Micro- and nanocrystals of the iron(iii) spin-transition material [FeIII(3-MeO-SalEen)2]PF6
Résumé
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 crystalline objects, whose size and shape can be modulated by varying the selected experimental parameters (temperature, solvent, polymeric confining agent). They are in the form of either needle-shaped (7500x640x215 (a); 3500x350x125 (b); 950x270 x35 nm 3 (c)) or spherical particles (18 ± 3 nm (d)). The chemical nature of these molecular materials has been confirmed by EDS and Raman spectroscopies. The RT 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 coworkers. Magnetic, EPR and Raman investigations demonstrate the occurrence of a low-spin high-spin transition. In agreement with literature, disappearence of the weak hysteresis and decrease of 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 HS residues 5%) contrast to those usually reported for coordination networks and point towards specificity of molecular nanomaterials.
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