Nanoparticles of [Fe(NH₂‐trz)₃]Br₂⋅3 H₂O (NH₂‐trz=2‐Amino‐1,2,4‐triazole) Prepared by the Reverse Micelle Technique: Influence of Particle and Coherent Domain Sizes on Spin‐Crossover Properties

Abstract

This paper describes the synthesis of iron(II) spin-crossover nanoparticles prepared by the reverse micelle technique by using the non-ionic surfactant Lauropal (Ifralan D0205) from the polyoxyethylenic family. By changing the surfactant/water ratio, the size of the particles of [Fe(NH2-trz)3]Br2.3H2O (with NH2trz=4-amino-1,2,4-triazole) can be controlled. On the macroscopic scale this complex exhibits cooperative thermal spin crossovers at 305 and 320 K. We find that when the size is reduced down to 50 nm, the spin transition becomes gradual and no hysteresis can be detected. For our data it seems that the critical size, for which the existence of a thermal hysteresis can be detected, is around 50 nm. Interestingly, the change of the particle size induces almost no change in the temperature of the thermal spin transition. A systematic determination of coherent domain size carried out on the nanoparticles by powder X-ray diffraction indicates that at approximately 30 nm individual particles consist of one coherent domain.

Crystallinity and Microstructural Versatility in the Spin‐Crossover Polymeric Material [Fe(Htrz)2(trz)](BF4)

“…The ratio between the size of the particles and the size of the coherent domains has, for example, already been investigated in SCO powders. [17] Essentially, the larger the coherent domain, the higher the crystallinity of the sample. Up to now, the morphologies of domains have not been investigated.…”

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

“…However, for fundamental studies as well as for practical applications, it still remains an experimental challenge to obtain precise control over the size and the shape of these switchable nanomaterials. Since the first descriptions in 2007 [19][20][21], a lot of works have been devoted to the influence of experimental synthesis parameters on the morphologies, sizes and properties of the [Fe(R-trz) 3 ].X 2 SCO materials: for example, parameters such as the surfactant nature [22,23], the surfactant ratio [23][24][25] and the Fe(II) concentration [26] have been considered. Despite these parameters appearing to influence the final size of the particles, no true rationalization of the synthesis has been done so far.…”

Molecules with Two Electronic Energy Levels: Study of Nanoparticles in the Atom‐Phonon Coupling Model Including a Surface Effect

“…Our results contained in Table 1 reproduce, at least qualitatively, those obtained by Forestier et al (see Table 2 of ref. [9] ). It is worth underlining that the results of Volatron et al and those of Forestier et al, which seem contradictory at first glance, are attributed in our study to the reduction of the surface effect.…”