Thin films of spin-crossover coordination polymers with large thermal hysteresis loops prepared by nanoparticle spin coating

Abstract

This communication describes the synthesis of spin-crossover nanoparticles, which can disperse in various organic solvents without an excess amount of surfactants. The nanoparticles form homogeneous thin films on substrates by spin coating. The films show abrupt spin transitions with large thermal hysteresis loops.

Ambient-Temperature Spin-State Switching Achieved by Protonation of the Amino Group in [Fe(H2Bpz2)2(bipy-NH2)]

“…The n -butyronitrile solution of complex 1 ·CH 3 OH exhibited color changes from pale pink to purple by adding of CF 3 SO 3 H (Figure , inset). In the UV-vis absorption spectra, the broad-band center at ∼550 nm can be assigned to a metal-to-ligand charge transfer (MLCT) band from the metal d π -orbitals into π*-orbitals of the ligands. , The addition of CF 3 SO 3 H, with the stoichiometric ratio of 1 ·CH 3 OH/CF 3 SO 3 H, from 1:0.1, 1:0.2, 1:0.3, ..., 1:1, resulted in the growth of the broad-band center at ∼550 nm, as well as generation of a new band center at 400 nm; the latter can be assigned to the d–d transition of the LS state Fe­(II) ions. , The foregoing spectral change suggested that the protonation of amino groups resulted in partial spin state conversion to give a mixture of HS and LS state species. It then can be presumed that the protonation of amino groups, on the one hand, leads to an increase in the π-accepting ability of ligand bipy-NH 2 (as have been confirmed by the growth of the MLCT band); on the other hand, it generates strong anion-ligand electrostatic interactions between CF 3 SO 3 –NH 2 and bipy–NH 2 .…”

Spin Crossover Nanomaterials: From Fundamental Concepts to Devices

“…Up to now, the synthesis of several dozens of SCO complexes as nanoparticles or nanorods has been reported in the literature with particle sizes ranging from a few nm to several hundreds of nm. In many cases the particles could be re‐dispersed in solvents and further processed to form films, surface patterns, and nanocomposite materials . Recently, more complex architectures, such as core–shell particles, multilayer films, hybrid plasmonic, and fluorescent SCO particles have been also synthesized attesting a certain degree of maturity of the field and providing scope for the development of multifunctional nanomaterials displaying synergistic effects.…”

Pyridazine‐Supported Polymeric Cyanometallates with Spin Transitions

“…This provides molecular, 1D, 2D and 3D motives with practically any desired transition temperature, hysteresis, abruptness, and completeness of the SCO, whose spin state can be communicated by means of temperature change, pressure, light irradiation, magnetic field or guest inclusion . SCO complexes can be processed to different functional materials: nanoparticles, thin films, surface motives,, composites,, gels, etc.…”