Anhydrous copper tellurite disulfate CuTeO(SO) featuring the coexistence of spin singlets and a long-range antiferromagnetic order.

Anhydrous copper tellurite sulfate, CuTeO(SO), has been synthesized vapor transport reactions in sealed silica glass ampoules. In measurements of magnetization , magnetic susceptibility , specific heat and X-band electron spin resonance, a long-range antiferromagnetic order at = 13 K and an - magnetic phase diagram have been established. One-third of Cu ions were found to form magnetically silent dimers. A peak in dielectric permittivity , which accompanies the Néel order, allows considering CuTeO(SO) as a magnetoelectric multiferroic material of the second type. Density functional theory calculations provided estimations of leading exchange interaction parameters.