Fe2(AsO4)F:: A new three-dimensional condensed fluoro-arsenate iron(II) compound with antiferromagnetic interactions

Fe-2(ASO(4))F has been synthesized under mild hydrothermal conditions in the form of single crystals. The compound crystallizes in C2/c monoclinic space group with the unit cell parameters a = 13.214(1), b = 6.623(1), c = 10.045(1) angstrom and beta = 116.90(2)degrees with Z = 8. The crystal structure consists of a three-dimensional framework constructed by two kinds of chains, A and B, with 50% of population. In the chains, the environments for the iron(II) cations show penta- and hexa-coordination. The chains establish an angle of approximately 120 degrees between them. The disordered fluoride anions in these chains given rise to [Fe(1)O4F(1)(0.5)(F(2)(0.5))(2)] and [Fe(2)O-4(F(1)(0.5))(2)F(2)(0.5)] edge-shared polyhedra in which the fluoride anions have occupancy factors of 50% over two distinct crystallographic sites. The IR spectrum shows the characteristic bands of the (ASO(4))(3-) groups. From the diffuse reflectance spectrum a D, parameter of 650 cm(-1) has been calculated for the Fe(II) a high spin cation. The Mossbauer spectrum in the paramagnetic state shows a doublet that has been fitted, according to the existence of two crystallographically independent iron environments, with two Lorentzian doublets. Magnetic measurements performed between room temperature and 5K exhibit a maximum at 22.6K. characteristic of antiferromagnetic interactions with a estimated "J"-exchange parameter of -1.2 K. (c) 2006 Elsevier Inc. All rights reserved.