Crystal-chemical features of high-calcium and hypercalcium eudialyte-group minerals (EGMs) from a carbonatite-related rock of the Tamazeght peralkaline complex, High Atlas Mountains, Morocco were studied using electron probe microanalysis, single-crystal X-ray structure analysis, infrared and Raman spectroscopy. The major components of the host rock are calcite, fluorite and EGMs; aegirine-augite is present in subordinate amounts. The specific features of the studied EGMs are chemical heterogeneity, a complex zoning, reaction zones around calcite and apatite inclusions, Na- and Cl-deficiency, high contents of Ca, Mn, REE, Nb, carbonate and H-bearing groups, positive correlation between Nb and Mn and negative correlations between the pairs Fe-Mn and Zr-Mn. These features confirm previous assumptions about the role of infiltration of carbonatite fluid rich in Ca, Mn, REE, Nb, CO2 and H2O and a depletion of Cl in the remaining fluid after the crystallization of sodalite at the expense of nepheline in the formation of carbonatite-related rocks of the Tamazeght complex. The crystal structure of a single-crystal fragment extracted from the Nb-rich zone refined to R-1 = 0.0335 has shown a high degree of ordering of Na, REE and H3O+ and the dominance of Fe3+ at the M2 site with five-fold coordination. The composition of EGMs from the reaction zones around calcite and apatite inclusions corresponds to Mn-dominant (with Mn > Fe at the M2 site) analogue of feklichevite with the simplified formula Ca-3(Na,K)(9)(H3O)(3)Ca6Zr3(Mn2+,Fe3+,Zr)(3)NbSi(Si24O72)(OH,H2O)(5)(F,Cl)(2/3)(CO3)(1/3).

The properties of a Ca9La(VO4)7 single crystal were studied using dielectric spectroscopy and second-harmonic generation. The crystal structure of Ca9La(VO4)7 grown using the Czochralski technique was refined using single-crystal data. The distribution of Ca2+ and La3+ cations over structural positions was determined. The crystal structure refinement results were compared with those obtained previously from powder X-ray diffraction data. It was shown that the refinement carried out using two different data sets leads to approximately the same results for the distances in the polyhedra, but their distortion is significantly less in the case of using single-crystal data for calculation. Dielectric properties and conductivity measurements were performed on polished single-crystal wafers cut parallel and perpendicular to the c axis. Second-harmonic generation and dielectric temperature measurements revealed the presence of a reversible ferroelectric first-order phase transition at about 1224 K from the ferroelectric β-phase (space group R3c) to the paraelectric β′-phase. The ferroelectric–paraelectric phase transition is accompanied by a complex structural rearrangement, including a 60° rotation of the V1O4 tetrahedron, as well as slight displacements of the Ca2+ and La3+ cations. It has been shown that the conductivity differs only slightly along the polar axis and perpendicular to it. Above the phase transition temperature, the activation energy of the conductivity is the same for all directions, Ea~1.2 eV. The influence of composition on the phase transition temperature and the formation of ferroelectric and nonlinear optical properties is discussed.

Isomorphic substitution of atoms in crystals, accompanied by solid solution formation, represents a fundamental phenomenon in natural and synthetic materials. This process follows two principal mechanisms: (1) isovalent substitution, where ions of equal charge replace each other, and (2) heterovalent substitution involving charge imbalance. The latter can be further categorized based on structural consequences: substitutions that preserve the unit cell stoichiometry versus those altering the total number of atoms/ions (N) per unit cell. The N-changing heterovalent substitutions are particularly significant in creating complex solid solutions across various inorganic systems. Beyond simple ionic replacements, more sophisticated structural transformations occur through “blocky isomorphism” – a process where extended structural fragments (blocks, chains, or layers) undergo collective substitution. This mechanism enables the formation of modular architectures, where the successful integration of different structural modules depends critically on their geometric compatibility at interfacial boundaries. This review systematically examines two key aspects of structural complexity in crystalline materials: (1) heteropolyhedral substitutions involving coordinated polyhedral units, and (2) “blocky isomorphism” phenomena. Through representative examples from mineral and synthetic systems, we analyze how these substitution mechanisms govern topological modifications in crystal structures, ultimately determining their physical properties and chemical behavior.

