Probing the structure of framework materials by high pressure and the example of a magnetic, non-porous coordination polymer

High pressure has become an indispensable research tool in the quest for novel functional materials. High-pressure crystallographic studies on non-porous framework materials based on coordination compounds are markedly on the rise, enabling the unravelling of structural phenomena and taking us a step closer to the derivation of structure–property relationships.

Structures beyond superspace

Once a contradiction in terms, aperiodic crystals show instead that `long-range order' has never been defined. Whatever it means, decades of intense research have shown it to be more complex and surprising than anyone suspected.

Pressure-induced structural phase transformation in cobalt(II) dicyanamide

High-pressure synchrotron powder diffraction studies of the magnetic molecular framework cobalt(II) dicyanamide, Co(dca)₂, revealed a reversible orthorhombic to monoclinic transformation at 1.1 GPa and negative linear compressibility over the measured pressure range up to 4.2 GPa.

Aperiodic crystals and beyond

The notion of order in spatial structures is discussed in the context of mathematical diffraction theory, with particular emphasis on aperiodic crystals and non-crystalline structures.

Neutron diffraction structures of water in crystalline hydrates of metal salts

Statistical analysis is made of the influence of the disposition of near neighbours on the water structure in hydrated metal complexes.

Synthesis, growth, structure and characterization of molybdenum zinc thiourea complex crystals

The molybdenum zinc thiourea complex crystals are observed in molecular orientations resulting in a facile charge transfer leading to non-linearity.

Neutron Laue and X-ray diffraction study of a new crystallographic superspace phase in n-nona­decane–urea

n-Nonadecane–urea is an aperiodic molecular composite. Neutron Laue and X-ray diffraction studies reveal there is a supplementary phase transition within the crystallographic superspaces.

Tilting structures in inverse perovskites, M₃TtO (M = Ca, Sr, Ba, Eu; Tt = Si, Ge, Sn, Pb)

Single-crystal X-ray diffraction experiments were performed for the whole series of inverse perovskites, M₃TtO (M = Ca, Sr, Ba, Eu; Tt = tetrel element: Si, Ge, Sn, Pb) in the temperature range 500–50 K. Depending on M and Tt, temperature-driven phase transitions were observed; they all take place together with multiple twinning.

Structure of magnesium selenate enneahydrate, MgSeO₄·9H₂O, from 5 to 250 K using neutron time-of-flight Laue diffraction

Single-crystal neutron diffraction, ab initio calculations and Raman spectroscopy are applied to study the structure and hydrogen bonding of magnesium selenate enneahydrate, a recently discovered new hydration state in M²⁺XO₄ hydrates and a unique example of a material with a cation: (oxy)anion:water ratio of 1:1:9, giving novel insights into the polymerization of water in highly hydrated materials.

Optical anomaly in artificial cubic hieratite, K₂[SiF₆]

Crystals of K₂[SiF₆] were grown in agar gel. They have a cubic structure as refined from X-ray diffraction data, however, they exhibit birefringence in six regular domains.

Crystal structure, atomic net charges and electric moments in pyroelectric LiNaSO₄ at 296 K

Crystal structure and atomic net charges of LiNaSO₄ are explored by X-ray diffraction and refined by the program MOLLY under integer ionic constraints. A relationship between the optical refractive indices and the second electric moment, derived from the model, is manifested.

Octahedral tilting in the tungsten bronzes

Group theoretical methods are used to explore the possibilities for tilting of the corner-connected octahedra in hexagonal and tetragonal tungsten bronzes. Connection is made with the structures reported for these materials.

Structural insights into M₂O–Al₂O₃–WO₃ (M = Na, K) system by electron diffraction tomography

The structure of two new nanocrystalline phases, K₅Al(W₃O₁₁)₂ and NaAl(WO₄)₂, was determined by automated electron diffraction tomography. Structure analysis was complicated by pseudo-symmetry and the presence of additional phases.

The modulated average structure of mullite

The first refinement of modulated mullite in the superspace approach is presented disclosing a modulated average structure of basically disordered mullite. It is discussed as to why mullite does not form a perfectly long-range ordered structure, although simple superstructures can easily be set up which are compatible with the chemical composition.

Structural analysis of the coordination of di­nitrogen to transition metal complexes

A structural analysis from the Cambridge Structural Database of the transition metal–dinitrogen fragment species was performed. The analysis of the bound precursor fragment can be useful to provide information about its fixation and activation.