A 3-D Organically Templated Mixed Valence (Fe²⁺/Fe³⁺) Iron Phosphate with Oxide-Centered Fe₄O(PO₄)4 Cubes: Hydrothermal Synthesis, Crystal Structure, Magnetic Susceptibility, and Mössbauer Spectroscopy of [H₃NCH₂CH₂NH₃]₂[Fe ₄O(PO₄)₄]·H₂O

A 3-D, open framework, mixed valence iron phosphate, [H₃NCH₂CH₂NH₃]₂[Fe ₄O-(PO₄)₄]·H₂O, which contains organic ethylenediammonium dications in the framework voids, has been prepared via hydrothermal synthesis and has been characterized by single-crystal X-ray diffraction, magnetic susceptibility, and variable temperature Mössbauer spectroscopy. Crystal data: tetragonal, space group I42m with a = 10.1383(8) Å, c = 9.628(1) Å, V = 989.6(1) ų, Z = 2, and R(R_W) = 7.7(6.5) for 276 reflections (I > 3σ(I)) and 32 variables. The fundamental building block of the structure is a novel cubane-like cluster with trigonal bipyramidal iron and tetrahedral phosphorus atoms lying at alternate vertexes of a cube with a tetrahedrally coordinated oxygen atom at the center of the cube. Each cluster is linked by eight Fe-O-P bonds that extend along what would be all 〈111〉 directions of the putative cube to eight similar clusters to form a framework that is only slightly distorted (by the presence of the organic cations) from cubic 43m symmetry. Mössbauer and ac magnetic susceptibility measurements show that equal amounts of valence trapped Fe²⁺ and Fe³⁺ are present, which undergo long range magnetic ordering at ∼12 K.