Crystals of two new alkaline-earth perrhenate halides, Sr(ReO4)Br⋅2H2O (1) and Ba(ReO4)I⋅2H2O (2) were obtained upon evaporation of aqueous solutions at 95 – 100 °C. Both compounds are isostructural to the previously reported Ca(ReO4)Cl⋅2H2O and crystallize in orthorhombic symmetry with the space group Cmcm (a = 7.3906(5) Å, b = 14.241(1) Å, c = 7.1032(5) Å for 1 and a = 7.8624(4) Å, b = 14.0202(5) Å, c = 7.7190(3) Å for 2). Both structures can be regarded as pseudo-layered 3D frameworks comprised of AO8X capped square antiprisms (A = Sr, Ba; X = Br, I) and ReO4 tetrahedra which share vertices with formation of slightly distorted tetragonal pseudo-layers linked by OH⋅⋅⋅X hydrogen bonds. The cationic centers (alkaline earths and rhenium) adopt a litharge-like arrangement. The structure seems to be very sensitive to the ratio of A2+ and X− constituents; it is as yet observed with calcium, only as a chloride, with strontium, only as a bromide, and with barium, only as an iodide.

Ultraviolet (UV) irradiation for synthesis of metal-organic frameworks (MOFs) has been applied for the first time. The use of UV radiation enabled the efficient synthesis of 2D-Ln-BTB and Am-MIL-103 MOFs. A comparative analysis was carried out to assess the viability of radiation-chemical and photochemical approaches for the synthesis of Ln(iii)- and Am(iii)-BTB MOFs. The yields from both methods for all lanthanides reached 90% depending on the cation. The obtained materials were characterized by pXRD, FTIR spectroscopy, SEM-EDX, CHN analysis, and TGA. For a novel Am-MIL-103, the crystal structure was determined using SCXRD and compared with that of previously known Ln-MIL-103 analogues. Solvent electron density removal revealed a void space of approximately 4311 & Aring;3 (49.2% of the total unit cell volume), which is smaller than that of the lanthanum analogue (52.3%) due to the smaller ionic radius of Am. It was demonstrated that a decrease in dose rate from 180 to 8.4 Gy s-1 results in a significant increase in the crystallinity of the material. In contrast to the photochemical method, the radiation-chemical approach yields only one type of Ln-BTB MOF. This study shows that by varying the conditions of the photochemical synthesis, it is possible to obtain three types of Ln-BTB MOFs with different structures.

Two new copper triethanolamine (tea) complexes, [Cu(tea)(H2O)(2)](SeO4)center dot H2O (1) and [Cu(tea)(H2O)(2)](BeF4)center dot H2O (2) were obtained from aqueous solutions. Their crystal structures are orthorhombic (sp. gr. Pbca) with the following unit cell parameters: a = 12.6763 (2) angstrom, b = 14.9699 (2) angstrom, c = 15.2092 (2) angstrom, V = 2886.14 (7) angstrom 3 (for 1) and a = 12.3858 (2) angstrom, b = 14.8016 (2) angstrom, c = 15.0535 (2) angstrom, V = 2759.75 (7) angstrom 3 (for 2). Both 1 and 2 are full structural analogs of the previously reported [Cu(tea)(H2O)(2)](SO4)center dot H2O sulfate and contain the pseudooctahedral [Cu(tea)(H2O)(2)](2+) cations, tetrahedral TX42- anions and hydration water molecules which form a complex hydrogen-bonded network. The tetrapodal tea ligand and two water molecules form a distorted octahedron around Cu2+ with four relatively short (1.95 - 2.03 angstrom; Cu-N and Cu-O) and two longer (2.30 - 2.38 angstrom; Cu-O) bonds, in agreement to the expected Jahn - Teller distortion for the 3d(9) configuration. The existence of full isostructural series between sulfates, selenates, and fluoroberyllates presents a manifestation of chemical analogy where chemically dissimilar anions ([TO4](2-) vs. [BeF4](2-)) can play identical structure-directing roles. However, this phenomenon is not universal but is governed by strict boundary conditions related to cation properties, anion stability, and synthetic protocol. As in the case of (enH(2))[Cu (H2O)(4)(TX4)](2), the three compounds [Cu(tea)(H2O)(2)](TX4)center dot H2O (TX4 = SO42-, SeO42-, and BeF42-) were found to be isostructural. The key structural feature is the specific chemical environment of the copper-containing complex cation which only weakly interacts (via hydrogen bonding) with the tetrafluoroberyllate anion preserving its integrity.

