K2Mn3O(OH)(VO4)(V2O7) with Sawtooth Chains of Multivalent Manganese Triangular Trimer Units: Magnetic Susceptibility Shrouding a Long-Range Antiferromagnetic Order of Ferromagnetic Triangles

ortho-Pyrovanadate (or ortho-diorthovanadate) K2Mn23+Mn2+O(OH)(VO4)(V2O7) synthesized hydrothermally crystallizes in the orthorhombic space group Pnma with a = 17.9155(5), b = 5.8940(2), c = 10.9971(3) Å, V = 1161.23(6) Å3, and Z = 4. Its crystal structure features linear chains of edge-sharing Mn3+O6 octahedra with every second pair of Mn3+O6 octahedra condensed with a Mn2+O6 octahedron on one side of a chain in a sawtooth pattern so that each sawtooth chain consists of a triangular trimer. These sawtooth chains, running parallel to the b axis and linked by the VO4 and V2O7 groups, form a framework with channels populated by K atoms. The new compound is a structural analogue of the mineral zoisite Ca2Al3O(OH)(SiO4)(Si2O7), showing a striking example of very different chemical compositions. K2Mn3O(OH)(VO4)(V2O7) undergoes a phase transition into an ordered antiferromagnetic (AFM) state at TN = 14.4 K, which was detected by high-frequency electron spin resonance as well as by both specific heat Cp and Fisher's specific heat d(χT)/dT measurements. However, this phase transition was not detected by magnetic susceptibility measurements. The origin of this puzzling observation was resolved by evaluating the spin exchanges of K2Mn3O(OH)(VO4)(V2O7), which revealed that each triangular trimer is a ferromagnetically coupled cluster, and the observed ordering involves an AFM ordering between the ferromagnetic (FM) clusters. This ordering is shrouded in magnetic susceptibility measurements due to the susceptibility contributions from the individual FM triangular trimers even below TN. We showed that the magnetic susceptibility of K2Mn3O(OH)(VO4)(V2O7) between ∼30 K and room temperature is satisfactorily described by an AFM chain made up of ferromagnetically coupled triangular clusters, as described by a few spin-exchange parameters.

Microporous framework polar silicate-germanates with a wide isomorphic substitution: (K2.9Cs0.1)(Sc0.7In0.3)[(Si2.95Ge0.05)O9]·H2O and (K2.16Cs0.84)Bi[(Si1.5Ge1.5)O9]·H2O

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.

(Na,Li)3(Cl,OH)[Cu3OAl(PO4)3]: a first salt-inclusion aluminophosphate oxocuprate with a new type of crystal structure

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, (M_0.5Cl)[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.

Novel first-row transition-metal phosphates: hydrothermal synthesis and crystal structures

Two new compounds, sodium copper nickel diorthophosphate, Na2CuNi(PO4)2 (I), and dimanganese copper diorthophosphate, Mn2Cu(PO4)2 (II), were synthesized hydrothermally, yielding single crystals, and were studied by X-ray diffraction. In the crystal structures, various transition metals of d-elements occupy symmetrically independent crystallographic positions with different coordination geometries. In the crystal structure of Na2NiCu(PO4)2, NiO6 and CuO6 octahedra share edges to form chains that PO4 groups link into a framework with cavities filled with Na atoms. Layered cationic fragments formed from dimers of MnO5 trigonal bipyramids and CuO4 square planes, sharing vertices, are connected through PO4 tetrahedra into a 3-periodic Mn2Cu(PO4)2 crystal structure. Structural correlations between Na2NiCu(PO4)2 and NaCuPO4 are discussed, and crystal–chemical details of the currently known exclusively synthetic mixed Mn/Cu and Ni/Cu phosphates are presented.

