Hydroxylammonium fluorometalates: Synthesis and characterisation of a new fluorocuprate and fluorocobaltate

The first layered hydroxylammonium fluorometalates, (NH3OH)2CuF4 and (NH3OH)2CoF4, were prepared by the reaction of solid NH3OHF and the aqueous solution of copper or cobalt in HF. Both compounds crystallize in monoclinic, P21/c, unit cell with parameters: a = 7.9617(2) Å, b = 5.9527(2) Å, c = 5.8060(2) Å, β = 95.226(2)° for (NH3OH)2CuF4 and a = 8.1764(3) Å, b = 5.8571(2) Å, c = 5.6662(2) Å, β = 94.675(3)° for (NH3OH)2CoF4, respectively. Magnetic susceptibility was measured between 2 K and 300 K giving the effective Bohr magneton number of 2.1 for Cu and 5.2 BM for Co. At low temperatures both complexes undergo a transition to magnetically ordered phase. The thermal decomposition of both compounds was studied by TG, DSC and X-ray powder diffraction. The thermal decomposition of (NH3OH)2CuF4 is a complex process, yielding NH4CuF3 as an intermediate product and impure Cu2O as the final residue, while (NH3OH)2CoF4 decomposes in two steps, obtaining CoF2 after the first step and CoO as the final product.