Thermal and Light-Induced Spin Transitions of Fe super(II) Complexes with 4- and 5-(Phenylazo)-2,2'-bipyridine Ligands: Intra- vs. Intermolecular Effects

• Published in: European journal of inorganic chemistry 2016-05, Vol.2016 (13-14), p.2175-2186
• Main Authors: Schmidt, Sven Olaf, Naggert, Holger, Buchholz, Axel, Brandenburg, Hannah, Bannwarth, Alexander, Plass, Winfried, Tuczek, Felix
• Format: Article
• Language: English
• Subjects: Attachment; Crossovers; Hysteresis; Ligands; Magnetic permeability; Parents; Spin transition; Stabilization
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201501252

Five new spin crossover complexes with 4- and 5-(phenylazo)-2,2-bipyridine (4-/5-PAbipy) ligands were synthesized and investigated with respect to their spin crossover (SCO) behavior. The results are compared to the thermal and light-induced spin transition properties of the parent SCO complexes [Fe(bpz) sub(2)(bipy)] (1) and [Fe(bipy) sub(2)(NCS) sub(2)] (2). [Fe(bpz) sub(2)(4-PAbipy)] (1a) undergoes a stepwise spin transition whereas [Fe(bpz) sub(2)(5-PAbipy)] (1b) exhibits a one-step transition with a 6K-wide hysteresis. For [Fe(bpz) sub(2)( super()tu-PAbipy)] (1c) the spin transition to the low-spin state is incomplete. Qualitatively similar changes of the SCO behavior are observed for the complexes [Fe(4-PAbipy) sub(2)(NCS) sub(2)] (2a) and [Fe(5-PAbipy) sub(2)(NCS) sub(2)] (2b). In comparison to the parent system 2, a strengthening of intermolecular interactions leads to a stabilization of the low-spin state. Evidence for the LIESST behavior could be obtained for all new compounds by means of magnetic susceptibility measurements as well as UV/Vis and resonance Raman spectroscopy. Attachment of a phenylazo unit in 4- and 5-position to 2,2'-bipyridine leads to characteristic changes in the spin crossover properties of Fe super(II) complexes with bipy ligands