Spin Crossover Phenomenon in Nanocrystals and Nanoparticles of [Fe(3-Fpy)₂M(CN)₄] (MII = Ni, Pd, Pt) Two-Dimensional Coordination Polymers

The two-dimensional spin crossover (SCO) polymers [Fe(3-Fpy) 2 M(CN) 4 ] (M II = Ni( 1 ), Pd( 2 ), Pt( 3 )) were nanostructured in the form of nanocrystals and nanoparticles, and their chemical, structural, and physical characterization was carried out using different experimental methods (powder X-ray diffraction, magnetic susceptibility measurements, Mössbauer and infrared spectroscopy, transmission and scanning electronic microscopy, etc.). Surfactant-free nanocrystals of average dimensions 400 × 400 × 30 nm ( 1a, 1a*, 2a, 3a ) were synthesized from water in oil microemulsions (w/o) while nanoparticles of average size 200 × 100, 100 × 60, and 70 × 30 nm were obtained in poly(vinylpyrrolidone) (PVP) coating polymer ( 1b − 1d, 2b, 2b′, and 3b ). The spin crossover process is drastically influenced by the dimensions of the crystal/particle. Nanocrystals of 1 − 3 exhibit a quasi complete first-order spin transition centered within the interval 200−225 K, while PVP-coated nanoparticles undergo continuous second order spin transition at much lower temperatures (ca. 160 K).