Synthesis and Characterization of Four Ethylenediamine-Templated Iron Arsenates

Four new ethylenediamine-templated iron arsenates and fluoroarsenates have been hydrothermally synthesized from iron metal, hydrofluoric and arsenic acids, and ethylenediamine. Fe(H2AsO4)(HAsO4)2·enH2·H2O (1) is one-dimensional and contains chains, FeIIIFeIIF2(HAsO4)(AsO4)·enH2·2H2O (2) is a layered fluoroarsenate, and Fe3(HAsO4)6·enH2·NH3·NH4 (3) and Fe2F2(AsO4)2(H2O)·enH2 (4) are an arsenate and a fluoroarsenate, respectively, with three-dimensional open-framework type structures. Compounds 1, 3, and 4 contain Fe(III) only, while 2 is a mixed-valence compound of Fe(III) and Fe(II). The structures were determined from single-crystal X-ray diffraction. Crystal data: (1) P21, a = 4.762(1) Å, b = 16.086(3) Å, c = 8.698(2) Å, β = 90.65(3)°, Z = 2; (2) P-1, a = 5.289(1) Å, b = 7.573 (1) Å, c = 8.888(2) Å, α = 67.32(3)°, β = 82.77(3)°, γ = 69.76(3)°, Z = 1; (3) C2/c, a = 18.384(3) Å, b = 8.785(1) Å, c = 16.052(2) Å, β = 111.11(1)°, Z = 4; (4) Pbca, a = 10.490(2) Å, b = 10.090(2) Å, c = 20.540(4) Å, Z = 8. Strong hydrogen bonding exists between the chains and the layers in 1 and 2, and between the diprotonated ethylenediamine and the inorganic part of the structures of 1, 2, and 4. The ethylenediamine in 3 is not hydrogen bonded, and as a result it is disordered. The compounds are characterized also by thermogravimetric analysis, infrared spectroscopy, elemental analysis, and magnetic measurements.