Characterization of nickel tetrahydroxy phthalocyanine complexes and the electrocatalytic oxidation of 4-chlorophenol: Correlation of theory with experiments

This work reports on the use of nickel(II) tetrahydroxy (NiPc(OH)4) and (poly -Ni(OH)Pc(OH)4) phthalocyanine complexes as films on ordinary poly graphite electrode (OPGE) for the electrochemical oxidation of 4-chlorophenol (4-CP). The NiPc(OH)4 film was electrotransformed to Ni(OH)Pc(OH)4 film in aqueous 0.1 M NaOH solution to the ‘O–Ni–O oxo’ bridge form. The result showed that the Ni(OH)Pc(OH)4 film on OPGE was more electroactive in terms of increase in current and less catalytic in terms of potential compared to the adsorbed NiPc(OH)4 on OPGE. The reactivity of the two molecules was explained by theoretical calculations. The energies of the frontier orbitals of NiPc(OH)4, Ni(OH)Pc(OH)4 and 4-chlorophenol were calculated using density functional theory (DFT) method. The inter molecular hardness (ηη) and donor–acceptor hardness (ηDAηDA) of Ni(OH)Pc(OH)4, NiPc(OH)4, Ni(OH)Pc(OH)4/4-chlorophenol and NiPc(OH)4/4-chlorophenol were estimated. The Ni(OH)Pc(OH)4, showed stronger interaction with 4-chlorophenol than NiPc(OH)4. DFT method was also used to model IR and Raman spectrum of H2Pc(OH)4 and NiPc(OH)4.