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

Synthesis experiments were conducted in the quaternary system K₂O-Na₂O-CaO-SiO₂, resulting in the formation of a previously unknown compound with the composition K_0.72Na_1.71Ca_5.79Si₆O₁₉. Single crystals of sufficient size and quality were recovered from a starting mixture with a K₂O:Na₂O:CaO:SiO₂ molar ratio of 1.5:0.5:2:3. The mixture was confined in a closed platinum tube and slowly cooled from 1150°C at a rate of 0.1°C min^-1 to 700°C before being finally quenched in air. The structure has tetragonal symmetry and belongs to space group P4₁22 (No. 91), with a = 7.3659 (2), c = 32.2318 (18) Å, V = 1748.78 (12) ų, and Z = 4. The silicate anion consists of highly puckered, unbranched six-membered oligomers with the composition [Si₆O₁₉] and point group symmetry 2 (C₂). Although several thousands of natural and synthetic oxosilicates have been structurally characterized, this compound is the first representative of a catena-hexasilicate anion, to the best of our knowledge. Structural investigations were completed using Raman spectroscopy. The spectroscopic data was interpreted and the bands were assigned to certain vibrational species with the support of density functional theory at the HSEsol level of theory. To determine the stability properties of the novel oligosilicate compared to those of the chemically and structurally similar cyclosilicate combeite, we calculated the electronegativity of the respective structures using the electronegativity equalization method. The results showed that the molecular electronegativity of the cyclosilicate was significantly higher than that of the oligostructure due to the different connectivities of the oxygen atoms within the molecular units.

A few real case examples are presented on how to report magnetic structures, with precise step-by-step explanations, following the guidelines of the IUCr Commission on Magnetic Structures [Perez-Mato et al. (2024). Acta Cryst. B80, 219-234]. Four examples have been chosen, illustrating different types of single-k magnetic orders, from the basic case to more complex ones, including odd-harmonics, and one multi-k order. In addition to acquainting researchers with the process of communicating commensurate magnetic structures, these examples also aim to clarify important concepts, which are used throughout the guidelines, such as the transformation to a standard setting of a magnetic space group.

In the course of an investigation of the supramolecular behaviour of copper(II) complexes with the 5-phenylimidazole/perchlorate ligand system (`blend') remarkable solvatomorphism has been observed. By employing a variety of crystallization solvents (polar protic, polar/non-polar aprotic), a series of 12 crystalline solvatomorphs with the general formula [Cu(ClO₄)₂(LH)₄]·x(solvent) have been obtained [LH = 5-phenylimidazole, x(solvent) = 3.3(H₂O) (1), 2(methanol) (2), 2(ethanol) (3), 2(1-propanol) (4), 2(2-propanol) (5), 2(2-butanol) (6), 2(dimethylformamide) (7), 2(acetone) (8), 2(tetrahydrofurane) (9), 2(1,4-dioxane) (10), 2(ethyl acetate) (11) and 1(diethyl ether) (12)]. The structures have been solved using single-crystal X-ray diffraction and the complexes were characterized by thermal analysis and infrared spectroscopy. The solvatomorphs are isostructural (triclinic, P1), with the exception of compound 9 (monoclinic, P2₁/n). The supramolecular structures and the role of the various solvents is discussed. All potential hydrogen-bond functionalities, both of the [Cu(ClO₄)₂(LH)₄] units and of the solvents, are utilized in the course of the crystallization process. The supramolecular assembly in all structures is directed by strong recurring N_imidazole-H...O_perchlorate motifs leading to robust scaffolds composed of the [Cu(ClO₄)₂(LH)₄] host complexes. The solvents are located in channels and, with the exception of the disordered waters in 1 and the diethyl ether in 12, participate in hydrogen-bonding formation with the [Cu(ClO₄)₂(LH)₄] complexes, serving as both hydrogen-bond acceptors and donors (for the polar protic solvents in 2-6), or solely as hydrogen-bond acceptors (for the polar/non-polar aprotic solvents in 7-11), linking the complexes and contributing to the stability of the crystalline compounds.

