Acta crystallographica Section B, Structural science, crystal engineering and materials最新文献

Three novel hydrated salts of ethacridine: 2-fluorobenzoate dihydrate, 3-fluorobenzoate monohydrate and 4-fluorobenzoate monohydrate were synthesized and structurally characterized using single-crystal X-ray diffraction. Analysis of intermolecular interactions in the crystal packing revealed that the number of water molecules in the asymmetric unit determines the formation of distinct centrosymmetric supramolecular synthons: [...water...acid...]₂ and [...water...water...acid...]₂. Hirshfeld surface analysis and lattice energy calculations were exploited to characterize intermolecular interactions and to elucidate the influence of small stereochemical differences among the three fluorobenzoate isomers on the crystal packing of the obtained molecular complexes.

Minerals of the ekanite group typically contain Th, U or REE (rare earth elements) as primary structural constituents. The ^CNa analogues of turkestanite, ^ATh^B(Ca,Na)^C(K_1-x□_x)^T(Si₈O₂₀) (□ is vacancy), and steacyite, ^ATh^B(Ca,Na)^C(K_1-x□_x)^T(Si₈O₂₀), isostructural minerals of the ekanite group, were experimentally synthesized during hydrothermal alteration of chevkinite-(Ce). The experiment was conducted at 550°C, 200 MPa, at an oxygen fugacity approximately equivalent to the Ni-NiO (NNO) buffer with NaF and Ca(PO₄)₂ added to the hydrous fluid. Both phases formed as a replacement of chevkinite-(Ce) and earlier alteration products. Their identity was confirmed by electron probe microanalysis and electron backscatter diffraction as ^CNa analogues of turkestanite and steacyite. Further SCXRD, and Raman spectroscopy analyses confirmed that it is a new ^CNa analogue with respect to the ekanite mineral group. Raman spectroscopy revealed the presence of H₂O within the crystal structure. A dedicated FIB workflow was designed to extract single crystals ready for SCXRD analysis. Compositionally, the phase is Na rich and depleted in K, REE and Fe. The mean formula based on 20 O atoms can be written as ^A(Th_0.94U_0.03)_0.97^B(Na_0.96Ca_0.90Mn_0.11Ce_0.02Nd_0.01Fe_0.01)_2.0^C(Na_0.83K_0.07)_0.9^TSi_8.05O₂₀·0.1^C(H₂O). It crystallizes in space group P4/mcc with a = 7.4757 (2) Å, c = 14.9658 (7) Å, V = 836.38 (6) ų, and Z = 2. Compositional variation is represented mainly by the relationship Ca²⁺ + □ → 2Na⁺, where □ is a vacancy which can also be filled by H₂O during crystallization. The synthesis from this study represents the first record of ^CNa analogues of turkestanite and steacyite. A dedicated microcrystal selection technique is presented allowing for easy single-crystal X-ray diffraction.

Acta Crystallographica Section B invites papers on advanced neutron scattering instrumentation to appear in a special issue of the journal that will be published in 2026.

Due to their potential applications in low-power consumption and/or multistate memory devices, multiferroic materials have attracted a lot of attention in the condensed matter community. As part of the effort to identify new multiferroic compounds, perovskite-based GdCrO₃ was studied in both bulk and thin film samples. A strong enhancement of the capacitance in a field suggested ferroelectric behaviour but significant leakage and no well developed P-E hysteresis loops were observed. Measurements clearly indicate the existence of a polar phase but only below 2 K (likely connected to Gd ordering). Here the determination of the magnetic structure through neutron diffraction collected on an isotopic ¹⁶⁰GdCrO₃ sample at the WISH diffractometer at ISIS is reported. The presence of three successive magnetic phases as a function of temperature (commensurate, spin re-orientation and incommensurate phases once the Gd order), previously only seen by magnetization, is confirmed. Using the most recent guidelines for reporting the determined structures, we highlight the benefits of using such nomenclature for discussing physical properties and consider possible mechanisms and couplings that led this seemingly rather isotropic system to display the complex structures observed.

Single crystals of a previously unknown caesium calcium silicate with the composition Ca₄Ca[Si₈O₁₉] have been obtained during a systematic study of the phase relations and compound formation in the system Cs₂O-CaO-SiO₂. Structure determination was based on a single-crystal diffraction data set recorded at 288 (2) K. The compound crystallizes in the monoclinic space group P2₁/n and has the following basic crystallographic parameters: a = 7.1670 (6) Å, b = 12.0884 (10) Å, c = 12.4019 (10) Å, β = 90.044 (8)°, V = 1074.47 (15) ų, Z = 2. The crystal structure was solved by direct methods. The sample showed twinning by pseudo-merohedry, which was accounted for in the subsequent least-squares refinements resulting in a residual of R1 = 0.036 for 1962 independent observed reflections and 149 parameters. The crystal structure of Cs₄Ca[Si₈O₁₉] belongs to the group of interrupted framework silicates, in which the [SiO₄] tetrahedra are linked in a three-dimensional network consisting of Q⁴ and Q³ groups in a 1:3 ratio. The linear backbones of the framework can be described as loop-branched dreier single chains. These ribbons are parallel to [100], and the translation period of about 7.2 Å along this axis reflects the periodicity of the chains. By sharing common corners, the condensation of these chains along the [001] direction leads to the formation of layers that are parallel to (010) and contain three- and nine-membered rings of tetrahedra. Alternatively, the crystal structure can be described as a mixed tetrahedral-octahedral framework between [SiO₄] tetrahedra and [CaO₆] octahedra containing cavities accommodating the caesium ions coordinated by seven and eight oxygen ligands, respectively. A detailed topological analysis of the mixed framework based on natural tiles is presented. Indeed, the net can be constructed from a total of only two different cages (tiles) having the following face symbols: [4³] and [3⁴.4⁶.6².7⁸]. A comparison with related silicates containing [Si₈O₁₉] anions and already classified as well as hitherto unclassified interrupted frameworks is presented. Finally, the thermal expansion tensor has been determined in the temperature interval between 193 K and 288 (2) K.

