Thermal and chemical decomposition of di(pyrazine)silver(ii) peroxydisulfate and unusual crystal structure of a Ag(i) by-product

Abstract

High purity samples of a [Ag(pyrazine)₂]S₂O₈ complex were obtained using modified synthetic pathways. Di(pyrazine)silver(II) peroxydisulfate is sensitive to moisture forming [Ag(pyrazine)₂](S₂O₈)(H₂O) hydrate which degrades over time yielding HSO₄⁻ derivatives and releasing oxygen. One polymorphic form of pyrazinium hydrogensulfate, β–(pyrazineH⁺)(HSO₄⁻), is found among the products of chemical decomposition together with unique [Ag(I)(pyrazine)]₅(H₂O)₂(HSO₄)₂[H(SO₄)₂]. Chemical degradation of [Ag(pyrazine)₂]S₂O₈ in the presence of trace amounts of moisture can explain the very low yield of wet synthesis (11–15%). Attempts have failed to obtain a mixed valence Ag(II)/Ag(I) pyrazine complex via partial chemical reduction of the [Ag(pyrazine)₂]S₂O₈ precursor with a variety of inorganic and organic reducing agents, or via controlled thermal decomposition. Thermal degradation of [Ag(pyrazine)₂]S₂O₈ containing occluded water proceeds at T > 90 °C via evolution of O₂; simultaneous release of pyrazine and SO₃ is observed during the next stages of thermal decomposition (120–285 °C), while Ag₂SO₄ and Ag are obtained upon heating to 400–450 °C.