A domain-resolved synchrotron single-crystal X-ray diffraction study of a LaAlO₃ pseudo-merohedral twin crystal was successfully carried out in combination with powder diffraction data from the same sample. Multiscale structure information ranging from micro- to nano- to atomic scale was determined from one single crystal. There is almost no change of domain ratios at temperatures of less than 400 K indicating no movement of the domain wall. The changes in domain ratio indicating domain-wall movement were observed in the temperature range of 450 to 700 K, which is consistent with the result of the previous mechanical measurement. It is also found that the ratio of four twin components becomes equal (25%), just below phase transition temperature. These findings are important for domain engineering and theoretical studies related to LaAlO₃. The temperature dependence of domain ratio was preserved in the heating and cooling cycle except for the first heating process to 840 K. Therefore, the domain structure after heating to 840 K is intrinsic to the crystal. Accurate structure parameters were determined through unit-cell parameter calibration and domain-resolved structure analysis. The method for calibration of unit-cell parameters from twin crystal data was derived and used to solve the inconsistent unit-cell parameters between single crystal and powder data in the present and previous studies.

Ion radii are derived here from the characteristic (grand mean) bond lengths for (i) 135 ions bonded to oxygen in 459 configurations (on the basis of coordination number) using 177 143 bond lengths extracted from 30 805 ordered coordination polyhedra from 9210 crystal structures; and (ii) 76 ions bonded to nitrogen in 137 configurations using 4048 bond lengths extracted from 875 ordered coordination polyhedra from 434 crystal structures. There are two broad categories of use for ion radii: (1) those methods which use the relative sizes of cation and anion radii to predict local atomic arrangements; (2) those methods which compare the radii of different cations (or the radii of different anions) to predict local atomic arrangements. There is much uncertainty with regard to the relative sizes of cations and anions, giving rise to the common failure of type (1) methods, e.g. Pauling's first rule which purports to relate the coordination adopted by cations to the radius ratio of the constituent cation and anion. Conversely, type (2) methods, which involve comparing the sizes of different cations with each other (or different anions with each other), can give very accurate predictions of site occupancies, physical properties etc. Methods belonging to type (2) can equally well use the characteristic bond lengths themselves (from which the radii are derived) in place of radii to develop correlations and predict crystal properties. Extensive quantum-mechanical calculations of electron density in crystals in the literature indicate that the radii of both cations and anions are quite variable with local arrangement, suggesting significant problems with any use of ion radii. However, the dichotomy between the experimentally derived ion radii and the quantum-mechanical calculations of electron density in crystals is removed by the recognition that ion radii are proxy variables for characteristic bond lengths in type (2) relations.

The synthesis of TaSe₃ ring-shaped crystals displaying the coffee ring effect is investigated. By recrystallizing TaSe₃ microcrystals dissolved in droplets of condensed Se gas, ring-shaped crystals were successfully grown. This novel method for ring formation effectively addressed the issue of connecting the edges of the crystal. Consequently, the synthesis method has the capability to grow MX₃ ring-shaped crystals in any location where droplets can condense, can now be grown in specific locations, thus creating opportunities for advancements in electronic component development.

The crystal structure of lithium xanthinate hydrate was studied by single crystal X-ray diffraction and Raman spectroscopy on cooling to 100 K and under compression to 5.3 GPa. A phase transition at ∼4 GPa is observed. No phase transitions occur on cooling. Anisotropy of lattice strain and changes in intermolecular interactions are compared.