The study of magnetic structures from a crystallographic perspective remains a niche field, largely confined to physical crystallography and microscopic magnetism. Unlike general or superspace crystallography, magnetic structure analysis lacks standardization, primarily due to the small research community and the reliance on specialized experimental techniques like neutron diffraction. However, emerging topics in condensed matter physics, such as topological materials, multiferroics, and skyrmions, have heightened the importance of understanding magnetic ordering. As a result, the analysis of magnetic neutron scattering data is becoming increasingly relevant, requiring unified methodologies. Since 2011, the IUCr Commission on Magnetic Structures has been working to improve the situation. This paper reviews the most commonly used methods for describing magnetic structures and highlights the capabilities of the FullProf Suite for analysing magnetic neutron diffraction data.

A comprehensive report is provided of the average structure of a high Curie temperature ferroelectric ceramic, (1 - x)BiFe_2/8Ti_3/8Mg_3/8O₃-xPbTiO₃ (BFTM-xPT) when x = 0.25-0.375 at room temperature. Both neutron and synchrotron X-ray powder diffraction data were collected and combined Rietveld refinements were completed. These data revealed that, of the compositions studied, BFTM-xPT crystallizes as mixed phase material. At x = 0.25-0.275, the average structure of each phase is best described by space groups R3c and Cc. At 0.30 ≥ x ≥ 0.35, a morphotropic phase boundary is present and is best modelled by space groups P4mm and Cc, where space group Cc is the dominant phase. As the concentration of PbTiO₃ increases, the amount of octahedral tilting decreases and x = 0.375 exhibits a loss of octahedral tilting and crystallizes in space groups P4mm and Cm. An updated phase diagram at room temperature of this novel system is given and structural intricacies responsible for its piezoelectric properties are revealed.

Layered hybrid organic-inorganic metal halides (CH₃CH₂NH₃)₂[MnCl₄] and (CH₃CH₂NH₃)₂[CoCl₄] were synthesized by the slow evaporation method to understand the relationship between the crystal structure and order-disorder phase transition. Calorimetric data and crystal structure determination across the phase transition temperature establish the order-disorder phase transition. (CH₃CH₂NH₃)₂[MnCl₄] undergoes the reversible structural phase transition from tetragonal I4/mmm to orthorhombic Pbca at 212/222 K (cooling/heating), whereas (CH₃CH₂NH₃)₂CoCl₄ demonstrates the phase transition at 220/239 K from orthorhombic Pnma to orthorhombic P2₁2₁2₁. Both compounds are characterized by disordered ethyl ammonium cations in the structure above the phase transition temperature, whereas they become ordered cations at temperatures below the phase transition. Dielectric results further support the observed structural phase transitions. Additionally, magnetic measurements show canted antiferromagnetic characteristics for (CH₃CH₂NH₃)₂[MnCl₄] and paramagnetic behaviour is observed for (CH₃CH₂NH₃)₂[CoCl₄]. The structural differences, the role of intermolecular interactions and the effect of transition metals on the phase transition were evaluated using Hirshfeld surface analysis and the topological properties of electron density distributions. An accurate description of the structure and intermolecular interactions is crucial for understanding the physical properties and designing multifunctional hybrid organic-inorganic metal halide perovskites.

A high-resolution charge density study using the Hansen-Coppens multipolar model was performed on tetraaquabis(hydrogenmaleato)iron(II). The experimental electron density was subjected to Bader's topological analysis. Hirshfeld atom refinement and topological analysis of the molecular wavefunction were also conducted. A comparison of the properties obtained under different resolution and acquisition conditions are presented. The performance of these models is evaluated in terms of their ability to achieve bond lengths close to those from neutron diffraction, provide accurate anisotropic displacement parameters and model electron densities precisely, and to determine atomic charges under different experimental and modeling conditions. The structure presents a short intramolecular hydrogen bond, which is found to have a distinct character compared to other interactions, as the hydrogen interacts covalently with two oxygen atoms. Different models were evaluated, each outperforming the others in specific aspects. Overall, the analysis of these models provide deeper insights into electron density distribution and the nature of the interactions present in the structure.