Micro- and nanocrystals of the iron(iii) spin-transition material [FeIII(3-MeO-SalEen)2]PF6

Abstract

The elaboration of micro- and nanometric particles of [Fe^III(3-MeO-SalEen)₂]PF₆ (H-3-MeO-SalEen being the condensation product of 3-methoxy-substituted salicylaldehyde and N-ethylethylenediamine), a spin-transition compound of molecular nature, is reported. A sudden precipitation approach, using butan-1-ol as an anti-solvent, has been shown to produce objects, whose size and shape can be modulated by varying the selected experimental parameters (temperature, solvent, and polymeric confining agent). They are in the form of either needle-shaped (7500 × 640 × 215 (a); 3500 × 350 × 125 (b); 950 × 270 × 35 nm³ (c)) or spherical particles (18 ± 3 nm (d)). The chemical nature of these molecular materials has been confirmed by Energy-dispersive X-ray and Raman spectroscopies. The room temperature powder X-ray diffractograms indicate the formation of size-reduced particles (a–d) of crystalline character, which correspond to the unperturbed phase previously reported by Hendrickson and co-workers. Magnetic, EPR and Raman investigations demonstrate the occurrence of a low-spin ↔ high-spin transition. In agreement with the literature, disappearance of the small hysteresis and decrease of the cooperative character indicate weaker interactions within size-reduced particles. Two striking features: (i) the small shift in the transition temperatures from 162 K (bulk) to 153 K (18 nm) and (ii) the very quantitative spin transformation (fraction of high-spin residues ≤5%) contrast to those usually reported for coordination networks and point towards specificity of molecular nanomaterials.