• Stimuli Responsive Hybrid Magnets: Tuning the Photoinduced Spin-Crossover in Fe(III) Complexes Inserted into Layered Magnets
    M. Clemente-León, E. Coronado, M. López-Jordà, J.C. Waerenborgh, C. Desplanches, H. Wang, J.-F. Létard, A. Hauser and A. Tissot
    Journal of the American Chemical Society, 135 (23) (2013), p8655-8667
    DOI:10.1021/ja402674x | unige:28703 | Abstract | Article HTML | Article PDF
The insertion of a [Fe(sal2-trien)]+ complex cation into a 2D oxalate network in the presence of different solvents results in a family of hybrid magnets with coexistence of magnetic ordering and photoinduced spin-crossover (LIESST effect) in compounds [FeIII(sal2-trien)][MnIICrIII(ox)3]·CHCl3 (1·CHCl3), [FeIII(sal2-trien)][MnIICrIII(ox)3]·CHBr3 (1·CHBr3), and [FeIII(sal2-trien)][MnIICrIII(ox)3]·CH2Br2 (1·CH2Br2). The three compounds crystallize in a 2D honeycomb anionic layer formed by MnII and CrIII ions linked through oxalate ligands and a layer of [Fe(sal2-trien)]+ complexes and solvent molecules (CHCl3, CHBr3, or CH2Br2) intercalated between the 2D oxalate network. The magnetic properties and Mössbauer spectroscopy indicate that they undergo long-range ferromagnetic ordering at 5.6 K and a spin crossover of the intercalated [Fe(sal2-trien)]+ complexes at different temperatures T1/2. The three compounds present a LIESST effect with a relaxation temperature TLIESST inversely proportional to T1/2. The isostructural paramagnetic compound, [FeIII(sal2-trien)][ZnIICrIII(ox)3]·CH2Cl2 (2·CH2Cl2) was also prepared. This compound presents a partial spin crossover of the inserted FeIII complex as well as a LIESST effect. Finally, spectroscopic characterization of the FeIII doped compound [Ga0.99Fe0.01(sal2trien)][MnIICrIII(ox)3]·CH2Cl2 (3·CH2Cl2) shows a gradual and complete thermal spin crossover and a LIESST effect on the isolated FeIII complexes. This result confirms that cooperativity is not a necessary condition to observe the LIESST effect in an FeIII compound.
Photoswitching of the dielectric constant has been observed for the first time in the spin-crossover complex [Fe(L)(CN)2]·H2O (L=2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, see picture). The electrical detection of a photoinduced change in spin state could allow the use of such complexes in optical information-storage devices.



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