Comparison of one-, two-, and three-dimensional iron phosphates containing ethylenediamine

A new two-dimensional (2d) iron phosphate, (C₂N₂H₁₀)Fe₂O(PO₄)₂, has been synthesized under hydrothermal conditions in the system of FeCl₃-H₃PO₄-C₂N₂H₈-H₂O. The crystal data is: space group P2₁/c, a=10.670(1) Å, b=10.897(1) Å, c=9.918(1) Å, β=105.632(1)°, Z=4. The layered structure consists of double sheet layers, of composition Fe₂O(PO₄)₂, built from FeO₅ trigonal bipyramids and PO₄ tetrahedra. The amine holds the layers together via H-bonding. The study of the magnetic properties reveals two magnetic transitions at 160 and 30 K with spin-glass-like behavior below 160 K. By varying the hydrothermal conditions, three other iron phosphates were synthesized: the one-dimensional (1d) (C₂N₂H₁₀)Fe(HPO₄)₂(OH)·H₂O, the 2d (C₂N₂H₁₀)Fe₂(PO₄)₂(OH)₂, and the three-dimensional (3d) (C₂N₂H₁₀)₂Fe₄O(PO₄)₄·H₂O. The 1d compound can be used as the starting reagent in the synthesis of both the 2d compound and the 3d lipscombite Fe₃(PO₄)₂(OH)₂ due to the similar building blocks in their structures. In the 3d phosphate (C₂N₂H₁₀)₂Fe₄O(PO₄)₄·H₂O, manganese can substitute for half of the iron atoms. Magnetic study shows ordering transitions at about 30 K, however, manganese substitution depresses the magnetic ordering temperature.     

Ferric Phosphate Hydroxide Microcrystals for Highly Efficient Visible‐Light‐Driven Photocatalysts

Fe₄(OH)₃(PO₄)₃ microcrystals are successfully synthesized by a simple hydrothermal method. Due to a possible self‐etching mechanism, different morphologies of Fe₄(OH)₃(PO₄)₃ microcrystals are obtained. Several reactions with different temperatures and times are performed to confirm the supposed self‐etching mechanism. Moreover, as a result of their different micro/nanostructures, these microcrystals present different photocatalytic activities for visible‐light‐driven photodegragadation of methylene blue.     

Four new hydroxymonophosphates with closely related intersecting tunnels structures: The series AM(PO3(OH))2 with A=Rb, Cs; M=Fe, Al, Ga, In

The family of hydroxymonophosphates of generic formula AM^III(PO₃(OH))₂ has been revisited using hydrothermal techniques. Four new phases have been synthesized: CsIn(PO₃(OH))₂, RbFe(PO₃(OH))₂, RbGa(PO₃(OH))₂ and RbAl(PO₃(OH))₂. Single crystal diffraction studies show that they exhibit two different structural types from previously observed other phases with A=H₃O, NH₄, Rb and M=Al, V, Fe. The “Cs-In” and “Rb-Fe” phosphates crystallize in the triclinic space group , with the cell parameters a=7.4146(3) Å, b=9.0915(3) Å, c=9.7849(3) Å, α=65.525(3)°, β=70.201(3)°, γ=69.556(3)° and V=547.77(4) Å³ (Z=3) for CsIn(PO₃(OH))₂ and a=7.2025(4) Å, b=8.8329(8) Å, c=9.4540(8) Å, α=65.149(8)°, β=70.045(6)°, γ=69.591(6)° and V=497.44(8) Å³ (Z=3) for α-RbFe(PO₃(OH))₂. The “Rb-Al” and “Rb-Ga” phosphates crystallize in the Rc space group, with a=8.0581(18) Å and c=51.081(12) Å (V=2872.5(11) Å³ and Z=18) for RbAl(PO₃(OH))₂ and a=8.1188(15) Å and c=51.943(4) Å (V=2965(8) Å and Z=18) for RbGa(PO₃(OH))₂. These two structural types are closely related. Both are built up from M^IIIO6 octahedra sharing their apices with PO₃(OH) tetrahedra to form [M₃(PO₃OH)₆] units, but the latter exhibits a different configuration of their tetrahedra. The three-dimensional host-lattices result from the connection of the [M₃(PO₃OH)₆] units and they present numerous intersecting tunnels containing the monovalent cations.     

