Fluoride-Rich, Hydrofluorothermal Routes to Functional Transition Metal (Mn, Fe, Co, Cu) Fluorophosphates

Crystal structure of KMnPO4F with short- and long-range order inside the layered magnetic system

Potassium manganese fluoride phosphate, KMnPO4F, has been obtained through mild hydrothermal synthesis and characterized by scanning electron microscopy, microprobe analysis and X-ray diffraction. The compound possesses an orthorhombic symmetry and chiral space group P212121 with a = 4.7884(2), b = 9.0172(4), c = 9.5801(4) Å, and Z = 4. Its crystal structure is composed of Mn3+O4F square pyramids sharing vertices with PO4 tetrahedra. This anionic framework is neutralized by K+ cations. As the temperature decreases, a short-range correlation state (Tmax ∼ 35 K) of KMnPO4F is formed, followed by the establishment of antiferromagnetic (AFM) long-range order at TN = 25 K. The latter is marked by sharp λ-type anomalies in both Fisher's specific heat d(χ‖T)/dT and heat capacity Cp. Pulsed magnetic field measurements on the single crystals identify the a axis as the easy magnetic axis and reveal a spin-flop transition at μ0Hspin-flop = 19 T. Density functional theory indicates that in variance with the three-dimensional network of KMnPO4F, it is a two-dimensional Ising magnetic system represented by buckled layers of integer spins S = 2 of Mn3+ ions. The strongest AFM exchange interaction, J1 ∼ -13 K, couples Mn3+ ions into linear chains running along the a axis. The chains themselves are ferromagnetically connected (J3 ∼ -4 K) within the ab plane. The interplane AFM exchange interaction (J2 ∼ -1 K) is weak and frustrated.

Strategy for a Rational Design of Deep-Ultraviolet Nonlinear Optical Materials from Zeolites

Deep-ultraviolet (DUV) nonlinear optical (NLO) materials play a crucial role in cutting-edge laser technology. In order to solve the serious layered growth tendency of the sole commercial DUV NLO crystal KBe2BO3F2 (KBBF), developing alternative systems of compounds with bulk crystal habits has become an urgent task for practical applications. Herein, a novel strategy was developed by applying non-centrosymmetric (NCS) cancrinite (CAN)-type zincophosphates {Na6(OH)2(H2O)2}Cs2[ZnPO4]6 with bulk-crystal habits as the prototype to design new DUV NLO crystals. Two new anhydrous alkali zincophosphates, namely, {(Li6 -xNaxO)A2}[(ZnPO4)6] (A = Cs, Rb; x = 2-3) crystallizing in the NCS hexagonal space group P63 (no. 173) with a CAN-type framework, were successfully synthesized via a modified fluoro-solvo-hydrothermal method by applying triethylamine (TEA) and concentrated NaF solution as a co-solvent. Interestingly, the rigidity of the NCS CAN-type framework acting as the host ensures the non-centrosymmetry of the resulting new compounds. Meanwhile, the replacement of water molecules by guest cationic species in the channels or cages can greatly improve the thermal stability of the resultant crystal and tune its NLO properties. The synergetic effect of the host framework and the guest species makes the two compounds transparent down to the DUV region (<200 nm) and exhibit SHG effects. Therefore, the proposed rational design strategy of applying the known zeotype NCS frameworks as prototypes together with the modified fluoro-solvo-hydrothermal method opens a great avenue for highly effectively exploring new DUV NLO materials.

Potential rules for stable transition metal hexafluorides with high oxidation states under high pressures

High pressure is a powerful tool in material sciences which can lead to the discovery of novel inorganic species in high oxidation states. Based on the prediction of the stability of PdF₆ with a high Pd oxidation state of +6, we propose three potential guiding rules for finding stable transition metal (TM) fluorides with high +6 oxidation states: (1) the existence of a large (>7 eV) valence orbitals energy differences of atoms between the TM d orbital and the F 2p orbital; (2) an appropriate number of valence electrons within the range of 6-11; and (3) suitable electronegativity values less than 2.3 on the Pauli scale. More importantly, by synergistically invoking all of these rules, we predict, by combining a particle swarm optimization algorithm with first-principles calculation on the phase stabilities of the various TM-F compounds, a collection of new TMF₆ species with the space group Pnma that have a +6 oxidation state. Subsequently, we develop an understanding of the high +6 oxidation state for the TM elements. These findings are expected to play a crucial role in the predictive discoveries of new fluorides with high oxidation states of +6.

