Thermal, spectroscopic and magnetic properties of the CoxNi1−x(SeO3)·2H2O (x = 0, 0.4, 1) phases

The CoxNi1−x(SeO3)·2H2O (x = 0, 0.4, 1) family of compounds has been hydrothermally synthesized under autogeneous pressure and characterized by elemental analysis, infrared and UV-vis spectroscopies and thermogravimetric and thermodiffractometric techniques. The crystal structure of Co0.4Ni0.6(SeO3)·2H2O has been solved from single-crystal X-ray diffraction data. This phase is isostructural with the M(SeO3)·2H2O (M = Co and Ni) minerals and crystallizes in the P21/n space group, with a = 6.4681(7), b = 8.7816(7), c = 7.5668(7) Å, β = 98.927(9)° and Z = 4. The crystal structure of this series of compounds consists of a three-dimensional framework formed by (SeO3)2− selenite oxoanions and edge-sharing M2O10 dimeric octahedra in which the metallic cations are coordinated by the oxygens belonging to both the selenite groups and water molecules. The diffuse reflectance spectra show the essential characteristics of Co(II) and Ni(II) cations in slightly distorted octahedral environments. The calculated values of the Dq and Racah (B and C) parameters are those habitually found for the 3d7 and 3d8 cations in octahedral coordination. The magnetic measurements indicate the existence of antiferromagnetic interactions in all the compounds. The magnetic exchange pathways involve the metal orbitals from edge-sharing dimeric octahedra and the (SeO3)2− anions which are linked to the M2O10 polyhedra in three dimensions.