Synthesis and crystal structure of phosphate Ba<Subscript>1.5</Subscript>Fe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Double phosphate Ba_1.5Fe₂(PO₄)₃ was synthesized and structurally studied. Single crystals were synthesized by the fusion method. Cubic crystals, Z = 4, space group P2₁3, a = 9.866(1) Å. This structure is built of polyhedrons of four types: PO₄ tetrahedrons, two virtually regular FeO₆ octahedrons, BaO₁₂ twelve-vertex polyhedrons, and BaO₉ nine-vertex polyhedrons. These polyhedrons share common oxygen vertices to form three-dimensional [Fe₂(PO₄)₃]_3∞ framework containing barium atoms in cavities.     

Magnetite solubility and phase stability in alkaline media at elevated temperatures

A platinum-lined flowing autocláve facility was used to investigate the solubility behavior of magnetite (Fe₃O₄) in alkaline sodium phosphate and ammonium hydroxide solutions between 21 and 288°C. Measured iron solubilities were interpreted via a Fe(II)/Fe(III) ion hydroxo-, phosphato-, and ammino-complexing model and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. A total of 14 iron ion species were fitted. Complexing equilibria are reported for 8 new species: Fe(OH)(HPO₄)^–, Fe(OH)₂(HPO₄)^2–, Fe(OH)₃(HPO₄)^2–, Fe(OH)(NH₃)⁺, Fe(OH)₂(PO₄)^3–, Fe(OH)₄(HPO₄)^3–, Fe(OH)₂(H₂PO₄)^–, and Fe(OH)₃(H₂PO₄)^3–. At elevated temperatures, hydrolysis and phosphato complexing tended to stabilize Fe(III) relative to Fe(II), as evidenced by free energy changes fitted to the oxidation reactions.

Direct Synthesis of Hydroxyapatite-Silk Fibroin Nano-Composite Sol via a Mechanochemical Route

In the presence of fine silk cocoon (silk fibroin, SF) powder, a low viscosity sol of nano-hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂)—SF was synthesized by a wet mechanochemical reaction. Nano crystals of HAp are oriented along their c-axis. The secondary structure of SF was changed by milling. A uniform thin gel film was obtained by a simple dip coating on the glass substrate precoated by chitosan.     

Cationic mobility in Li3?2xNbxFe2?x(PO4)3 complex phosphates

Synthesis and ionic conductivity of Li_3−2x Nb _x Fe_2−x (PO₄)₃ complex phosphates were studied by X-ray powder diffraction and impedance spectroscopy. These phosphates are formed only at 900–1000°C. Variations in their thermal expansivity and unit cell parameters induced by aliovalent doping were characterized. The conductivity of these materials increases monotonically in the series Li_0.5Nb_1.25Fe_0.75(PO₄)₃-LiNbFe(PO₄)₃ and Li_1.2Nb_0.9Fe_1.1(PO₄)₃-Li₃Fe₂(PO₄)₃, which is explained by consecutive occupation of the Li(1) and Li(2) positions in their structures. Original Russian Text ? A.R. Shaikhlislamova, I.A. Stenina, A.B. Yaroslavtsev, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 12, pp. 1957–1962.     

High-Voltage Polyanion Positive Electrode Materials

High-voltage generation (over 4 V versus Li⁺/Li) of polyanion-positive electrode materials is usually achieved by Ni³⁺/Ni²⁺, Co³⁺/Co²⁺, or V⁴⁺/V³⁺ redox couples, all of which, however, encounter cost and toxicity issues. In this short review, our recent efforts to utilize alternative abundant and less toxic Fe³⁺/Fe²⁺ and Cr⁴⁺/Cr³⁺ redox couples are summarized. Most successful examples are alluaudite Na₂Fe₂(SO₄)₃ (3.8 V versus sodium and hence 4.1 V versus lithium) and β₁-Na₃Al₂(PO₄)₂F₃-type Na₃Cr₂(PO₄)₂F₃ (4.7 V versus sodium and hence 5.0 V versus lithium), where maximizing ΔG by edge-sharing Fe³⁺-Fe³⁺ Coulombic repulsion and the use of the 3d²/3d³ configuration of Cr⁴⁺/Cr³⁺ are essential for each case. Possible exploration of new high-voltage cathode materials is also discussed.     