Formation of guanidinium and 4-aminoguanidinium cations with 18-crown-6 ether was observed upon interaction of the respective thiosulfates and crown ether. The new compounds [(CN3H6)2(C12H24O6)][(CN3H6)2(C12H24O6)(H2O)2](S2O3)2 (1) and [(CN4H7)2(C12H24O6)]2(S2O3) (2), have been characterized by single-crystal and powder diffraction, IR and Raman spectroscopy, and topological analysis. The unit cell parameters are: a = 7.78660(1) Å, b = 9.9999(2) Å, c = 16.7675(3) Å, α = 97.9586(2)°, β = 96.4350(2)°, γ = 99.3458(2)°, space group P-1 for 1 and a = 10.0887(2) Å, b = 17.9587(3) Å, c = 14.1896(3) Å, β = 103.5963(2)°, γ = 99.3458(2)°, space group P21/c for 2. The structures can be referred to as complex hydrogen-bonded 3D networks. In both structures, the crown ether ligands coordinate two (amino)guanidinium cations; in 1, the crown ether molecules and guanidinium cations exhibit two different environments. The size and shape complementarity between the relatively small thiosulfate anions and the cationic complexes is also a critical factor: with the smaller guanidinium cation, the resulting void space is occupied by water molecules, which provide additional stabilization. In contrast, the structure containing the larger aminoguanidinium cation is anhydrous.

The use of bone cements offers the significant advantage of enabling precise, minimally invasive filling of complex bone defects, which ensures optimal implant adaptation and stability. Furthermore, bone cements can be functionalized with bioactive or antibacterial agents to promote osseointegration and prevent post-surgical infections. This study investigates the synthesis, structure, and multifunctional properties of a novel series of Cu,Na-doped β-tricalcium phosphate (β-TCP) with the general formula Ca10–xNaCux(PO4)7 (NCx), designed for applications as antibacterial bone cements and radiopaque agents and fille for poly(methyl methacrylate) (PMMA)-based bone cements. The compounds were synthesized via high-temperature solid-state reaction and characterized by XRD with Rietveld refinement, SEM, and antibacterial assays. All NCx sample were found to be isostuctural to the β-TCP, and structural refinement reveals preferential Cu2+ occupancy at the octahedral M5 site, leading to progressive structural stabilization as evidenced by reduced distortion indices. Brushite cement (NCx-cem) and PMMA-phosphate composite were produced from NCx samples. Antimicrobial efficacy against E. coli and S. aureus increased with Cu²⁺ content, with the NC1.0 composition achieving complete bacterial inhibition within 3 hours, and effective inhibition of E. coli growth for brushite NCx cements. Filling of PMMA by NC powder lowers hardening temperature (≤ 35 °C). When incorporated as a 15 wt.% filler into PMMA bone cement, the Na/Cu-doped phosphate (NC0.1) imparted excellent radiopacity, increasing the X-ray attenuation value from 70 ± 10 Hounsfield Units (H.U.) for pure PMMA to 400 ± 30 H.U., thereby enabling clear visualization in computed tomography (CT) imaging. The results demonstrate that Ca10–xNaCux(PO4)7 compounds successfully integrate antibacterial functionality, bioactive cement formation, and enhanced radiopacity into a single material, presenting a promising multifunctional candidate for advanced bone tissue engineering and orthopedic applications.

