Charge Density in Orthorhombic NiSO₄.7H₂O at Room Temperature and 25 K

The charge density in orthorhombic nickel sulfate heptahydrate has been determined at room temperature and 25 K from single crystal X-ray data. Hydrogen parameters at 25 K were determined by neutron diffraction.

Cu₁₂Sb₄S₁₃: A Temperature-Dependent Structure Investigation

The crystal structure of synthetic tetrahedrite, Cu₁₂Sb₄S₁₃, is refined from single crystal X-ray data in the 295–573 K temperature range, with respect to non-harmonic displacement parameters of the Cu atoms. A suggestion for ion conduction pathways is derived.

A New Structural Transformation Mechanism in Catalytic Oxides

During dynamic reduction of vanadyl pyrophosphate (VPO) catalysts used in butane oxidation to maleic anhydride, by in situ electron diffraction and microscopy, recurrent dislocations of atoms are observed by a novel glide shear process. Ordering transforms the orthorhombic VPO into an anion-deficient tetragonal structure. The results have important implications in oxide catalysis and oxide crystallography.

Structural Systematics of the High-Pressure Phases of Phosphorus, Arsenic, Antimony and Bismuth

Structural phase transitions in phosphorus, arsenic, antimony and bismuth are reviewed and the transition sequence is expressed in a unified table. It is shown how the network of the densest atomic plane changes on transition.

Structure of Magnesium Hydroxide Sulfate [2MgSO₄.Mg(OH)₂] and Solid Solution in Magnesium Hydroxide Sulfate Hydrate and Caminite

The structure of magnesium hydroxide sulfate contains ternary groups of face-shared Mg octahedra, permitting a new understanding of the complex solid solution 2MgSO₄.xMg(OH)₂.(2-2x)H₂O and revising the structure assumed for magnesium hydroxide sulfate hydrate and the ocean-floor sulfate caminite.

Structure of Mn₈Sn₅

The incommensurately modulated structure of Mn₈Sn₅ has been solved using standard crystallographic methods, as well as by a modulated structure approach. The advantages of the latter method are demonstrated.

Structural Studies of Rutile-Type Metal Dioxides

The structures of four rutile-type metal dioxides, GeO₂, SnO₂, RuO₂ and IrO₂, have been redetermined from neutron diffraction powder data. Taking these results, along with those available from previous neutron diffraction studies, the systematic structural trends in rutile-type metal dioxides have been explored.

Influence of Chemical and Spatial Constraints on the Structures of Inorganic Compounds

Possible long-range orderings in a crystal are restricted to those allowed by the space groups that are compatible with the short-range (chemical) order.

Distortion of Crystal Structures of Some Co^III Ammine Complexes. I. Distortion of Crystal Structure of [Co(NH₃)₅NO₂]Cl(NO₃) on Cooling

The anisotropy of [Co(NH₃)₅NO₂]Cl(NO₃) structural distortion on cooling from 290 to 150 K was studied by variable- temperature single-crystal X-ray diffraction. Lattice strain on cooling was compared with that under high hydrostatic pressure and with the distortion induced in the same structure by homogeneous nitro–nitrito linkage isomerization. The role of non-covalent interactions, in particular, of hydrogen bonds, in the anisotropy of structural distortion was considered.

Distortion of Crystal Structures of Some Co^III Ammine Complexes. II. Distortion of Crystal Structures of [Co(NH₃)₅NO₂]X₂ (X = Cl, Br) on Cooling

The anisotropy of [Co(NH₃)₅NO₂]Cl₂ and [Co(NH₃)₅NO₂]Br₂ structural distortion on cooling from 290 to 150 K was studied by variable-temperature single-crystal X-ray diffraction. Lattice strain on cooling was compared with that under high hydrostatic pressure and with the distortion induced in the same structures by homogeneous nitro–nitrito linkage isomerization. The role of non-covalent interactions, in particular, of hydrogen bonds, in the anisotropy of structural distortion was considered.

Use of X-ray Anomalous Dispersion: the Superstructure of PbZrO₃

The Pb and Zr displacements in the superstructure of PbZrO₃ were examined by a method using the effect of anomalous dispersion. Zr participates in the superstructure along z.

Synchrotron X-ray Studies of LiNbO₃ and LiTaO₃

Exchange interactions move electrons from where heavy Nb(Ta) overlap towards more open regions nearer the Li atom. The electron density basis of ferroelectricity in crystalline LiNbO₃ and LiTaO₃, as inferred from synchrotron radiation measurements, is consistent with the structural and vibrational evidence.

Zeolite Rho Loaded with Methylamines. I. Mono­methylamine Loadings

X-ray and neutron diffraction Rietveld analyses of monomethylamine (MMA) loaded zeolites rho revealed the MMA molecule in the α-cage with the N atom pointing to the single eight-ring. Upon dehydration it migrates into the double eight-ring accompanied by a transition from Im-3 to I-43m.

Zeolite Rho Loaded with Methylamines. II. Di­methylamine Loadings

X-ray Rietveld analysis of dimethylamine (DMA) loaded zeolites rho revealed the DMA molecule to reside on the center axis through the α-cage with the N atoms pointing to the single eight-ring and the two methyl groups oriented towards the center of the α-cage.

Zeolite Rho Loaded with Methylamines. III. Tri­methylamine Loadings

X-ray and neutron diffraction Rietveld analyses on trimethyl-amine (TMA) loaded zeolites rho showed that the TMA mole-cules reside with the N and H atoms on the central axis pointing towards the center of the single eight-ring, whilst the three methyl groups point away to the center of the α-cage.