From a Dense Structure to Open Frameworks: The Structural Plethora of Alkali Metal Iron Fluorophosphates

By employing the pyridinium hexafluorophosphate task-specific ionic liquids 1-butyl-4-methylpyridinium hexafluorophosphate ([C₄mpyr][PF₆]) and 1-ethylpyridinium hexafluorophosphate ([C₂pyr][PF₆]) as the reaction medium, mineralizer, structure-directing agent, and, in the case of the smaller pyridinium cation, even a structural component, it was possible to obtain five new alkali metal iron phosphates featuring interconnected FeX₆ octahedra and PX₄ (X = F, O, or OH) tetrahedra. NaFe(PO₃F)₂ (1) is a dense 3D structure, RbFe(PO₃F)(PO₂(OH)F)(PO₂(OH)₂) (2) features 1D strands, (C₂pyr)LiFe(PO₃F)₃(PO₂F₂)F (3) has 2D layers, and LiFe(PO₃F)(PO₂F₂)F (4) as well as Cs_0.75Fe(PO_2.75(OH)_0.25F)(PO₂F₂)₂ (5) are 3D open frameworks. While in 1–2 as well as in 4 and 5, FeX₆ octahedra and PX₄ (X = F, O, or OH) tetrahedra alternate, 3 features octahedra dimers, Fe₂X₁₁ (X = F, O, or OH). The magnetic behavior of all compounds is governed by antiferromagnetic interactions. Interestingly, 3 exhibits a broad maximum in the temperature dependence of the magnetic susceptibility, characteristic of a low-dimensional magnetic system consistent with the presence of Fe–Fe dimers in its crystal structure.

Application of ionic liquids as the reaction medium, structure templates, and mineralizer led to a series of active-metal-iron phosphates with structural motifs of varied dimensionality and, ultimately, an open-framework structure.

Open-Framework Iron Fluoride Phosphates Based on Chain, Trinuclear, and Tetranuclear Chain FeIII Building Units: Crystal Structures and Magnetic Properties

We report the synthesis and characterization of a series of new open-framework iron fluoride-fluorophosphates based on linear, trinuclear, and tetranuclear chain Fe^III building units. KFe₂(PO₃F)₂F₃ (I) consists of {Fe₂(O₃F)₂F₂}^10- zigzag chains interconnected by P(O/F)₄ tetrahedra forming a three-dimensional (3D) open framework. K₂Fe(PO_2.5F_1.5)₂F₂ (II) is built up by {Fe(PO_2.5F_1.5)₂F₂}^2- chains separated by K⁺ cation layers. The framework for K₃Fe₃(PO₄)(PO₃F)₂F₅ (III) contains two-dimensional {Fe₃O₄F₄(PO₃F)₂}^2- sheets, which are built from trimeric Fe-octahedra insulated by PO₃F tetrahedra. The macroanionic framework of K₃Fe₄(PO₄)₂F₉ (IV) comprises linear {Fe₄O₈F₉}^10- chains consisting of tetranuclear magnetic clusters of [Fe₄O₈F_9]^10- formed via corner-sharing fluorine atoms decorated with PO₄ groups. The magnetic characterization of three iron fluorophosphates reveals diversified magnetism: S = 5/2 spin chains for I, antiferromagnetically coupled triangular Fe units for III, and coupled tetrahedral S = 5/2 spin chains for IV. IV shows strong geometric frustration thanks to its spin motifs of corner-shared tetrahedral clusters.

