Fe 2(AsO 4)F: A new three-dimensional condensed fluoro-arsenate iron(II) compound with antiferromagnetic interactions

Abstract

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 ) Å and β = 116.90 ( 2 ) ° 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° between them. The disordered fluoride anions in these chains given rise to [Fe(1)O 4F(1) 0.5(F(2) 0.5) 2] and [Fe(2)O 4(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 (AsO 4) 3− groups. From the diffuse reflectance spectrum a D q parameter of 650 cm −1 has been calculated for the Fe(II) d 6 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.