Stimuli Responsive Hybrid Magnets: Tuning the Photoinduced
Spin-Crossover in Fe(III) Complexes Inserted into Layered Magnets
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Abstract
The
insertion of a [Fe(sal<sub>2</sub>-trien)]<sup>+</sup> 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
[Fe<sup>III</sup>(sal<sub>2</sub>-trien)][Mn<sup>II</sup>Cr<sup>III</sup>(ox)<sub>3</sub>]·CHCl<sub>3</sub> (<b>1·CHCl</b><sub><b>3</b></sub>), [Fe<sup>III</sup>(sal<sub>2</sub>-trien)][Mn<sup>II</sup>Cr<sup>III</sup>(ox)<sub>3</sub>]·CHBr<sub>3</sub> (<b>1·CHBr</b><sub><b>3</b></sub>), and [Fe<sup>III</sup>(sal<sub>2</sub>-trien)][Mn<sup>II</sup>Cr<sup>III</sup>(ox)<sub>3</sub>]·CH<sub>2</sub>Br<sub>2</sub> (<b>1·CH</b><sub><b>2</b></sub><b>Br</b><sub><b>2</b></sub>). The three compounds crystallize in a 2D honeycomb anionic layer
formed by Mn<sup>II</sup> and Cr<sup>III</sup> ions linked through
oxalate ligands and a layer of [Fe(sal<sub>2</sub>-trien)]<sup>+</sup> complexes and solvent molecules (CHCl<sub>3</sub>, CHBr<sub>3</sub>, or CH<sub>2</sub>Br<sub>2</sub>) 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(sal<sub>2</sub>-trien)]<sup>+</sup> complexes at different temperatures <i>T</i><sub>1/2</sub>. The three compounds present a LIESST effect with a relaxation
temperature <i>T</i><sub>LIESST</sub> inversely proportional
to <i>T</i><sub>1/2</sub>. The isostructural paramagnetic
compound, [Fe<sup>III</sup>(sal<sub>2</sub>-trien)][Zn<sup>II</sup>Cr<sup>III</sup>(ox)<sub>3</sub>]·CH<sub>2</sub>Cl<sub>2</sub> (<b>2·CH</b><sub><b>2</b></sub><b>Cl</b><sub><b>2</b></sub>) was also prepared. This compound presents a
partial spin crossover of the inserted Fe<sup>III</sup> complex as
well as a LIESST effect. Finally, spectroscopic characterization of
the Fe<sup>III</sup> doped compound [Ga<sub>0.99</sub>Fe<sub>0.01</sub>(sal<sub>2</sub>trien)][Mn<sup>II</sup>Cr<sup>III</sup>(ox)<sub>3</sub>]·CH<sub>2</sub>Cl<sub>2</sub> (<b>3·CH</b><sub><b>2</b></sub><b>Cl</b><sub><b>2</b></sub>) shows a gradual
and complete thermal spin crossover and a LIESST effect on the isolated
Fe<sup>III</sup> complexes. This result confirms that cooperativity
is not a necessary condition to observe the LIESST effect in an Fe<sup>III</sup> compound
