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投稿者: Yuma Morimoto

Article

Tuning Spin–Spin Coupling in Quinonoid-Bridged Dicopper(II) Complexes through Rational Bridge Variation

† Institut für Chemie und Biochemie, Freie Universität Berlin, Fabeckstrasse 34-36, D-14195, Berlin, Germany
‡ Department Chemie und Pharmazie, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstrasse 1, 91058, Erlangen, Germany
§ Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569, Stuttgart,Germany
 Lehn Institute of Functional Materials, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, China
Inorg. Chem., Article ASAP
DOI: 10.1021/ic400955c
Publication Date (Web): September 6, 2013
Copyright © 2013 American Chemical Society

Abstract

Abstract Image
Bridged metal complexes [{Cu(tmpa)}2(μ-L1–2H)](ClO4)2 (1), [{Cu(tmpa)}2(μ-L2–2H)](ClO4)2 (2), [{Cu(tmpa)}2(μ-L3–2H)](BPh4)2 (3), and [{Cu(tmpa)}2(μ-L4–2H)](ClO4)2 (4) (tmpa = tris(2-pyridylmethyl)amine, L1 = chloranilic acid, L2 = 2,5-dihydroxy-1,4-benzoquinone, L3 = (2,5-di-[2-(methoxy)-anilino]-1,4-benzoquinone, L4 = azophenine) were synthesized from copper(II) salts, tmpa, and the bridging quinonoid ligands in the presence of a base. X-ray structural characterization of the complexes showed a distorted octahedral environment around the copper(II) centers for the complexes 1–3, the donors being the nitrogen atoms of tmpa, and the nitrogen or oxygen donors of the bridging quinones. In contrast, the copper(II) centers in 4 display a distorted square-pyramidal coordination, where one of the pyridine arms of each tmpa remains uncoordinated. Bond-length analyses within the bridging ligand exhibit localization of the double bonds inside the bridge for 1–3. In contrast, complete delocalization of double bonds within the bridging ligand is observed for 4. Temperature-dependent magnetic susceptibility measurements on the complexes reveal an antiferromagnetic coupling between the copper(II) ions. The strength of antiferromagnetic coupling was observed to depend on the energy of the HOMO of the bridging quinone ligands, with exchange coupling constants J in the range between −23.2 and −0.6 cm–1 and the strength of antiferromagnetic coupling of 4 > 3 > 2 > 1. Broken-symmetry density functional theory calculations (DFT) revealed that the orientation of magnetic orbitals in 1and 2 is different than that in 3 and 4, and this results in two different exchange pathways. These results demonstrate how bridge-mediated spin–spin coupling in quinone-bridged metal complexes can be strongly tuned by a rational design of the bridging ligand employing the [O] for [NR] isoelectronic analogy.

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