Synthesis, crystal structure and magnetic properties of a new copper oxo-antimony sulphate CuSb6O8(SO4)2

Abstract

The new copper oxo-antimony sulphate CuSb₆O₈(SO₄)₂ crystallizes in the triclinic space group P with the unit cell parameters a = 5.5342(4) Å, b = 7.6706(6) Å, c = 9.2374(7) Å, α = 96.505(5)°, β = 93.818(4)°, γ = 109.733(4)° and Z = 1. The crystal structure is made up of layers stacking along [001]. The layers are charge neutral and are connected to each other by only weak interactions. The copper atoms adopt a square planar [CuO₄] coordination and such units are well separated from each other by corner and edge sharing to [SbO₄] building blocks. The latter polymerize to form sheets with the formula [Sb₃O₈]_∞. Sulphate groups connect to the antimony oxide sheets by corner sharing and are located at the interface of the layers. Above ∼10 K the magnetic susceptibility follows very well a Curie–Weiss law whereas below 10 K increasing deviations indicate the onset of antiferromagnetic correlations. Fitting the data in the range 10–50 K yields a Curie–Weiss temperature θ of −2.25(5) K. A sharp anomaly centered at T_C = 0.67 K in the heat capacity data indicates long-range magnetic ordering. Short range antiferromagnetic correlations well above T_C are seen in the magnetic contribution to the heat capacity and the magnetic susceptibility. These can be well described by the magnetism of a spin S = 1/2 Heisenberg chain with the nearest neighbor antiferromagnetic spin exchange interaction of J_intra = ∼2.8 K.