forthcoming articles

The following articles are a selection of those recently accepted for publication in Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials.

See also Forthcoming articles in all IUCr journals.

Accepted 21 July 2017

Multidimensional structural variation in the cyano­trichite family of merotypes: camerolaite-3b-F-1

This is the first refined example of a cyano­trichite-group mineral in which long-range order of interlayer anions produces a superstructure.

Accepted 28 June 2017

Approaches to crystal structure landscape exploration

Three approaches to the exploration of the crystal structure landscape are outlined. These are crystal structure prediction, non-ambient crystallography and charge density analysis.

Accepted 27 June 2017

Crystal chemistry and the role of ionic radius in rare earth tetrasilicates: Ba2RE2Si4O12F2 (RE = Er3+-Lu3+) and Ba2RE2Si4O13 (RE = La3+-Ho3+)

Multiple structure types were found in a systematic study of barium rare earth tetrasilicates. The ionic radius of the rare earth element and the presence of fluorine in the crystal structures direct both the phase stability and the structural dimensionality.

Accepted 19 June 2017

A note to the Distortion theorem

Accepted 19 June 2017

The index of dispersion as a metric of quanta – unravelling the Fano factor

The need for high-quality assessments of data motivates appreciation of shot noise as a data resource. The index of dispersion is a critical but often overlooked metric in this regard. When properly understood and carefully used it reveals the energies of quanta, in both monochromatic and polychromatic situations. To accomplish this, and in due course its wider application, its conceptual origins and quantitative and physical bounds are identified. Situations are examined that involve large numbers of quanta, but in which individual quanta are below measurement noise threshold. Practical applications are extremely diverse, so relevant considerations and how to use the metric are shown in broad contexts.

Accepted 9 June 2017

Effect of cationic substitution on the double well hydrogen bond potential in (K1-x(NH4)x)3H(SO4)2 proton conductors: A Single Crystal Neutron Diffraction Study

Single crystal neutron diffraction was performed on (K1-x(NH4)x)3H(SO4)2 in order to get the exact hydrogen bonding network, a correlation between the kinetics of superprotonic phase transition in the crystals and hydrogen bond strength is described.

Accepted 9 June 2017

Experimental observation of charge-shift bond in fluorite CaF2

F⋯F interactions in fluorite have properties associated with the recently recognized type of interaction referred to as `charge-shift' bonding. This finding is supported by the topology of the electron localization function and the analysis of quantum theory of atoms in molecules and crystals. These interactions are attractive in character, which is additionally indicated by the topology of non-covalent interactions based on the reduced density gradient.

Accepted 7 June 2017

Nanoscale symmetry fluctuations in ferroelectric barium titanate, BaTiO3

The crystal symmetry of ferroelectric BaTiO3 is determined by scanning convergent-beam electron diffraction. The results show inhomogeneous symmetry with nanometre-sized regions of almost perfect symmetry interspersed in regions of lower symmetry.

Accepted 7 June 2017

Solvent exchange in a metal–organic framework single crystal monitored by dynamic in situ X-ray diffraction

Dynamic in situ single crystal X-ray diffraction revealed unique and important information about the structural reorganization that occurs upon guest exchange in a cobalt-based metal organic framework.

Accepted 6 June 2017

Exploring charge density analysis in crystals at high pressure: data collection, data analysis and advanced modelling

This paper reports on the determination of charge density distributions from crystals compressed at high pressure. Although much less accurate than traditional charge density analysis, these studies provide valuable information because the electronic states of molecules confined in highly condensed space are not easily predictable by theory and therefore experimental validation is a must.

Accepted 6 June 2017

Exploring the rare S—H⋯S hydrogen bond using charge density analysis in isomers of mercapto­benzoic acid

The appearance of an elusive S—H⋯S hydrogen bond with the S atom acting as a donor in 2-, 3-mercapto­benzoic acids has been analysed based on charge density calculations. The importance of the locking potential provided by an intramolecular S⋯O chalcogen bond is highlighted.

Accepted 2 June 2017

When combined X-ray and polarized neutron diffraction data challenge high-level calculations: spin-resolved electron density of an organic radical

Experimental joint refinement against X-ray and polarized neutron diffraction data has been performed to simultaneously model the charge and spin density of a free radical; the resulting model challenges density functional theory (DFT) calculations, but is in fair agreement with ab initio complete active-space self-consistent field (CASSCF) calculations.

Accepted 31 May 2017

Insights on spin delocalization and spin polarization mechanisms in crystals of azido copper(II) dinuclear complexes through the electron spin density Source Function

Electron spin density at a point may be seen as determined by a local Source Function for such density, operating at all other points of space. Integration of the local source over Bader's quantum atoms measures their contribution in determining the spin density features at any system's location. This novel tool is able to provide interesting insights on the electron spin delocalization and polarization mechanisms along with their dependence from the spin density quality.

Accepted 24 May 2017

Formation of local spin-state concentration waves during the relaxation from a photoinduced state in a spin-crossover polymer

Broken symmetry and spin-state concentration waves compete during the relaxation from the photoinduced high-spin to the ground low-spin phase of a two-dimensional spin-crossover polymer.

