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The article describes the results of a comprehensive study of the extra-framework components of scapolites using quantum–chemical calculations, electronic and vibrational spectroscopy, and single-crystal X-ray diffraction and crystal structure refinement. The ab initio calculations were performed using an embedded-cluster approach of extra-framework components in various cation surroundings. As a result, through comparing the experimental and ab initio calculation results, the energies of the electronic and vibrational transitions of various extra-framework components (CO3)2−, (CO3)·−, S3·−, S2·−—as well as the role of these components in the process of the lowering of the symmetry—were determined for scapolites belonging to the marialite–meionite solid–solution series. The nature of the various colors of the scapolites has also been established. Colors from purple to blue are a result of the presence of radiation-induced pairs of defects: carbonate radical anions (CO3)·− and F-centers. However, polysulfide S3·− radical anions are found in some violet scapolites.

This review contains data on a wide class of microporous materials with frameworks belonging to the sodalite topological type. Various methods for the synthesis of these materials, their structural and crystal chemical features, as well as physical and chemical properties are discussed. Specific properties of sodalite-related materials make it possible to consider they as thermally stable ionic conductors, catalysts and catalyst carriers, sorbents, ion exchangers for water purification, matrices for the immobilization of radionuclides and heavy metals, hydrogen and methane storage, and stabilization of chromophores and phosphors. It has been shown that the diversity of properties of sodalite-type materials is associated with the chemical diversity of their frameworks and extra-framework components, as well as with the high elasticity of the framework.

A new series of Sr-based phosphates, Sr9−xMnxEu(PO4)7, were synthesized using the high-temperature solid-state method in air. It was found that these compounds have the same structure as strontiowhitlockite, which is a β-Ca3(PO4)2 (or β-TCP) structure. The concentration of Mn2+ ions required to form a pure strontiowhitlockite phase was determined. An unusual partial reduction of Eu3+ to Eu2+ in air was observed and confirmed by photoluminescence (PL) and electron spin resonance (ESR) spectra measurements. The PL spectra recorded under 370 nm excitation showed transitions of both 4f5d–4f Eu2+ and 4f–4f Eu3+. The total integral intensity of the PL spectra, monitored at 395 nm, decreased with increasing Mn2+ concentration due to quenching effect of Eu3+ by the Mn2+ levels. The temperature dependence of Eu2+ photoluminescence in a Sr9−xMnxEu(PO4)7 host was investigated. The conditions for the reduction of Eu3+ to Eu2+ in air were discussed.

β-Tricalcium phosphate (β-TCP) is widely used as bone implant material. It has been observed that doping the β-TCP structure with certain cations can help in combating bacteria and pathogenic microorganisms. Previous literature investigations have focused on tricalcium phosphate structures with silver, copper, zinc, and iron cations. However, there are limited studies available on the biological properties of β-TCP containing nickel and cobalt ions. In this work, Ca10.5−xNix(PO4)7 and Ca10.5−xCox(PO4)7 solid solutions with the β-Ca3(PO4)2 structure were synthesized by a high-temperature solid-state reaction. Structural studies revealed the β-TCP structure becomes saturated at 9.5 mol/% for Co2+ or Ni2+ ions. Beyond this saturation point, Ni2+ and Co2+ ions form impurity phases after complete occupying of the octahedral M5 site. The incorporation of these ions into the β-TCP crystal structure delays the phase transition to the α-TCP phase and stabilizes the structure as the temperature increases. Biocompatibility tests conducted on adipose tissue-derived mesenchymal stem cells (aMSC) using the (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) (MTT) assay showed that all prepared samples did not exhibit cytotoxic effects. Furthermore, there was no inhibition of cell differentiation into the osteogenic lineage. Antibacterial properties were studied on the C. albicans fungus and on E. coli, E. faecalis, S. aureus, and P. aeruginosa bacteria strains. The Ni- and Co-doped β-TCP series exhibited varying degrees of bacterial growth inhibition depending on the doping ion concentration and the specific bacteria strain or fungus. The combination of antibacterial activity and cell-friendly properties makes these phosphates promising candidates for anti-infection bone substitute materials.

