Correlating theory with experimental data on the effect of symmetry on the electrocatalytic behaviour of Co phthalocyanines

Abstract

An account on the synthesis of an unsymmetrically substituted cobalt phthalocyanine, 2-(4-carboxyphenoxy)-9,16,23-tri-tert-butyl-phthalocyaninato-cobalt(II) (complex 1) and its symmetric counterpart, 2,9,16,23-tetra-tert-butylphthalocyanine cobalt (II) (complex 2) is provided in this work. The complexes reported were applied in the electrooxidation of hydrazine with a glassy carbon electrode serving as a support for the electrocatalysts. In comparing the two, complex 1 produced the more favourable result with a higher peak current. A further assessment on the reactivity of the complexes was carried out using theoretical calculations. Using the density functional theory method, the electronic parameters including the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, electrophilicity (ω), electronegativity (χ), chemical softness (S) and hardness (η) were determined. The theoretical results deemed complex 1 as the more reactive structure as it had higher values for both the electronegativity and electrophilicity. The donor–acceptor hardness (ηDA) values were also found to be in alignment with the experimental results were complex 1 produced the lower oxidation potential as it had the higher ηDA value.