Stimuli Responsive Hybrid Magnets: Tuning the Photoinduced Spin-Crossover in Fe(III) Complexes Inserted into Layered Magnets

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.