Rational Control of Spin-Crossover Particle Sizes: From Nano- to Micro-Rods of [Fe(Htrz)2(trz)](BF4)

Lucie Moulet,Jean-François Létard,Nathalie Daro,Céline Etrillard,Philippe Guionneau,Arnaud Grosjean

doi:10.3390/magnetochemistry2010010

Abstract

The spin-crossover (SCO) materials based on iron (II) and triazole ligands can change their spin state under an external perturbation such as temperature, pressure or light irradiation, exhibiting notably large hysteresis in their physical properties’ transitions. If these aspects are investigated for decades, it is only in the recent years that the design of SCO particles has attracted the attention of the scientific community with increasing interest focusing on the possibility of getting wide ranges of sizes and shapes of nanoparticles. In this context, we rationalized the reverse-micellar synthesis, thanks to the scrutiny of the experimental parameters, to produce SCO particles with controlled size and shape. This approach has been performed for the reference one-dimensional (1D) polymeric spin-crossover compound of formula [Fe(Htrz)2(trz)](BF4). A synergetic effect of both time and temperature is revealed as being of paramount importance to control the final particle size. Consequently, under well-defined experimental conditions, we can now offer rod-shaped SCO particles with lengths ranging from 75 to 1000 nm.

Highlights

Among all the molecular materials, spin-crossover (SCO) complexes of Fe(II) ions represent an important class of bistable materials for which switching between the high-spin (HS) and the low-spin (LS) electronic configurations can be obtained by diverse external stimuli such temperature, pressure, light irradiation or magnetic field
Even if this procedure appears quite basic at first sight, many experimental parameters are involved such as, for example, the concentrations of the reactant, the surfactant nature and its rate, the mixing protocol, the time and the temperature of the reaction
The reaction time and temperature seem to be the ones with the most influence

Summary

Introduction

Among all the molecular materials, spin-crossover (SCO) complexes of Fe(II) ions represent an important class of bistable materials for which switching between the high-spin (HS) and the low-spin (LS) electronic configurations can be obtained by diverse external stimuli such temperature, pressure, light irradiation or magnetic field. The examination of the reverse-micelle method experimental protocol allowed us to extract two potentially predominant parameters that may impact the size of the final particles The influence of these parameters, which are the time and the temperature of the reaction, is examined for the compound [Fe(Htrz)2(trz)](BF4) (Htrz = 1H-1,2,4-triazole and trz = deprotonated triazolato ligand). This well-known compound has been chosen for its chemical stability, its large hysteresis loop between 345 K and 385 K, together with clear evidence that it is possible to get diverse particle sizes from the nano- to the micro-range [13,14,17,18,21,27,28]. We study the influence of these two major experimental parameters on the morphological aspects of the [Fe(Htrz)2(trz)](BF4) particles and on their SCO properties

Objectives

Results

Conclusion