Quantum crystallography is an emerging research field of science that has its origin in the early days of quantum physics and modern crystallography when it was almost immediately envisaged that X-ray radiation could be somehow exploited to determine the electron distribution of atoms and molecules. Today it can be seen as a composite research area at the intersection of crystallography, quantum chemistry, solid-state physics, applied mathematics and computer science, with the goal of investigating quantum problems, phenomena and features of the crystalline state. In this article, the state-of-the-art of quantum crystallography will be described by presenting developments and applications of novel techniques that have been introduced in the last 15 years. The focus will be on advances in the framework of multipole model strategies, wavefunction-/density matrix-based approaches and quantum chemical topological techniques. Finally, possible future improvements and expansions in the field will be discussed, also considering new emerging experimental and computational technologies.

Results of the neutron powder diffraction measurements carried out for R₅Pt₂In₄ (R = Tb-Tm) are reported. The compounds crystallize in an orthorhombic crystal structure of the Lu₅Ni₂In₄-type with the rare earth atoms occupying three different sublattices. Neutron diffraction data reveal that at low temperatures the rare earth magnetic moments order below the critical temperature equal to 105, 93, 28, 12 and 3.8 K for R = Tb, Dy, Ho, Er and Tm, respectively. With decreasing temperature the rare earth magnetic moments at the 2a and 4g2 sites order first, while the moments at the 4g1 site order at lower temperatures. Ferrimagnetic order along the c axis, described by the propagation vector k₁ = [0, 0, 0], develops in Tb₅Pt₂In₄ below the Curie temperature (T_C = 105 K). At lower temperatures, an antiferromagnetic component in the ab plane appears. The component is incommensurate with the crystal structure (k₂ = [0, 0.66, ½]), but it turns into a commensurate one (k₃ = [0, 0, ½]) with decreasing temperature. Antiferromagnetic order along the c axis, described by k₄ = [½, 0, 0], is found in Dy₅Pt₂In₄ below the Néel temperature (T_N = 93 K). The k₄-related component disappears below 80 K and the magnetic structure transforms into a ferro/ferrimagnetic one described by k₁ = [0, 0, 0]. Further decrease in temperature leads to the appearance of an incommensurate antiferromagnetic component within the ab plane below 10 K (k₂ = [0, 0.45, ½]), which finally turns into a commensurate one (k₅ = [0, ½, ½]). In Ho₅Pt₂In₄, a sine-modulated magnetic structure with moments parallel to the c axis (k₆ = [⅓,0,0]) is observed below 28 K. With a decrease in temperature, new components, related to k₁ = [0, 0, 0] (bc plane) and k₄ = [½, 0, 0] (c axis), appear. The coexistence of two orderings - in the ab plane (k₁ = [0, 0, 0]) and a modulated one with moments along the b axis (k₇ = [k_x, 0, 0]) - is found in Er₅Pt₂In₄ below 12 K. Decreasing temperature leads to the order-order transformation of the k₁-related component to another one with magnetic moments still constrained to the ab plane and preserved value of the propagation vector (i.e. k₁ = [0, 0, 0]). Tm₅Pt₂In₄ orders antiferromagnetically below T_N = 3.8 K. Thulium magnetic moments lie in the ab plane, while the magnetic structure is described by k₅ = [0, ½ , ½]. The direction of magnetic moments depends on the rare earth element involved and indicates an influence of single ion anisotropy resulting from interaction with the crystalline electric field.

The structures of three multicomponent crystals formed with imidazole-based drugs, namely metronidazole, ketoconazole and miconazole, in conjunction with trithiocyanuric acid are characterized. Each of the obtained adducts represents a different category of crystalline molecular forms: a cocrystal, a salt and a cocrystal of salt. The structural analysis revealed that in all cases, the N-H...N hydrogen bond is responsible for the formation of acid-base pairs, regardless of whether proton transfer occurs or not, and these molecular pairs are combined to form unique supramolecular motifs by centrosymmetric N-H...S interactions between acid molecules. The complex intermolecular forces acting in characteristic patterns are discussed from the geometric and energetic perspectives, involving Hirshfeld surface analysis, pairwise energy estimation, and natural bond orbital calculations.