The structure of orange HgI₂. I. Polytypic layer structure

Orange polytypic crystals of mercuric iodide (HgI) are fractal complications of the stable red HgI structure, exhibiting frequent stacking faults with an average thickness of ordered domains of 30 Å.

The structure of orange HgI₂. II. Diamond-type structure and twinning

Metastable orange crystals of HgI present three types of structures built from HgI supertetrahedra, that are corner-linked into a three-dimensional network or into layers that can be stacked in two different ways.

Prediction of new displacive ferroelectrics through systematic pseudosymmetry search. Results for materials with Pba2 and Pmc2₁ symmetry

New ferroelectrics are predicted among the structures with symmetry and using a systematic pseudosymmetry search. An empirical relation between the transition temperature and the atomic displacements in the case of proper ferroelectrics permits the estimation of the transition temperature for materials proposed as possible ferroelectrics.

Group-theoretical analysis of octahedral tilting in ferroelectric perovskites

Ferroelectric patterns of cation displacement together with simple tilting of the octahedral units in perovskite give rise to considerable structural variation. 61 possible structures are listed along with the pertinent group–subgroup relationships and an indication of which transitions between the different structures are allowed to be continuous.

Pressure-induced phase transitions of piezoelectric single crystals from the langasite family: La₃Nb_0.5Ga_5.5O₁₄ and La₃Ta_0.5Ga_5.5O₁₄

The hydrostatic compression of piezoelectric single crystals of La₃Nb_0.5Ga_5.5O₁₄ and La₃Ta_0.5Ga_5.5O₁₄ was studied at pressures of up to 23 GPa in diamond-anvil high-pressure cells.

Crystal chemistry of orthosilicates and their analogs: the classification by topological types of suprapolyhedral structural units

A method is developed for the analysis and classification of orthosilicates and their analogs M_x(TO₄)_y containing M cations and tetrahedral TO₄ anions. First, the suprapolyhedral level of crystal structure organization was studied, where T tetrahedra were considered as templates for the condensation of M polyhedra. Using this methodology, the crystal structures of 54 orthosilicates and orthogermanates were analyzed within the first 12 coordination spheres of T nodes and were arranged into 21 topological types.

Atomic displacement parameters for spessartine Mn₃Al₂Si₃O₁₂ and their lattice-dynamical interpretation

Lattice-dynamical calculations on the silicate garnet spessartine Mn₃Al₂Si₃O₁₂ are presented, with an evaluation of the atomic displacement parameters, vibrational spectra and thermodynamic functions.

The incommensurate modulation of the structure of Sr₂Nb₂O₇

The incommensurately modulated structure of the ferroelectric SrNbO is determined by single-crystal X-ray diffraction. The driving force for the modulation is found to be the internal strain around the Sr atoms.

Commensurate and incommensurate structures of the hexa­bromotellurate(IV) bis­{di­bromodiselenate(I)} ion – [(C₂H₅)_n(C₆H₅)_4−nP]₂[TeBr₆(Se₂Br₂)₂], n = 0,1

Structure analysis of [(C₂H₅)_n(C₆H₅)_4−nP]₂[TeBr₆(Se₂Br₂)₂] is presented for n = 1 and 0. The latter is an incommensurate one-dimensionally modulated structure with alternating cis- and trans- arrangements of the bromine atoms. The alternations are caused by modulation.

Modified photoreactivity due to mixed crystal formation. II. Enhanced reactivity upon conformational mimicry and cavity enlargement

Single-crystal-to-single-crystal photoisomerization in two mixed cobaloxime complex crystals is reported. The enhanced photoreactivity of the 2-cyanopropyl and the 2-cyanoethyl groups in the mixed crystal is well explained qualitatively and quantitatively by conformational change of the reactive groups and by the size of the reaction cavity.

Atomic thermal motions studied by variable-temperature X-ray diffraction and related to non-linear optical properties of crystalline meta-di-nitro­benzene

The meta-dinitrobenzene crystal structure and thermal expansion and a rigid-body analysis of its anisotropic displacement parameters are studied over the 100–300 K temperature range. Ab initio calculations evaluate the vibrational contribution to the static first-order hyperpolarizability of the molecule.

