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New acentric bismuth-sodium apatite (Bi5Na5)[PO4]6Cl2 with doubled c-axis and space group P6¯ is obtained first under mild hydrothermal conditions in excess of NaCl in solution. Structural solution was carried out on single crystal. The new apatite demonstrated wide heterovalence isomorphic substitution of Bi3+–Na+ in large cation positions, which allowed the final chemical formula to be established. This fact determines the doubling of the c-axis and the new space group P6¯ compared with other widely known apatites. Non-centrosymmetry of the structure agrees with a distinct effect of optical second harmonic generation, but the SHG intensity is small due to proximity to the parent centrosymmetric apatite structure as well as lack of phase matching for SHG and YAG:Nd laser emission. From a structural viewpoint, optical nonlinearity is determined by the difference in the isomorphic occupation of positions by large cations, with a slight deviation from the centrosymmetry of the whole structure. Disordered structural variants of isomorphic apatites are predicted, and a group–subgroup relation is found for three apatite variants: one well known and two new. [ABSTRACT FROM AUTHOR]

New polar K2NbO2F3 crystals were obtained under mild hydrothermal conditions, which differ from the higher temperature synthesis of previously known Nb-containing oxyfluorides. X-ray diffraction analysis of the single crystal, performed in the polar space group Pna21, is consistent with the existence of the second harmonic generation (SHG) effect in powders. A monotonous increase in SHG power in samples with increasing powder grain size indicates phase matching of neodymium laser radiation and its second harmonic. However, SHG is relatively small and does not exceed a third of the intensity of standard KH2PO4 powders. The weakness of the second-order optical nonlinearity in K2NbO2F is related to the strong pseudo-symmetry of the crystal structure, corresponding to the space group Pnam-D2h16, and thus the structure is very close to centrosymmetric. Structural evidence for the polarity of the K2NbO2F3 crystal is the subtle differences in the Nb–O bonds along the c axis in the (NbO3F3) octahedra, together with the presence of similar differences in the K1–O bonds. Extremely weak, close to the detection limit, very small deviations from the centrosymmetry of the entire structure also correlate with the existence of an almost second-order irreversible transformation of K2NbO2F3 into a centrosymmetric phase at temperatures 50–60 °C below the decomposition temperature of the substance at 560 °C. [ABSTRACT FROM AUTHOR]

Transparent single crystals of a new iodate Cs5[Sc2(IO3)9](IO3)2 were synthesized under mild hydrothermal conditions. X-ray diffraction of single crystal was used to determine the large crystal structure with 52 independent atoms, sp. gr. P21/c. The building blocks [Sc(IO3)6]3− of Sc octahedra and six (IO3) groups are condensed into a framework; the structure contains additional isolated (IO3) groups. Large Cs cations occupy holes and form an intercrossing framework. Similar building blocks [M(IO3)6] are known for many iodates; however, most are isolated. Their topology and symmetry differ and determine the properties of the compounds. [ABSTRACT FROM AUTHOR]

New polar iodate Cs3Ta(IO3)8, space group P31c, has been obtained under mild hydrothermal conditions and its structural determination was carried out with a single crystal. Two types of layers were selected and characterized using topology and symmetry analysis. The structure of the new iodate has relation with KSc(IO3)3Cl determined earlier. The polar space group corresponds to the presence of the distinct effect of optical second harmonic generation, but the SHG intensity is limited due to lack of phase matching for neodymium laser radiation and its second harmonic. The low optical nonlinearity is consistent with the structural feature of the crystal, and the polarity is determined mainly by the positions of Cs cations with a slight deviation from the centrosymmetry of the entire structure as a whole. Two structural variants of Cs3Ta(IO3)8 are predicted based on a OD topology-symmetry approach. [ABSTRACT FROM AUTHOR]

