Iron fluorophosphates

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.

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.

Crystal structure of (1,4-diphenyl-4H-1,2,4-triazol-3-yl)phenyl-amine di-fluoro-phosphate, and a survey of the di-fluoro-phosphate anion (PO2F2 -)

Nitron is the trivial name of (1,4-diphenyl-4H-1,2,4-triazol-3-yl)phenyl-amine (C20H16N4), a triazole derivative used as an analytical reagent for gravimetric analysis of the nitrate anion. The crystal structure of the di-fluoro-phosphate salt of Nitron, 3-anilino-1,4-diphenyl-1H-1,2,4-triazol-4-ium di-fluoro-phosphate, C20H17N4 +·PO2F2 -, is reported here. Within the protonated Nitron mol-ecule, the triazole ring, one of the phenyl rings and the NHPh moiety are virtually co-planar, with the third phenyl ring inclined to the least-squares plane of the other three rings by 56.07 (3)°. Inter-molecular N-H⋯O and C-H⋯O hydrogen bonds between cations and di-fluoro-phosphate anions lead to the formation of a three-dimensional network that is consolidated by additional π-π stacking inter-actions between the triazole ring and one of the phenyl rings. Database surveys on inorganic, metal-organic and organic structures comprising the tetra-hedral PO2F2 group reveal mean bond lengths of P-O = 1.459 (27) Å, P-F = 1.530 (21) Å, and angles of O-P-O = 121.2 (2.9)°, O-P-F = 108.7 (6)°, and F-P-F = 98.5 (2.6)°, using a dataset of 67 independent PO2F2 - anions or PO2F2 entities.

Joint crystallization of KCuAl[PO4]2 and K(Al,Zn)2[(P,Si)O4]2: crystal chemistry and mechanism of formation of phosphate-silicate epitaxial heterostructure

Two novel phases, potassium copper aluminium bis(phosphate), KCuAl[PO4]2 (I), and potassium zinc aluminium bis(phosphate-silicate), K(Al,Zn)2[(P,Si)O4]2 (II), were obtained in one hydrothermal synthesis experiment at 553 K. Their crystal structures have been studied using single-crystal X-ray diffraction. (I) is a new member of the A + M 2+ M 3+[PO4]2 family. Its open 3D framework built by AlO5 and PO4 polyhedra includes small channels populated by columns of CuO6 octahedra sharing edges, and large channels where K+ ions are deposited. It is assumed that the stability of this structure type is due to the pair substitution of Cu/Al with Ni/Fe, Co/Fe or Mg/Fe in different representatives of the series. From the KCuAl[PO4]2 structural features, one may suppose it is a potentially electrochemically active material and/or possible low-temperature antiferromagnet. In accordance with results obtained from X-ray diffraction data, using scanning electron microscopy, microprobe analysis and detailed crystal chemical observation, (II) is considered as a product of epitaxial intergrowth of phosphate KAlZn[PO4]2 and silicate KAlSi[SiO4]2 components having closely similar crystal structures. The assembly of `coherent intergrowth' is described in the framework of a single diffraction pattern.

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.

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.

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.

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).

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.

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.