Synthesis of hydroxyapatite by hydrolysis of α-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Conditions for hydroxyapatite (HAP) synthesis in aqueous solutions by hydrolysis of α-Ca₃(PO₄)₂ were studied. Temperature exerts a substantial effect on the rate of α-Ca₃(PO₄)₂ hydrolysis and also changes the morphology of the reaction products. At 40 °C, the plate-like intersecting (perpendicular to the surface of the initial particles) crystals of HAP grow. Their maximum size after the 24-h hydrolysis is 1–2 µm. Needle like HAP crystals are formed upon boiling of the suspension. The morphology observed for the HAP particles agrees well with the conclusions obtained by analysis of the kinetics of tricalcium phosphate hydrolysis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 78–85, January, 2005.     

Characterization and reactivity study of non-heme high-valent iron–hydroxo complexes

A terminal Fe^IIIOH complex, [Fe^III(L)(OH)]²⁻ (1), has been synthesized and structurally characterized (H₄L = 1,2-bis(2-hydroxy-2-methylpropanamido)benzene). The oxidation reaction of 1 with one equiv. of tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBAH) or ceric ammonium nitrate (CAN) in acetonitrile at −45 °C results in the formation of a Fe^IIIOH ligand radical complex, [Fe^III(L˙)(OH)]⁻ (2), which is hereby characterized by UV-visible, ¹H nuclear magnetic resonance, electron paramagnetic resonance, and X-ray absorption spectroscopy techniques. The reaction of 2 with a triphenylcarbon radical further gives triphenylmethanol and mimics the so-called oxygen rebound step of Cpd II of cytochrome P450. Furthermore, the reaction of 2 was explored with different 4-substituted-2,6-di-tert-butylphenols. Based on kinetic analysis, a hydrogen atom transfer (HAT) mechanism has been established. A pK_a value of 19.3 and a BDFE value of 78.2 kcal/mol have been estimated for complex 2.

One-electron oxidation of an Fe^III–OH complex (1) results in the formation of a Fe^III–OH ligand radical complex (2). Its reaction with (C₆H₅)₃C˙ results in the formation of (C₆H₅)₃COH, which is a functional mimic of compound II of cytochrome P450.     

A Raman and infrared spectroscopic study of the phosphate mineral laueite

A laueite mineral sample from Lavra Da Ilha, Minas Gerais, Brazil has been studied by vibrational spectroscopy and scanning electron microscopy with EDX. Chemical formula calculated on the basis of semi-quantitative chemical analysis can be expressed as (Mn²⁺_0.85,Fe²⁺_0.10Mg_0.05)_∑1.00(Fe³⁺_1.90,Al_0.10)_∑2.00(PO₄)₂(OH)₂·8H₂O.The laueite structure is based on an infinite chains of vertex-linked oxygen octahedra, with Fe³⁺ occupying the octahedral centers, the chain oriented parallel to the c-axis and linked by PO₄ groups. Consequentially not all phosphate units are identical. Two intense Raman bands observed at 980 and 1045 cm⁻¹ are assigned to the ν₁ PO₄³⁻ symmetric stretching mode. Intense Raman bands are observed at 525 and 551 cm⁻¹ with a shoulder at 542 cm⁻¹ are assigned to the ν₄ out of plane bending modes of the PO₄³⁻. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Intense Raman bands are observed at 3379 and 3478 cm⁻¹ and are attributed to the OH stretching vibrations of the hydroxyl units. Intense broad infrared bands are observed. Vibrational spectroscopy enables subtle details of the molecular structure of laueite to be determined.     

Mechanochemical synthesis of nanostructured fluorapatite/fluorhydroxyapatite and carbonated fluorapatite/fluorhydroxyapatite

Powder mixture of Ca(OH)₂-P₂O₅-CaF₂ were milled in planetary ball mill. A carbonated fluorhydroxyapatite, FHA Ca₁₀(PO₄)_1−y(CO₃)_y(PO₄)₅(OH)_2−2x1(F)_2x1 was formed after 5 h of milling and carbonated fluoroapatite Ca₁₀(PO₄)_1−y(CO₃)_y(PO₄)₅(F)₂ was formed after 9 h of milling. Complete transformation of the carbonated form of FA into then single phase of FA occurred after 9 h milling and thermally treating. The various experimental techniques like X-ray Diffraction (XRD), Differential Thermal Analysis (DTA), Infrared Spectroscopy (IR), Transmission Electron Microscopy and Scanning Electron Microscopy (SEM) were used to characterize the synthesized powders and to postulate reaction mechanisms’ steps- transformations of reactants involved.     