Pressure-stabilized hexafluorides of first-row transition metals

Fluorine chemistry was demonstrated to show the importance of stretching the limits of chemical synthesis, oxidation state, and chemical bonding at ambient conditions. Thus far, the highest fluorine stoichiometry of a neutral first-row transition-metal fluoride is five, in VF₅ and CrF₅. Pressure can stabilize new stoichiometric compounds that are inaccessible at ambient conditions. Here, we attempted to delineate the fluorination limits of first-row transition metals at a high pressure through first-principles swarm-intelligence structure searching simulations. Besides reproducing the known compounds, our extensive search has resulted in a plethora of unreported compounds: CrF₆, MnF₆, FeF₄, FeF₅, FeF₆, and CoF₄, indicating that the application of pressure achieves not only the fluorination limit (e.g., hexafluoride) but also the long-sought bulky tetrafluorides. Our current results provide a significant step forward towards a comprehensive understanding of the fluorination limit of first-row transition metals.

Pushing KTiOPO4-like Nonlinear Optical Sulfates into the Deep-Ultraviolet Spectral Region

Accurately designing and synthesizing new deep-ultraviolet (deep-UV) nonlinear optical (NLO) crystals that are limited by the so-called "200 nm wall" on their transparency windows remain challenging. On the basis of a bandgap-directed computer-aided material design approach, two new NLO sulfates, KMgSO₄F and KZnSO₄F, are designed and successfully synthesized. They feature three-dimensional frameworks closely related to the commercial NLO crystal, KTiOPO₄ (KTP). Remarkably, the transmittance spectrum based on a single crystal indicates that the transparency window of KZnSO₄F is significantly blue-shifted to <190 nm from 350 nm for KTP. The microscopic origin of this significant transparent window blue shift is illustrated well by first-principles calculations. This work pushes the transparency windows of KTP-like NLO sulfates into the deep-UV spectral region for the first time and will pave a prospective way to the accurate design and synthesis of new deep-UV NLO materials.

Monofluorophosphates—New Examples and a Survey of the PO3F2− Anion

During a systematic study of monofluorophosphates, i.e., compounds comprising the tetrahedral anion PO3F2−, twelve, for the most part new, compounds were obtained from aqueous solutions. Crystal structure refinements based on single crystal X-ray diffraction data revealed the previously unknown crystal structures of CdPO3F(H2O)2, Cr2(PO3F)3(H2O)18.8, Pb2(PO3F)Cl2(H2O), (NH4)2M(PO3F)2(H2O)2 (M = Mg, Mn, Co), NH4Cr(PO3F)2(H2O)6, NH4Cu2(H3O2)(PO3F)2, (NH4)2Zn(PO3F)2(H2O)0.2, and (NH4)2Zn3(PO3F)4(H2O), as well as redeterminations of ZnPO3F(H2O)2.5 and (NH4)2Ni(PO3F)2(H2O)6. From the previously unknown crystal structures, CdPO3F(H2O)2 (space group P1¯), Cr2(PO3F)3(H2O)18.8 (P1¯), Pb2(PO3F)Cl2(H2O) (Pnma), NH4Cr(PO3F)2(H2O)6 (R3¯m), (NH4)2Zn(PO3F)2(H2O)0.2 (C2/c), and (NH4)2Zn3(PO3F)4(H2O) (I4¯3d) each crystallizes in an unique crystal structure, whereas compounds (NH4)2M(PO3F)2(H2O)2 (M = Mg, Co) crystallize in the (NH4)2Cu(PO3F)2(H2O)2 type of structure (C2/m) and (NH4)2Mn(PO3F)2(H2O)2 in a subgroup thereof (P21/n, with a klassengleiche relationship of index 2), and NH4Cu2(H3O2)(PO3F)2 (C2/m) crystallizes isotypically with natrochalcite-type KCu2(H3O2)(SO4)2. A survey on the PO3F2− anion, including database entries of all inorganic compounds comprising this group, revealed mean bond lengths of P–O = 1.506(13) Å, P–F = 1.578(20) Å, and angles of O–P–O = 113.7(1.7)° and O–P–F = 104.8(1.7)°, using a dataset of 88 independent PO3F2− anions or entities. For those crystal structures of monofluorophosphates where hydrogen bonding is present, in the vast majority of cases, hydrogen bonds of the type D–H···F–P (D = O, N) are not developed.