A continuous series of anion-mixed solid solutions Sr8MgEu(PO4)7-& khcy;(VO4)& khcy; (SMEPV) with the strontiowhitlockite (or beta-Ca3(PO4)2) structure was successfully synthesized via a conventional solid-state reaction route. Powder Xray diffraction confirms phase purity across the entire concentration range. Rietveld structure refinements, coupled with Second Harmonic Generation (SHG) measurements, reveal an abrupt structural change within the series: all samples with 0 <= x <= 6 adopt a centrosymmetric structure (space group R3 m), whereas the pure vanadate end-member, Sr8MgEu(VO4)7, crystallizes in a non-centrosymmetric polar space group (R3c), closely resembling calcium whitlockites. Rietveld refinements further show that incorporation of the larger V5+ ion induces significant splitting of the M1, M2, and M3 cation sites, attributed to the size mismatch between Sr2+ and Eu3+. This structural transformation is accompanied by a reversible ferroelectric-type phase transition, confirmed by dielectric spectroscopy and DSC. The influence of these structural variations on the luminescence properties was systematically investigated through a combination of theoretical calculations and experimental optical measurements. Photoluminescence studies demonstrate that progressive substitution PO4 -> VO4 tetrahedra significantly enhances the red emission intensity of Eu3+ ions under both direct and host excitation. Under blue excitation (464 nm), the SMEPV phosphors exhibit bright, narrow-band red emission corresponding to the hypersensitive 5D0 -> 7F2 transition of Eu3+ at 613 nm. The integrated intensity of this emission increases progressively with VO43- content. The increased asymmetry ratio and Judd-Ofelt parameters (Omega 2, Omega n) calculated from emission spectra indicate a more distorted local environment and higher covalency of Eu-O bonds with increasing vanadate content, in excellent agreement with structural data. Notably, Sr8MgEu(VO4)7 represents a new class of strontium vanadate phosphors, distinguished by its intense, ultra-narrow red emission, high color purity, and a high quantum efficiency of up to 79%. These results highlight the potential of this material family as promising red-emitting phosphors for solid-state lighting applications, with excitation profiles well-matched to commercial blue LED chips.

New solid solutions of Sr9-xBaxIn(VO4)(7) (SBIV) and Sr9-xBaxYb(VO4)(7) (SBYV) with whitlockite-type structure were obtained by solid-phase synthesis within the ranges of 0 <= x <= 1.75 and 0 <= x <= 2, respectively. Incorporation of Ba2+ cations reduces phase transition temperatures from 959 K to 826 K for SBIV, and from 950 K to 800 K for SBYV. All synthesized samples showed nonlinear second harmonic generation (SHG) efficiency 10 times more than that of the quartz standard. SHG response remained largely constant as x increased. Sr2+ cation conductivity is suggested for both SBIV and SBYV. The incorporation of barium cations hinders the migration paths for Sr2+ cation. Barium atoms are located predominantly in the M3 position, which complicates the migration paths for strontium. The key result is creating a model for future finding of Sr-based ion conducting materials.

Magnesium-containing whitlockite powders doped with up to 1.0at.% Eu³⁺ were synthesized via chemical precipitation, heat-treated at 1000 °C, and used as cement powders. The powders exhibit photoluminescence in the visible range due to 4f–4f electronic transitions of Eu³⁺ ions, with emission intensity increasing proportionally to Eu³⁺ concentration. Cements prepared from these powders and a magnesium phosphate-based liquid showed open porosity of 22–29%, compressive strength of 5–6MPa, and a setting time of 3–4minutes. Biodegradation studies in simulated body fluid revealed a mass loss up to 47% and porosity increase to approximately 39% after prolonged soaking. The cements retained Eu³⁺-dependent photoluminescence, similar to the powders. All formulations exhibited antibacterial activity against gram-negative E. coli bacteria and demonstrated cytocompatibility on the MG-63 cell line in vitro. These results suggest that the developed cements are promising candidates for bone regeneration applications, with the added potential for luminescence-based biovisualization of bone tissue restoration.

