Ag2S2O8 meets AgSO4: the second example of metal–ligand redox isomerism among inorganic systems

Abstract

Valence (redox) isomerism based on electron exchange between a metal and a ligand is immensely rare in purely inorganic systems, with only one documented case, that of PbS₂ which adopts two polymorphic forms corresponding to Pb(IV)(S²⁻)₂ and Pb(II)(S₂²⁻). Here we have taken advantage of metathetic reactions using salts of weakly coordinating anions and we have prepared for the first time Ag(I)₂S₂O₈, silver(I) peroxydisulphate. The title compound crystallizes in the non-centrosymmetric Cc space group with partial disorder of the anionic sublattice. Ag(I)₂S₂O₈ is a highly thermally unstable diamagnetic and colourless valence isomer of the antiferromagnetic and black Ag(II)SO₄, described by us in the past.