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) P2(1), a = 4.762(1) A, b = 16.086(3) A, c = 8.698(2) A, beta = 90.65(3) degrees, Z = 2; (2) P-1, a = 5.289(1) A, b = 7.573 (1) A, c = 8.888(2) A, alpha = 67.32(3) degrees, beta = 82.77(3) degrees, gamma = 69.76(3) degrees, Z = 1; (3) C2/c, a = 18.384(3) A, b = 8.785(1) A, c = 16.052(2) A, beta = 111.11(1) degrees, Z = 4; (4) Pbca, a = 10.490(2) A, b = 10.090(2) A, c = 20.540(4) A, 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.