Nonstoichiometric Ellenbergerite-Type Phosphates: Hydrothermal Synthesis, Crystal Chemistry, and Magnetic Behavior

We synthesized single crystals of Na_0.55Ni₆(OH)₃(H_0.61PO₄)₄ (I) and polycrystals of (Na, Ni)_0.64Ni_5.68(OH)₃(H_0.67PO₄)₄ (II) with ellenbergerite-like structures using the hydrothermal method. The phases crystallize in the hexagonal space group P6₃mc with the following unit cell parameters: a = 12.5342(1) Å, c = 4.9470(1) Å, and V = 673.08(2) ų for I; a = 12.4708(2) Å, c = 4.9435(2) Å, and V = 665.82(2) ų for II; and Z = 2. Their crystal structures are based on a 3D framework built from NiO₆ octahedra and PO₄ tetrahedra. The difference between I and II lies in the way the structural channels are filled along the [001] direction. These channels accommodate segments of Na- and (Na, Ni)-centered chains of face-sharing octahedra in the structures I and II, respectively. The magnetic susceptibility χ and the specific heat C_p evidence pronounced low-dimensional magnetic behavior at elevated temperatures and the formation of the weakly ferromagnetic long-range order at T_N^I = 61 K and T_N^II = 63 K. Analysis of the χ(T) data within both chain and dimer spin models allows the estimation of the leading exchange interaction parameters in the compounds under study.

Sawtooth chains self-assembled from clusters of MnO6 octahedra within the silicate framework of K3Mn4Si10O24.33(H2O,OH)3/V,B

A disordered mineralogically probable silicate hydrate K3Mn4Si10O24.33(H2O,OH)3/V,B, obtained hydrothermally, demonstrates low-dimensional magnetic behavior.

Hydrothermal Synthesis and a Composite Crystal Structure of Na6Cu7BiO4(PO4)4[Cl,(OH)]3 as a Candidate for Quantum Spin Liquid

A novel sodium bismuth oxo-cuprate phosphate chloride, Na₆Cu₇BiO₄(PO₄)₄[Cl_2.23(OH)_0.77], containing square-kagomé layers of Cu²⁺ has been synthesized by hydrothermal techniques. The compound crystallizes in the tetragonal space group P4/nmm, a = 10.0176(4), c = 10.8545(6), Z = 2, V = 1089.3(1) ų, R₁ = 0.021, wR = 0.053, S = 1.32. Its composite crystal structure includes [O₄Cu₆Bi]⁷⁺ layers, which are formed by the clusters of oxygen-centered tetrahedra [OCu₃Bi]. These positively charged two periodic fragments are intercalated in a negatively charged [CuNa₆Cl₃(PO₄)₄]^7- matrix built by Na-centered polyhedra, PO₄ tetrahedra, and CuO₄Cl pyramids. The composite character of the crystal structure of Na₆Cu₇BiO₄(PO₄)₄[Cl_2.23(OH)_0.77], as well as the way of its self-assembly, are discussed in close connection with the sulfohalite Na₆ClF(SO₄)₂ salt. It is shown that the "host-guest" model of the formation of the tetragonal Na₆Cu₇BiO₄(PO₄)₄[Cl_2.23(OH)_0.77] phase is due to the group-subgroup symmetry relation with the cubic crystal structure of mineral sulfohalite and is also supported by the crystallization condition in excess sodium chloride. The magnetic subsystem of Na₆Cu₇BiO₄(PO₄)₄[Cl_2.23(OH)_0.77] is represented by a dense square-kagomé network of 2Cu1 and 4Cu2 ions, decorated with weakly bonded Cu3 ions. Measurements of magnetization and heat capacity indicate the absence of long-range order up to 2 K, which makes this compound a candidate for a highly demanded spin liquid.

