Complexes with 2,2′-azobispyridine and related ‘S-frame’ bridging ligands containing the azo function

• Published in: Coordination chemistry reviews Vol. 219; pp. 463 - 488
• Main Author: Kaim, Wolfgang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2001
• Subjects: Azo compounds; Bridging ligands; Dinuclear complexes; Electronic structure; π Interaction; Azo compounds; Electronic structure; π Interaction; Bridging ligands; Dinuclear complexes
• ISSN: 0010-8545; 1873-3840
• DOI: 10.1016/S0010-8545(01)00347-2

Bridging ligands involving the azo group NN as coordinating π acceptor function can yield dinuclear complexes with unusual electronic and structural features. In particular, 2,2′-azobispyridine (abpy) as formally derived from the ubiquitous 2,2′-bipyridine ligand is now known to form a variety of complexes. The strong electronic interaction between the ligand and one or two metal centers was first noted in 1969 by Baldwin, Lever and Parish. Among the special properties of such systems are several easily accessible oxidation states, long-wavelength charge-transfer absorptions, relatively small metal–metal distances, various forms of isomerism, and the stability of radical intermediates and/or mixed-valent states.