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

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

Iron(II) spin transition coordination polymers with a zigzag structure

The synthesis and characterisation of seven iron(ii) 1D chain coordination polymers with tetradentate Schiff-base like equatorial ligands and bis(4-pyridylmethyl)sulfide (bpms) as a flexible bridging axial ligand is reported. This new family of materials displays a wide spectrum of spin transition properties in the solid state ranging from gradual, abrupt, incomplete to even step-wise that have all been characterized by SQUID magnetometry. The X-ray structure analysis of two complexes at several temperatures is discussed in the frame of their spin crossover properties. © 2012 The Royal Society of Chemistry

57Fe Mössbauer spectroscopy study of a 2D spin transition coordination polymer built from a tris-1R-tetrazole ligand

[Fe{N(entz)3}2](ClO4)2 (N(entz)3 = tris(2-(1H-tetrazol-1-yl)ethyl)-amine) is a 2D FeII coordination polymer built from a tris-1-R tetrazole building block. This thermochromic FeII complex which was investigated by variable temperature 57Fe Mossbauer spectroscopy (78–300 K) displays on cooling a complete, abrupt and hysteretic spin transition at T ↑ c = 170(1) K and T ↓ c = 149(1) K. The reversibility of the spin transition over several thermal cycles was deduced from SQUID magnetometry. Differential scanning calorimetry reveals a reversible first order phase transition on cooling below room temperature, with entropy data consistent with the highly cooperative character of the spin transition

Pressure sensor via optical detection based on a 1D spin transition coordination polymer

We have investigated the suitability to use the 1D spin crossover coordination polymer [Fe(4-(2'-hydroxyethyl)-1,2,4-triazole) 3 ]I 2 ·H 2 O, known to crossover around room temperature, as a sensor via optical detection using various contact pressures up to 250MPa. A dramatic persistent colour change is observed. The experimental data, obtained by calorimetric and Mössbauer measurements, have been used for a theoretical analysis, in the framework of the Ising-like model, of the thermal and pressure induced spin state switching