An Orthorhombic Modification of KCoPO4 Stabilized under Hydrothermal Conditions: Crystal Chemistry and Magnetic Behavior

A novel modification of the KCoPO₄, δ-phase has been prepared by hydrothermal synthesis at 553 K. The compound crystallizes in the orthorhombic system with the unit-cell parameters a = 8.5031(8), b = 10.2830(5), c = 54.170(4) Å. The crystal structure was determined based on synchrotron low-temperature single-crystal X-ray diffraction data obtained from an inversion twin in the space group P2₁2₁2₁ and refined to R = 0.077 for 5156 reflections with I > 3σ(I). The δ-KCoPO₄ possesses a new structure type which is based on a framework built from sharing vertices Co- and P-centered tetrahedra. The {CoPO₄^-}_∞ construction of tetrahedra may be described as assembled from networks formed by two topologically diverse six-membered rings of tetrahedra stacked together through vertex-bridging contacts along the a axis. The ratio of the (UUUDDD) and (UUDUDD) rings, where (U) and (D) denote the orientation of the tetrahedra in the six-membered rings up and down relative to the plane grids, is equal to 5:1. The (UUDUDD) rings form bands parallel to the [010] direction each surrounded from both sides along the c axis by slabs of five ribbons width having alternative (UUUDDD) topology. Open in the [100] direction channels incorporate K⁺ ions; this structural feature permits to suppose ion-conductive and/or electrochemical properties of the title compound. The possible mechanism of the δ → γ phase transition is discussed on the basis of the crystal chemical analysis of the KCoPO₄ polymorphs. The title compound orders magnetically at T_N = 24.8 K.

Novel aluminophosphate Na6[Al3P5O20] with the original microporous crystal structure established in the study of a pseudomerohedric microtwin

The synthesis and characterization of a new aluminophosphate, Na₆[Al₃P₅O₂₀], obtained as single crystals in the same experiment together with Cl-sodalite, Na₈[Al₆Si₆O₂₄]Cl₂, is reported. Na₆[Al₃P₅O₂₀], with a strongly pseudo-orthorhombic lattice, is described by the monoclinic crystal structure established in the study of a pseudomerohedric microtwin. The design of Na₆[Al₃P₅O₂₀] can be interpreted as an alternative to sodalite, with a monoclinic (pseudo-orthorhombic) 2×4×1 super-structure and unit-cell parameters multiples of those of sodalite: a ≃ 2a_s, b ≃ 4b_s and c ≃ c_s. The triperiodic framework is built by AlO₆, AlO₄ and PO₄ polyhedra having vertex-bridging contacts. While all the oxygen vertices of the Al-centred octahedra and tetrahedra are shared with phosphate groups, some of the PO₄ tetrahedra remain `pendant', e.g. containing vertices not shared with other polyhedra of the aluminophosphate construction. Na atoms occupy framework channels and cavities surrounded by eight-, six- and four-membered windows with maximal effective pore widths of 4.86 × 3.24 and 4.31 × 3.18 Å. The generalized framework density is equal to 19.8, which means that the compound may be classified as a microporous zeolite. The Na₆[Al₃P₅O₂₀] crystal structure is discussed as being formed from octahedral rods arranged in two perpendicular directions, similar to the rods elongated in one direction in the NASICON-type compounds, which have been intensively investigated as promising materials for batteries. Analogous properties can be expected for phases with a modified composition of the Na₆Al₃P₅O₂₀ topology, where the Al atoms at the centres of octahedra are replaced by Fe, V or Cr.

Crystal structure and thermodynamic properties of dinickel diphosphate dihydrate Ni2(H2O)2[P2O7]

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) ų, 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[combining macron]] 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 T_max = 11.9 K accompanied by the onset of long-range magnetic order at T_N = 9.4 K. Below T_N, 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 C_p and magnetization M studies, the magnetic phase diagram of Ni₂(H₂O)₂[P₂O₇] has been established.

