Phenyl conjugation effect on Fe3+/2+ formal potential of FeN4-macryclic complex

The monitoring of shifting of the redox potential of macrocyclic complexes towards anodic or cathodic regions, which acts as a mediator in many electrocatalytic events, is made possible by inserting electron donating or electron withdrawing group into their frameworks. Herein, using a template strategy, two [14]-membered N₄-macrocyclic complexes (denoted as complex A and complex B) with similar molecular cores but different phenyl moieties were prepared and characterized using multiple characterization techniques. The characterization results suggested a saddle-shaped geometry for these complexes, which might be due to the steric repulsions between the benzenoid and amidic moieties on the macrocyclic framework, as also supported by theoretical computations. Further, to investigate the electrochemical behaviors of these complexes, cyclic voltammetry was used and found that the Fe^3+/2+ redox potential was systematically shifted in anodic direction with the increment of phenyl moieties on the [14]-membered N₄-macrocyclic core. DFT calculations indicated the down-shifting in the most occupied molecular orbital due to the increased phenyl conjugation, which could be correlated with the shifting of Fe^3+/2+ redox potential. Biological evaluation of these complexes has also been carried out.