This article examines the historical development of the Russian Arctic, the current status of Russia’s claims to extend its continental shelf, and the delimitation of maritime boundaries under the United Nations Convention on the Law of the Sea. It also discusses the substantial natural resources of the Far North. The region accounts for one-tenth of global oil production and one-quarter of natural gas output. It contains deposits of solid minerals, including tin, manganese, gold, nickel, lead, platinum, and diamonds. The article traces the history of establishing the Northern Sea Route, from the first expedition seeking a maritime passage to China to projects proposed by M. V. Lomonosov and D. I. Mendeleev, and outlines its contemporary development. The article further considers an emerging dimension of Russia’s Arctic policy: the restoration of strategically important military bases to support both nuclear and non-nuclear capabilities. These measures are aimed at deterring potential aggression and safeguarding Russia’s diverse interests in the region. The authors conclude that the Russian Arctic encompasses key resource, technological, military, and political assets that are critical to the country’s future. The region serves not only as a major center for resource extraction but also as the base for a powerful icebreaker fleet, a hub of industrial activity supporting year-round navigation along the Northern Sea Route, and a locus of infrastructure essential for national defense. The article also addresses and challenges external claims regarding the status of Arctic territories as “common” or “neutral,” as well as allegations concerning environmental degradation.

The purpose of this work was the development of bone whitlockite (WH) nanopowders doped with europium ions (Eu3+; via a precipitation route) for biomedical and phosphor-related applications. The introduction of Eu3+ ions into the WH lattice was confirmed by X-ray powder diffraction and transmission microscopy mapping, while the formation of bone WH was proven by examination of HPO4 2- group bands in infrared spectra. The crystals have rhombohedral morphology, and an increase of Eu3+ concentration to 0.5 at.% decreased particle size down to 30-40 nm. Photoluminescence spectra of all samples consist of a series of bands corresponding to transitions of Eu3+ from the lowest excited state 5D0 to ground state 7FJ. The emission reached maximum intensity at 0.5 at.% of Eu3+, while a further increase of the Eu3+ concentration had the concentration quenching effect. Decay times and Comission Internationale de l'Eclairage (CIE) chromaticity coordinates were determined too. CIE color coordinates (X, Y) at 0.5 at.% of Eu3+ were (0.648; 0.351), lying in a red region of color space and close to a red standard, indicating good potential for red-light-emitting phosphor applications. Thus, we obtained bone WH nanopowders with photoluminescent properties promising for optical elements, electronics, and medical applications including photoluminescent biovisualization.

The reaction between anhydrous BaX2 (X = Cl, Br) and Ba(SCN)2 results in the formation of two novel compounds with the general formula BaX(SCN), where X = Br-(I) and I-(II). The new compounds have been characterized by single-crystal X-ray diffraction and vibrational (IR and Raman) spectroscopy. Both compounds correspond to known, yet modestly represented, structure types. Compound I is monoclinic with the unit cell parameters a = 5.9873(2) & Aring;, b = 4.7074 (2) & Aring;, c = 8.8044(3) & Aring;, beta = 99.121(3)degrees; space group P21/m, which is isostructural to compounds BaCl(SCN) and BaCl(OCN). The crystal structure of I is analogous to that of the respective chloride thiocyanate and is based on the litharge-type layers, formed by edge-shared anion-centered BrBa4-tetrehedra. Compound II is orthorhombic with the unit cell parameters a = 9.3150(6) & Aring;, b = 4.8168(2) & Aring;, c = 11.9968(7) & Aring;; space group Pnma, and it is isostructural to compounds PbCl(SCN) and o-BaI(OCN). The crystal structure of II is based on edge-shared anion-centered IBa4-tetrahedra, which form a tetrahedral framework. The DFT studies on the relative stability of possible polytypes indicate that, contrary to BaI(OCN), BaI(SCN) is unlikely to exhibit dimorphism. We also discuss the crystal chemical and topological relationships among the three known structural families of MX(ABC) compounds (M = metal cation, X = halide anion, and ABC-linear triatomic anion), as well as their relations to the PbFCl, PbClI, and Nd2O2Te archetypes.

