Synthesis and Characterization of a New Ferrimagnetic Mixed-Valent Iron Fluorophosphate [C<sub>6</sub>N<sub>4</sub>H<sub>21</sub>][Fe<sup>III</sup><sub>3</sub><sub>-</sub><i><sub>x</sub></i>Fe<sup>II</sup><i><sub>x</sub></i>F<sub>2</sub>(PO<sub>4</sub>)(HPO<sub>4</sub>)<sub>2</sub>]<sub>2</sub> (<i>x</i> ∼ 1.5) with a Layered Structure
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The synthesis, structure, and magnetic properties of a mixed valent iron fluorophosphate, [C6N4H21][FeIII3-xFeIIxF2(PO4)(HPO4)2]2 (x ∼ 1.5) has been described. The structure consists of a network of FeO4F2 octahedra and PO4 tetrahedra linked through their vertexes, forming infinite two-dimensional sheets separated by the organic amine molecules, triethylenetetrammonium cations (TETA). A remarkable feature of this structure is the presence of chains of FeII−O−FeII that are connected by FeIII octahedra, forming infinite two-dimensional sheets of Fe−O/F−Fe. This is the first time such linkages have been observed in two-dimensional iron fluorophosphates. Magnetic studies indicate ferrimagnetic behavior with a Curie temperature of Tc = 25 K. Mössbauer studies show mixed occupancies in the FeII sites. Crystal data: M = 567.61, triclinic, space group = P1̄ (no. 2), a = 6.431(4) Å, b = 10.274(5) Å, c = 10.439(3) Å, α = 80.56(4)°, β = 89.53(2)°, γ = 87.94(4)°, V = 680.0(6) Å3, Z = 2, ρ(calc.) = 2.772 g cm-3, μ(Mo Kα) = 3.610 mm-1, R1 = 0.0634 [1943 observed reflections with I > 2σ(I)].
