Thermal and spectroscopic studies on a double-salt-type pyridine–silver perchlorate complex having κ1-O coordinated perchlorate ions

A simple synthetic method was developed to prepare 4[Agpy2ClO4]·[Agpy4]ClO4 in a low-temperature decomposition process of [Agpy4]ClO4. A detailed IR, Raman and far-IR study including factor group analysis has been performed, and the assignation of bands is given. The compound decomposes quickly with a multistep ligand loss process with the formation of [Agpy2]ClO4 and AgClO4 intermediates and AgCl as an end product around ~ 85, ~ 350 and 450 °C, respectively. During the first decomposition step, a small fraction of the ligands is lost in a redox reaction: perchlorate oxidizes the pyridine, forming carbon, carbon dioxide, water and NO, while it itself is reduced into AgCl. In the next step, when AgClO4 forms after complete ligand loss and reacts with the carbon formed in the degradation of pyridine at lower temperatures and produces NO, CO2 and H2O. This reaction becomes possible because the AgCl formed in the redox reactions makes a eutectic melt with AgClO4 in situ, which is a favorable medium for the carbon oxidation reaction. AgCl is known to reduce the temperature of decomposition of AgClO4, in which process forms AgCl as well as O2 and so is an autocatalytic process. The loss and degradation of pyridine ligand are endothermic; the redox reactions including carbon oxidation and AgClO4 decomposition into AgCl and O2 are exothermic. The amount of absorbed/evolved heats corresponding to these processes was determined by DSC both under N2 and O2 atmospheres.