Synthesis of a d1-titanium fluoride kagome lattice antiferromagnet

The kagome lattice, composed of a planar array of corner-sharing triangles, is one of the most geometrically frustrated lattices. The realization of a spin S = 1/2 kagome lattice antiferromagnet is of particular interest because it may host an exotic form of matter, a quantum spin liquid state, which shows long-range entanglement and no magnetic ordering down to 0 K. A few S = 1/2 kagome lattice antiferromagnets exist, typically based on Cu²⁺, d⁹ compounds, though they feature structural imperfections. Herein, we present the synthesis of (CH₃NH₃)₂NaTi₃F₁₂, which comprises an S = 1/2 kagome layer that exhibits only one crystallographically distinct Ti³⁺, d¹ site, and one type of bridging fluoride. A static positional disorder is proposed for the interlayer CH₃NH₃⁺. No structural phase transitions were observed from 1.8 K to 523 K. Despite its spin-freezing behaviour, other features-including its negative Curie-Weiss temperature and a lack of long-range ordering-imply that this compound is a highly frustrated magnet with unusual magnetic phase behaviours.

Pressure-Stabilized Zinc Trifluoride

By combining the particle swarm optimization algorithm with first-principles calculation, the high-pressure phase diagram of Zn-F binary compounds was established. An unexpected stoichiometry of ZnF₃ with space group Cccm is thermodynamically stable above 183 GPa. The new structure is fascinating with the appearance of Zn²⁺[F₃]^2- units. The stability of the new phase stems from the mixed ionic and covalent chemical bonding in ZnF₃. The electronic properties indicate that Zn has a tendency to form high oxidation states under higher pressure. Our work is an important step in understanding the bonding behavior of Zn under extreme conditions and provides a valuable reference for experimental synthesis and identification of ZnF₃.

Topotactic desolvation and condensation reactions of 3D Zn3TiF7(H2O)2(taz)3·S (S = 3H2O or C2H5OH)

Thermodiffraction, IR, DFT calculations, and ¹H and ¹⁹F NMR characterizations of the desolvatation and reversible condensation reactions of Zn₃TiF₇(taz)₃ family.

Open-framework ammonium transition metal fluorophosphates with a Kagomé lattice network: synthesis, structure and magnetic properties

Two open-framework fluorophosphates (NH₄)M₃(PO₃F)₂(PO₂F₂)F₂ (M = Mn and Co) featured transition metal layers with a staircase Kagomé network exhibiting canted anti-ferromagnetism.

Ionothermal Synthesis, Structures, and Magnetism of Three New Open Framework Iron Halide-Phosphates

A set of different open framework iron phosphates have been synthesized ionothermally using a task-specific ionic liquid, 1-butyl-4-methylpyridinium hexafluorophosphate, that acts in the synthesis as the reaction medium and mineralizer: (NH₄)₂Fe₂(HPO₄)(PO₄)Cl₂F (1) and K₂Fe₂(HPO₄)(PO₄)Cl₂F (2) exhibit similar composition and closely related structural features. Both structures consist of {Fe₂(HPO₄)(PO₄)Cl₂F}^2- macroanions and charge balancing ammonium or potassium cations. Their open framework structure contains layers and chains of corner-linked {Fe(1)O₂Cl₄} and {Fe(2)F₂O₄} octahedra, respectively, interconnected by PO₄ tetrahedra forming 10-ring channels. KFe(PO₃F)F₂ (3) is built up by {Fe[(PO₃F)_4/3F_2/2]}{Fe(PO₃F)_2/3F_2/2F₂} layers separated by K⁺ cations. Chains of alternating {FeF₂O₄} and {FeO₂F₄} octahedra, which are linear for 1 but undulated for 2, are linked to each other via corner-sharing {PO₃F} tetrahedra with the fluorine pointing into the interlayer space. The compounds were characterized by means of single crystal and powder X-ray diffraction, infrared spectroscopy, and magnetic measurements. 1 reveals a strong ground state spin anisotropy with a spin 5/2 state and a magnetic moment of 5.3 μ_B/Fe³⁺. Specific heat and magnetic data unveil three magnetic transitions at 95, 50, and 3.6 K. Compound 2 has a very similar crystal structure as compared to 1 but exhibits a different magnetic behavior: a slightly lower magnetic moment of 4.7 μ_B/Fe³⁺ and a magnetic transition to a canted antiferromagnetic state below 90 K. Compound 3 exhibits typical paramagnetic behavior close to room-temperature (5.71 μ_B/Fe³⁺). There are no clear indications for a phase transition down to 2 K despite strong antiferromagnetic spin-spin interactions; only a magnetic anomaly appears at 50 K in the zero-field cooled data.