Accepted 18 May 2017

Revisiting the charge density analysis of 2,5-di­chloro-1,4-benzo­quinone at 20 K

The charge density of 2,5-di­chloro-1,4-benzo­quinone has been redetermined at 20 K. Two different multipole refinement models lead to similar topological properties of the total electron density.

Accepted 15 May 2017

A commensurately modulated structure of parabutlerite, Fe3+SO4(OH)·2H2O

Accepted 13 May 2017

Charge density studies of 3d metal (Ni/Cu) complexes with a non-innocent ligand

The redox characteristics of pairs of square planar complexes M(mnt)22−/M(mnt)2, where mnt is the non-innocent maleo­nitrile­dithiol­ate ligand, are established through charge density analysis and X-ray absorption spectroscopy: the oxidation is ligand based in Ni complexes and are metal based for the Cu case.

Accepted 10 May 2017

Experimental charge-density studies: data reduction and model quality: the more the better?

In experimental charge-density investigations, it is essential to reach the highest possible quality of data and the most resilient model. Recent developments concerning data and model quality are reviewed.

Accepted 3 May 2017

Qu­antitative analysis of solid-state diversity in tri­fluoro­methyl­ated phenylhydrazones

The crystal structures of six tri­fluoro­methyl­ated phenyl­hydrazones have been studied in detail, particularly in terms of the solid-state diversity (like polymorphism and isostructurality) associated with different supramolecular architectures with H/CF3 substitution in the absence of any strong hydrogen bonding. The most stabilizing molecular building blocks have a higher dispersion contribution due to the greater overlap between molecular surfaces, leading to an increase in the magnitude of van der Waals interactions.

Accepted 2 May 2017

Crystal structure of the OH-dominant gadolinite-(Y) analogue (Y,Ca)2(Fe,???)Be2Si2O8(OH,O)2 from Heftetjern pegmatite, Norway

Accepted 28 April 2017

Phase transition sequences in tetra­methyl­ammonium tetra­chloro­metallates by X-ray diffraction and spectroscopic measurements

Structures and phase sequences for two tetra­methyl­ammonium tetra­chloro­metallate compounds have been determined as a function of temperature. Crystal-packing analysis and first-principles calculations were used to rationalize the experimentally determined sequence.

Accepted 27 April 2017

Accurate charge densities from powder X-ray diffraction – a new version of the Aarhus vacuum imaging plate diffractometer

The present state of X-ray electron density determination from powder diffraction data is briefly reviewed together with the first results from a new large diameter in-vacuum diffractometer.

Accepted 24 April 2017

Crystal structures of η′′-Cu3+xSi and η′′′-Cu3+xSi

The incommensurately modulated structures of η′′-Cu3+xSi and η′′′-Cu3+xSi are described in the superstructure approximation. The structures are compared.

Accepted 23 April 2017

Qu­antitative characterization of new supramolecular synthons involving fluorine atoms in the crystal structures of di- and tetrafluorinated benzamides

New supramolecular synthons in crystal structures involving organic fluorine have been observed and characterized. The nature, energetics and topological properties of these contacts derived from electron-density studies establish their bonding character. The enhanced acidic nature of the participating H atoms is responsible for short, strong and highly directional contacts with fluorine. Their hydrogen-bonding character is thus established unequivocally, with a pronounced modification of the features associated with crystal packing.

Accepted 22 April 2017

Anharmonic motions versus dynamic disorder at the Mg ion from the charge densities in pyrope (Mg3Al2Si3O12) crystals at 30 K: six of one, half a dozen of the other

A very accurate single-crystal X-ray diffraction study of synthetic pyrope (Mg3Al2Si3O12, Ia\bar 3d) at 30 K reveals that residual density features around Mg2+ ions, previously attributed to static disorder, can be better accounted for by anharmonicity/dynamic disorder.

Accepted 20 April 2017

Comparison of the crystal structures and thermochemistry of a novel soluble guanylate cyclase stimulator riociguat and its solvates

Intermolecular interactions and molecular conformations are compared for riociguat molecules in the solvent-free drug [form (II)] and three different solvate structures. Desolvation of solvates result in form (I) of the riociguat.

Accepted 19 April 2017

Validation of missed space-group symmetry in X-ray powder diffraction structures with dispersion-corrected density functional theory

Two hundred crystal structures with missed symmetry were investigated by dispersion-corrected density functional theory. In 98.5% of the cases the correct space group is found.

Accepted 12 April 2017

Interplay of point multipole moments and charge penetration for intermolecular electrostatic interaction energies from the University at Buffalo pseudoatom databank model of electron density

University at Buffalo DataBank (UBDB)-derived electrostatic energies (E_{\rm es}) closely approach those computed using quantum mechanics mainly because the UBDB allows for a direct account of charge penetration effects. For interactions between polar molecules, penetration constitutes up to 50% of Ees, but for nonpolar molecules, it may reach 100% of Ees at the equilibrium distance.

Accepted 7 April 2017

Synthesis, structure and non-linear optical properties of new isostructural β-D-fructo­pyran­ose alkaline halide metal–organic frameworks: a theoretical and an experimental study

Theoretical and experimental investigations on non-linear optical properties of four metal–organic framework isomorphs, based on fructose and alkali-earth halogenides, show that both the intrinsic nature of the anion and the induced dissociation of the cation and anion by fructose play a role in the second-harmonic generating properties of such compounds.

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