Reversible Single-Crystal-to-Single-Crystal Transformations in a salEen Fe(III) Spin Crossover Sponge

The storage of guest molecules in nonporous single crystals is an important development in the field of smart materials. We describe the synthesis and characterization of the new spin crossover Fe(III) compound [Fe(3-Br,5-ClsalEen)2]BPh4 center dot CH3CN center dot H2O (salEen = N-ethyl-N-(2-aminoethyl)salicylaldiminate) and its reversible single-crystal-to-single-crystal transformation upon desolvation and resolvation of the crystals. This process affects the magnetic behavior of the compound while the desolvation of single crystals is made in several steps. The magnetic profiles of the cooling/heating routines are never coincident until the compound reaches the high-spin state after complete desolvation of the single crystals. This is further reflected in temperature-dependent Raman profiles where desolvated and high spin state spectra match after the temperature cycle. Kinetic studies gave insights on the desolvation/ resolvation dynamics with the new Fe(III) compound behaving as a spin crossover sponge.