Structural and magnetic studies on three new mixed metal copper(ii) selenites and tellurites

Abstract

Three new transition metal copper(II) selenites or tellurites, namely, CdCu(SeO₃)₂ (1), HgCu(SeO₃)₂ (2), and Hg₂Cu₃(Te₃O₈)₂ (3), have been obtained by conventional hydrothermal reactions of CdO (or Hg₂Cl₂), CuO and SeO₂ (or TeO₂). Compounds 1 and 2 are isostructural and crystallize in P2₁/c. Their structures feature a 3D anionic framework of Cu(SeO₃)₂²⁻ with 1D channels of eight-membered rings (MRs) along the c-axis and a-axis, respectively, which are filled by Cd²⁺ or Hg²⁺ cations. Compound 3 crystallizes in a tetragonal system of space group P42₁2. Its structure is characterized by a [Cu₃(Te₃O₈)₂]²⁻ honeycomb layer composed of [Te₃O₈]⁴⁻ anions interconnected by Cu²⁺ ions with 1D channels of 8-MRs along the c-axis. TOPOS analysis indicates that the copper(II) tellurite layer exhibits a new topological structure with a Schläfli symbol of {4⁶·8⁹}²{4⁶}³. The above anionic copper(II) tellurite layers are further linked by dumbbell Hg₂²⁺ cations to form a novel 3D framework. Magnetic measurements based on magnetic susceptibility and heat capacity indicate that compounds 1 and 2 show a spin-singlet ground state with a spin gap based on the [Cu₂O₈]¹²⁻ dimeric model, whereas compound 3 exhibits a 2D spin-system with an antiferromagnetic ordering around 25 K correlated with its honeycomb [Cu₃(Te₃O₈)₂]²⁻ layer. Furthermore, crystalline structures, thermal stabilities, IR spectra and UV-Vis diffuse reflectance spectra have also been studied.