Spin Transition Sensors Based on β-Amino-Acid 1,2,4-Triazole Derivative

Marinela M Dîrtu,J Marchand-Brynaert,France Schmit,Yann Garcia,Aurelian Rotaru,Anil D Naik

doi:10.3390/ijms12085339

Abstract

A β-aminoacid ester was successfully derivatized to yield to 4H-1,2-4-triazol-4-yl-propionate (βAlatrz) which served as a neutral bidentate ligand in the 1D coordination polymer [Fe(βAlatrz)3](CF3SO3)2·0.5H2O (1·0.5H2O). The temperature dependence of the high-spin molar fraction derived from 57Fe Mossbauer spectroscopy recorded on cooling below room temperature reveals an exceptionally abrupt single step transition between high-spin and low-spin states with a hysteresis loop of width 4 K (Tc↑ = 232 K and Tc↓ = 228 K) in agreement with magnetic susceptibility measurements. The material presents striking reversible thermochromism from white, at room temperature, to pink on quench cooling to liquid nitrogen, and acts as an alert towards temperature variations. The phase transition is of first order, as determined by differential scanning calorimetry, with transition temperatures matching the ones determined by SQUID and Mössbauer spectroscopy. The freshly prepared sample of 1·0.5H2O, dried in air, was subjected to annealing at 390 K, and the obtained white compound [Fe(βAlatrz)3](CF3SO3)2 (1) was found to exhibit a similar spin transition curve however much temperature was increased by (Tc↑ = 252 K and Tc↓ = 248 K). The removal of lattice water molecules from 1·0.5H2O is not accompanied by a change of the morphology and of the space group, and the chain character is preserved. However, an internal pressure effect stabilizing the low-spin state is evidenced.

Highlights

Bistable molecular systems, materials exhibiting captivating scenario of spin crossover (SCO) [1], are versatile switchable units in the thriving field of molecular electronics [2]
The synthesis time is relatively longer than the synthesis of previous ligands and the final product had to be purified by “flash” column chromatography
A 1D coordination polymer was obtained as a white powder by reaction of the corresponding FeII

Summary

Introduction

Materials exhibiting captivating scenario of spin crossover (SCO) [1], are versatile switchable units in the thriving field of molecular electronics [2]. A SCO compound meeting display and data processing requirements would, in addition, have a good shelf life and an detectable optical response, and would ideally operate near room temperature [6,7]. Applications envisioned in these fields largely depend on molecular conformations precursors adopt during the coordination process which directs structure-properties relationships. As a continuation of our work on amino acid functionalization, [12] ethyl-4H-1,2,4-triazol-4-yl-acetate was used as a prospective precursor for magnetic sensors [13]. Molecular structure of (a) ethyl 4H-1,2,4-triazol-4-yl-propionate ( Alatrz); and (b) complex [Fe( Alatrz)3]2+

Results and Discussion

SQUID Magnetometry

Differential Scanning Calorimetry

Chemicals

Physical Measurements

Concluding Remarks