Phthalocyanines Complexes in Solution

Metallophthalocyanines have been reported to be active toward the electroreduction of Most of them modified electrodes and not many 

Nevertheless the voltammetry of mixed solutions of CO2 and sulfoph-thalocyanines was informed in 1998 1998 and the results indicate that an observed at potentials more negative than the second reduction process for both, Ni and Cu tetrasulfophthalocyanine under CO2 atmosphere, and this wave depends on the concentration of carbon dioxide. This behavior can be connected with the formation of an adduct since Gangi and Durand demonstrated by pulse differential voltammetry the formation of adducts with similar macrocycles. On the other hand Co tetrasulphophthalocyanine did not present any other additional wave indicating different mechanism for different metals The reduction products of mixed solutions of CO2 and sulfonatedphthalocyanines were mostly oxalate and CO . 

For Co and Fe phthalocyanines, Grodowski and coworkers studied the electrochemical and photochemical reduction of CO2. The combined results of flash photolysis, chemical reduction, cyclic voltammetry and IR and UV-Vis spectroscopy allowed the authors to conclude that the cation radical [Co(I)Pc ] is the species responsible of the catalysis. However for Fe phthalocyanine the results are not very clear. Other contributions to the reduction mechanism with Co phthalocyanine have been report recently . The authors found a dependence of the substituents in the periphery of the ring with the mechanism of the reaction. The reaction studied by in situ potential-step chronoamperospec-troscopy (PSCAS) inferred the formation of different radical species . For Co-phthalocyanine and Co-octacyano-phthalocyanine the anion radical species is [Co(I)Pc(-3)X] (where X is the peripheric substituents of the phthalocyanine ring) 22, for Co-octabutoxy-phthalocyanine the responsible species is [Co(I)Pc (-3)X(H)] . The formation of the hydride intermediate is explained in terms of the electron donor properties of the butoxy substituents. This fact could affect the stability of the dianion species and for stabilization purposes the dianion formed needs atomic H before its coordinates to the CO2 molecule .  

From the results shown here, it is clear that depending on the metal, the formation of an adduct is feasible. However, in the majority of the cases, the species responsible for the catalysis is an anion radical complex instead the double reduced complex. For that reason in some cases oxalate is obtained as product. 

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With increasing concentration of phthalocyanine complexes in solutions, a regular increase in intensity were observed in accordance with the Bouguer-Lambert-Ber s law at the same time the position of the bands is not changed. 

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