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.

将[Fe(sal₂-trien)]⁺配合物阳离子嵌入不同溶剂体系下的二维草酸盐网络中，可得到一系列兼具磁有序与光诱导自旋交叉（LIESST效应）的杂化磁体，对应化合物包括[FeIII(sal₂-trien)][MnIICrIII(ox)₃]·CHCl₃（1·CHCl₃）、[FeIII(sal₂-trien)][MnIICrIII(ox)₃]·CHBr₃（1·CHBr₃）与[FeIII(sal₂-trien)][MnIICrIII(ox)₃]·CH₂Br₂（1·CH₂Br₂）。上述三种化合物均具有如下晶体结构：由二价锰（MnII）与三价铬（CrIII）离子通过草酸盐配体桥联形成的二维蜂窝状阴离子层，以及夹于该二维草酸盐网络之间的[Fe(sal₂-trien)]⁺配合物层与溶剂分子（CHCl₃、CHBr₃或CH₂Br₂）。磁性能测试与穆斯堡尔谱（Mössbauer spectroscopy）表征结果显示，这三种化合物均在5.6 K时发生长程铁磁有序，且插层的[Fe(sal₂-trien)]⁺配合物在不同的半转变温度T1/2下发生自旋交叉。三种化合物均表现出LIESST效应，其弛豫温度TLIESST与半转变温度T1/2呈反比关系。此外，本研究还制备了同构顺磁化合物[FeIII(sal₂-trien)][ZnIICrIII(ox)₃]·CH₂Cl₂（2·CH₂Cl₂），该化合物中插入的FeIII配合物发生部分自旋交叉，同时也表现出LIESST效应。最后，对FeIII掺杂化合物[Ga₀.₉₉Fe₀.₀₁(sal₂-trien)][MnIICrIII(ox)₃]·CH₂Cl₂（3·CH₂Cl₂）的光谱表征结果表明，孤立的FeIII配合物存在逐步且完全的热诱导自旋交叉，并表现出LIESST效应。该实验结果证实，在FeIII化合物中观测到LIESST效应并非必须依赖协同性。