Silicate-germanate K2Y[(Si3Ge)O10(OH)] with unusual complex corrugated layer and its correlation to ring silicate gerenite and chain silicate chkalovite

A new silicate-germanate K2Y[(Si3Ge)O10(OH)] was synthesized hydrothermally in a system Y2O3:GeO2:SiO2 = 1:1:2 (T = 280 °C; P = 90–100 atm.); K2CO3 was added to the solution as a mineralizer. Single-crystal X-ray diffraction experiment was carried out at low temperature (150 K). The unit cell parameters are a = 10.4975(4), b = 6.9567(2), c = 15.4001(6) Å, β = 104.894(4)°; V = 1086.86(7) Å3; space group is P 21/c. A novel complex anion is presented by corrugated (Si,Ge) tetrahedral layers connected by couples of YO6 octahedra into the mixed microporous framework with the channels along b and a axes, the maximal size of cross-section is ~5.6 Å. This structure has similarity with the two minerals: ring silicate gerenite (Ca,Na)2(Y,REE)3Si6O18 · 2H2O and chain silicate chkalovite Na2BeSi2O6. Six-member rings with 1̅ symmetry as in gerenite are distinguished in the new layer. They are mutually perpendicular to each other and connected by additional tetrahedra. Straight crossing chains in chkalovite change to zigzag four-link chains in the new silicate-germanate layer.

Novel K/Mn phosphate hydrates, K2Mn3(H2O)2[P2O7]2 and KMn(H2O)2[Al2(PO4)3]: hydrothermal synthesis and crystal chemistry

Two novel K/Mn phosphate hydrates, namely, dipotassium trimanganese dipyrophosphate dihydrate, K₂Mn₃(H₂O)₂[P₂O₇]₂, (I), and potassium manganese dialuminium triphosphate dihydrate, KMn(H₂O)₂[Al₂(PO₄)₃], (II), were obtained in the form of single crystals during a single hydrothermal synthesis experiment. Their crystal structures were studied by X-ray diffraction. Both new compounds are members of the morphotropic series of phosphates with the following formulae: A₂M₃(H₂O)₂[P₂O₇]₂, where A = K, NH₄, Rb or Na and M = Mn, Fe, Co or Ni, and AM²⁺(H₂O)₂[M³⁺₂(PO₄)₃], where A = Cs, Rb, K, NH₄ or (H₃O); M²⁺ = Mn, Fe, Co or Ni; and M³⁺ = Al, Ga or Fe. A detailed crystal chemical analysis revealed correlations between the unit-cell parameters of the members of the series, their structural features and the sizes of the cations. It has been shown that a mixed type anionic framework is formed in (II) by aluminophosphate [(AlO₂)₂(PO₄)₂]_∞ layers, with a cationic topology similar to the Si/Al-topology of the crystal structures of feldspars. A study of the magnetic susceptibility of (II) demonstrates a paramagnetic behaviour of the compound.

Rb2CaCu6(PO4)4O2, a novel oxophosphate with a shchurovskyite-type topology: synthesis, structure, magnetic properties and crystal chemistry of rubidium copper phosphates

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) ų. 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 T_C = 25 K, Rb₂CaCu₆(PO₄)₄O₂ reaches a magnetically ordered state with large residual magnetization.

A first Mn member in the struvite morphotropic series, CsMn(H2O)6(PO4): hydrothermal synthesis, crystal structure and interconnections within the family of related phosphates

Caesium manganese hexahydrate phosphate, CsMn(H₂O)₆(PO₄), was synthesized under hydrothermal conditions. Its crystal structure was determined from single-crystal X-ray diffraction data. The novel phase crystallizes in the hexagonal space group P6₃mc and represents the first manganese member in the struvite morphotropic series, AM(H₂O)₆(TO₄). Its crystal structure is built from Mn(H₂O)₆ octahedra and PO₄ tetrahedra linked into a framework via hydrogen bonding. The large Cs atoms are encapsulated in the framework cuboctahedral cavities. It is shown that the size of the A⁺ ionic radius within the morphotropic series AM(H₂O)₆(XO₄) results is certain types of crystal structures and affects the values of the unit-cell parameters. Structural relationships with Na(H₂O)Mg(H₂O)₆(PO₄) and the mineral hazenite, KNa(H₂O)₂Mg₂(H₂O)₁₂(PO₄)₂, are discussed.

