Observation of 4f electron transfer from Ce to B₆ in the Kondo crystal CeB₆ and its mechanism by multi-temperature X-ray diffraction

Multi-temperature electron density measurements of the Kondo crystal CeB₆ and analysis based on a spin-orbit interaction model revealed an entropy-driven mechanism of the 4f-electron transfer from Ce to B—B bonds connecting B₆ octahedra. The charge accumulation changes the effective atomic potentials, which causes large anharmonic vibrations of Ce and B at low temperature and an increase in entropy.

Klockmannite, CuSe: structure, properties and phase stability from ab initio modeling

The crystal structure and phase stability of CuSe polymorphs under pressure is investigated using density functional formalism.

On the structure of aragonite – Lawrence Bragg revisited

Aragonite has previously been described in the space group Pnma. In this work, weak reflections that violate the systematic extinctions of Pnma are shown to be Bragg reflections. A twinned triclinic model is proposed that goes some way towards explaining these weak reflections.

Anion packing density: a universal qu­antity for both dense and porous crystalline inorganic phases

To compare densities or porosities of inorganic phases of almost any kind, the anion packing density is introduced and compared with the framework density used by zeolite scientists. It becomes evident that the Shannon–Prewitt effective ionic radii are inadequate to quantitatively describe inroganic structures at high pressures.

Nucleophilic addition reaction in coordinated non-linear pseudohalides: experimental charge density analysis in trans-bis­(cyanamidonitrato-N:O)bis-(imidazole-N³)copper(II) complex

Structural, multipole and orbital analyses of the electron density for the title complex using high-resolution X-ray diffraction data collected at 120 K have been performed. Analysis of the atomic charges indicates the possibility of nucleophilic addition reaction.

Crystal and electronic structure of a new metallic modification of (ET)₂[KHg(SCN)₄]

The crystal and electronic structures of a new polymorphous metallic modification of the (ET)₂[KHg(SCN)₄] salt have been determined, using X-ray diffraction and tight-binding band structure calculations.

Refinement of obverse/reverse twins

Two examples of the refinement of obverse/reverse twinned structures are discussed. The second example shows additional merohedral twinning.

Reversible dimerization of C₆₀ molecules in the crystal structure of the bis­(arene)chromium fulleride [Cr(C₇H₈)]₂C₆₀

Bis(arene)chromium fulleride [Cr(C₇H₈)₂]⁺C₆₀⁻ exhibits a reversible first-order phase transition forming (C₆₀)₂²⁻ dimers. The structures of the high- and low-temperature phase are determined via high-resolution X-ray powder diffraction and are compared with the structures of Rb⁺C₆₀⁻, the other prominent example in which (C₆₀)₂²⁻ dimers are present.

Fast estimation of crystal densities

By a least-squares fit the average volume of elements in organic and metal-organic crystals is determined as a function of the temperature and a method for fast density estimation and its mean error is presented.

Novel, predicted patterns of supramolecular self-assembly, afforded by tetrameric rings of C₂ symmetry in the crystal structures of 2-hy­droxy-1-cyclo­pentane­carboxylic acid, 2-hy­droxy-1-cyclo­hexane­carboxylic acid and 2-hy­droxy-1-cycloheptane­carboxylic acid

Racemic crystals of three optically active molecules formed by saturated five-, six- and seven-membered rings bearing two vicinal (either cis or trans) hydrogen-bond donor/acceptor functions were found to represent a novel form of supramolecular close packing. It had been predicted on the basis of five related patterns of close packing revealed in analogous cyclopentane derivatives.

Two phases of C₉H₁₂O₄: why is the structure at 295 K so complicated?

The structures of two modulated phases of a small organic molecule have been determined. The structure at 295 K has five mirror-symmetric molecules in the asymmetric unit; four of the molecules are disordered. At 130 K the unit cell and asymmetric unit are smaller and the structure is ordered.

β Turns, water cage formation and hydrogen bonding in the structures of L-valyl-L-phenylalanine

Two L-Val-L-Phe structures present unique dipeptide conformations and crystal packing arrangements, provide comprehensive hydrogen-bond data and display detailed interactions between hydrophobic groups and solvent water molecules.

Charge density study of hydrogen [(2,4-di­aminopyrimidin-1-io)methyl]phosphonate monohydrate

The crystal structure and charge density of hydrogen [(2,4-diaminopyrimidin-1-io)methyl]phosphonate monohydrate have been determined by means of single-crystal X-ray diffraction. Preferential polarization of lone-pair electron densities of hydrogen-bond acceptor atoms into shorter hydrogen bonds was observed.

Chiral versus racemic building blocks in supramolecular chemistry: malate salts of organic di­amines

In salt-type adducts of organic diamines with chiral or racemic malic acids, the hard hydrogen bonds can generate molecular ladders, sheets or three-dimensional frameworks. The supramolecular structures formed by the chiral acid can closely mimic centrosymmetry.

Structural investigations of phosphorus–nitrogen compounds. 4. Steric and electronic effects in di­benzylamino derivatives of hexa­chloro­cyclotriphosphazatriene and 4,4,6,6-tetra­chloro-2,2-di­phenylcyclotriphosphazatriene

The synthesis and crystal structures of N₃P₃Cl₅[N(CH₂Ph)₂], N₃P₃Cl₄[N(CH₂Ph)₂]₂, N₃P₃Ph₂Cl₃[N(CH₂Ph)₂] and N₃P₃Ph₂Cl₂[N(CH₂Ph)₂]₂ are reported. These compounds are included in two series of crystal structures that are used to investigate steric and electronic effects in substituted cyclophosphazenes.

Planar packing of tetra­chlorodi­cyano­benzene isomers

All three isomers of the title compound form crystalline complexes with hexamethylbenzene. For each isomer there is at least one complex in which the title compound forms a pseudo-hexagonal two-dimensional layer in which every nitrile group is in contact with Cl atoms in two adjacent molecules.

Polymorphism of maleic hydrazide. I. Erratum

Erratum to Acta Cryst. (2001), B57, 697–704.

Coupling of the lactone-ring conformation with crystal symmetry in 6-hy­droxy-4,4,5,7,8-penta­methyl-3,4-di­hydrocoumarin. Erratum

Erratum to Acta Cryst. (2001), B58, 125–133.

Two fluoradene derivatives: pseudosymmetry, eccentric ellipsoids and a phase transition. Erratum

Erratum to Acta Cryst. (2001), B57, 507–516.

Group-Theoretical Analysis of Octahedral Tilting in Perovskites. Erratum

Erratum to Acta Cryst. (1998), B54, 782–789.