Magnetic crystallography comes of age

A special issue of Acta Crystallographica Section B reports the great progress made recently in the determination, reporting, and archiving of magnetic structures, of which there are now more than 2000. The infrastructure needed to support the field is now in place. The special issue also highlights new science made possible by these developments.

The seventh blind test highlights exciting developments in crystal structure prediction

Two reports on the seventh blind test on crystal structure prediction extensively discuss the cutting-edge avant-garde methods of structure generation and energy ranking.

The seventh blind test of crystal structure prediction: structure generation methods

The results of the seventh blind test of crystal structure prediction are presented, focusing on structure generation methods.

The seventh blind test of crystal structure prediction: structure ranking methods

The results of the seventh blind test of crystal structure prediction are presented, focusing on structure ranking methods.

Polymorph sampling with coupling to extended variables: enhanced sampling of polymorph energy landscapes and free energy perturbation of polymorph ensembles

A design is tested for a polymorph search algorithm relevant for enhanced sampling of crystal structures based on the relation between internal molecular structure variables and corresponding crystal polymorphs as representative of the inherent vapor to crystal transitions that exist in nature. Molecules are represented as extended variables within a thermal reservoir. Unit-cell variables are generated using pseudo-random sampling incorporating a harmonic coupling to extended variables.

Assessment of the exchange-hole dipole moment dispersion correction for the energy ranking stage of the seventh crystal structure prediction blind test

Density-functional calculations using numerical atomic orbitals and the exchange-hole dipole moment dispersion model were applied to the energy ranking stage of the seventh crystal structure prediction blind test. This methodology gave successful predictions of the experimentally isolated polymorphs as being low in energy for three of the compounds considered, and for one additional compound upon inclusion of a vibrational free-energy correction.

Contrasting conformational behaviors of molecules XXXI and XXXII in the seventh blind test of crystal structure prediction

The conformational energies and crystal energy landscapes for molecules XXXI and XXXII from the seventh blind test of crystal structure prediction are investigated with a variety of electronic structure methods. Whereas molecule XXXI can be modeled relatively straightforwardly, molecule XXXII proves challenging even for state-of-the-art quantum chemistry techniques.

Predicting co-crystal structures of N-halide phthalimides with 3,5-di­methyl­pyridine

It is shown that the evolutionary algorithm USPEX can successfully predict stable stoichiometries of co-crystals and how synthon analysis helps to aid crystal structure prediction by identifying the likeliest structures.

Crystal structure predictions for molecules with soft degrees of freedom using intermonomer force fields derived from first principles

Crystal structure predictions for targets of CCDC's seventh blind test, all containing monomers with soft degrees of freedom, were performed using intermonomer force fields (FFs) fitted to ab initio computed interaction energies. The protocol accounting for monomers' flexibility by considering low-energy conformers was reasonably successful, but the protocol using empirical intramonomer FFs was not, even if some parameters in these FFs were refitted to ab initio data.

Spin reorientation and the interplay of magnetic sublattices in Er₂CuMnMn₄O₁₂

We show that the interplay of multiple magnetic sublattices in Er₂CuMnMn₄O₁₂ leads to four magnetic phase transitions characterized by the onset of ferrimagnetic order, spin-reorientation, spin canting, and the polarization of Er ions. While we elucidate numerous features of this complex magnetic system, the exact nature of the low-temperature coupling between erbium and manganese, and the origin of a k = (0, 0, ½) modulation, remain intriguing topics for future studies.

Symmetry, magnetic transitions and multiferroic properties of B-site-ordered A₂MnB′O₆ perovskites (B′ = [Co, Ni])

A comparative description is presented of the symmetry and the magnetic structures found in the family of double perovskites A₂MnB′O₆ (mainly B′ = Co and some Ni compounds for comparative purposes).

Crystal structure of the incommensurate modulated high-pressure phase of the potassium guaninate monohydrate

Incommensurate phase of potassium guaninate monohydrate is the first example of a modulation in purine derivatives and of a high-pressure incommensurate crystal structure to be solved for an organic compound.

From `crystallographic accuracy' to `thermodynamic accuracy': a redetermination of the crystal structure of calcium atorvastatin trihydrate (Lipitor^®)

The crystal structure of calcium atorvastatin trihydrate was redetermined from previously published synchrotron powder diffraction data to give a much-improved agreement with two independent density-functional theory calculations.

Synthesis and structural study of the partially disordered complex hexagonal phase δ₁-MnZn_9.7

A detailed structural characterization of the δ₁-MnZn_9.7 phase is presented.

