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

Piotr J. Leszczyński, Armand Budzianowski, Łukasz Dobrzycki, Michał K. Cyrański, Mariana Derzsia and Wojciech Grochala

Dalton Trans., 2012,41, 396-402 DOI: 10.1039/C1DT10744E

Unusual crystal structure of a Ag(I)

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 reductionof the [Ag(pyrazine)2]S2O8 precursor with a variety of inorganic and organic reducing agents, orvia 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 andSO3 is observed during the next stages of thermal decomposition (120–285°C), while Ag2SOand Ag are obtained upon heating to 400–450°C.

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