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.

Two halide-containing cesium manganese vanadates: synthesis, characterization, and magnetic properties

Two new halide-containing cesium manganese vanadates have been synthesized by a high-temperature (580 °C) hydrothermal synthetic method from aqueous brine solutions.

Structural diversities induced by cation sizes in a series of fluorogermanophosphates: A2[GeF2(HPO4)2] (A = Na, K, Rb, NH4, and Cs)

Germanophosphates, in comparison with other metal phosphates, have been less studied but potentially exhibit more diverse structural chemistry with wide applications. Herein we applied a hydro-/solvo-fluorothermal route to make use of both the "tailor effect" of fluoride for the formation of low dimensional anionic clusters and the presence of alkali cations of different sizes to align the anionic clusters to control the overall crystal symmetries of germanophosphates. The synergetic effects of fluoride and alkali cations led to structural changes from chain-like structures to layered structures in a series of five novel fluorogermanophosphates: A₂[GeF₂(HPO₄)₂] (A = Na, K, Rb, NH₄, and Cs, denoted as Na, K, Rb, NH4, and Cs). Although these fluorogermanophosphates have stoichiometrically equivalent formulas, they feature different anionic clusters, diverse structural dimensionalities, and contrasting crystal symmetries. Chain-like structures were observed for the compounds with the smaller sized alkali ions (Na⁺, K⁺, and Rb⁺), whereas layered structures were found for those containing the larger sized cations ((NH₄)⁺ and Cs⁺). Specifically, monoclinic space groups were observed for the Na, K, Rb, and NH4 compounds, whereas a tetragonal space group P4/mbm was found for the Cs compound. These compounds provide new insights into the effects of cation sizes on the anionic clusters built from GeO₄F₂ octahedra and HPO₄ tetrahedra as well as their influences on the overall structural symmetries in germanophosphates. Further characterization including IR spectroscopy and thermal analyses for all five compounds is also presented.

Synthesis and magnetic properties of two isostructural fluorophosphates BaMPO4F (M = Cu, Co) with a tunnel structure

Two fluorophosphates, BaMPO₄F (M = Cu, Co), have been synthesized by a conventional hydrothermal method, and they crystallize in the orthorhombic system with the space group P2₁2₁2₁, exhibiting a tunnel structure built by distorted MO₄F square-pyramids and PO₄ tetrahedra. The magnetic behaviors of the two compounds are investigated by means of magnetic susceptibility, magnetization, and heat capacity measurements. The results indicate that BaCuPO₄F exhibits a paramagnetic behavior down to 2 K, while BaCoPO₄F undergoes long-range antiferromagnetic ordering at 11.3 K and short-range magnetic ordering at ∼22 K.

A highly fluorinated lithium iron phosphate with interpenetrating lattices: electrochemistry and ionic conductivity

A fluorinated iron phosphate with interpenetrating lattices containing large channels filled with lithium ions has been synthesized in low-melting flux.

KB(PO4)F: a novel acentric deep-ultraviolet material

A rational design using the [PO₄] group to replace the [BeO₄] group in KBBF results in a new acentric deep-UV material KB(PO₄)F, free of beryllium.

