Structural deformations and bond length alternation in porphyrin π-cation radicals

Abstract

This review discusses the structural changes that occur when the porphyrin ring of metalloporphyrin complexes is oxidized to form a pi-cation radical species. Although various differences in core conformation between the pi-cation derivative and the unoxidized homologue have been observed, there does not appear to be a general pattern of change. A frequently observed feature in pi-cation derivatives is the appearance of an alternating bond distance pattern in the inner ring of the porphyrin consistent with a localized structure rather the delocalized structure usually seen. The pattern, first seen in cofacial dimeric structures, has now been seen in monomeric systems as well. The nature and frequency of the observation and possible explanation are given.

Electronic Structures and Reactivities of Corrole−Copper Complexes

“…In porphyrins, an alternation of shorter and longer bonds within the inner 16‐membered ring π‐network (comprised of the N, α‐C and meso ‐C) atoms is one of the criteria for oxidation of the macrocycle 29. Although not always present, it provides a strong indication that oxidation of the copper( II ) complex of octaethyltetraphenylporphyrin affects the porphyrin rather than the metal ion, resulting in a porphyrin−Cu II cation radical species.…”

DFT Study on Structural Distortion and Vibronic Coupling of Vanadyl Porphyrin Anion and Cation

“…It is clear that investigation on the redox properties of porphyrins and the structures of porphyrin radicals is crucial not only for understanding the mechanisms of biological charge-transfer processes of porphyrin prosthetic groups but also for developing metalloporphyrin-based new materials. For these reasons, the metalloporphyrin radicals have been extensively studied using various spectroscopic methods [5−8], X-ray crystallography [9,10], and theoretical calculations [11−16].…”

Not Limited to Iron: A Cobalt Heme–NO Model Facilitates N–N Coupling with External NO in the Presence of a Lewis Acid to Generate N2O

“…The Co–N–O angle of 121.3(2)° for the major disordered nitrosyl O‐atom (71 % occupancy) is similar to that of the neutral (OEP)Co(NO) precursor (at 122.70(8)°), consistent with the positive charge being remote from the Co II NO moiety and the low Δυ NO of +45 cm −1 observed in the π‐radical cation. Its identity as a π‐radical cation is further substantiated by the following observations: i) the porphyrin macrocycle is significantly distorted from planarity (Supporting Information, Figure S8 D) when compared with its neutral (OEP)Co(NO) precursor, ii) the N–C α and N–C m bond lengths within the 16‐membered porphyrin core display alternating short‐long distances (Supporting Information, Figure S8 E) characteristic of some (but not all) porphyrin π‐radical cations, and iii) adjacent porphyrin macrocycles form an almost completely overlapping π–π dimer (right of Figure ) with a mean plane separation (M.P.S.) and lateral shift of 3.16 Å and 0.21 Å, respectively.…”