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) ų, space group P1̅, and Z = 2. The crystal chemical formula that reflects the presence of oxo-centered tetrahedra and triangles is ^2D[O^IIIO^IV₂Bi₃](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, I_G = 3.459 bits/atoms, and I_G,total = 76.107 bits/unit cell, and thus Bi₃(PO₄)O₃ is the simplest pure bismuth(III) oxophosphate.

Band Filling Control of the Dzyaloshinskii-Moriya Interaction in Weakly Ferromagnetic Insulators

We observe and explain theoretically a dramatic evolution of the Dzyaloshinskii-Moriya interaction (DMI) in the series of isostructural weak ferromagnets, MnCO_{3}, FeBO_{3}, CoCO_{3}, and NiCO_{3}. The sign of the interaction is encoded in the phase of the x-ray magnetic diffraction amplitude, observed through interference with resonant quadrupole scattering. We find very good quantitative agreement with first-principles electronic structure calculations, reproducing both sign and magnitude through the series, and propose a simplified "toy model" to explain the change in sign with 3d shell filling. The model gives insight into the evolution of the DMI in Mott and charge transfer insulators.

Magnetically frustrated synthetic end member Mn2(PO4)OH in the triplite-triploidite family

The manganese end member of triplite-triploidite series of compounds, Mn₂(PO₄)OH, is synthesized by a hydrothermal method. Its crystal structure is refined in the space group P2₁/c with a = 12.411(1) Å, b = 13.323(1) Å, c = 10.014(1) Å, β = 108.16(1), V = 1573.3 ų, Z = 8, and R = 0.0375. Evidenced in measurements of magnetization M and specific heat C_p, Mn₂(PO₄)OH reaches a long range antiferromagnetic order at T_N = 4.6 K. As opposed to both triplite Mn₂(PO₄)F and triploidite-type Co₂(PO₄)F, the title compound is magnetically frustrated being characterized by the ratio of Curie-Weiss temperature Θ to Néel temperature T_N of about 20. The large value of frustration strength |Θ|/T_N stems from the twisted saw tooth chain geometry of corner sharing triangles of Mn polyhedra, which may be isolated within tubular fragments of a triploidite crystal structure.

Crystal structure and spin-trimer magnetism of Rb2.3(H2O)0.8Mn3[B4P6O24(O,OH)2]

The novel borophosphate Rb_2.3(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) ų, 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 Rb_2.3(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.

An open framework crystal structure and physical properties of RbCuAl(PO4)2

Single crystals of the RbCuAl(PO₄)₂ compound with an open 3D framework structure were obtained by a hydrothermal route. The compound orders antiferromagnetically at T_N = 10.5 K and exhibits spontaneous magnetization at lower temperature.

One-dimensional decavanadate chains in the crystal structure of Rb4[Na(H2O)6][HV10O28]·4H2O

New decavanadate minerals, the products of the leaching or metasomatic processes, are possible in natureviaNa/Rb removal/inclusion reactions. As part of our search for novel vanadate phases with varying functionalities, a new phase, tetrarubidium hexaaquasodium hydrogen decavanadate tetrahydrate, Rb4[Na(H2O)6][HV10O28]·4H2O, has been synthesized by the hydrothermal technique at 553 K. Ten shared edges of V-centred octahedra form monoprotonated decavanadate cages, which are joined togetherviahydrogen bonds into one-dimensional chains parallel to the [101] direction. Within these chains, H atoms are sandwiched between neighbouring polyanions. Na and Rb atoms and H2O molecules occupy interstices flanked by the anionic chains providing additional crosslinking in the structure. This compound is the second decavanadate withP2/nsymmetry. Structural relationships among protonated and deprotonated decavanadates with inorganic cations, including minerals of the pascoite group, are discussed.

