Thermal induced spin crossover in Fe(PyrDer)2[Fe(CN)5NO] with PyrDer = 4-substituted pyridine derivatives
Abstract. The 2D hybrid inorganic-organic solids herein under study were prepared by intercalation of the organic molecules between neighboring layers of ferrous nitroprusside. In the formed solid, the organic molecule (4-methylpyridine, 4-acetylpyridine, 4-pyridinecarboxyaldehyde, 4-vinylpyridine) is found occupying the axial coordination sites for the iron atom linked at the equatorial N ends from the CN ligands in the pseudo-octahedral [Fe(CN)5NO] block. The resulting 3D framework of these hybrid solids is supported by intermolecular dispersive, C-H and dipole-dipole interactions, in the interlayer region, with contribution from dipolar coupling between unlinked NO and CN ligands from neighboring layers. Such intermolecular interactions modulate the coordination geometry for the iron atom. The local crystal field sensed by this last one is such that on the material cooling and then on heating, a spin crossover transition, with a pronounced thermal hysteresis is observed. Both, transition temperatures and hysteresis are determined by the nature of the intercalated molecule. The mentioned structural features and the thermal induced spin transition were studied from the refined crystal structures, magnetic measurements, Mössbauer, Raman, and IR spectra, and DSC data. These experimental studies were complemented with computational calculations for the iron atom coordination environment. To the best of our knowledge, this is the first study on the preparation and characterization of this series of hybrid 2D solids, and of their thermal induced spin crossover effect.