Thermal analysis of some cyano compounds

Abstract

The thermal behaviour of the cyano compounds NaCN, K,,Fe(CN)6.3H20, KaFe(CN)6 , K3Co(CN)6 and K2Hg(CN)4 has been investigated by using conventional thermal analysis techniques and infrared spectroscopy. The results indicate the absence of "decomplexing'" reactions for all the complexes, and "internal" redox reactions for the compounds KaFe(CN)6, K3Co(CN) 6 and K2Hg(CN)4. In all the investigated cases, the formation of cyanate and carbonate is demonstrated.In aqueous solution the cyanide ion binds to transition metal ions to form complexes of high thermodynamic stability [1][2][3]. Some of them are inert too and they readily give rise to heteropolynuclear complexes with variable stoichiometry, depending on the experimental conditions of formation [4--6]. Compounds such as Ag4Fe(CN) 6, KAg3Fe(CN)6 and Hg2Fe(CN)6 (white) alter swiftly in air, while others, such as K2Zna[Fe(CN)6]2 or KLaFe(CN)6 (white), are stable for a long time. Very different behaviour is evident as regards "internal" and/or "external" reactions, depending on the nature both of the central ion of the cyano complex (inside the anion moiety of the compound) and of the counter cations [7]. On the whole, the presence of highly polarizing cations favours the oxidative decomposition of cyanide compounds [9].Seifer [10][11][12][13][14][15] has investigated the thermal behaviour of hexacyanoferrates(II) in an inert atmosphere by using compounds where the cation moiety was constitued by "free" or at most hydrated ions. The results showed a very complicated set of endo-and excthermic effects, but the interpretation given by Seifer allows one to outline a scheme of behaviour.* Supported by the Italian MPI. Presented at "Journ6es

A thermogravimetric study of thermal dehydration of copper hexacyanoferrate by means of model-free kinetic analysis

“…Steps above 400°C show also MS signals from NO 2 and NO. Similar thermal behaviours of decomposition of hexacyanoferrates in air have been reported in other studies [29].…”