Diosmium compounds containing bis(imidazole)--quinone bridging ligands

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 51; no. 1; pp. 458 - 467
• Main Authors: Dhara, Suman, Ansari, Mohd. Asif, Schwederski, Brigitte, Filippou, Vasileios, Kaim, Wolfgang, Lahiri, Goutam Kumar
• Format: Journal Article
• Published: 08.03.2022
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d2dt00184e

The doubly deprotonated bridging ligand L 1 2− derived from 2,6-bis(2-pyridyl)-1,5-dihydro-1′,4′-benzoquinono[2′,3′- d :5′,6′- d ′]diimidazole H 2 L 1 forms coordination compounds with two bis(2,2′-bipyridine)osmium( ii ) complex fragments in anti ([ 1 ](ClO 4 ) 2 ) and syn configurations ([ 2 ](ClO 4 ) 2 ) of {(μ-L 1 )[Os(bpy) 2 ] 2 }(ClO 4 ) 2 , as evident from crystal structure analyses. Exchange of the metal-coordinating 2-pyridyl functions in the bridge through non-coordinating 4-tolyl substituents (L 1 2− → L 2 2− ) leads to [ 3 ](ClO 4 ) 2 which involves chelation of the [Os(bpy) 2 ] 2+ groups through imidazole-N and carbonyl-O atoms of the central p -quinone function. In addition to identification, the compounds were subjected to electrochemical (CV, DPV) and spectroelectrochemical (UV-vis-NIR, EPR) analyses of electron transfer, the results being supported by results from TD-DFT calculations. Essential differences between [ 1 n + ]/[ 2 n + ] and [ 3 n + ] systems were found regarding variable but mostly metal centred oxidation, the two processes separated much more for [ 3 n + ]. The first reduction is bpy ([ 1 + ], [ 2 + ]) or quinone ligand centred ([ 3 + ]). Electronic structures and electron transfer behaviour are thus highly sensitive to differences of configuration and coordination. Isomeric [ 1 2+ ] and [ 2 2+ ] and the analogous [ 3 2+ ] exhibit comparable metal-based oxidation, however, they display different bpy or quinone based first reduction processes, respectively.