The Spin‐Crossover Phenomenon at the Coherent‐Domains Scale in 1D Polymeric Powders: Evidence for Structural Fatigability

Abstract

The coherent-domain morphology was determined for a crystalline powder of the 1D polymeric spin-crossover [Fe(Htrz) 2 (trz)](BF 4 ) {Htrz = 1H-1,2,4-triazole, trz = deprotonated triazolato(-) ligand} compound. This morphology is in adequacy with the crystal packing and proved that the long axis of the domain corresponds to the iron-triazole chains axis, which gives information on the crystal-growth process. Furthermore, thermal cycling clearly demonstrated that the coherent-domain [a] CNRS, Univ. Bordeaux, ICMCB, UPR 9048,

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

“…Note that this result is coherent with a recent study of the particle size vs. hysteresis width on rod particles of this compound [35] while it slightly differs from recent studies performed on particles that show larger hysteresis [28,36]. However, in the latter case, the investigated particles adopt a different morphology and lay in a smaller size range (< 16 nm).…”

“…the chosen experimental synthesis parameters, the crystalline phase is the same and corresponds to the reported one. Bragg peaks appear large, in accordance with the particle sizes, showing an average crystalline quality that is, in any case, lower than the one obtained for the powders optimized for the crystallographic studies performed for [Fe(Htrz) 2 (trz)](BF 4 ) [28,37,38]. Regarding that, it is clear that increasing T R slightly improves the crystallinity of the particles.…”

“…From the SCO properties' point of view, the different particle batches exhibit a sharp transition with the presence of a hysteresis loop as expected for this compound (Figures 2 and 3) [13,14,17,18,21,22,25,27,28,35,36]. Within the investigated (t R , T R ) values, the SCO temperatures lay indeed within the known values for this compound with T 1/2up in the range of 372-390 K and T 1/2down in the range of 351-364 K. However, some small fluctuations of the SCO temperatures can be noted along with the (t R , T R ) variations (Figure 2).…”

“…It is, however, worth noting that examination of the whole literature shows that, when comparing SCO temperatures from various studies for this compound, one has to be very careful not to overestimate the significance of small differences, and only tendency must be taken into account. It has been effectively demonstrated that small differences of a few degrees in T 1/2 may originate from many experimental parameters, including, for instance, aging of the powder or thermal history of the batch [28,35]. The aim of the present work is not to enter into a detailed description of the origins of the small discrepancy in the SCO temperatures observed in the literature for this compound but to focus on the control of the particle sizes due to the relevant choice of synthesis parameters, which is the (t R , T R ) couple.…”

“…The influence of these parameters, which are the time and the temperature of the reaction, is examined for the compound [Fe(Htrz) 2 (trz)](BF 4 ) (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]. In this contribution, we therefore study the influence of these two major experimental parameters on the morphological aspects of the [Fe(Htrz) 2 (trz)](BF 4 ) particles and on their SCO properties.…”