Effect of Geometrical Distortion on the Electronic Structure: Synthesis and Characterization of Monoradical-Coordinated Mononuclear Cu(II) Complexes

Abstract

Ligand H3Sami(Mixed(tBu)) was composed of two different compartments, a redox-active 2-aminophenol and a salen salicylidene. Both compartments were linked via a benzyl linker. The ligand reacted with CuCl2·2H2O under air in the presence of Et3N and provided the corresponding monoradical-coordinated mononuclear Cu(II) complex (1). Complex 1, in solution, reacted with air and provided complex 2 via ligand-centered oxygenation at the benzyl-CH2 position. Both complexes were characterized via IR, mass spectrometry, X-ray single-crystal diffraction, variable-temperature magnetic susceptibility, cyclic voltammograms (CVs), and UV-vis/NIR spectroscopic techniques. X-ray crystallographic analyses clearly showed almost equally distorted square planar geometry around the Cu(II) atom in both complexes. However, the bending of the radical-containing C6 ring compared to the N1-Cu1-O1 plane was different in both complexes. While complex 1 was paramagnetic and showed a ferromagnetic coupling between the d(x(2)-y(2)) magnetic orbital of Cu(II) ion and the p(z) orbital of coordinated π-radical, complex 2 was diamagnetic by experiencing a strong antiferromagnetic coupling between the two magnetic orbitals. UV-vis/NIR spectra of the complexes were dominated by charge-transfer transitions. CVs of the complexes showed two reversible one-electron oxidations and one reversible one-electron reduction. E(1/2)(ox2) and E(1/2)(red1) potentials were different in both complexes, while E(1/2)(ox1) values were almost the same and the process corresponded to the formation of phenoxyl radical. Theoretical studies were also performed to understand the magnetic coupling phenomena, and TD-DFT calculations were employed for the assignment of charge-transfer absorption bands.

Interactions of Metal-Based and Ligand-Based Electronic Spins in Neutral Tripyrrindione π Dimers

“…36, 40 In this complex, a metal-based unpaired electron formally resides in the d x2−y2 orbital of the Cu(II) center, which is orthogonal to the π orbitals of the tripyrrindione scaffold hosting the ligand-based electronic spin. This results in a ferromagnetic interaction between the unpaired electrons and in stabilization of the triplet state, as previously observed in Cu(II) complexes featuring planar radical ligands, 40–44 including porphyrin cation radicals, 36, 45 in which the magnetic orbitals are orthogonal.…”

Activation of dioxygen by copper metalloproteins and insights from model complexes

“…More remarkably, this complex was able to catalytically, and selectively, oxidize primary alcohols to aldehydes in the presence of O 2 and NaOH. Mukherjee and coworkers recently reported the synthesis of a mononuclear Cu II complex using an aminophenol-salen derivative [111]. Upon metallation of the ligand with Cu II , formation of a monoradical on the aminophenol ring occurs, yielding an isolable iminosemiquinone complex.…”

A two-dimensional mixed-valence CuII/CuIcoordination polymer constructed from 2-(pyridin-3-yl)-1H-imidazole-4,5-dicarboxylate

“…From a chemical point of view, the empirical formula of coordination polymer (I), namely [Cu II Cu I 2 (HPIDC) 2 -(H 2 O)] n , contains one Cu II and two Cu I ions, in which the presence of Cu I does not influence the conclusions about magnetism, since the outer orbital of the Cu II ions is populated by a single unpaired electron and thus associated with the magnetism. The M T value for (I) increases continuously as the temperature decreases and reaches a value of 0.404 cm 3 mol À1 K at 50 K and then slightly decreases to 0.401 cm 3 mol À1 K at 25 K, indicating a dominant ferromagnetic behaviour between the Cu II ions in (I) (Ghorai et al, 2016). As shown in Fig.…”

“…3, the M T value of (I) is 0.374 cm 3 mol À1 K at 300 K, which fits well the spin-only value of 0.375 cm 3 mol À1 K per Cu II with g = 2.0 (Zhang et al, 2015). The M T value for (I) increases continuously as the temperature decreases and reaches a value of 0.404 cm 3 mol À1 K at 50 K and then slightly decreases to 0.401 cm 3 mol À1 K at 25 K, indicating a dominant ferromagnetic behaviour between the Cu II ions in (I) (Ghorai et al, 2016). The temperature dependence of M À1 obeys the Curie-Weiss law = C/(T À ), with C = 0.37 (8) cm 3 mol À1 K and = 2.12 (5) K (see Fig.…”