Centrosymmetric and pseudo-centrosymmetric structures refined as non-centrosymmetric

An analysis of the Flack parameter based on published (pseudo-)centrosymmetric crystal-structure determinations.

Bond analyses of borates from the Inorganic Crystal Structure Database

More precise bond-valence parameters d₀ of B—O bonds are recommended for various kinds of fundamental building blocks (FBBs) in borates, considering dominant factors such as the detailed configurations of borate FBBs, anhydrous or hydrous, the interstitial halogen anions, and the substitution of borate anions. Current structural analysis may be helpful for us to search for novel nonlinear optical borates.

Modulated corrugations in the crystal structure of the superconductor CaAlSi

We report the crystal structure analyses of CaAlSi from single-crystal and powder X-ray diffraction and the existence of two commensurately modulated structures.

Structural phase transition and hydrogen ordering of TlH₂PO₄ at low temperature

The crystal structure of TlH₂PO₄ (TDP) has been studied at low temperatures. Lattice parameters were derived from high-resolution X-ray powder diffraction in the temperature range between 8 and 300 K. A detailed crystal structure analysis of the antiferroelectric low-temperature phase (TDP-III) has been performed based on neutron diffraction data measured at 210 K. The polymorphism of TDP and the fully deuterated TlD₂PO₄ (DTDP) is presented in the form of group–subgroup relations between the different space groups.

Structural characterization of Ni₂Si pseudoepitaxial transrotational structures on [001] Si

This work reports the structural characterization of very thin Ni₂Si layers grown at low temperature by transrotational domains. A non-conventional mechanism of strain relaxation has been proposed, which is competitive with respect to the usual formation of misfit dislocations, consisting of Ni₂Si lattice bending and rearrangement of the interface to minimize the Gibbs free energy of the domain.

Superspace description of the homologous series Ga₄Ti_m−4O_2m−2 with the crystallographic shear structure based on that of rutile

An ideal (3 + 1)-dimensional model was proposed for the homologous series Ga₄Ti_m−4O_2m−2 with crystallographic shear structures based on that of rutile. The Rietveld fitting of the X-ray diffraction profile of Ga₄Ti₁₃O₃₂ was performed using the model.

Bond-valence parameters of lanthanides

Ln—O and Ln—N bond-valence parameters of four classical `not trivalent' elements (Ce^IV, Sm^II, Eu^II and Yb^II), and Ln—Cl, Ln—S and Ln—C(π-bonded) bond-valence parameters are presented, as calculated for coordination compounds.

LnO_n coordination polyhedra (Ln = La–Lu) in crystal structures

Using the Voronoi–Dirichlet polyhedra and the method of intersecting spheres, 2917 compounds containing 3903 crystallographically non-equivalent types of LnO_n polyhedron (Ln = La–Lu) were analyzed. Despite a great diversity in coordination numbers and types of coordination polyhedra, the volume of the Voronoi–Dirichlet polyhedron of an Ln atom was found to depend only on the identity of the Ln atom and its oxidation state.

Specific twin junctions in doped zirconia

Special twin boundaries in monoclinic zirconia phases doped with different trivalent cations of rare earths are characterized in detail. The suitability of using selected-area diffraction patterns for this kind of study is demonstrated.

Structure and phase transition of the Se-rich variety of antimonpearceite, [(Ag,Cu)₆(Sb,As)₂(S,Se)₇][Ag₉Cu(S,Se)₂Se₂]

The crystal structure of a natural Se-rich antimonpearceite, [(Ag,Cu)₆(Sb,As)₂(S,Se)₇][Ag₉Cu(S,Se)₂Se₂], has been solved and refined from X-ray single-crystal diffraction data at room temperature in its ionic-conducting form and at 120 K in its non-conducting ordered form.

First (3 + 2)-dimensional superspace approach to the structure of levyclaudite-(Sb), a member of the cylindrite-type minerals

The structure of levyclaudite-(Sb), a member of the cylindrite mineral group, has been determined from a synthetic sample by single-crystal X-ray diffraction on the basis of the (3 + 2)-dimensional superspace approach.

Commensurate (C₆H₁₄N₂)₂[Mo₈O₂₆]·4H₂O and incommensurate (C₆H₁₄N₂)₂[Mo₈O₂₆]·4.66H₂O: a structural versatility linked to solvent content

The syntheses and structure determinations by means of single-crystal X-ray diffraction of commensurate (C₆H₁₄N₂)₂[Mo₈O₂₆]·4H₂O and incommensurate (C₆H₁₄N₂)₂[Mo₈O₂₆]·4.66H₂O, two new organic–inorganic hybrid compounds based on polyoxomolybdates, are reported.

Stoichiometry-dependent structures: an X-ray and neutron single-crystal diffraction study of the effect of reaction stoichiometry on the crystalline products formed in the potassium–cyanurate system

Among a family of related structures, a single-crystal neutron diffraction study was carried out on a fully deuterated potassium cyanurate complex to study potential deuterium-atom disorder. Instead it revealed that the true unit cell is a supercell of that identified by X-rays, corresponding to the doubling of one axis, caused by just two deuterium atoms which break apparent crystallographically imposed mirror symmetry.

