Crystal Structures and Spin Crossover in the Polymeric Material [Fe(Htrz)₂(trz)](BF₄) Including Coherent‐Domain Size Reduction Effects

Abstract

The high‐spin and low‐spin crystal structures of [Fe(Htrz)2(trz)](BF4) (Htrz = 1H‐1,2,4‐triazole, trz– = deprotonated triazolato ligand) were determined and refined on the basis of X‐ray diffraction data obtained from a high‐quality crystalline powder. Noteworthy differences to the previously reported structural hypothesis are obtained, which includes a revision of the space group to orthorhombic Pnma. Notably, the distinction between the positions of the Htrz and the trz– ligand along the chains reveals their respective roles in the formation of direct interchain interactions. The latter are also mediated by the anions. In addition, the pair‐distribution‐function (PDF) method was applied to investigate the potential modification of the crystal structure by a reduction of the coherent‐domain size from 50 nm to 10 nm. First, the PDF investigation confirms the validity of the crystal structures presented here. Furthermore, in a first approach, it reveals that the crystal structure description remains suitable for the whole range of coherent‐domain sizes investigated.

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

“…A Rietveld refinement was performed for each one on the basis of the atomic positions previously derived from their crystal structures. [14] These refinements first confirmed that these samples all have the same crystallographic structure. The sole difference observed between their diffractograms is the width of the Bragg peaks.…”

“…The structural investigation of [Fe(Htrz) 2 (trz)](BF 4 ) was limited until the recent determination of its crystal structure by means of X-ray diffraction. [14] The crystal packing is based on infinite [Fe(Htrz) 2 (trz)] + chains linked together through interactions mediated by the anions and hydrogen bonding. This SCO material shows the largest known volume expansion (ca.…”

Coupling Mechanical and Electrical Properties in Spin Crossover Polymer Composites

“…[35,36] If this mechanical strain is efficiently transferred to the electroactive polymer matrix a change of the polarization level of this latter should take place due to the electro-mechanical coupling. Under short-circuit conditions one would therefore expect a transient current flow during the spin transition.…”

Spin-Crossover Materials towards Microwave Radiation Switches

“…However, reaching the transition temperature, an abrupt increase of the refraction index is observed with SCO induced change of refraction index estimated at Δn/n ~ 6%. This cannot be explained via the density change related to SCO (d LS  = 1.98 g cm −3 , d HS  = 1.778 g cm −3 )37, which decreases about 11% during the transition from LS to HS states, whereas with SCO the refraction index of 1 increases.…”