Unusual Solvent Dependence of a Molecule-Based FeII Macrocyclic Spin-Crossover

This work illustrates in detail the reversible hydration dehydration process of a molecule-based material, which involves a drastic change of the switchable magnetic properties of the sample. Concretely, the complex [FeL222N3O2(CN)2]center dot H2O exhibits a spin crossover (SCO) accompanied by a change of the coordination number. The dehydration and rehydration of this SCO complex was carried out and monitored by different methods, which include X-ray diffraction analysis. The corresponding samples display a thermal spin transition as well as a thermal quenching of the metastable high-spin state at low temperature. In particular it was observed that the rehydrated material exhibits a particularly high temperature of relaxation, T(TIESST), of the metastable high-spin. state. On the other hand, it was shown that this compound exhibits a uncommon correlation between T(TIESST) and the thermal SCO, as compared with other spin-crossover compounds that do not exhibit a change in coordination number.