A microporous potassium vanadyl phosphate analogue of mahnertite: hydrothermal synthesis and crystal structure

The novel phase K2.5Cu5Cl(PO4)4(OH)0.5(VO2)•H2O was prepared by hydrothermal synthesis at 553 K. Its crystal structure was determined using low-temperature (100 K) single-crystal synchrotron diffraction data and refined against F 2 to R = 0.035. The compound crystallizes in the tetragonal space group I4/mmm, with unit-cell parameters a =9.8120(8), c = 19.954(1) Å, V = 1921.1(2) Å3, and Z = 4. Both symmetrically independent Cu2+ sites show elongated square-pyramidal coordination. The V5+ ions reside in strongly distorted five-vertex VO5 polyhedra with 50% occupancy. The structure is based on a 3D anionic framework built from Cu- and V-centered five-vertex polyhedra and PO4 tetrahedra. Channels in the [100] and [010] directions accommodate large K atoms and H2O molecules. The compound is a new structural representative of the topology shown by the lavendulan group of copper arsenate and phosphate minerals. Their tetragonal or pseudotetragonal crystal structures are characterized by two types of 2D slabs alternating along one axis of their unit cells. One slab, described by the formula [Cu4 X(TO4)4]∞ (where X = Cl, O and T = As, P), is common to all phases, whereas the slab content of the other set differs among the group members. We suggest interpreting this family of compounds in terms of the modular concept and also consider the synthetic phase Ba(VO)Cu4(PO4)4 as a simplest member of this polysomatic series.

A novel cobalt sodium phosphate hydroxide with the ellenbergerite topology: crystal structure and physical properties

The novel phosphate hydroxide Na_2−xCo₆(OH)₃[HPO₄][H_x/3PO₄]₃with the mineral ellenbergerite topology and alkaline cations in the framework channels shows strong antiferromagnetic interaction and magnetic transition atT_N= 44 K.

12-Membered borophosphate rings in KNi5[P6B6O23(OH)13]

The title compound, potassium pentanickel hexaborophosphate tridecahydroxide, was synthesized under hydrothermal conditions from the NiCl(2)-K(3)PO(4)-B(2)O(3)-K(2)CO(3)-H(2)O system. The crystal structure was determined using single-crystal X-ray diffraction at 100 K. The KNi(5)[P(6)B(6)O(23)(OH)(13)] phase is cubic. For the three crystallographically distinct Ni centers, two occupy sites with 3 symmetry, while the third Ni and the K atom are located on 3 sites. The structure is built from alternating borate and phosphate tetrahedra forming 12-membered puckered rings with K(+) ions at the centers. These rings are arranged as in cubic dense sphere packing. A novel feature of the new crystal structure is the presence of linear trimers of face-sharing [NiO(6)] octahedra occupying the octahedral interstices of this sphere packing, and of single [NiO(6)] octahedra in the tetrahedral interstices. All oxygen corners of the Ni octahedra are linked to phosphate or borate tetrahedra of the 12-membered rings to form a mixed anionic framework.

Proton-stabilized three-dimensional anionic framework in H[Zn6O2(BO3)3]

A three-dimensional anionic framework built up from [ZnO4] tetrahedra and planar [BO3] groups, stabilized by H atoms, has been found for hydrogen zinc oxide borate, H[Zn6O2(BO3)3]. Boron and one of the borate O atoms are on 18e (2) positions. Triple units of [ZnO4] tetrahedra sharing a common oxygen vertex on a 12c (3) site and strong asymmetrical linear hydrogen bonds with the H atom [on a 12c (3) position] disordered over a twofold axis are specific structural features of this zincoborate. There is evidence that the reported Zn4O(BO3)2 [Harrison, Gier & Stuky (1993). Angew. Chem. Int. Ed. Engl. 32, 724-726] corresponds to this structure.

A new cubic form of caesium hexaaquamagnesium phosphate, Cs[Mg(H2O)6](PO4)

A new cubic form (space group F-43m) of the title compound has been found which is isostructural with the analogous arsenate. [Mg(H(2)O)(6)](2+) cations and phosphate anions are connected by hydrogen bonds, forming a sphalerite-like three-dimensional framework.