Dicopper(II) Anthraquinophanes as Multielectron Reservoirs for Oxidation and Reduction: A Joint Experimental and Theoretical Study

Abstract

Two new dinuclear copper(II) metallacyclophanes with 1,4-disubstituted 9,10-anthraquinonebis(oxamate) bridging ligands are reported that can reversibly take and release electrons at the redox-active ligand and metal sites, respectively, to give the corresponding mono- and bis(semiquinonate and/or catecholate) Cu(II)2 species and mixed-valent Cu(II)/Cu(III) and high-valent Cu(III)2 ones. Density functional calculations allow us to give further insights on the dual ligand- and metal-based character of the redox processes in this novel family of antiferromagnetically coupled di- copper(II) anthraquinophanes. This unique ability for charge storage could be the basis for the development of new kinds of molecular spintronic devices, referred to as molecular magnetic capacitors (MMCs).

When Molecular Magnetism Meets Supramolecular Chemistry: Multifunctional and Multiresponsive Dicopper(II) Metallacyclophanes as Proof-of-Concept for Single-Molecule Spintronics and Quantum Computing Technologies?

“…In subsequent works, Cangussu and Julve, on the one hand, and Armentano and Lloret, on the other hand, provided further support of the occurrence of a spin polarization mechanism in the related oxamato-based dicopper(II) metallacyclophanes with 2,6-pyridine and 1,4-anthraquinone spacers (Scheme 1c,k) [128][129][130][131]. In each case, the ferro-or antiferromagnetic nature of the EE interaction is likely explained by the meta-or para-substitution pattern of the 2,6-pyridine and 1,4anthraquinone spacers, respectively, as illustrated in Scheme 3.…”

“…In both cases, however, the magnitude of the ferro-and antiferromagnetic coupling for these novel oxamato-based dicopper(II) metapyridenophanes and paraanthraquinophanes (J = 7.9 and −84 cm −1 , respectively) decreases when compared with their parent unsubstituted dicopper(II) meta-and paracyclophanes. This feature is likely explained by the reduction in the Lewis basicity of the amidate donor groups from the electron-poor 2,6-pyridine and 1,4-anthraquinone spacers, which causes a decrease in the metal-ligand covalency and thus of the electron spin delocalization and polarization effects on the bridging ligands, as supported by DFT calculations [128,131]. On the other hand, oxamato-based dicopper(II) metallacyclophanes with oligo-p-phenylene (OP) and oligo-p-phenylene-ethyne (OPE) spacers have been examined by Cano and Lloret as potential candidates to obtain molecular antiferromagnetic wires (Scheme 1e,f) [132][133][134].…”

Crystal Structure and Magnetic Properties of an Oxamato‐Bridged Heterobimetallic Tetranuclear [NiIICuII]2 Complex of the Rack Type

“…Since then, many other systems containing functionalized oxamate/oxamidate bridging ligands have been described, with special attention paid to their multifunctional character . Some illustrative results are the achievement of magnetic sponges, molecular magnetic electroswitches, multielectron transfer systems, molecular switches for reversible biphasic processes, Single‐Ion Magnets (SIMs), Chiral Single‐Chain Magnets (CSCMs), chiral homo‐ and heterobimetallic wheels, dynamic, chiral and luminescent porous 3D magnets, three‐dimensional (3D) proton‐conducting chiral biological metal–organic frameworks (bioMOFs), SIM hosting into magnetic MOFs and palladium(II) compounds exhibiting cytotoxic activity against leukaemia cells or catalytic activity …”

“…The objects display several molecular architectures such as metal grids, ladders, racks, polyhedral metal cages, metallodendrimers, interlocked networks, corrugated planes and so forth , . The easy functionalization of the N ‐substituted oxamate ligands together with their good coordinating properties and remarkable ability to mediate magnetic interactions between the paramagnetic centres bridged by them is at the origin of the variety of multifunctional magnetic systems obtained during recent years …”

The interplay between spin densities and magnetic superexchange interactions: case studies of mono- and trinuclear bis(oxamato)-type complexes

“…For example, we reported on the first chiral bis(oxamato)-type metalloligand [ 9 ], later on used by Ferrando-Soria et al for the design of the first chiral single-chain magnets (SCMs) [ 10 ]. Additionally, we reported how to introduce the redox-active anthrachinone functionality into bis(oxamato)-type metalloligands [ 11 ], later on adapted for the design of higher nuclear complexes that could potentially act as molecular magnetic capacitors [ 12 ], or we reported to which extent a ferrocene group in multinuclear bis(oxamato)-type complexes is suited to vary magnetic properties with respect to its oxidation state [ 13 ].…”