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Using Redox-Active π Bridging Ligand as a Control Switch of Intramolecular Magnetic Interactions

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posted on 2019-04-26, 00:00 authored by Xiaozhou Ma, Elizaveta A. Suturina, Mathieu Rouzières, Mikhail Platunov, Fabrice Wilhelm, Andrei Rogalev, Rodolphe Clérac, Pierre Dechambenoit
Intramolecular magnetic interactions in the dinuclear complexes [(tpy)­Ni­(tphz)­Ni­(tpy)]n+ (n = 4, 3, and 2; tpy, terpyridine; tphz, tetrapyridophenazine) were tailored by changing the oxidation state of the pyrazine-based bridging ligand. While its neutral form mediates a weak antiferromagnetic (AF) coupling between the two S = 1 Ni­(II), its reduced form, tphz•–, promotes a remarkably large ferromagnetic exchange of +214(5) K with Ni­(II) spins. Reducing twice the bridging ligand affords weak Ni–Ni interactions, in marked contrast to the Co­(II) analogue. Those experimental results, supported by a careful examination of the involved orbitals, provide a clear understanding of the factors which govern strength and sign of the magnetic exchange through an aromatic bridging ligand, a prerequisite for the rational design of strongly coupled molecular systems and high TC molecule-based magnets.