Eudialyte-group minerals are of scientific interest as important concentrators of rare elements (mainly Zr and REE) in agpaitic alkaline rocks and a potential source of REE, Zr, Hf, Nb, and Ta for industrial use. Extraction of uranium(VI), thorium(IV), zirconium(IV), hafnium(IV), titanium(IV), and scandium(III) by a binary extractant based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyl trioctylammonium nitrate from eudialyte breakdown solutions is studied. Extraction isotherms were obtained and exhaustive extraction was investigated. It is shown that uranium, thorium, hafnium, zirconium, scandium, and titanium are almost completely recovered in two-stage extraction by a mixture of 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyltrioctylammonium nitrate in 1,2-dichloroethane. Quantitative characteristics were compared for uranium(VI), thorium(IV), zirconium(IV), hafnium(IV), titanium(IV), and scandium(III). It was shown that the extraction efficiency of the metals by the binary extractant based on 1,5-bis[2-(hydroxyethoxyphosphoryl)-4-ethylphenoxy]-3-oxapentane and methyltrioctylammonium nitrate in 1,2-dichloroethane is much higher in comparison with the commercially available tributyl phosphate.

Eudialyte-group minerals (EGMs) are typical accessory or rock-forming minerals of the Lovozero peralkaline massif (Kola Peninsula, Russia). The EGM grains in the rocks of the massif are often replaced by an association of various secondary minerals such as lovozerite and wöhlerite group minerals, as well as terskite, catapleiite, elpidite, gaidonnayite, vlasovite, zircon, and loparite-(Ce). However, EGMs in the Lovozero massif can be not only pseudomorphized, but also partially or completely dissolved. The partial dissolution of eudialyte grains was simulated in three series of experiments, and the results obtained were compared with natural samples. Observations in natural samples and experimental studies have shown that the partial dissolution of eudialyte-group minerals occurs in two stages: (1) loss of sodium and hydration; (2) loss of other cations not included in the zirconosilicate framework. This process proceeds most intensively in acidic hydrothermal solutions and may be responsible for the appearance of new mineral species in the eudialyte group.

Nepheline is a nominally anhydrous aluminosilicate that typically contains an impurity of ferric iron replacing aluminum in tetrahedral sites. However, previous researchers noted the constant presence of ferrous iron in the chemical composition of nepheline from the rocks of the Khibiny and Lovozero massifs (Kola Peninsula, Russia). We have carried out microprobe, spectroscopic, chemical and crystal chemical studies of nepheline from the Lovozero massif. We have established the presence of molecular water in nepheline, and also that the incorporation of ferrous iron into nepheline crystal structure is associated with the simultaneous increasing of the coordination number from four to five (or six) due to the inclusion of the ‘additional’ water molecules that form point [FeO4(H2O)n]-defects (where n = 1, 2) in the tetrahedral framework. The nepheline iron content is closely related to the presence of small needle-like aegirine inclusions. The total iron content in nepheline saturated with aegirine needles is approximately an order of magnitude lower than in nepheline free from aegirine inclusions. Most likely the aegirine inclusions in nepheline are formed as a result of the decomposition of the nepheline–“iron nepheline” solid solution. We propose that this process is triggered by the oxidation of ferrous iron in the crystal structure of nepheline.

Our systematic explorations of the complex rare earth tellurite halide family have added several new [Ln12(TeO3)12][M6X24] (M = Cd, Mn, Co) representatives containing strongly deficient and disordered metal-halide layers based on transition metal cations. The degree of disorder increases sharply with decrease of M2+ radius and the size disagreements between the cationic [Ln12(TeO3)12]+12 and anionic [M6Cl24]−12 layers. From the crystal chemical viewpoint, this indicates that the families of both rare-earth selenites and tellurites can be further extended; one can expect formation of some more complex structure types, particularly among selenites. Analysis of the polytypism of compounds have been performed using the approach of OD (“order–disorder”) theory.

Eudialyte-group minerals are important accessory minerals of peralkaline rocks of nepheline-syenite massifs and alkaline–ultramafic complexes. Here, we report the complex study of a eudialyte-group mineral (EGM) from peralkaline pegmatite of the alkaline-ultrabasic Odikhincha massif (Polar Siberia). The chemical composition of the studied EGM is intermediate between those of taseqite and eudialyte, with small admixtures of other members of the eudialyte group. The crystals of EGMs were formed during the postmagmatic stage in the temperature range of 300–350 °C and partly replaced by late eudialite along cracks during the zeolite stage (~230 °C). The chemical compositions, structural features and mineral association of the studied EGM are similar to those of Sr-Nb-dominant EGM found in other nepheline-syenite massifs, such as Khibiny, Lovozero and Pilansberg. The EGM studied in this work is a Cl-deficient taseqite variety (“monochlore taseqite”), which differs from “dichlorotaseqite” (found only in the Ilimaussaq massif) by a lower amount of chlorine.

