In Situ AFM Imaging of Microstructural Changes Associated with The Spin Transition in [Fe(Htrz)₂(Trz)](Bf₄) Nanoparticles.

María Manrique-Juárez,Lionel Salmon,Iurii Suleimanov,Edna Hernández,Azzedine Bousseksou,Gábor Molnár

doi:10.3390/ma9070537

Abstract

Topographic images of [Fe(Htrz)2(trz)](BF4) nanoparticles were acquired across the first-order spin transition using variable-temperature atomic force microscopy (AFM) in amplitude modulation mode. These studies revealed a complex morphology of the particles consisting of aggregates of small nanocrystals, which expand, separate and re-aggregate due to the mechanical stress during the spin-state switching events. Both reversible (prompt or slow recovery) and irreversible effects (fatigue) on the particle morphology were evidenced and correlated with the spin crossover properties.

Highlights

The change of the molecular and crystal structure in spin crossover (SCO) complexes has been extensively investigated in the past for its central role in the SCO mechanism [1,2,3]
(382 K) during the first heating while the reverse transition occurs around 348 K on cooling both cycles
We have succeeded in imaging the morphology changes associated with the phase transition in nanoparticles of the spin crossover complex [Fe(Htrz)2](BF4 ) using variable-temperature atomic force microscopy (AFM) in amplitude modulation mode

Summary

Introduction

The change of the molecular and crystal structure in spin crossover (SCO) complexes has been extensively investigated in the past for its central role in the SCO mechanism [1,2,3]. In the case of the most common FeII N6 coordination sphere, a ~10% (average) increase of the Fe-N bond lengths and a ~25% increase of the octahedron volume were systematically observed when going from the low spin (LS) to the high spin (HS) state. This change of metal-ligand bond lengths implies a drastic change of the ligand field strength; it can be considered as the driving force of the SCO at the molecular level [8]. This leads to sizeable elastic interactions between the molecules, manifested by first-order spin transitions, hysteresis, self-acceleration and other collective properties

Methods

Results

Conclusion