Hydrothermal synthesis, crystal structure, spectroscopic and magnetic properties of (C3H12N2)(0.75)[(Fe1.5Fe1.5III)-Fe-II(AsO4)F-6]

摘要

A new iron(II)-iron(III) mixed valence fluoro-arsenate compound templated by propanediammonium cations has been synthesized by using mild hydrothermal conditions. The crystal structure has been solved from single-crystal x-ray diffraction data. This phase crystallizes in the Imam space group with the unit-cell parameters a = 7.566(2), b = 11.034(3) and c = 13.233(5) angstrom. The compound exhibits a three-dimensional framework constructed from two kinds of chains which delimit cavities in which the propanediammonium cations are located. Mossbauer and diffuse reflectance spectroscopies confirm the presence of Fe(II,III) mixed valence cations and the existence of slightly distorted octahedral environments for the metallic centres. Magnetic measurements indicate the existence a three-dimensional antiferromagnetic ordering at 6 K. However, at low temperatures, a small hysteresis loop is observed. The values of the remanent magnetization and coercitive field are 400 emu/mol and 1180 G, respectively. These results are in good agreement with the existence of a ferromagnetic component due to a spin descompensation by the mixed valence nature of this phase.