Multiple Fluorine-Substituted Phosphate Germanium Fluorides and Their Thermal Stabilities

Anhydrous compounds are crucially important for many technological applications, such as achieving high performance in lithium/sodium cells, but are often challenging to synthesize under hydrothermal conditions. Herein we report that a modified solvo-/hydro-fluorothermal method with fluoride-rich and water-deficient condition is highly effective for synthesizing anhydrous compounds by the replacement of hydroxyl groups and water molecules with fluorine. Two anhydrous phosphate germanium fluorides, namely, Na₃[GeF₄(PO₄)] and K₄[Ge₂F₉(PO₄)], with chainlike structures involving multiple fluorine substitutions, were synthesized using the modified solvo-/hydro-fluorothermal method. The crystal structure of Na₃[GeF₄(PO₄)] is constructed by the common single chains _∞¹{[GeF₄(PO₄)]^3-} built from alternating GeO₂F₄ octahedra and PO₄ tetrahedra. For K₄[Ge₂F₉(PO₄)], it takes the same single chain in Na₃[GeF₄(PO₄)] as the backbone but has additional flanking GeOF₅ octahedra via an O-corner of the PO₄ groups, resulting in a dendrite zigzag single chain _∞¹{[Ge₂F₉(PO₄)]^4-}. The multiple fluorine substitutions in these compounds not only force them to adopt the low-dimensional structures because of the "tailor effect" but also improve their thermal stabilities. The thermal behavior of Na₃[GeF₄(PO₄)] was investigated by an in situ powder X-ray diffraction experiment from room temperature to 700 °C. The modified solvo-/hydro-fluorothermal method is also shown to be effective in producing the most germanium-rich compounds in the germanophosphate system.

Synthesis and structural characterisation of transition metal fluoride sulfates

Eleven first row transition metal fluoride sulfates synthesised in hydrofluorothermal conditions have been structurally characterised by single crystal X-ray diffraction and exhibit a wide variety of structural motifs. The polyionic structures containing Ti, V, Mn and Fe vary from discrete polyhedral units in Na4TiF4(SO4)2 and [N2C10H12] TiF4SO4, through one dimensional chains in (K2FeF3SO4, Li3FeF2(SO4)2·H2O, Li1.87Ti1.13O0.39F1.61(SO4)2, [N2C10H12]TiF2(SO4)2, [N2C6H16]Fe(SO4)2F and [N2C6H16]V(SO4)2F), and to two dimensional layers in ([N2C6H16](2+)Mn2F2(SO4)2, Na2VF3SO4 and Na3CrF2(SO4)2).

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.

Gallium fluoroarsenates

Six new phases in the gallium-fluoride-arsenate system have been synthesised hydrofluorothermally using a fluoride-rich medium and "HAsF6" (HF : AsF5) as a reactant. RbGaF3(H2AsO4), KGaF(H2AsO4) and [piperazine-H2]2[Ga2F8(HAsO4)]·H2O have one dimensional structures, [DABCO-H2]2[Ga4F7O2H(AsO4)2]·4H2O consists of two dimensionally connected polyhedral layers, while GaF(AsO3[OH,F])2 and (NH4)3Ga4F9(AsO4)2 both have three-dimensionally connected polyhedral frameworks.

Dimensional Reduction From 2D Layer to 1D Band for Germanophosphates Induced by the "Tailor Effect" of Fluoride

The "tailor effect" of fluoride, exclusively as a terminal rather than a bridge, was applied successfully to design low-dimensional structures in the system of transition metal germanophosphates for the first time. Two series of new compounds with low-dimensional structures are reported herein. K[M(II)Ge(OH)2(H0.5PO4)2] (M = Fe, Co) possess flat layered structures built from single chains of edge-sharing M(II)O6 and GeO6 octahedra interconnected by HPO4 tetrahedra. Their fluorinated derivatives, K4[M(II)Ge2F2(OH)2(PO4)2(HPO4)2]·2H2O (M = Fe, Co), exhibit band structures of two four-membered ring germanium phosphate single chains sandwiched by M(II)O6 octahedra via corner-sharing. Both of these structures contain anionic chains of the condensation of four-membered rings built from alternating GeO4Φ2 (Φ = F, OH) octahedra and PO4 tetrahedra via sharing common GeO4Φ2 (Φ = F, OH) octahedra, the topology of which is the same as that of the mineral kröhnkite [Na2Cu(SO4)2·2H2O]. Note that the switch from the two-dimensional layered structure to the one-dimensional band structure was performed simply by the addition of a small amount of KF·2H2O to the reaction mixture. This structural alteration arises from the incorporation of one terminal F atom to the coordination sphere of Ge, which breaks the linkage between the transition metal and germanium octahedra in the layer to form the band structure.

