New CuSO4-related high-temperature polymorph of AgIISO4

Silver(II) compounds exhibit powerful oxidizing properties and strong magnetic superexchange, but most of them comprise fluoride ligands. AgSO4 is a rare fluorine-free salt of Ag(II) which found some application in organic chemistry. Here, we report a discovery of a new AgSO4 polymorph (beta). The distinct nature of the two polytypes of AgSO4 is established using powder X-ray diffraction, vibrational spectroscopy and theoretical calculations. The beta polymorph crystallizes in the monoclinic system (P2(1)/n) and shows structural similarities with CuSO4. DFT calculations indicate very small differences in the energy of the two AgSO4 polymorphs and that the relative stability of the beta polymorph should increase with temperature. The monoclinic distortion of the orthorhombic CuSO4 prototype originates from an unprecedented strong antiferromagnetic interaction between Ag sites along the unit cell diagonal.