Molecular and Crystal Structure of the Complex Composed of 2,3,5-Tri­phenyltetrazolium Cation and Di­chloro-(1,3,5-tri­phenylformazanato)cobaltate(II) Anion

The molecular and crystal structure of the complex composed of 2,3,5-triphenyltetrazolium dichloro-(1,3,5-triphenylforma- zanato)cobaltate(II) is reported. Tetrahedral geometry is realized around the high spin state cobalt(II) ion in the complex.

The Pseudo-Symmetric Structure of Pb(SPh)₂

Pb(SC₆H₅)₂ has equally spaced polymeric layers perpendicular to a^* that are partially disordered over alternative origins b/2 apart. The average structure can be either monoclinic or orthorhombic, centrosymmetric or non-centrosymmetric, depending on the disorder parameters.

The Deformation of Di-μμ-halide Dinuclear Five-Coordinate Copper(II) Complexes in the Crystalline State

The linear relationship between the degree of coordination polyhedra deformation (τ) on the SQP ⇌ TBP paths and Cu^II bond lengths and valence angles has been established by a structural correlation method. Six different paths of deformation between trigonal bipyramid (TBP) and square pyramid (SQP) have been proposed.

Conformational Analysis of Macrocyclic Ether Ligands. II. 1,4,7,10,13-Pentaoxa­cyclo­penta­decane and 1,4,7,10,13-Penta­thia­cyclo­penta­decane

Structural data from the Cambridge Structural Database have been used to perform a conformational classification of free and metal-coordinated 15-membered oxa and thia macrocycles.

Hydrogen-Bonding Schemes of Galactonic Acid Hydrazide and its Hemihydrate

The hydrogen-bonding scheme of galactonic acid hydrazide is mainly characterized by an antidromic hydrogen-bonding cycle, whereas the hemihydrate exhibits an intricate pattern. Both structures crystallize in a herringbone arrangement.

The Elusive Crystal Structure of Uric Acid Dihydrate: Implication for Epitaxial Growth During Biomineralization

The crystal structure of uric acid dihydrate, a known component of human pathological biomineralizations, fully clarifies on a structural basis the observed epitaxial growth of uric acid dihydrate with associated phases in human stones, such as anhydrous uric acid and whewellite.

Energetic Materials: The Preparation and Structural Characterization of Three Biguanidinium Dinitramides

The structures of biguanidinium mono-dinitramide, biguani- dinium bis-dinitramide and biguanidinium bis-dinitramide monohydrate are characterized by cations with two planar halves twisted with respect to each other, anions of variable geometry and extensive hydrogen bonding.

Crystal Engineering Using Bisphenols. Chains, Ladders and Sheets Formed by the Adducts of 1,4-Di­azabi­cyclo[2.2.2]octane with Bisphenols: Structures of Adducts with 4,4'-Iso­propylidenediphenol (1/1), 4,4'-Oxodiphenol (1/1) and 4,4'-Thiodiphenol (1/1 and 2/1)

Bisphenols X(C₆H₄OH)₂, where X = Me₂C, O or S, form hydrogen-bonded adducts with the cage diamine N(CH₂CH₂)₃N having chain, ladder and sheet topologies.

Crystal Engineering Using Bisphenols and Trisphenols. Complexes with Hexa­methylene­tetramine (HMTA): Strings, Multiple Helices and Chains-of-Rings in the Crystal Structures of the Adducts of HTMA with 4,4'-Thiodiphenol (1/1), 4,4'-Sulfonyldiphenol (1/1), 4,4'-Iso­propylidenediphenol (1/1), 1,1,1-Tris(4-hydroxyphenyl)ethane (1/2) and 1,3,5-Tri­hydroxybenzene (2/3)

The cage tetra-annular HMTA (CH₂)₆N₄ forms hydrogen- bonded adducts giving chain or double-helix topologies with bisphenols and triple-helix or chain-of-rings topology with trisphenols.

Crystal Engineering Using Trisphenols. Three-Dimensional Hydrogen-Bonding Networks in 1,1,1-Tris(4-hydroxyphenyl)ethane, its Hydrated Adduct with 1,4-Di­azabi­cyclo[2.2.2]octane (1/1/1) and its Adduct with Piperazine (4/3)

The trisphenol CH₃C(C₆H₄OH)₃ and its adducts with both DABCO and piperazine form three-dimensional hydrogen- bonded networks are interwoven.

Modulated Structure of the Composite Crystal Urea/n-Hepta­decane

The structure of the inclusion compound urea/n-heptadecane was refined as a composite crystal. A nonnegligible contribution of the guest structure satellite scattering to main host reflections and an adaptation of the guest structure to the host structure was found.

Retrieval of Structure-Factor Phases in Non-centrosymmetric Space Groups. Model Studies Using Multipole Refinements

Structure factors with known magnitude and phase are con- structed for several molecular crystals in non-centrosymmetric space groups and used to calibrate the retrieval of structure-factor phase information with a variety of scattering factor models. For several systems (urea, hydrogen peroxide, L-alanine and bora- zine) the results confirm that multipole refinements against experimental data yield highly accurate phases and hence reliable distributions; for the exceptional case of HMT a simple eigenvalue filtering provides phases of comparable accuracy.

The piezoelectric tensor element d₃₃ of KTiOPO₄ determined by single crystal X-ray diffraction

X-ray diffraction of a single crystal in an external electric field was used to determine the piezoelectric tensor element d₃₃ of KTP.

Two crystal structures towards the discotic columnar mesophase of (1,4,8,11,15,18,22,25-octa­hexylphthalocyaninato)nickel. Erratum

Correction to Acta Cryst. (1997). B53, 231-240.