Control of the thermal hysteresis of the prototypal spin-transition FeII(phen)2(NCS)2 compound via the microcrystallites environment: experiments and mechanoelastic model

International audienceMicrocrystals of Fe II (phen)2(NCS)2 (phen = 1,10-Phenanthroline), isolated by solvent-induced precipitation, were dispersed in glassy or semicrystalline matrices and subjected to thermal or chemical treatments. Interactions occurring between crystals and their macromolecular (or molecular) surroundings were revealed by drastic alteration of the first-order spin-transition afforded by this material. Depending on matrices and experimental treatments, the cooperativity in particles dispersion can be dampened, resulting in a more gradual transition or enhanced, providing a large hysteresis. The hysteresis broadening was also demonstrated with the incorporation of another first-order transition molecular material (bulk) in similar matrices. The different features associated to the in-polymers dispersions are accounted for in the framework of a mechanoelastic model based on a Monte-Carlo standard procedure