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

Fe2(AsO4)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)a=13.214(1), b=6.623(1)b=6.623(1), c=10.045(1)Å and β=116.90(2)°β=116.90(2)° with Z=8Z=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° 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)O4(F(1)0.5)2F(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 (AsO4)3− groups. From the diffuse reflectance spectrum a Dq parameter of 650 cm−1 has been calculated for the Fe(II) d6 high spin cation. The Mössbauer 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 5 K exhibit a maximum at 22.6 K, characteristic of antiferromagnetic interactions with a estimated “J”-exchange parameter of −1.2 K.

Two types of chain in Fe2(AsO4)F showing the five- and hexa-coordination polyhedra.Figure optionsDownload as PowerPoint slide