CH₃CN: X-ray structural investigation of a unique single crystal. β → α phase transition and crystal structure

The unusual solid–solid phase transition (β → α) preserving the single-crystal form of acetonitrile, CH₃CN, has been studied. Single crystals of the β form transform to single crystals of the α form when warmed through the transition.

Electron density study of 2H-chromene-2-thione

Topological analysis of the electron density in 2-thiocoumarin crystals using a multipole model fitted to the experimental X-ray diffraction data at 90 K is presented and the dipole moment components are compared with those obtained from theoretical estimates.

Pressure-induced polymorphism in phenol

The crystal structure of phenol (C₆H₅OH) at 0.16 GPa has been determined using a combination of single-crystal X-ray diffraction techniques and ab initio density-functional calculations. In contrast to the ambient-pressure phase, in which the molecules are linked by OH⋯O hydrogen bonds into a pseudo-threefold helix, chains are formed about 2₁ and pseudo-2₁ screw axes.

Crystal packing in vicinal diols C_nH_m(OH)₂

A survey of the O—H⋯O bonds in vic-diols C_nH_m(OH)₂ reveals a variety of hydrogen-bonding patterns. The space-group frequencies are anomalous for the half of the vic-diols that form complete, or almost complete, sets of O—H⋯O bonds.

A reexamination of the low-temperature crystal structure of the p-tert-butylcalix[4]arene–toluene inclusion compound. Differences in spatial averaging with Cu and Mo Kα radiation

The low-temperature crystal structure of the p-tert-butylcalix[4]arene–toluene inclusion compound exhibits significant guest-induced distortion of the host calixarene molecule. Remarkably, the space group and unit cell that best describe the structure appear to depend on the wavelength of the incident radiation.

Crystal structure of the inclusion complex of β-cyclodextrin with mefenamic acid from high-resolution synchrotron powder-diffraction data in combination with molecular-mechanics calculations

Mefenamic acid and β-cyclodextrin form a monomeric inclusion complex. Mefenamic acid is partially included in β-cyclodextrin with either the xylyl or the benzoic-acid moiety inside the cavity.

Diastereomeric salts of lactic acid and 1-phenyl­ethylamine, their structures and relative stabilities

The crystal structures of two diastereomeric salts are investigated. Differences in solubilities between the two salts are related to differences in enthalpy and entropy of the crystals.

X-ray studies on crystalline complexes involving amino acids and peptides. XL. Conformational variability, recurring and new features of aggregation, and effect of chirality in the malonic acid complexes of DL- and L-arginine

The requirements of hydrogen bonds that involve the guanidyl group appear to affect the frequency of occurrence of different arginine conformations. The aggregation pattern in the DL-arginine complex exhibits varying degrees of resemblance to patterns in similar structures while that in the L-arginine complex is observed for the first time.

The formation of paracetamol (acetaminophen) adducts with hydrogen-bond acceptors

The crystal structures of five hemiadducts of paracetamol with 1,4-dioxane, N-methylmorpholine, morpholine, N,N-dimethylpiperazine and piperazine and a related 1:1 adduct of paracetamol with 4,4′-bipyridine are described. All structures are characterized by the formation of chains of paracetamol molecules, linked via either OH⋯O=C or NH⋯O=C interactions, depending on the presence or absence of substituent groups on the guest molecule.

Structural investigations of phosphorus–nitrogen compounds. 5. Relationships between molecular parameters of 2,2-di­phenyl-4,6-cis-oxytetra­(ethyl­ene­oxy)-4,6-R₂-cyclotriphosphazatrienes (R = Cl, OCH₂CF₃, OPh, OMe, NHPh, NHBu^t) and substituent basicity constants

The syntheses and crystal structures of six new cis-ansa derivatives N₃P₃Ph₂[O(CH₂CH₂O)₄]R₂ (R = Cl, OCH₂CF₃, OPh, OMe, NHPh, NHBu^t) are reported and the observed relationship between molecular parameters of the N₃P₃ ring and substituent basicity constants is discussed.

Crystal structure analysis. Principles and practice

Perovskites modern and ancient

Fundamentals of solid-state phase transitions, ferromagnetism and ferroelectricity