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

Abstract

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-Cl-salEen)2]BPh4·CH3CN·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.

The role of intermolecular interactions in [Fe(X-salEen)2]ClO4 spin crossover complexes

“…We previously reported the halide (Cl, Br, I) derivatives of [Fe(3,5-halide-salEen) 2 ]X (X = ClO 4 − , BPh 4 − ) and tried to understand the origin of their interesting and unusual magnetic profiles. 34,35,37–40 For ClO 4 − salts, the bromine derivative was obtained in two polymorphic forms each with very distinct magnetic profiles, one exhibiting the thermosalient effect while changing the spin state and the other displaying abrupt spin transition at 172 K. The iodine derivative, in turn, behaved very similarly to one of the polymorphic forms of the bromine derivative and also displayed the thermosalient effect while changing the spin state. However, this behaviour was only found in the first heating/cooling cycle and after this, the magnetic profile of the compound was only gradual and matched the profile obtained for the cooling routine.…”