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

Two new hydroxylammonium compounds, (NH 3OH) 2CuF 4 and (NH 3OH) 2CoF 4, were prepared and structurally characterised. These are the first examples with 2D layered fluorometalate anions amongst structures with hydroxylammonium cations. Their magnetic properties were studied by SQUID measurements and the thermal decomposition studied by TG analysis and X-ray powder diffraction. The first layered hydroxylammonium fluorometalates, (NH 3OH) 2CuF 4 and (NH 3OH) 2CoF 4, were prepared by the reaction of solid NH 3OHF and the aqueous solution of copper or cobalt in HF. Both compounds crystallize in monoclinic, P2 1/ 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 (NH 3OH) 2CuF 4 and a = 8.1764(3) Å, b = 5.8571(2) Å, c = 5.6662(2) Å, β = 94.675(3)° for (NH 3OH) 2CoF 4, 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 (NH 3OH) 2CuF 4 is a complex process, yielding NH 4CuF 3 as an intermediate product and impure Cu 2O as the final residue, while (NH 3OH) 2CoF 4 decomposes in two steps, obtaining CoF 2 after the first step and CoO as the final product.