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.

Copper(ii) chlorofluorophosphate: a new layered square-net for intercalating amines

Three different cationic species, [NH₄]⁺, [H-piperazine]⁺ and [H-1,4-diaminocyclohexane]⁺, can be incorporated between the inorganic square-net layers of the composition [Cu₄Cl(PO₃F)₄]⁻.

Synthesis and characterization of mixed-valence manganese fluorophosphate and analogues with clathrate-like structures: MnIII6F12(PO3(OH))8[Na8(Kx(H3O)4−x(H2O)2)MIV(OH)6] (MIV = Mn, Ti, Ge)

A water-deficient hydrothermal method has been applied to synthesize the first-ever, mixed- and high-valence manganese (Mn³⁺/Mn⁴⁺) fluorophosphate with a clathrate-like structure.

Ionothermal synthesis of open-framework metal phosphates with a Kagomé lattice network exhibiting canted anti-ferromagnetism†Electronic supplementary information (ESI) available: Cif files, atomic parameters, X-ray diffraction patterns, IR spectra, TG curves, and thermal ellipsoid plot and atomic label schemes of compound . See DOI: 10.1039/c4tc00290cClick here for additional data file

Four open-framework transition-metal phosphates; (NH4)2Co3(HPO4)2F4 (1), (NH4)Co3(HPO4)2(H2PO4)F2 (2), KCo3(HPO4)2(H2PO4)F2 (3), and KFe3(HPO4)2(H2PO4)F2 (4); are prepared by ionothermal synthesis using pyridinium hexafluorophosphate as the ionic liquid. Single-crystal X-ray diffraction analyses reveal that the four compounds contain cobalt/iron-oxygen/fluoride layers with Kagomé topology composed of interlinked face-sharing MO3F3/MO4F2 octahedra. PO3OH pseudo-tetrahedral groups augment the [M3O6F4] (1)/[M3O8F2] layers on both sides to give M3(HPO4)2F4 (1) and M3(HPO4)2F2 (2-4) layers. These layers are stacked along the a axis in a sequence AA…, resulting in the formation of a layer structure for (NH4)2Co3(HPO4)2F4(1). In NH4Co3(HPO4)2(H2PO4)F2 and KM3(HPO4)2(H2PO4)F2, the M3(HPO4)2F2 layers are stacked along the a axis in a sequence AA i … and are connected by [PO3(OH)] tetrahedra, giving rise to a 3-D open framework structure with 10-ring channels along the [001] direction. The negative charges of the inorganic framework are balanced by K+/NH4+ ions located within the channels. The magnetic transition metal cations themselves form layers with stair-case Kagomé topology. Magnetic susceptibility and magnetization measurements reveal that all four compounds exhibit a canted anti-ferromagnetic ground state (Tc = 10 or 13 K for Co and Tc = 27 K for Fe) with different canting angles. The full orbital moment is observed for both Co2+ and Fe2+.

Manganese(III) fluorophosphate frameworks

Nine new manganese(III) fluorophosphates have been synthesised hydrothermally in a fluoride-rich medium, through the use of MnF(3), HPF(6) and monovalent metal fluorides as reactants. Products have been structurally characterised using single crystal X-ray diffraction. Reaction in fluoride-rich conditions produces chain, layer and three dimensional framework structures containing new and unusual structural features based on the linking of PO(3)F, PO(2)(OH,F)(2) and Mn(O(6-n),F(n)) octahedra, with n averaging 2.8 over the family of compounds. The Mn(III), d(4), oxidation state is stabilised under these reaction conditions and products frequently show Jahn-Teller distorted Mn(O,F)(6) units with axially elongated Mn-O or, less commonly, Mn-F distances. Structures exhibiting inter-layer spaces and channels frequently have these lined by terminal fluoride anions of the PO(3)F, PO(2)(OH,F)(2) and Mn(O,F)(6) octahedra.