Среди большого числа слоистых неорганических соединений с модулярными структурами, для которых характерна политипия, особое место занимают природные и синтетические бораты. В данной работе повторно выполнен модулярный анализ кристаллических структур курчатовита и клинокурчатовита CaMg[B2O5] с использованием формализма OD-теории, топологический анализ геометрии и сложности кристаллических структур политипов, а также проведена их оптимизация методами квантовой химии. На основе полученных данных по строению курчатовита и клинокурчатовита, а также SrCd[B2O5], был подтвержден политипный характер строения данных соединений. Полученные теоретические и экспериментальные ИК-спектры находятся в полном согласии друг с другом для клинокурчатовита. Для политипных структур ИК-спектр может, в какой-то степени, рассматриваться как эмпирическая мера сложности структуры: чем ниже симметрия и чем больше колебательных степеней свободы на ячейку, тем больше нормальных мод. Сравнительный кристаллохимический анализ также позволил выявить симметрийное родство между большим числом пироборатов двухвалентных катионов с общей формулой M2+2[B2O5] (M = Ca, Sr, Pb, Mg, Mn–Ni, Zn, Cd), которые также можно объединить в единой структурное OD-семейство шимазакиита (или Cd2[B2O5]), которое состоит из трех типов OD-слоев.

The study shows that any two fullerenes from the Cn variety (n >= 36) can be transformed into each other by a sequence of local topological transformations of their lattice. Thus, for the considered set of fullerenes a connected interconversion map exists, similar to those considered by other authors using the Stone-Wales transformation.

The re-study of the crystal structure of the second find of low-calcium and rare-earths bearing voronkovite in the Lovozero alkaline complex, Kola Peninsula has revealed new features of its structure, which lower the symmetry of the mineral. Ordering of Ca, Mn, Ce, and Na atoms in octahedra of six-membered rings, as well as Zr, Fe, and Na atoms in M2 positions, combining translationally identical six-membered rings as well as Nb, Ti, and Si atoms and vacancies in axial fragments of the structure, has been established within the P3 symmetry. The trigonal-cell parameters of the mineral are a = 14.1617(1) Å, c = 30.1815(1) Å, and V = 5242.09(4) Å3; the number of independent positions is 184. The crystal structure has been refined to the R factor of 3.74

The structure of unique compound Cs4Ca[Si8O19] reported recently by Kahlenberg [(2025), Acta Cryst. B81, 325-336] contributes to the broader understanding of structure-property relationships in open-framework silicates (as well as silicates with mixed octahedral-tetrahedral frameworks), with potential implications for ion-exchange, catalysis, and materials with tailored thermal expansion.

The Laakso–Taagepera index belongs to Hill numbers, which characterize diversity of species. The paper demonstrates application of this index for comparing the distributions of structures from the databases ICSD (116 860 records), CSD (1 294 724 records), PDB (184 841 records), and RRUFF ( 5.5 thousand mineral species) over space-group types, crystal classes, and crystal systems.

A re-study of the crystal structure of low-calcium and high-zirconium eudialyte from the Khibiny Mountains of Kola Peninsula has revealed new features of its structure, which decrease the symmetry of the mineral. The ordering of Ca, Fe, Mn, and Na atoms in octahedra of six-membered rings, as well as Zr and Na atoms in M2 positions at the centers of square pyramids, with a common base, formed by the edges of these octahedra, has been established with the P3 symmetry. The trigonal unit cell parameters are a = 14.222(3) Å, c = 30.165(5) Å, and V = 5283.9 Å3. Taking into account the new data, the studied low-calcium eudialyte can be assigned to the subtype of oneillite or raslakite, being a high-zirconium variety of the latter. The study of the structure of this mineral in rhombohedral symmetry (sp. gr. R3m and R3) and trigonal Р3 symmetry has shown that the decrease in symmetry of the structural model of low-calcium representatives of the eudialyte group makes it possible to clarify the nature of ordering of the cations occupying key framework positions.