The local entrapment of the spin crossover complex Fe(II)-tris[2-(2′-pyridyl)benzimidazole] into the pluronic polymeric matrix (P123, PEG20–PPG70–PEG20, MW ∼ 5800) yielded the formation of magnetic nanoparticles of ∼26 nm (SCO-Np). Formation of SCO-Np was driven by the emergence of noncovalent interactions between the aromatic −NH group of the benzimidazole moieties present in Fe(II)-tris[2-(2′-pyridyl)benzimidazole] with the aliphatic ether (−O−) groups of the pluronic polymeric matrix. The nanoparticles show spin crossover behavior, two-step spin bistability, and wide magnetic hysteresis, expressed in the temperature range of 170–280 K (ΔTmax = 38 K). The neat SCO molecules, Fe(II)-tris[2-(2′-pyridyl)benzimidazole], on the contrary show only first-order spin transition and negligible hysteresis. The developed matrix-confinement approach of SCO molecules shown in this work yielded an unprecedented and significant improvement of the magnetic cooperativity compared to the neat spin crossover system, despite the decreased dimension of the magnetic domain in the nanosized architecture.

Zoppellaro G., Tucek J., Ugolotti J., Aparicio C., Malina O., Cepe K., Zboril R.: „Triggering Two-Step Spin Bistability and Large Hysteresis in Spin Crossover Nanoparticles via Molecular Nanoengineering“, Chemistry of Materials, 29(20) (2017) 8875-883. IF: 9,466. DOI: 10.1021/acs.chemmater.7b03633