Insight into the reactivity difference of two iron phthalocyanine catalysts in chromogenic reaction: DFT theoretical study

Chromogenic reaction catalyzed by metal phthalocyanine (MPc) complexes is a novel and practical method for the facile identification of phenolic pollutants. Exploring the catalytic reaction mechanism is the current concern in the investigation. In this work, tetranitro iron (II) phthalocyanine (TNFe(II)Pc) and iron (II) phthalocyanine (Fe(II)Pc) catalyzed chromogenic reactions were studied at the B3LYP level on the basis of the density functional theory (DFT) calculation. The molecular structure, atomic charge, and frontier molecular orbital of these two kinds of iron phthalocyanine complex were investigated. The calculation results demonstrate that no obvious difference for geometry structures of Fe(II)Pc and TNFe(II)Pc macrocycle can be found, while the atomic charge of Fe atom increases obviously with the four nitro groups substituted on the peripheral of macrocycle. By applying the descriptor of donor–acceptor molecular hardness, the difference of electron transfer from chlorophenol substrates to TNFe(II)Pc/Fe(II)Pc was well explained. Our investigations could provide a new strategy in designing various MPc catalysts for chromogenic identification of chlorophenol pollutants.