The preparation and properties of cobalt(II) tellurates

Cobalt(II) tellurates with the composition CoTeO4, CoTeO4.1/2 H2O and Co3TeO6 were prepared. The first two are cubic with octahedral coordination around the cobalt atom and with TeO6 octahedra joined at the edges. In Co3TeO6, which is isostructural with Ni3TeO6, the TeO6 octahedra are isolated. At least one cobalt atom is tetrahedrally coordinated by oxygen atoms. The high values of the temperature independent paramagnetism, 11 m3 kg-1, and the Weiss constant, Θ = -64 K, indicate marked magnetic exchange interaction. The thermal decomposition of all three tellurates leads to formation of cobalt tellurates and finally to CoO and TeO2. At laboratory temperature all three substances are paramagnetic with μeff values corresponding to divalent cobalt.