title: A Dicobalt Complex with an Unsymmetrical Quinonoid Bridge Isolated in Three Units of Charge: A Combined Structural, (Spectro)electrochemical, Magnetic and Spectroscopic Study.
abstract: Quinonoid ligands are excellent bridges for generating redox-rich dinuclear assemblies. A large majority of these bridges are symmetrically substituted, with examples of unsymmetrically substituted quinonoid bridges being extremely rare. We present here a dicobalt complex in its various redox states with an unsymmetrically substituted quinonoid bridging ligand. Two homovalent forms and one mixed-valent form have been isolated and characterized by single crystal X-ray diffraction. The complex displays a large comproportionation constant for the mixed-valent state which is three orders of magnitude higher than that observed for the analogous complex with a symmetrically substituted bridge. Results from electrochemistry, UV/Vis/NIR spectroelectrochemistry, SQUID magnetometry, multi-frequency EPR spectroscopy and FIR spectroscopy are used to probe the electronic structures of these complexes. FIR provides direct evidence of exchange coupling. The results presented here display the advantages of using an unsymmetrically substituted bridge: site specific redox chemistry, high thermodynamic stabilization of the mixed-valent form, isolation and crystallization of various redox forms of the complex. This work represents an important step on the way to generating heterodinuclear complexes for use in cooperative catalysis.
authors.affiliation: Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstraße 34-36, 14195, Berlin, Germany.
authors.forename: Margarethe
authors.initials: M
authors.lastname: van der Meer
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Rechkemmer
authors.affiliation: Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstraße 34-36, 14195, Berlin, Germany.
authors.forename: Uta
authors.initials: U
authors.lastname: Frank
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Frauke D
authors.initials: FD
authors.lastname: Breitgoff
authors.affiliation: Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstraße 34-36, 14195, Berlin, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Hohloch
authors.affiliation: School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou, 510275, China.
authors.forename: Cheng-Yong
authors.initials: CY
authors.lastname: Su
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Petr
authors.initials: P
authors.lastname: Neugebauer
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: Raphael
authors.initials: R
authors.lastname: Marx
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
authors.forename: María
authors.initials: M
authors.lastname: Dörfel
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany. ipcjosl@ipc.uni-stuttgart.de.
authors.forename: Joris
authors.initials: J
authors.lastname: van Slageren
authors.affiliation: Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin, Fabeckstraße 34-36, 14195, Berlin, Germany. biprajit.sarkar@fu-berlin.de.
authors.forename: Biprajit
authors.initials: B
authors.lastname: Sarkar
keywords: EPR spectroscopy; cobalt; quinones; redox chemistry; spectroelectrochemistry