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

摘要

High purity samples of a [Ag(pyrazine) _2]S _2O _8 complex were obtained using modified synthetic pathways. Di(pyrazine)silver(ii) peroxydisulfate is sensitive to moisture forming [Ag(pyrazine) _2](S _2O _8)(H _2O) hydrate which degrades over time yielding HSO _4 ~- derivatives and releasing oxygen. One polymorphic form of pyrazinium hydrogensulfate, β-(pyrazineH ~+)(HSO _4 ~-), is found among the products of chemical decomposition together with unique [Ag(i)(pyrazine)] _5(H _2O) _2(HSO _4) _2[H(SO _4) _2]. Chemical degradation of [Ag(pyrazine) _2]S _2O _8 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]S _2O _8 precursor with a variety of inorganic and organic reducing agents, or via controlled thermal decomposition. Thermal degradation of [Ag(pyrazine) _2]S _2O _8 containing occluded water proceeds at T > 90 °C via evolution of O _2; simultaneous release of pyrazine and SO _3 is observed during the next stages of thermal decomposition (120-285 °C), while Ag _2SO _4 and Ag are obtained upon heating to 400-450 °C.