title: Multiple Bistability in Quinonoid-Bridged Diiron(II) Complexes: Influence of Bridge Symmetry on Bistable Properties.
abstract: Quinonoid bridges are well-suited for generating dinuclear assemblies that might display various bistable properties. In this contribution we present two diiron(II) complexes where the iron(II) centers are either bridged by the doubly deprotonated form of a symmetrically substituted quinonoid bridge, 2,5-bis[4-(isopropyl)anilino]-1,4-benzoquinone (H2L2') with a [O,N,O,N] donor set, or with the doubly deprotonated form of an unsymmetrically substituted quinonoid bridge, 2-[4-(isopropyl)anilino]-5-hydroxy-1,4-benzoquinone (H2L5') with a [O,O,O,N] donor set. Both complexes display temperature-induced spin crossover (SCO). The nature of the SCO is strongly dependent on the bridging ligand, with only the complex with the [O,O,O,N] donor set displaying a prominent hysteresis loop of about 55 K. Importantly, only the latter complex also shows a pronounced light-induced spin state change. Furthermore, both complexes can be oxidized to the mixed-valent iron(II)-iron(III) form, and the nature of the bridge determines the Robin and Day classification of these forms. Both complexes have been probed by a battery of electrochemical, spectroscopic, and magnetic methods, and this combined approach is used to shed light on the electronic structures of the complexes and on bistability. The results presented here thus show the potential of using the relatively new class of unsymmetrically substituted bridging quinonoid ligands for generating intriguing bistable properties and for performing site-specific magnetic switching.
authors.affiliation: Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin , Fabeckstraße 34-36, D-14195 Berlin, Germany.
authors.forename: Margarethe
authors.initials: M
authors.lastname: van der Meer
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Rechkemmer
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
authors.forename: Frauke D
authors.initials: FD
authors.lastname: Breitgoff
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
authors.forename: Raphael
authors.initials: R
authors.lastname: Marx
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
authors.forename: Petr
authors.initials: P
authors.lastname: Neugebauer
authors.affiliation: Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universität Berlin , Fabeckstraße 34-36, D-14195 Berlin, Germany.
authors.forename: Uta
authors.initials: U
authors.lastname: Frank
authors.affiliation: Institut für Physikalische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany.
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, D-14195 Berlin, Germany.
authors.forename: Biprajit
authors.initials: B
authors.lastname: Sarkar