Two-dimensional metal-organic frameworks containing linear di­carboxylates

Metal-organic framework structures adopting either square grid or triangular grid architectures are reported. A family of the latter type incorporating different solvent molecules sheds light on the flexibility of these layered structures in previously reported solvent loss/uptake.

High-pressure neutron diffraction study of L-serine-I and L-serine-II, and the structure of L-serine-III at 8.1 GPa

The hydrostatic compression of L-serine-d₇ has been studied to 8.1 GPa by neutron powder diffraction. Over the course of this pressure range the compound undergoes two phase transitions, the first between 4.6 and 5.2 GPa, and the second between 7.3 and 8.1 GPa.

Exploration of the high-pressure behaviour of polycyclic aromatic hydrocarbons: naphthalene, phenanthrene and pyrene

Recrystallization from a dichloromethane solution at 0.5 GPa affords new polymorphs of phenanthrene and pyrene. Structural analysis of the high-pressure polymorphs of pyrene and phenanthrene shows that intermolecular interactions are substantially different from those found in the ambient-pressure structures and do not fit a previously established packing model for polycyclic aromatic hydrocarbons. Recrystallization of naphthalene from a dichloromethane solution in the 0.2–0.6 GPa pressure range does not result in the formation of a new polymorph, and its crystal structure is reported to be stable to compression to 2.1 GPa.

Invariom structure refinement, electrostatic potential and toxicity of 4-O-methylalpinumiso­flavone, O,O-di­methylalpinumisoflavone and 5-O-methyl-4-O-(3-methylbut-2-en-1-yl)alpinum­isoflavone

An invariom refinement, electrostatic properties and toxicities of three alpinumisoflavones isolated from Milletia thonningii are reported.

π-Bond cooperativity and anticooperativity effects in resonance-assisted hydrogen bonds (RAHBs)

In typical intramolecular resonance-assisted hydrogen bonds (RAHBs), enolones (⋯O=C—C=C—OH⋯) and enaminones (⋯O=C—C=C—NH⋯) form π-cooperative six-membered rings closed by strong O—H⋯O or N—H⋯O bonds. This paper studies the ways of fusion of two of these rings through a common C=O or C—C bond, and shows that such a fusion gives rise to unusual forms of prototropic tautomerism whose relative energies can be explained in terms of π-cooperative and π-anticooperative relationships of the two cumulated RAHBs.

Molecular versus crystal symmetry in tri-substituted triazine, benzene and isocyanurate derivatives

The crystal structures of triethyl-1,3,5-triazine-2,4,6-tricarboxylate, triethyl-1,3,5-benzenetricarboxylate and tris-2-hydroxyethyl isocyanurate have been determined from laboratory X-ray powder and single-crystal diffraction data, despite the presence of disorder and significant preferred orientation. The materials display contrasting packing behaviour, with only the triazine derivative retaining threefold molecular symmetry in its crystal structure.

Anisotropic displacement parameters for H atoms using an ONIOM approach

Ab initio ONIOM cluster calculations are combined with TLS analysis of heavy-atom ADPs from X-ray diffraction data to provide accurate estimates of H-atom ADPs for charge-density analysis.

New monocyclic and acyclic hNK-2 antagonists retaining the β-turn feature. X-ray and molecular modelling studies

Structural characterization of two new monocyclic and linear human tachykinin NK-2 antagonists showing the β-turn feature.

Distribution of molecular pairs in Z′ = 2 structures

The positions of molecular pairs in structures with Z′ = 2 are considered for space groups common for that class of structure in the Cambridge Structural Database.

On hydrogen bonding in 1,6-anhydro-β-D-gluco­pyranose (levoglucosan): X-ray and neutron diffraction and DFT study

The geometry of hydrogen bonds in 1,6-anhydro-β-D-glucopyranose is accurately determined by single-crystal neutron diffraction. DFT calculations predict red (blue) shifts of stretching frequencies of O—H (C—H) in this material due to the formation of hydrogen bonds.

Supercell and subcell description of the crystal structure of tri­ammonium bis­(O-phospho-L-serinate) trihydrate

The crystal structure of triammonium bis(O-phospho-L-serinate) trihydrate is described assuming a monoclinic supercell. Omission of weak superstructure reflections leads to a structure solution in an orthorhombic subcell.

Accurate molecular structures and hydrogen bonding in two polymorphs of ortho-acetamidobenzamide by single-crystal neutron diffraction

The structures of both known forms of the polymorphic material ortho-acetamidobenzamide have been determined by low-temperature neutron single-crystal diffraction.

Isomeric N-(iodo­phenyl)nitrobenzamides form different three-dimensional framework structures

Seven isomeric N-(iodophenyl)nitrobenzamides all display different direction-specific intermolecular interactions and all form different three-dimensional framework structures.

Order–disorder twinning model and stacking faults in α-NTO

Fourfold twinning in the structure of 5-nitro-2,4-dihydro-1,2,4-triazol-3-one with Z′ = 4 arises from layer stacking faults.

Accurate bond-valence parameters for the Bi³⁺/Br⁻ ion pair

Using a new calculation scheme, reliable and physically meaningful values of the bond-valence parameters (r₀ = 2.567 Å and b = 0.421 Å) have been deduced for the Bi³⁺/Br⁻ ion pair from the molecular geometry and from the crystal structure of BiBr₃.