Ligand elimination process, condensation

Badea and coworkers [179] reported an investigation on the thermal stability of a series of new complexes with azo- and azomethinic-chromophores of the type [Er(HL)2(H20)2](H0) (where H2L is o,o -dihydroxy-azobenzene, N-(2-hydroxy-1 -naphthalidene)aminophenol or N-(2-hydroxy-1 -naphthalidene)anthranilic acid). The thermal behaviour steps of complexes were compared with those of the corresponding ligands. The thermal transformations are complex processes according to TG and DTG curves, including phenol elimination, oxidative condensation and thermolysis processes. The final product of decomposition of all the complexes was Er203. 

This reaction implies proton transfer, from the previously formed ol bridge (in the transition state) to an adjacent hydroxo ligand, followed by elimination of the formed water molecule. Proton transfer is possible only if 6(OH) is negative on the dated species, and as long as 6(OH) remains negative during condensation, the oxide MOj/2 may, in theory, form. As soon as 6(OH) becomes positive, at any stage of the process, the polymer behaves as an acid and form s polyanions. 

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