Comparative Studies of Structures and Peroxidase-like Activities of Copper(II) and Iron(III) Complexes with an EDTA-Based Phenylene-Macrocycle and Its Acyclic Analogue Beltran-TorresMelissa Sugich-MirandaRocío Santacruz-OrtegaHisila MachiLorena InoueMotomichi Velázquez-ContrerasEnrique F. SoberanesYedith HöpflHerbert Pérez-GonzálezRefugio NavarroRosa Elena Salazar-MedinaAlex J. Sotelo MundoRogerio R. 2019 With the objective of studying the conformational and macrocyclic effects of selected metal chelates on their peroxidase activities, Cu<sup>2+</sup> and Fe<sup>3+</sup> complexes were synthesized with a macrocyclic derivative of ethylenediaminetetraacetic acid and <i>o</i>-phenylenediamine (abbreviated as edtaodH<sub>2</sub>) and its new open-chain analogue (edtabzH<sub>2</sub>). The Fe<sup>3+</sup> complex of edtaodH<sub>2</sub> has a peroxidase-like activity, whereas the complex of edtabzH<sub>2</sub> does not. The X-ray study of the former shows the formation of a dimeric molecule {[Fe­(edtaod)]<sub>2</sub>O} in which each metal with an octahedral coordination is overposed over the macrocyclic cavity, as a result of rigid macrocyclic frame, to form an Fe–O–Fe bridge; the exposure of the central metal to the environment facilitates the capture of oxygen to drive the biomimetic activity. The peroxidase-inactive Fe<sup>3+</sup> complex consists of a mononuclear complex ion [Fe­(edtabz)­(H<sub>2</sub>O)]<sup>+</sup>, the metal ion of which is suited in a distorted pentagonal bipyramid to be protected from environmental oxygen. The copper­(II) complexes, which have mononuclear structures with high thermodynamic stability compared with the iron­(III) complexes, show no peroxidase activity. The steric effects play a fundamental role in the biomimetic activity.