Hydrothermal synthesis, crystal structure, thermal behaviour and magnetic properties of a new ammonium-chromium-iron(III) bis(hydrogenphosphate)

The hydrothermal synthesis and the chemical-physical characterization of an ammonium-chromium-(III)iron(III) bis(hydrogenphosphate), Cr0.34Fe0.66NH4(HPO4)(2) [CrFeNP] is reported. It was obtained in aqueous media by reaction between chromium(III) chloride, iron(III) chloride, urea, and orthophosphoric acid. The crystal structure of CrFeNP was determined from single-crystal X-ray diffraction data. It crystallizes in the triclinic system, space group P-1, and exhibits two types of different infinite tunnels along [0 1 0] and [1 0 0] directions, where the ammonium cations are located. Thermal analysis shows that the solid is stable up to ca. 600 K. The activation energy of the thermal decomposition up to 1273 K was computed by isoconversional methods. In addition, the magnetic behaviour of the material was investigated from magnetic susceptibility and magnetization measurements. CrFeNP undergoes two successive magnetic transitions at temperatures T-C = 17.9 K and T-t = 3.1 K, which could be related to a ferri- and an antiferromagnetic magnetic phase transitions, respectively.