Cadmium copper selenite chloride, CdCu2(SeO3)2Cl2, an insulating spin gap system

Highlights: • New compound, cadmium copper selenite chloride, CdCu₂(SeO₃)₂Cl₂, has been synthesized. • The copper polyhedra form magnetically isolated dimers with a spin gap 38.7±0.8meV. • Kubelka - Munk estimation gives value of an electron band gap 2.82±0.02eV. Novel copper cadmium selenite chloride has been synthesized via vapor transport reaction as well as by solid state process. CdCu₂(SeO₃)₂Cl₂ crystallizes in a monoclinic space group I2/a with cell constants a=7.8057(3) Å, b=9.6036(4) Å, c=10.7817(5) Å and β=102.362(4)°, Z=4. Its crystal structure can be described as an open channel three-dimensional framework, formed by [CdO₂Cl₄] and [CuO₄Cl₂] polyhedra interconnected by pyramidal SeO₃ groups. The copper polyhedra form magnetically isolated dimers with a spin gap Δ=38.7±0.8meV, as defined from magnetic susceptibility measurements. The electron band gap estimated by diffuse reflectance method E_g=2.82±0.02eV is in agreement with the yellow-green color of the substance. Density functional theory provides the values of electron (2.4eV) and spin (36.6meV) gaps consistent with experimental observations.