A. S. Volkov

The first vanadate-carbonate, K2Mn3(VO4)2(CO3): crystal structure and physical properties.

Mixed potassium-manganese vanadate-carbonate, K(2)Mn(3)(VO(4))(2)(CO(3)), represents a novel structure type; it has been synthesized hydrothermally from the system MnCl(2)-K(2)CO(3)-V(2)O(5)-H(2)O. Its hexagonal crystal structure was determined by single-crystal X-ray diffraction with a = 5.201(1) Å, c = 22.406(3) Å, space group P6(3)/m, Z = 2, ρ(c) = 3.371 g/cm(3), and R = 0.022. The layered structure of the compound can be described as a combination of honeycomb-type modules of [MnO(6)] octahedra and [VO(4)] tetrahedra, alternating in the [001] direction with layers of [MnCO(3)] built by [MnO(5)] trigonal bipyramids and [CO(3)] planar triangles, sharing oxygen vertices. The K(+) ions are placed along channels of the framework, elongated in the [100], [010], and [110] directions. The title compound exhibits rich physical properties reflected in a phase transition of presumably Jahn-Teller origin at T(3) = 80-100 K as well as two successive magnetic phase transitions at T(2) = 3 K and T(1) = 2 K into a weakly ferromagnetic ground state, as evidenced in magnetization, specific heat, and X-band electron spin resonance measurements. A negative Weiss temperature Θ = -114 K and strongly reduced effective magnetic moment μ(eff)(2) ~ 70 μ(B)(2) per formula unit suggest that antiferromagnetic exchange interactions dominate in the system. Divalent manganese is present in a high-spin state, S = 5/2, in the octahedral environment and a low-spin state, S = ½, in the trigonal-bipyramidal coordination.

KNa2Tm[Si8O19] · 4H2O, a new layered silicate related to rhodezite-shlykovite-delhayelite-umbrianite-guenterblassite-hilleshaymite: Topology-symmetry analysis of the OD-family and structure prediction

Crystals of a new silicate KNa2Tm[Si8O19] · 4H2O, space group P12/m1 (the chemical formula was determined in the course of structure solution), are obtained under hydrothermal conditions. KNa2Tm[Si8O19] · 4H2O is the first synthetic representative of the family, which contains the following well-known and recently discovered minerals: rhodezite, delhayelite (fivegite, hydrodelhayelite), mountainite, shlykovite (cryptofillite), and guenterblassite (umbrianite, hilleshaymite). A crystal chemical analysis within the extended OD theory revealed the similarity of the structures of the family, including the new simplest representative and the factors responsible for structural diversity, namely, different symmetry of sheets of octahedra connected with layers of tetrahedra, which are distinguished in all the structures, and different patterns of symmetry relation between the sheets. Hypothetic structures with a higher degree of disordering are deduced. Crystals with these structures can be found in nature or obtained synthetically.

Iodide-Iodates M3[IO3]12·Ag4I, M = Bi, Tb, with a Framework Structure and High Second-Harmonic Generation Optical Response

Single crystals of two new iodide-iodates, Bi3[IO3]12·Ag4I and Tb3[IO3]12·Ag4I, are synthesized in hydrothermal systems. The anionic parts in both iodide-iodates are characterized as a complex charged framework of isolated IO3 umbrella-like groups and large Bi(Tb)-O polyhedra similar to those previously found in La3[IO3]12[IO3](Pb3O). Broad channels along the c-axis contain compensators: (Ag3I)2+ umbrella-like groups and additional Ag+ ions which form Ag44+ tetrahedral clusters augmented with I- halogen. New iodates possess significantly higher second-order nonlinear optical characteristics compared to the previously known lead-containing compounds REE3[IO3]12[IO3](Pb3O), REE = La, Pr, Nd. The difference is related to the polar ordering of umbrella-like (Ag3I)2+ groups in the channels in the new iodide-iodate. Additionally, planar-coordinated Ag atoms add three Ag atoms in umbrellas forming [Ag4I]3+ polar clusters in the channels.

Synthesis, Crystal Structure, and Topology–Symmetry Analysis of a New Modification of NaIn[IO 3 ] 4

Crystals of new iodate NaIn[IO3]4 were prepared by the hydrothermal synthesis. The unit cell parameters are a = 7.2672(2) Å, b = 15.2572(6) Å, c = 15.0208(6) Å, β = 101.517(3)°, sp. gr. P21/c. The formula was determined during the structure determination and refinement of a twinned crystal based on a set of reflections from the atomic planes of the major individual. The refinement with anisotropic displacement parameters was performed for both twin components to the final R factor of 0.050. The In and Na atoms are in octahedral coordination formed by oxygen atoms. The oxygen octahedra are arranged into columns by sharing edges, and the columns are connected by isolated umbrella-like [IO3]– groups to form layers. The new structure is most similar to the isoformular iodate NaIn[IO3]4, which crystallizes in the same sp. gr. P21/c and is structurally similar, but has a twice smaller unit cell and is characterized by another direction of the monoclinic axis. The structural similarity and difference between the two phases were studied by topologysymmetry analysis. The formation of these phases is related to different combinations of identical one-dimensional infinite chains of octahedra.

