Spin Crossover in Bipyridine Derivative Bridged One-Dimensional Iron(III) Coordination Polymer

Ryuta Ishikawa,Takeshi Noda,Takashi Okubo,Ken-Ichi Sakamoto,Satoshi Kawata,Hirofumi Yamakawa,Shunya Ueno

doi:10.3390/magnetochemistry6030029

Ryuta Ishikawa, Takeshi Noda + Show 5 more

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https://doi.org/10.3390/magnetochemistry6030029

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Abstract

Herein, the syntheses, solid-state molecular structures, and characterization of two types of one-dimensional FeIII coordination polymers showing thermally induced spin crossover are reported. The reaction of [Fe(acen)Cl] (acen2− = N,N′-ethylenebis(acetylacetonylideneaminate) with 3,3′-bpy or 4,4′-bpy (bpy = bipyridine) produced zigzag and linear one-dimensional chain complexes, [Fe(acen)(3,3′-bpy)][BPh4] (1) or [NEt3H][Fe(acen)(4,4′-bpy)][BPh4]2·0.5(4,4′-bpy) (2), respectively, as confirmed by single crystal X-ray diffraction analysis. Variable-temperature single crystal X-ray diffraction measurements, continuous-wave X-band electron paramagnetic resonance (EPR) spectra, 57Fe Mössßauer spectra, and DC magnetic susceptibility data revealed that complex 1 exhibited a gradual and complete spin crossover at a transition temperature of 212 K, while complex 2 undergoes an incomplete spin crossover even at 400 K.

Highlights

First-row transition metal complexes with a d4–d7 electron configuration can adopt two electron configurations, high spin (HS), and low spin (LS), which differ in terms of spin ground states
Subsequent reaction of [Fe(acen)]+ and 3,3 -bpy with NaBPh4 in a 1:1:1 molar ratio in MeOH afforded dark green block-shaped crystals of 1, suitable for single crystal X-ray diffraction (SCXRD) analysis
Anhydrous FeCl3, MeOH, and EtOH were purchased from Wako Pure Chemical Industries, Ltd. (Osaka, Japan). 3,3′-bpy, 4,4′-bpy, and NaBPh4 were purchased from Tokyo Chemical Industry (TCI) Co., Ltd. (Tokyo, Japan)

Summary

Introduction

First-row transition metal complexes with a d4–d7 electron configuration can adopt two electron configurations, high spin (HS), and low spin (LS), which differ in terms of spin ground states. FeIII SCO complexes have not been as extensively reported as FeII SCO complexes, mostly due to the lack of cooperativity associated with FeIII SCO complexes [27,28] To overcome this obstacle, several fascinating FeIII SCO complexes that exhibit high cooperativity have been realized by introducing relatively weak supramolecular contacts, including hydrogen bonding and π-π stacking interactions between SCO active centers in the packed crystal. Several fascinating FeIII SCO complexes that exhibit high cooperativity have been realized by introducing relatively weak supramolecular contacts, including hydrogen bonding and π-π stacking interactions between SCO active centers in the packed crystal These have been shown to result in abrupt spin transition, multistep spin transition, wide thermal hysteresis loop, and light-induced excited spin state trapping effect [27,28]. As an initial attempt to create novel FeIII SCO coordination polymers, a one-dimensional (1D) coordination polymer structure was proposed

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