Sodium plays an important role in the crystal structures of eudialyte-group minerals given that it can occupy different crystallographic sites. Predominantly, it distributes between the N(1–5) sites situated in the large cavities of the heteropolyhedral framework. Rarely, Na occupies split sites of the M(2) microregion where it can predominate over other elements (predominantly Mn, Fe2+, and Fe3+). The crystal structure of the Mn-deficient manganoeudialyte from the Lovozero alkaline complex (Kola Peninsula, Russia) has been refined. The trigonal unit–cell parameters are: a = 14.1848(2) Å, c = 30.4726(3) Å, V = 5309.90(11) Å3. The sample is a rare example of a high-sodium and high-calcium representative of the eudialyte group with Fe + Mn < 2 apfu. The idealized formula is Na14Ca6[(Mn,Fe)2Na]Zr3Si2[Si24O72]O(OH)·2H2O with bivalent components, Mn2+ and Fe2+, dominating at the M(2) site. The regularities of isomorphism involving M(2)Na in EGMs and the problem of the existence of the M(2)Na-dominant analogue of eudialyte are discussed. The new data obtained in this work confirm the previous conclusion that the complete isomorphism between Ca-deficient and Ca-rich members of the eudialyte group cannot be realized in frames of a single-space group (R3m, R-3m or R3). Thus, the existence of the M(2)Na analogue of eudialyte remains questionable.

Eudialyte-group minerals (EGMs) are Na-Ca zirconosilicates typical for peralkaline plutonic rocks. In the zeolite-like crystal structure of these minerals, there are many sites of different volumes and configurations, and therefore EGMs can include up to one-third of the periodic table. Although there are preferred sites for many elements in the crystal structure of eudialyte-group minerals, the same element can appear in several sites. In addition, many sites may be partially or fully vacant. Currently, 30 mineral species are established in the eudialyte group. However, this diversity is, in fact, limited to holotype specimens. To name any mineral from the eudialyte group, you need to solve its crystal structure and compare it with holotypes. Meanwhile, the composition (and, therefore, the name) of any mineral of the eudialyte group is an excellent indicator of the composition of the mineral-forming media, which is very important to petrological and mineralogical studies. In this article, we propose a diagnostic scheme for minerals of the eudialyte group, based only on the chemical composition. The scheme includes five consecutive steps, each of which evaluates the content of a species-forming element (or the sum of such elements). This scheme can be supplemented by new members without changing its hierarchical structure.

A series of novel phosphates with the general formulas Ca9Gd0.9−xTm0.1Smx(PO4)7 and Ca9Gd0.9−yTmySm0.1(PO4)7 were synthesized by solid-state method. As-obtained phosphates were characterized by powder X-ray diffraction and second harmonic generation analyses, dielectric measurements, luminescence spectroscopy. All samples were single phase and characterized by the whitlockite-type structure with space group R3c. An influence of admixture concentration of REE3+ ions in the initial host on dielectric properties was studied in details. Synthesized phosphates are characterized by intensive luminescence. The emission in the orange region of the visible spectrum is observed for Ca9Gd0.9Sm0.1(PO4)7 with a maximum intensity band at 602 nm. The line in blue region at 455 nm, which corresponds to 1D2 → 3F4 Tm3+ transition, is registered for Ca9Gd0.9Tm0.1(PO4)7. Emission in the white region of CIE coordinates was registered for Tm-Sm co-doped compounds.

The molecular net complexity (HmolNet) is an extension of the combinatorial complexity (Hmol) of a crystal structure introduced by Krivovichev. It was calculated for a set of 4152 molecular crystal structures with the composition of CxHyOz characterized by the structural class P21/c, Z = 4 (1). The molecular nets were derived from the molecular Voronoi–Dirichlet Polyhedra (VDPmol). The values of the molecular coordination number (CNmol) and critical coordination number (CNcrit) are discussed in relation with the complexity of the crystal structures. A statistical distribution of the set of molecular crystals based on the values of CNmol, CNcrit, and the complexity parameters is obtained. More than a half of the considered structures has CNmol = 14 and CNmol′ = 9 with the Wyckoff set of edges e5dcba. The average multiplicity of intermolecular contacts statistically significantly decreases from 1.58 to 1.51 upon excluding all contacts except those bearing the molecular net. The normalized value of HmolNet is of the logistic distribution type and is distributed near 0.85HmolNet with a small standard deviation. The contribution of Hmol into HmolNet ranges from 35 to 95% (mean 79%, SD 6%), and the subset of bearing intermolecular contacts accounts for 41 to 100% (mean 62%, SD 11%) of the complexity of the full set of intermolecular contacts.