Synthesis, Crystal Structure Refinement, and Nonlinear-Optical Properties of CaB3O5(OH): Comparative Crystal Chemistry of Calcium Triborates

Calcium triborate CaB3O5(OH) obtained by hydrothermal synthesis in the Ca(OH)2–H3BO3–Na2CO3–KCl system is studied by single-crystal X-ray diffraction. The parameters of the orthorhombic unit cell are as follows: a = 13.490(1), b = 6.9576(3), and c = 4.3930(2) Å; V = 412.32(3) Å3 and space group Pna21. The structure is refined in the anisotropic approximation of the atomic displacement parameters to R = 4.28% using 972 |F| > 4σ(F). It is confirmed that the crystal structure of Ca triborate CaB3O5(OH) is identical to that described earlier. The hydrogen atom is localized. An SHG signal stronger than that of the quartz standard is registered. The phase transition of calcium triborate into calciborite is found on heating. The comparative crystal-chemical analysis of a series of borates with the general chemical formula 2CaО · 3В2О3 · nH2О (n = 0–13) with the constant CaО: В2О3= 2: 3 ratio and variable content of water is performed.

Bi3(PO4)O3, the Simplest Bismuth(III) Oxophosphate: Synthesis, IR Spectroscopy, Crystal Structure, and Structural Complexity

The bismuth(III) oxophosphate Bi3(PO4)O3 was obtained by hydrothermal synthesis. The unit cell has a = 5.6840(6) Å, b = 7.0334(7) Å, c = 9.1578(9) Å, α = 78.958(2)°, β = 77.858(2)°, γ = 68.992(2)°, V = 331.41(6) Å3, space group P1̅, and Z = 2. The crystal chemical formula that reflects the presence of oxo-centered tetrahedra and triangles is 2D[OIIIOIV2Bi3](PO4). The crystal structure contains [O3Bi3]3+∞∞-heteropolyhedral corrugated layers parallel to (001), which alternate along [001] with isolated (PO4) tetrahedra. The structural complexity parameters are v = 22 atoms, IG = 3.459 bits/atoms, and IG,total = 76.107 bits/unit cell, and thus Bi3(PO4)O3 is the simplest pure bismuth(III) oxophosphate.

The first layer potassium–bismuth-nickel oxophosphate KBi4Ni2(PO4)3O4: Synthesis, crystal structure, and expected magnetic properties

The new potassium–bismuth–nickel oxophosphate obtained by hydrothermal synthesis in the Bi(OH)3–NiCO3–K2CO3–K3PO4 system is studied by X-ray diffraction, IR spectroscopy, and Raman spectroscopy. Parameters of the orthorhombic cell are as follows: a = 13.632(1) Å, b = 19.610(2) Å, and c = 5.4377(3) Å; V = 1452.64(2) Å3; and space group Pnma. The structure is solved and refined to the final discrepancy factor R1 = 5.76% in the anisotropic approximation of atomic displacements using 3606 reflections with I > 2σ(I). The crystal-chemical formula (Z = 4) is KBi4{Ni2O4(PO4)3}, where the composition of the layer nickel–phosphate polyanion is enclosed in braces. Theoretical calculations show that all exchange spin interactions between Ni2+ ions are antiferromagnetic and very weak (J < 0.1 cm–1) because of the polyatomic character of bridging Ni–O–P–O–Ni and Ni–O–Bi–O–Ni groups. Thus, this compound is expected to be paramagnetic with very weak antiferromagnetic exchange interactions and appreciable energy of zero-field splitting of the spin levels of Ni2+ ions.

Crystal Structure of Rb2Mn3(H2O)2[P2O7]2, a New Representative of the Family of Hydrated Diphosphates

The crystal structure of Rb2Mn3(H2O)2[P2O7]2, a new phase obtained in the form of single crystals under hydrothermal conditions in the MnCl2–Rb3PO4–H2O system, is determined by X-ray diffraction (Xcalibur-S-CCD diffractometer, R = 0.0270): a = 9.374(2), b = 8.367(2), c = 9.437(2) Å, ß = 99.12(2)°, space group P21/c, Z = 2, Dx = 3.27 g/cm3. A correlation between the unit-cell parameters and the size of cations forming the crystal structures of isostructural A2M3(H2O)2[P2O7]2 diphosphates (A = K, NH4, Rb, or Na; M = Mn, Fe, Co, or Ni) is revealed. It is shown that, due to the topological similarity, the structures of diphosphates and orthophosphates of the farringtonite structural type can undergo mutual transformations.

Na3Tb3[Si6O18] · H2O, a synthetic analogue of microporous mineral gerenite

Crystals of a new silicate, Na3Tb3[Si6O18] · H2O, space group