Crystal structure and compressibility of magnesium chloride heptahydrate found under high pressure

In-situ diffraction measurements reveal that magnesium chloride forms a unique high-pressure phase, a heptahydrate, above 2 GPa. The hydrogen-bonding structure appears to contain orientational disorder.

A contribution to the crystal chemistry and topology of organic thio­sulfates: bis­(1-methylpiperazinium)·S₂O₃·H₂O versus 1-methylpiperazinediium·S₂O₃·3H₂O

Crystal structure and topology of two new thiosulfates formed with mono- and diprotonated species of 1-methylpiperazine is reported.

Crystal structure of nickel orthovanadate (Ni₃V₂O₈) at 299 (3) K and 1323 (8) K: an X-ray diffraction study

The structure of Ni₃V₂O₈ was studied using X-ray diffraction at temperatures of 299 and 1323 K. No phase transition at high temperature is observed. The variation in V—O bond length is small as compared with the Ni—O bond due to its high rigidity.

The incommensurate composite Y_xOs₄B₄ (x = 1.161)

Tetragonal Y_xOs₄B₄ (x = 1.161) is an incommensurate composite of columns of Y atoms in a three-dimensional Os₄B₄ framework. The structure was refined using the superspace approach.

Morphological control for hollow rod crystals of a photochromic di­aryl­ethene on spherulites by surface properties of substrates

1,2-Bis(3,5-di­methyl-2-thienyl)perfluoro­cyclo­pentene formed its own spherulites by sublimation onto the hydro­philic surfaces of the (0001) planes of α-quartz and sapphire substrates. The formation of different morphologies of these spherulites was attributed to the surface properties of each substrate. Depending on the morphology of the spherulites, hollow rod crystals with cross sections of different sizes and shapes and branching structures were generated on the surfaces of the spherulites.

Atypical phase transition, twinning and ferroelastic domain structure in bis­(ethylenedi­ammonium) tetra­bromozincate(II) bromide, [NH₃(CH₂)₂NH₃]₂[ZnBr₄]Br₂

A unique phase transition, twinning and ferroelastic domain structure in [NH₃(CH₂)₂NH₃]₂[ZnBr₄]Br₂ is found. The new additional domain structure is observed at the phase transition on heating, which is preserved after cooling to room temperature.

Polymorphism of Pb₅(PO₄)₃OH_δ within the LK-99 mixture

A new orthorhombic crystal Pb₅(PO₄)₃OH_δ of space-group symmetry Pnma significantly differs differing from the hexagonal apatite phases of Pb₁₀(PO₄)₆O and Pb₅(PO₄)₃OH.

Structures of hexa­methyl-[1,1′-bi­phenyl]-4,4′-di­ammonium salts

The structures of nine hexa­methyl-[1,1′-bi­phenyl]-4,4′-di­ammonium (HMB) salts are described

Seed layer formation by deposition of microcrystallites on a revolving substrate: modeling of the effective linear elastic, piezoelectric, and dielectric coefficients

The rotating-substrate method of crystallite deposition is modeled, allowing computation of effective material coefficients of the layers resulting from the averaging. A numerical example particularized to ZnO is provided.

Conformational disorder in quercetin dihydrate revealed from ultrahigh-resolution synchrotron diffraction

The charge-density distribution at ultrahigh resolution of quercetin dihydrate crystal reveals a subtle disorder in the catechol ring system. The electrostatic complementarity between the quercetin molecule and its surroundings is good with the water molecules, but less so in the aromatic stacking region.

Coordination geometry flexibility driving supramolecular isomerism of Cu/Mo pillared-layer hybrid networks

The hydro­thermal synthesis and structural characterization of four novel 3D pillared-layer metal–organic frameworks are studied, revealing how the malleability of copper coordination geometries drives diverse supramolecular isomerism. The findings provide new insights into designing advanced hybrid materials with tailored properties, emphasizing the significant role of reaction conditions and metal ion flexibility in determining network topologies.

Variable stoichiometry and a salt–cocrystal intermediate in multicomponent systems of flucytosine: structural elucidation and their impact on stability

Five multicomponent solid forms of antifungal drug flucytosine are reported and the hygroscopic stability was evaluated. A detailed Crystal Structure Database search on the cocrystal/salts of flucytosine was carried out, and the salt/cocrystal formation was assessed based on bond angles and bond distances.

Density functional theory investigation of the phase transition, elastic and thermal characteristics for AuMTe₂(M = Ga, In) chalcopyrite compounds

The first theoretical predictions of the phase transitions, elastic properties and thermal behavior of AuMTe₂ (M = Ga, In) chalcopyrite compounds are presented. Using density functional theory and the quasi-harmonic Debye model, key mechanical and thermodynamic properties are analyzed, offering insights valuable for future experimental validation.