The Cobalt(II) Oxidotellurate(IV) Hydroxides Co₂(TeO₃)(OH)₂ and Co₁₅(TeO₃)₁₄(OH)₂

Previously unknown Co2(TeO3)(OH)2 and Co15(TeO3)14(OH)2 were obtained under mild hydrothermal reaction conditions (210 °C, autogenous pressure) from alkaline solutions. Their crystal structures were determined from single-crystal X-ray diffraction data. Co2(TeO3)(OH)2 (Z = 2, P1¯, a = 5.8898(5), b = 5.9508(5), c = 6.8168(5) Å, α = 101.539(2), β = 100.036(2), γ = 104.347(2)°, 2120 independent reflections, 79 parameters, R[F2 > 2σ(F2)] = 0.017) crystallizes in a unique structure comprised of undulating 2∝[Co2(OH)6/3O3/3O2/2O1/1]4− layers. Adjacent layers are linked by TeIV atoms along the [001] stacking direction. Co2(TeO3)(OH)2 is stable up to 450 °C and decomposes under the release of water into Co6Te5O16 and CoO. Magnetic measurements of Co2(TeO3)(OH)2 showed antiferromagnetic ordering at ≈ 70 K. The crystal structure of Co15(TeO3)14(OH)2 (Z = 3, R3¯, a = 11.6453(2), c = 27.3540(5) Å, 3476 independent reflections, 112 parameters, R[F2 > 2σ(F2)] = 0.026) is isotypic with Co15(TeO3)14F2. A quantitative structural comparison revealed that the main structural difference between the two phases is connected with the replacement of F by OH, whereas the remaining part of the three-periodic network defined by [CoO6], [CoO5(OH)], [CoO5] and [TeO3] polyhedra is nearly unaffected. Consequently, the magnetic properties of the two phases are similar, namely being antiferromagnetic at low temperatures