by chemical analysis and IR spectroscopy.

Accurate hydrogen parameters for the amino acid L-leucine

Modern neutron Laue diffraction has been used to determine the structure of the primary amino acid L-leucine.

(Na,□)₅[MnO₂]₁₃ nanorods: a new tunnel structure for electrode materials determined ab initio and refined through a combination of electron and synchrotron diffraction data

Octahedral molecular sieves (OMS) attract increasing interest in the search for novel electrode materials for energy storage and water desalination. While a nanometric particle size is desirable for such applications, this makes ordinary single-crystal characterization difficult and many OMS structures are still waiting for elucidation. Here we present the long awaited structure of a well known material, (Na,□)₅[MnO₂]₁₃, resolved by a combination of electron diffraction tomography, dynamical scattering theory and X-ray powder Rietveld refinement. A new type of tunnel structure was found, able to explain previously reported electrochemical properties. This structure also suggests a possible mechanism for topotactic transformations between different manganese oxide OMS frameworks.

Incommensurate density modulation in a Na-rich plagioclase feldspar: Z-contrast imaging and single-crystal X-ray diffraction study

Z-contrast images and X-ray diffraction (XRD) show both Ca–Na ordering and density modulation in an Na-rich plagioclase feldspar. The neighboring lamellar domains with I1 symmetry are in an inversion twinning relationship.

Comparison of hydrogen bonds and diverse weak interactions of the nitro group in 2-methyl-4-nitroanilinium nitrate, bi­sulfate and two hexa­fluoridosilicates: elementary graph-set approach

Hydrogen-bonding patterns of four 2-methyl-4-nitroanilinium salts were analysed using a graph-set approach and mathematical relations among elementary graph-set descriptors. The diversity of interactions of the nitro group was also discussed.

Unique thermodynamic relationships for Δ_fH^o and Δ_fG^o for crystalline inorganic salts. I. Predicting the possible existence and synthesis of Na₂SO₂ and Na₂SeO₂. Addendum

Addendum to Vegas et al. [(2012), Acta Cryst. B68, 511–527].

Bonding, Structure & Solid-state Chemistry

Snow, Ice and Other Wonders of Water. A Tribute to the Hydrogen Bond

Industrial Inorganic Chemistry