Chromium complexes porphyrin complex, formation

The adsorption of transition metal complexes by minerals is often followed by reactions which change the coordination environment around the metal ion. Thus in the adsorption of hexaamminechromium(III) and tris(ethylenediamine) chromium(III) by chlorite, illite and kaolinite, XPS showed that hydrolysis reactions occurred, leading to the formation of aqua complexes (67). In a similar manner, dehydration of hexaaraminecobalt(III) and chloropentaamminecobalt(III) adsorbed on montmorillonite led to the formation of cobalt(II) hydroxide and ammonium ions (68), the reaction being conveniently followed by the IR absorbance of the ammonium ions. Demetallation of complexes can also occur, as in the case of dehydration of tin tetra(4-pyridyl) porphyrin adsorbed on Na hectorite (69). The reaction, which was observed using UV-visible and luminescence spectroscopy, was reversible indicating that the Sn(IV) cation and porphyrin anion remained close to one another after destruction of the complex. 

Photooxidation of the metal center is not a commonly observed reaction with metalloporphyrins, but examples do exist. Both chromium(III) and manganese(III) porphyrins will undergo photooxidation reactions under appropriate conditions. Perchlorate amine-, oxides, and methyl viologen (MV " ) have been used as oxidants in these photoreactions, and photolysis of the corresponding azido complexes results in the formation of a nitrido complex where the metal ion has undergone a two-electron oxidation. Examples of such reactions are ... 

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