Heptairon bis(phosphate) tetrakis(hydrogenphosphate)

A new iron hydrogen phosphate, heptairon bis­(phosphate) tetrakis­(hydrogen­phosphate), Fe₇(PO₄)₂(HPO₄)₄, has been prepared hydro­thermally and characterized by single‐crystal X‐ray diffraction. The compound has one Fe atom on an inversion centre and is isostructural with Mn₇(PO₄)₂(HPO₄)₄ and Co₇(PO₄)₂(HPO₄)₄. The structure is based on a framework of edge‐ and corner‐sharing FeO₆, Fe₅ and PO₄ polyhedra, isotypic with that found in the mixed‐valence iron phosphate Fe₇(PO₄)₆. The Fe atoms in the title compound are purely in the divalent state, just like the Co atoms in Co₇(PO₄)₂(HPO₄)₄, the necessary charge balance being maintained by the addition of H atoms in the form of bridging Fe—OH—P groups.     

Chromium(III) Hydroxide Solubility in The Aqueous Na+-OH?-H2PO?4-HPO2?4-PO3?4-H2O System: A Thermodynamic Model

Chromium(III)-phosphate reactions are expected to be important in managing high-level radioactive wastes stored in tanks at many DOE sites. Extensive studies on the solubility of amorphous Cr(III) solids in a wide range of pH (2.8–14) and phosphate concentrations (10^–4 to 1.0 m) at room temperature (22±2)°C were carried out to obtain reliable thermodynamic data for important Cr(III)-phosphate reactions. A combination of techniques (XRD, XANES, EXAFS, Raman spectroscopy, total chemical composition, and thermodynamic analyses of solubility data) was used to characterize solid and aqueous species. Contrary to the data recently reported in the literature,⁽¹⁾ only a limited number of aqueous species [Cr(OH)₃H₂PO^–₄, Cr(OH)₃(H₂PO₄)^2–₂), and Cr(OH)₃HPO^2–₄] with up to about four orders of magnitude lower values for the formation constants of these species are required to explain Cr(III)-phosphate reactions in a wide range of pH and phosphate concentrations. The log K^o values of reactions involving these species [Cr(OH)₃(aq)+H₂PO^–₄&#x21CC;Cr(OH)₃H₂PO^–₄; Cr(OH)₃(aq)+2H₂PO^–₄&#x21CC;Cr(OH)₃(H₂PO₄)^2–₂; Cr(OH)₃(aq)+HPO^2–₄&#x21CC;Cr(OH)₃HPO^2–₄] were found to be 2.78±0.3, 3.48±0.3, and 1.97±0.3, respectively.     

Apatites of divalent europium

The preparation methods of Eu₃(PO₄)₂, Eu₅(PO₄)₃F, Eu₃(PO₄)Cl and Eu₅(AsO₄)₃OH are described. Eu₃(PO₄)₂ crystallizes in a rhombohedral unit cell and the apatite like compounds in the $\text{P6}{}_3\text{m}$ hexagonal structure. All the compounds are isomorphous with the corresponding Sr compounds, and similar in size. Magnetic susceptibility measurements show that Eu₃(PO₄)₂ is magnetically ordered below 5 K and Eu₅(PO₄)₃F and Eu₅(PO₄)₃Cl are paramagnetic. Solid solution of the Eu_5?xCa_x(PO₄)₃F system obey Vegard's law, while the Eu_5?xBa_x(PO₄)₃F and Eu_5?xBa_x(PO₄)₃Cl systems show a trend to form ordered solid solutions.     

A new sodium hydroxygallophosphate containing tetrameric gallium units: Na3[Ga4O(OH)(H2O)(PO4)4]·H2O

A new sodium hydroxygallophosphate, Na₃Ga₄O(OH)(H₂O)(PO₄)₄·H₂O, has been prepared by hydrothermal synthesis. Its structure has been determined from a single-crystal X-ray diffraction study. It crystallizes in the P2₁/c space group with the cell parameters a=9.445(2) Å, b=9.028(1) Å, c=19.209(3) Å, β=102.08(2), V=1603.4(4) Å³. Its three-dimensional framework can be described from PO₄ monophosphate groups sharing their apices with original Ga₄O₁₆(OH)(H₂O) tetrameric building units, which result from the assembly of one GaO₄ tetrahedron, one GaO₅ trigonal bipyramid and two octahedra: GaO₅(OH) and GaO₄(OH)(H₂O). The sodium cations and one water molecule are located in tunnels running along b.     

