Mean bond-length variations in crystals for ions bonded to oxygen

Variations in mean bond length are examined in oxide and oxysalt crystals for 55 cation configurations bonded to O²⁻. Bond-length distortion is confirmed as a statistically significant causal factor of mean bond-length variation. The assignment of a coordination-based radius to O²⁻ is found not to be supported by experimental data.

Conformational and structural diversity of iridium di­methyl sulfoxide complexes

Iridium(III) di­methyl sulfoxide complexes, analogues to clinically significant metallodrugs, exhibiting different rotamers in their solid-state structures are investigated. The effect of the amount of the crystallized water and the hydrogen-bonded network in their supramolecular structures on the conformational preferences is studied.

A review of the oxidation–pressure concept (OPC) and extended Zintl–Klemm concept (EZKC), and the emergence of the high-pressure Ni₂In-type phase of lithium sulfide (Li₂S) rationalized by reference to a newly defined stability enhancement ratio (S)

The Ni₂In phase of Li₂S (P6₃/mmc), recently observed at 30 GPa as the final step in the transition antifluorite→anticotunnite→Ni₂In, provides evidence of the oxidation–pressure concept, since the [Li₂S] subarray of the high-pressure phase of Li₂SO₄ (Cmcm) is a distortion of the new Li₂S phase. Following the extended Zintl–Klemm concept (EZKC), Li₂S can be formulated as Li⁺[LiS]^– ≡ Li⁺[Ψ-BeS] and its usefulness has been enhanced by calculating the values of the ionic strength I. The enhancement factor, S = I[Ψ-BeS]/I[Li₂S] = 1.16, denotes increased stability in [Ψ-BeS] as brought about by the EKZC.

The extended Zintl–Klemm concept, ionic strength I and assessment of the relative stability of lattices using the stability enhancement ratio S

Ionic stregth (I) calculations on 25 silicates indicate that the I values of the Zintl polyanions are higher than those of the original compound. The extended Zintl–Klemm concept is reinforced by the application of the thermodynamically related ionic strength, I.

Orientational order-disorder γ ↔ β ↔ α′ ↔ α phase transitions in Sr₂B₂O₅ pyroborate and crystal structures of β and α phases

Hitherto unknown crystal structures of β- and α-Sr₂B₂O₅ are presented and a unified description of the Sr₂B₂O₅ modifications based on the formalism of commensurately modulated structures is created. Data of the γ ↔ β ↔ α′ ↔ α thermal phase transitions are revisited and extended.

A new high-pressure polymorph of phosphoric acid

The high-pressure behaviour of monoclinic phosphoric acid is presented and a new high-pressure orthorhombic phase is reported. The molecule–molecule interaction energies of the orthorhombic phase are shown to be more attractive than those of the low-pressure monoclinic phase.

On the stacking disorder of DL-norleucine

Diffraction patterns of norleucine frequently show diffuse streaks, which indicates a stacking disorder of the double layers. The disorder is explained by symmetry analysis and lattice-energy minimizations using DFT-D.

Orientational disorder and phase transitions in ammonium oxo­fluoro­vanadates, (NH₄)₃VOF₅ and (NH₄)₃VO₂F₄

The high-temperature elpasolite-like crystal structure of (NH₄)₃VOF₅ with six spatial orientations of the VOF₅³⁻ octahedron undergoes an order–disorder phase transition with the existence of two octahedral dynamic states at room temperature.

Effect of processing parameters on microstructural properties of lead magnesium niobates

Microstructural analysis of the room-temperature synchrotron X-ray diffraction (XRD) data of lead magnesium niobate samples prepared under different processing conditions has been carried out using the Rietveld method to study the polar nanoregions (R3m phase). This is the minor phase and normally not accessible at room temperature using laboratory-source XRD data. It is found that the Gaussian component of size broadening is apposite for the polar rhombohedral phase (R3m) and the Lorentzian component of strain broadening is apposite for the paraelectric cubic phase (Pmm).

New superprotonic crystals with dynamically disordered hydrogen bonds: cation replacements as the alternative to temperature increase

The single-crystal structure of [K_0.43(NH₄)_0.57]₃H(SO₄)₂ has been determined using X-ray diffraction; its dielectric properties have been studied to define the structural influence on the abnormal physical properties.

Migrating hydrogen in 2,4,6-tri­amino­pyrimidin­ium(1+)_x hydrogen trioxo­fluoro­phosphate(−)_x monohydrate/2,4,6-tri­amino­pyrimidinium(2+)_1–x trioxo­fluoro­phosphate(2–)_1–x monohydrate (0.0 < x < 0.73) with changing temperature

Structure determinations of the title compounds at different temperatures revealed the presence of a moderate, though still strong, O—H⋯N/O⋯H—N hydrogen bond in which the electron density distribution of its bridging hydrogen is temperature dependent. The structural properties of the anions [PO₃F]²⁻ and [HPO₃F]⁻, namely the interdependence of the longest P—F and P—O bond lengths, which reflects the bonding of the latter anion, are also discussed.

Atomic structures of ternary Yb–Cd–Mg icosahedral quasicrystals and a 1/1 approximant

A systematic study of the structures of ternary icosahedral Yb–Cd–Mg quasicrystals with different Mg contents has been carried out by single-crystal X-ray diffraction; occupational and positional disorder in the resulting structures was compared with that in a Yb–Cd–Mg 1/1 approximant.

The crystal structure of Rb₂Ti₂O₅

Structural investigation of Rb₂Ti₂O₅ was carried out using X-ray diffraction, Raman spectroscopy along with calculations of phonon modes using DFT.

Compression of glycolide-h₄ to 6 GPa

Fully hydrogenated glycolide (C₄H₄O₄) has been studied as a function of pressure on the high-pressure beamline, PEARL, at ISIS Neutron and Muon Source. It undergoes a phase transition but remains monomeric to 6 GPa.

Multi-temperature structure of thermoelectric Mg₂Si and Mg₂Sn

Accurate structural parameters of Mg₂Si and Mg₂Sn are reported. They are useful for studying these promising thermoelectric materials and their solid solutions.

Out-of-plane ionicity versus in-plane covalency interplay in high-T_c cuprates

The microscopic order parameter, which is responsible for the physics of high-T_c superconductors, especially the insulator–metal transition and the metal–superconductor transition, is the local field that reflects interlayer polarization.

Phase transition and proton ordering at 50 K in 3-(pyridin-4-yl)pentane-2,4-dione

At ambient temperature, the H atom in the short intramolecular hydrogen bond of 3-(pyridin-4-yl)pentane-2,4-dione is disordered; below 50 K, a structural phase transition and proton ordering are observed.

Solid-state structure of cyclic dipeptides: an X-ray and computational study of cis- and trans-diketopiperazines of N-methyl-phenyl­alanine with the thia-pipecolic acids and thia-prolines

X-ray and computational study of cis- and trans-diketopiperazines of N-methyl-phenyl­alanine with the thia-pipecolic acids and thia-prolines are presented. The effect of sulfur on the geometry of diketopiperazine ring and amide bond non-planarity is discussed.

Intermetallics. Structures, Properties, and Statistics

Intelligent Materials and Structures

Crystal Chemistry. From Basics to Tools for Materials Creation