The Lovozero peralkaline massif (Kola Peninsula, Russia) has several deposits of Zr, Nb, Ta and rare earth elements (REE) associated with eudialyte-group minerals (EGM). Eudialyte from the Alluaiv Mt. often forms zonal grains with central parts enriched in Zr (more than 3 apfu) and marginal zones enriched in REEs. The detailed study of the chemical composition (294 microprobe analyses) of EGMs from the drill cores of the Mt. Alluaiv-Mt. Kedykvyrpakhk deposits reveal more than 70% Zr-enriched samples. Single-crystal X-ray diffraction (XRD) was performed separately for the Zr-rich (4.17 Zr apfu) core and the REE-rich (0.54 REE apfu) marginal zone. It was found that extra Zr incorporates into the octahedral M1A site, where it replaces Ca, leading to the symmetry lowering from R3¯m to R32. We demonstrated that the incorporation of extra Zr into EGMs makes the calculation of the eudialyte formula on the basis of Si + Al + Zr + Ti + Hf + Nb + Ta + W = 29 apfu inappropriate.

Structural complexity measures based on Shannon information entropy are widely used for inorganic crystal structures. However, the application of these parameters for molecular crystals requires essential modification since atoms in inorganic compounds usually possess more degrees of freedom. In this work, a novel scheme for the calculation of complexity parameters (HmolNet, HmolNet,tot) for molecular crystals is proposed as a sum of the complexity of each molecule, the complexity of intermolecular contacts, and the combined complexity of both. This scheme is tested for several molecular crystal structures.

The crystal structures of compounds with the general formula Cs{[6]Al2[[4]TP6O20]} (where T = Al, B) display order-disorder (OD) character and can be described using the same OD groupoid family. Their structures are built up by two kinds of nonpolar layers, with the layer symmetries Pc(n)2 (L2n+1-type) and Pc(a)m (L2n-type) (category IV). Layers of both types (L2n and L2n+1) alternate along the b direction and have common translation vectors a and c (a ~ 10.0 Å, c ~ 12.0 Å). All ordered polytypes as well as disordered structures can be obtained using the following partial symmetry operators that may be active in the L2n type layer: the 21 screw axis parallel to c [– – 21] or inversion centers and the 21 screw axis parallel to a [21 – –]. Different sequences of operators active in the L2n type layer ([– – 21] screw axes or inversion centers and [21 – –] screw axes) define the formation of multilayered structures with the increased b parameter, which are considered as non-MDO polytypes. The microporous heteropolyhedral MT-frameworks are suitable for the migration of small cations such as Li+, Na+ Ag+. Compounds with the general formula Rb{[6]M3+[[4]T3+P6O20]} (M = Al, Ga; T = Al, Ga) are based on heteropolyhedral MT-frameworks with the same stoichiometry as in Cs{[6]Al2[[4]TP6O20]} (where T = Al, B). It was found that all the frameworks have common natural tilings, which indicate the close relationships of the two families of compounds. The conclusions are supported by the DFT calculation data.

A new sodium manganese-nickel phosphate of alluaudite supergroup with the general formula NaMnNi2(H2/3PO4)3 was synthesized by a hydrothermal method. The synthesis was carried out in the temperature range from 540 to 660 K and at the general pressure of 80 atm from the oxides mixture in the molar ratio MnCl2: 2NiCl2: 2Na3PO4: H3BO3: 10H2O. The crystal structure was studied by a single-crystal X-ray diffraction analysis: space group C2/c (No. 15), a = 16.8913(4), b = 5.6406(1), c = 8.3591(3) Å, β = 93.919(3), V = 794.57(4) Å3. The compound belongs to the alluaudite structure type based upon a mixed hetero-polyhedral framework formed by MX6-octahedra and TX4-tetrahedra. The characteristic feature of the title compound is the absence of cations or H2O molecules in channel II, while the negative charge of the framework is balanced by the partial protonation of PO4 tetrahedra. The presence of the transition metals at the A-type sites results in the changes of stoichiometry and the local topological features. Topological analysis of the hetero-polyhedral alluaudite-type frameworks and its derivatives (johillerite-, KCd4(VO4)3-, and keyite-type) and quantitative characterization of their differences was performed by means of natural tilings.