New silicate-germanates (K2.9Cs0.1)(Sc0.7In0.3)[(Si2.95Ge0.05)O9]·H2O and (K2.16Cs0.84)Bi[(Si0.5Ge0.5)3O9]·H2O have been synthesized in multi-component systems under mild hydrothermal conditions. The new compounds are classified as new representatives of close related K3ScSi3O9·H2O parent structure, sp. gr. Pmn21. Their structural and isomorphic peculiarities are compared with it as well as with earlier investigated K1.46Pb1.54Сa[(Ge0.23Si0.77)3O9](ОН)0.54·0.46Н2О. Together with other known compounds, silicate-germanates form the extensive family A3M[T3O9]·H2O, A = K, Cs, Ca, Pb; M = Ho, Sc, Lu, Tb, Er, Y, Bi, Pb, In; T = Si, Ge, with a mixed microporous framework combined of M-octahedra and T-tetrahedra. Large alkali metal or/and Ca, Pb cations fill broad framework channels with cross-section up to 7.3 Å. Because of wide isomorphic substitution in the channels, and in tetrahedra and octahedra, ion exchange properties in the family are expected. Due to polar symmetry, all the crystals possess second-order nonlinearity which was confirmed with positive SHG tests for four compositions. Powder SHG experiments demonstrated moderate second harmonic intensities of order of α-quartz standard signals. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a first salt‐inclusion aluminophosphate oxocuprate, (Na,Li)3(Cl,OH)[Cu3OAl(PO4)3], obtained as single crystals, is reported. A novel phase, with a strongly pseudo‐orthorhombic structure, is described as a monoclinic crystal structure established by the study of a pseudomerohedric microtwin. It was investigated using scanning electron microscopy, microprobe analysis and low‐temperature X‐ray diffraction. The composite crystal structure represents an original framework assembled from Cu‐centered polyhedra, AlO6 octahedra and PO4 tetrahedra with channels, which incorporate the Na/Li salt component [(Na,Li)3(Cl,OH)]2+ that ensures electroneutrality of the compound. Layers of strongly corrugated chains of Cu‐centered octahedra with shared edges and linked by PO4 tetrahedra are shown to be topologically identical with the layers also built from Cu‐centered polyhedra and AsO4/VO4 tetrahedra forming the crystal structure of a fumarolic mineral aleutite, (M0.5Cl)[Cu5O2(AsO4)(VO4)] [Siidra et al. (2019). MinMag, 83, 847–853]. 'Sawtooth chains' and pairs of Cu‐centered octahedra inherent in the title structure may be of interest in solid‐state physics, engaging studies in the field of low‐dimensional and frustrated magnetism. [ABSTRACT FROM AUTHOR]

Single crystals of a novel phase, potassium manganese silicate hydrate, K3Mn4Si10O24.33(H2O,OH)3, doped with B and V, were obtained under hydrothermal conditions and studied using scanning electron microscopy, microprobe analysis and low temperature synchrotron X-ray diffraction. The title structure represents an original silicate framework assembled from layers with various n-membered SiO4 rings that restrict channels open in the [001] direction. The corrugated chains of face-sharing MnO6 octahedra are incorporated into the space between "pendant" vertices of the tetrahedra framing 12-membered windows. This is the first example of combining two topologically different trimeric clusters of octahedra sharing faces into a single construction. The framework channels with 5- and 6-membered windows incorporate K atoms, and H2O molecules are located in the channels with 7-membered openings. We assume that the stability of this crystal structure is due to the partial substitution of Mn for V and Si for B. The magnetic subsystem in the title compound represents a rare case of the quasi-one-dimensional arrangement of MnO6 octahedra forming sawtooth-like chains. Measurements of magnetization and heat capacity of K3Mn4Si10O24.33(H2O,OH)3/V,B indicate the absence of long-range order up to 2 K. Structural features of the K3Mn4Si10O24.33(H2O,OH)3/V,B allow supposing it as potential multifunctional material, electrochemically active and having properties of low-dimensional magnet. [ABSTRACT FROM AUTHOR]

