Model structures for C-(A)-S-H(I)

C-(A)-S-H(I) is a structurally imperfect form of 14 Å tobermorite that is studied extensively as a model for the main binding phase in concrete. Crystal-chemically plausible structures are developed that account for a wide range of experimental observations, including variations in calcium to silicon ratio, water to silicon ratio, (alumino)silicate anion structure and layer spacing.

Reconstructive phase transition in (NH₄)₃TiF₇ accompanied by the ordering of TiF₆ octahedra

Distorted Archimedian polyhedron in (NH₄)₃TiF₇ as the superposition of TiF₆ octahedra disordered among four postions.

Metal distribution and disorder in the crystal structure of [NH₂Et₂][Cr₇MF₈(^tBuCO₂)₁₆] wheel molecules for M = Mn, Fe, Co, Ni, Cu, Zn and Cd

The heterometal distribution over the cyclic {Cr₇M} cage molecule is partly ordered over the molecular wheel in the crystal structure of [NH₂Et₂][Cr₇MF₈(^tBuCO₂)₁₆][C₄H₈O₂]_0.5 for the divalent transition metals M = Mn, Fe, Co, Ni, Cu, Zn and Cd.

Unusual crystal structure of N-substituted maleamic acid – very strong effect of intramolecular hydrogen bonds

The contrasting behaviour of N-(carboxymethyl) maleamic acid and N-carbamyl maleamic acid under cyclodehydration conditions are discussed in the light of X-ray diffraction and modelling studies.

Structure, hydrogen bonding and thermal expansion of ammonium carbonate monohydrate

Single-crystal neutron diffraction, ab initio calculations and Raman spectroscopy are applied to understand the structure and hydrogen bonding of ammonium carbonate monohydrate, a hitherto poorly characterized substance, particularly in relation to other ammonium-bearing compounds.

Refinement of cronstedtite-1M

The structure of an extremely rare 1M polytype of the 1:1 layer silicate cronstedtite from Eisleben (Saxony-Anhalt, Germany) was refined against a single-crystal X-ray data set. The deformation parameters of tetrahedral and octahedral sheets, arrangement of hydrogen bonds, stacking rule and desymmetrization are presented and discussed.

Isomorphism and solid solution as shown by an accurate high-resolution diffraction experiment

High-resolution crystal structure determination and refinement of 1-(4′-chlorophenyl)-2-methyl-4-nitro-1H-imidazole-5-carbonitrile revealed the presence of 2.5% of its bromine derivative, which would not be found using standard resolution data (ca 0.8 Å), as disorder was visible only at high resolution.

Reassessment of the electron density in Cu₂O using γ-ray diffraction

The electron-density distribution in Cu₂O has been critically reexamined to test controversial conclusions from earlier experimental and theoretical studies.

Enantiopure and racemic alanine as bridging ligands in Ca and Mn chain polymers

Chain polymers crystallize from aqueous solutions of Ca^II and Mn^II halides with enantiopure or racemic alanine to form a series of closely related structure types.

Atomic structure solution of the complex quasicrystal approximant Al₇₇Rh₁₅Ru₈ from electron diffraction data

The crystal structure of the novel Al₇₇Rh₁₅Ru₈ phase (which is an approximant of decagonal quasicrystals) was determined from automated electron diffraction tomography (ADT) data. It has one of the most complicated intermetallic structures solved solely by electron diffraction methods.

Assembled structures of tetra­kis­(bi­imidazole)dirhodium complexes hydrogen-bonded with common inorganic anions

Metal–metal-bonded dirhodium complexes with four chelating biimidazole ligands at equatorial sites and two axial ligands gave novel assembled structures with common inorganic anions.

Validation of molecular crystal structures from powder diffraction data with dispersion-corrected density functional theory (DFT-D)

The accuracy of 215 experimental organic crystal structures from powder diffraction data is validated against a dispersion-corrected density functional theory method.

Diamond structure cannot be stable in nm-sized particles

Impurities in the form of surface-terminating H atoms and/or functional groups are indispensible for the stabilization of a diamond structure in nanodiamond particles.

Frank H. Allen (1944–2014)

Obituary for Frank H. Allen.