The new eudialyte-group mineral, odikhinchaite, was discovered in a peralkaline pegmatite vein hosted by melteigite at the Odikhincha ultrabasic alkaline–carbonatite intrusion, Taimyr Peninsula, Krasnoyarsk Krai, Russia. Associated minerals are orthoclase, albite, aegirine, cancrinite, ancylite-(Ce), catapleiite, and wadeite. Odikhinchaite occurs as dense rosette-like aggregates up to 11 mm across, consisting of split lamellar individuals. The mineral is translucent to transparent, deep purple, with vitreous luster. Odikhinchaite is brittle, with uneven fracture; distinct cleavage on (001) is observed. Hardness determined by the micro-indentation method is equal to 430 kgf/mm2; the Mohs hardness is 5. D(meas.) is 2.97(1) g·cm−3, D(calc.) is 3.04 g·cm–3. Odikhinchaite is optically uniaxial (–), ω = 1.638(2), ε = 1.630(2). The IR spectrum shows the presence of the IVMn2+O4 polyhedra, H2O molecules and CO32– anions. The chemical composition is (electron microprobe, H2O determined by the modified Penfield method, CO2 determined by selection sorption of gaseous annealing products; wt%): Na2O 9.25, K2O 0.59, CaO 12.77, MnO 5.49, FeO 0.75, MgO 0.24, La2O3 0.38, Ce2O3 0.39, Nd2O3 0.15, Al2O3 0.07, SiO2 44.80, ZrO2 11.13, TiO2 0.07, Nb2O5 4.17, Cl 0.69, CO2 0.90, H2O 2.22, –O = Cl –0.16, total 99.72. The crystal structure was solved using single-crystal X-ray diffraction data. Odikhinchaite is trigonal, space group R3m; the unit-cell parameters are: a = 14.2837(2) Å, c = 30.0697(3) Å, V = 5313.04(12) Å3. The new mineral is isostructural with other 12-layered members of the eudialyte group with the space group R3m. Its crystal chemical formula is (Z = 3): {N1(Na2.58Ca0.42)N2[Na2.37Ca0.51(H2O)0.12]N3(Sr2.00K0.45Na0.35REE0.20)N4Na3N5[(H2O)1.8Na1.2]}{ZZr3M1Ca6M2(Mn2.49Fe2+0.51)[M3Nb(OH)1.82O1.18](M4SiOH)[Si3O9]2[Si9O27]2X1[(CO3)0.53Cl0.47]X2[(H2O)0.6(O,F)0.4]XM4(CO3)0.15. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 11.42 (64) (101), 4.309 (41) (205), 3.405 (53) (131), 3.208 (45) (208, 036), 3.167 (44) (217), 2.978 (100) (315), 2.858 (86) (404).

The Na2−nHn[Zr(Si2O7)]∙mH2O family of minerals and related compounds (n = 0–0.5; m = 0.1) consist of keldyshite, Na3H[Zr2(Si2O7)2], and parakeldyshite, Na2[Zr(Si2O7)], and synthetic Na2[Zr(Si2O7)]∙H2O. The crystal structures of these materials are based upon microporous heteropolyhedral frameworks formed by linkage of Si2O7 groups and ZrO6 octahedra with internal channels occupied by Na+ cations and H2O molecules. The members of the family have been studied by the combination of theoretical (geometrical–topological analysis, Voronoi migration map calculation, structural complexity calculation), and empirical methods (single-crystal X-ray diffraction, microprobe analysis, and Raman spectroscopy for parakeldyshite). It was found that keldyshite and parakeldyshite have the same fsh topology, while Na2ZrSi2O7∙H2O is different and has the xat topology. The microporous heteropolyhedral frameworks in these materials have a 2-D system of channels suitable for the Na+-ion migration. The crystal structure of keldyshite can be derived from that of parakeldyshite by the Na+ + O2− ↔ OH− + □ substitution mechanism, widespread in the postcrystallization processes in hyperagpaitic rocks.