Coordination compounds, decomposition mechanisms

Formulation of the detailed mechanisms of decomposition of coordination compounds are likely to remain difficult. Reliable kinetic and supporting observations are not easily obtained where several initiating reactions are possible and subsequent chemical changes may occur, before the first-formed product has left the crystallite of reactant. 

A2ido coordination compounds. Kinetic studies [23] of the isothermal (370 to 420 K) decompositions of solid hexaammine-, azidopentaammine- and cis- and trans-diazidotetraamminecobalt(III) azides included investigations of the influences of ammonia and residual products on reaction rates and were supplemented by optical microscopy and X-ray identification of the phases present. Reactions were little influenced by the composition of the coordinated cation, the nature of the salt or the crystal structure. The decompositions of all four reactants were so similar that the operation of a common reaction mechanism was indicated. This similarity of behaviour was unexpected. Decompositions of simple ionic azides (Chapter 11) are believed to be initiated by an electron promotion step or exciton formation whereas... 

From the standpoint of systems theory, the coordination (complex) compounds/ MOCPs can be considered as integrative systems, characterized by new properties, different from those of the component parts, /.e., the metallic ions and ligands. This is also valid for their thermal reactivity, either in solution or solid state. Although there are many articles which investigate the thermal behavior of these compounds in order to obtain materials with different properties, a critical analysis of the data reveals that the thermal transformations are treated relatively superficial, the mechanistic aspects being most often omitted. In the relatively rare cases when an assessment of the reactions decomposition mechanism is carried out, it is frequently limited to an evaluation of the activation parameters (activation energy and preexponential factor). A correlation of these parameters with... 

Scheme 3.2 Thermal decomposition mechanism of [FeCurealJCNOjlj coordination compound [17].

Scheme3.3 Thermal decomposition mechanism of [Co(urea)g](NOj)2 coordination compound [16].

Scheme 3.4 Thermal decomposition mechanism of [Ni(2,2 -bipy)3]Cl2 5H20 and [Ni(2,2 -bipy)3] Clj-SH O coordination compounds [158].

The main goal of the present chapter is to highlight that an efficient exploitation of coordination compounds and MOCPs as precursors of materials requires (0 a detailed knowledge of their thermoreactivity and (ii) a correlation of their decomposition mechanism with their structural and morphological peculiarities. Only so, some general... 

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