title: Spin Crossover and Valence Tautomerism in Neutral Homoleptic Iron Complexes of Bis(pyridylimino)isoindolines.
abstract: Homoleptic iron complexes of six bis(pyridylimino)isoindoline (bpi) ligands with different substituents (H, Me, Et, tBu, OMe, NMe2) at the 4-positions of the pyridine moieties have been prepared and studied with regard to temperature-dependent spin and redox states by a combination of (57)Fe Mössbauer spectroscopy, SQUID magnetometry, single-crystal X-ray diffraction analysis, X-band EPR, and (1)H NMR spectroscopy. While the H-, methyl-, and ethyl-substituted complexes remain in a pure high-spin state irrespective of the temperature, the 4-tert-butyl-substituted derivative shows spin-crossover behavior. The methoxy- and dimethylamino-substituted compounds were found to easily undergo oxidation. In the crystalline state, valence tautomeric behavior was observed for the methoxy derivative as a thermally activated charge-transfer transition, accompanied by a spin crossover above 200 K. The valence tautomerism leads to a chelate with one of the bpi ligands as a dianion radical L(2-·) and with an effective spin of S=2.
authors.affiliation: Institut für Anorganische und Analytische Chemie, TU Braunschweig, Hagenring 30, 38106 Braunschweig (Germany) http://www.tu-braunschweig.de/iaac/personal/broering.
authors.forename: Anne
authors.initials: A
authors.lastname: Scheja
authors.affiliation: Institut für Anorganische und Analytische Chemie, TU Braunschweig, Hagenring 30, 38106 Braunschweig (Germany) http://www.tu-braunschweig.de/iaac/personal/broering.
authors.forename: Dirk
authors.initials: D
authors.lastname: Baabe
authors.affiliation: Institut für Physik der Kondensierten Materie, TU Braunschweig, Mendelssohnstraße 2-3, 38106 Braunschweig (Germany).
authors.forename: Dirk
authors.initials: D
authors.lastname: Menzel
authors.affiliation: Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerweinstraße, 35032 Marburg (Germany).
authors.forename: Clemens
authors.initials: C
authors.lastname: Pietzonka
authors.affiliation: Institut für Anorganische und Analytische Chemie, TU Braunschweig, Hagenring 30, 38106 Braunschweig (Germany) http://www.tu-braunschweig.de/iaac/personal/broering.
authors.forename: Peter
authors.initials: P
authors.lastname: Schweyen
authors.affiliation: Institut für Anorganische und Analytische Chemie, TU Braunschweig, Hagenring 30, 38106 Braunschweig (Germany) http://www.tu-braunschweig.de/iaac/personal/broering. m.broering@tu-bs.de.
authors.forename: Martin
authors.initials: M
authors.lastname: Bröring
keywords: N ligands; bis(pyridylimino)isoindoline; iron; spin crossover; valence tautomerism