Low-dimensional compounds containing cyano groups. III: a structural,spectral and thermal study of dicyanoargentates containing 4-methylpyridine

The complexes Cu^II(4-Mepy)₂Ag₂(CN)₄ (1) and Cu^II(4-Mepy)₃Ag_2–x Cu^I _x (CN)₄ (2) (4-Mepy = 4-methylpyridine, x = 0.07) were isolated from a reaction mixture containing 4-Mepy, KAg(CN)₂] and CuSO₄. I.r. spectra indicated the presence of both monodentate and bridging cyano groups in (1) and (2), confirmed by their known structures, both consisting of neutral zigzag chains. Two neighbouring chains in (2) are linked by argentophilic interactions between Ag atoms of bridging dicyanoargentate anions, whose positions are partly occupied by Cu^I ions to the extent of 7 at.%, with an unusually short Ag...Ag distance of 2.9264(5) Å, to form a ladder. Individual ladders are tied together as sheets by weaker argentophilic interactions between silver atoms of interdigitated monodentate dicyanoargentate anions of two different ladders. Thermal decomposition of (2) occurs in two separated stages. In the first stage, three 4-Mepy molecules are liberated from the formula unit and, in the second stage, redox decomposition of the cyano groups occurs. The thermal decomposition of (1) is more complicated as the release of two 4-Mepy molecules is overlapped by decomposition of one cyano group followed by further redox decomposition of the remaining cyano groups.