Effect of CS2 and CO2 adsorption on the thermally-induced spin crossover in ferrous nitroprussides. Nature of the guest-host interactions

Abstract

Tuning physical and functional properties in porous solids by introducing guest species in their framework is an attractive research area in functional materials. Such a possibility is realizable in spin-crossover (SCO) materials, where an external stimulus induces the spin transition. 2D ferrous nitroprusside pillared with organic ligands forms a novel series of porous solids with SCO behavior. This study reports the effect of CS2 and CO2 adsorption on the thermally-induced SCO in 2D ferrous nitroprusside with pyrazine, pyridine, 3-fluor pyridine, 4-methyl pyridine, and 4-pyridine carboxaldehyde as pillar molecules. The adsorption of CS2 and CO2 in the framework of these five materials produces relevant changes in the temperature values where the spin transition is observed and the kinetic effects of that process. The nature of the guest-host interactions was elucidated using IR and Mössbauer spectroscopies, XRD structural analysis of the guest-host systems, and SQUID magnetic measurements. That experimental study was complemented by computational calculations, using the VASP software package, of the most stable structure for the materials with and without the presence of the guest species in the host framework. The adsorption forces for these two guest molecules in the considered solids are related to electrostatic guest-host interactions in the interlayer region. No similar study has been reported for the effect of guest species on the SCO properties of ferrous nitroprussides.