Single crystals of dinickel diphosphate dihydrate, Ni2(H2O)2[P2O7], have been synthesized by a hydrothermal method. Its structure was refined in the monoclinic P21/n space group (unit cell parameters a = 6.2517(1) Å, b = 13.7892(3) Å, c = 7.2894(2) Å, β = 94.507(2)°, V = 626.45(2) Å3, and Z = 4) based on low-temperature X-ray diffraction data until R – 0.016. Corrugated chains of NiO5(H2O) octahedra sharing edges are aligned in the [101¯] direction. They are linked into a three-dimensional framework through diphosphate groups and hydrogen bonds. A detailed crystal chemical analysis of the family Me2(H2O)2[X2O7] revealed correlations between the unit-cell parameters of the isotypic transition metal phosphates and arsenates, their structural features and the sizes of structure forming cations. Despite the isolation of the cis and trans edge-sharing infinite zigzag chains of Ni-centered octahedra from each other no pronounced low dimensionality is seen in the magnetic response of Ni2(H2O)2[P2O7]. The magnetic susceptibility χ evidences a short range correlation maximum at Tmax = 11.9 K accompanied by the onset of long-range magnetic order at TN = 9.4 K. Below TN, the title compound exhibits the features of an archetype three-dimensional easy-axis antiferromagnet which experiences a sequence of spin–flop and spin–flip phase transitions. Basing on specific heat Cp and magnetization M studies, the magnetic phase diagram of Ni2(H2O)2[P2O7] has been established. [ABSTRACT FROM AUTHOR]

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Single crystals of Rb2CaCu6(PO4)4O2 were synthesized by a hydrothermal method in the multicomponent system CuCl2–Ca(OH)2–RbCl–B2O3–Rb3PO4. The synthesis was carried out in the temperature range from 690 to 700 K and at the general pressure of 480–500 atm [1 atm = 101.325 kPa] from the mixture in the molar ratio 2CuO:CaO:Rb2O:B2O3:P2O5. The crystals studied by single‐crystal X‐ray analysis were found to be monoclinic, space group C2, a = 16.8913 (4), b = 5.6406 (1), c = 8.3591 (3) Å, β = 93.919 (3)°, V = 794.57 (4) Å3. The crystal structure of Rb2CaCu6(PO4)4O2 is similar to that of shchurovskyite and dmisokolovite and is based upon a heteropolyhedral open framework formed by polar layers of copper polyhedra linked via isolated PO4 tetrahedra. The presence of well‐isolated 2D heteropolyhedral layers in the title compound suggests low‐dimensional magnetic behavior which is masked, however, by the fierce competition between multiple ferromagnetic and antiferromagnetic exchange interactions. At TC = 25 K, Rb2CaCu6(PO4)4O2 reaches a magnetically ordered state with large residual magnetization. [ABSTRACT FROM AUTHOR]

The novel borophosphate Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] was prepared under hydrothermal conditions at 553 K. Its crystal structure was determined using single-crystal X-ray diffraction data obtained from a non-merohedral twin and refined against F2 to R = 0.057. The compound crystallizes in the orthorhombic space group Pbcn, with unit-cell parameters a = 20.076(2) Å, b = 9.151(1) Å, c = 12.257(1) Å, V = 2251.8(2) Å3, and Z = 4. The title compound is the first example of a borophosphate with manganese ions adopting both octahedral and tetrahedral coordinations. Its unique crystal structure is formed by borophosphate slabs and chains of Mn2+-centered polyhedra sharing edges and vertices. These 2D and 1D fragments interconnect into a framework with open channels that accommodate Rb+ cations and water molecules. Topological relationships between borophosphates built from three-membered rings of two borate and one phosphate tetrahedra sharing oxygen vertices, amended by additional PO4 and HPO4 tetrahedra, are discussed. The temperature dependence of the magnetic susceptibility of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2] reveals predominant antiferromagnetic exchange interactions and the high-temperature effective magnetic moment corresponding to the high-spin S = 5/2 state of Mn2+ ions. At 12.5 K, a magnetic transition is evidenced by ac-susceptibility and specific heat measurements. A spin-trimer model with the leading exchange interaction J∼ 3.2 K is derived from density-functional band-structure calculations and accounts for all experimental observations. [ABSTRACT FROM AUTHOR]