FeII2(PO4)(OH), a synthetic analogue of wolfeite

This paper reports the hydrothermal synthesis and crystal structure refinement of diiron(II) phosphate hydroxide, Fe^II₂(PO₄)(OH), obtained at 1063 K and 2.5 GPa. This phosphate is the synthetic analogue of the mineral wolfeite, and has a crystal structure topologically identical to those of minerals of the triplite–triploidite group. The complex framework contains edge‐ and corner‐sharing FeO₄(OH) and FeO₄(OH)₂ polyhedra, linked via corner‐sharing to the PO₄ tetrahedra (average P—O distances are between 1.537 and 1.544 Å). Four five‐coordinated Fe sites are at the centers of distorted trigonal bipyramids (average Fe—O distances are between 2.070 and 2.105 Å), whereas the coordination environments of the remaining Fe sites are distorted octahedra (average Fe—O distances are between 2.146 and 2.180 Å). The Fe—O distances are similar to those observed in natural Mg‐rich wolfeite, except for two Fe—O bond distances, which are significantly longer in synthetic Fe²⁺₂(PO₄)(OH).     

Synthesis, crystal structure and characterization of iron pyroborate (Fe2B2O5) single crystals

Single crystals of iron(II) pyroborate, Fe₂B₂O₅, were prepared at 1000–1050 °C under an argon atmosphere. The crystals were transparent, yellowish in color and needle-like or columnar. The crystal structure of Fe₂B₂O₅ was analyzed by single-crystal X-ray diffraction. Refined triclinic unit cell parameters were a=3.2388(2), b=6.1684(5), c=9.3866(8) Å, α=104.613(3)°, β=90.799(2)° and γ=91.731(2)°. The final reliability factors of refinement were R1=0.020 and wR2=0.059 [I > 2σ(I)]. Transmittance over 50% in the visible light region from 500 to 750 nm was observed for a single crystal of Fe₂B₂O₅ with a thickness of about 0.3 mm. The light absorption edge estimated from a diffuse reflectance spectrum was at around 350 nm (3.6 eV). Magnetic susceptibility was measured for single crystals at 4–300 K. Fe₂B₂O₅ showed antiferromagnetic behavior below the Néel temperature, T_N≈70 K, and the Weiss temperature was T_W=36 K. The effective magnetic moment of Fe was 5.3μ_B.     

A novel route for FePO4 olivine synthesis from sarcopside oxidation

Heterosite FePO₄ is synthesized for the first time by direct thermal oxidation of sarcopside Fe₃(PO₄)₂. Both FePO₄ and Fe₃(PO₄)₂ have a pseudo olivine structure. Complete isostructural conversion of sarcopside into FePO₄ is achieved at a temperature of 450 °C within 3 days according to the reaction Fe₃(PO₄)₂ + ¾ O₂ → 2 FePO₄ + ½ Fe₂O₃ which leads to the extraction of iron from the sarcopside structure. Appropriate heating ramp must be applied in order to avoid the crystallization of Fe₇(PO₄)₆. Electrochemical performances of the oxidation product are consistent with those of olivine FePO₄.     

Two New Ferrous Molybdophosphates as Temperature-Dependent Hydrothermal Reaction Products

Two new ferrous molybdophosphates, (H₂enMe)₇Fe^II[Mo₁₂^V(HPO₄)₂(PO₄)₆(OH)₆O₂₄]·7H₂O 1 and (H₂enMe)₆Fe^II[Mo₁₂^V(HPO₄)₄(PO₄)₄(OH)₆O₂₄]·4H₂O 2 (enMe = 1,2-propanediamine), have been synthesized from an identical starting mixture through hydrothermal reactions using temperature as the only independent variable, and thoroughly characterized by IR, TG, single crystal X-ray diffraction and cyclic voltammetry. The structures of both 1 and 2 are built from the building blocks of the formula, {Fe^II[Mo₆P₄O₃₁]₂}, consisting of a network of MO₆ (M = Fe, Mo) octahedra and PO₄ tetrahedra linked through their vertices as anions, and protonated 1,2-propanediamine as cations, respectively. The most important aspect is that the non-hydrogen atomic ratio of Mo, Fe, P, O in the anions of 1 and 2 is the same, but the protonation of the PO₄ groups is different in 1 and 2. Less protonation of the PO₄ groups in 1 obtained at high temperature results in the anion carrying more charges and gives rise to more H₂enMe cations per [Fe^II(P₈Mo₁₂^V)] unit compared with that in 2 obtained at low temperature, and as a consequence, different interpenetrating hydrogen-bonded network structures are formed in the two different compounds in terms of packing efficiency and the system energy minimization.