Fe(II) Spin Transition Materials Including an Amino-Ester 1,2,4-Triazole Derivative, Operating at, below, and above Room Temperature

Marinela M Dîrtu; Anil D Naik; Aurelian Rotaru; Leonard Spinu; Dirk Poelman; Yann Garcia

doi:10.1021/acs.inorgchem.6b00015

Fe(II) Spin Transition Materials Including an Amino-Ester 1,2,4-Triazole Derivative, Operating at, below, and above Room Temperature

Inorg Chem. 2016 May 2;55(9):4278-95. doi: 10.1021/acs.inorgchem.6b00015. Epub 2016 Apr 22.

Authors

Marinela M Dîrtu¹, Anil D Naik¹, Aurelian Rotaru², Leonard Spinu³, Dirk Poelman⁴, Yann Garcia¹

Affiliations

¹ Institute of Condensed Matter and Nanosciences, Molecules, Solids and Reactivity, Université catholique de Louvain , Place L. Pasteur 1, 1348 Louvain-la-Neuve, Belgium.
² Department of Electrical Engineering and Computer Science & MANSiD Research Center, "Stefan cel Mare" University , University Street, 13, Suceava 720229 Romania.
³ Advanced Materials Research Institute, Department of Physics, University of New Orleans (UNO) , New Orleans, Louisiana 70148 United States.
⁴ Lumilab Department Solid State Sciences, Ghent University , Krijgslaan 281, S1, B-9000 Gent, Belgium.

PMID: 27104913
DOI: 10.1021/acs.inorgchem.6b00015

Abstract

A new family of one-dimensional Fe(II) 1,2,4-triazole spin transition coordination polymers for which a modification of anion and crystallization solvent can tune the switching temperature over a wide range, including the room temperature region, is reported. This series of materials was prepared as powders after reaction of ethyl-4H-1,2,4-triazol-4-yl-acetate (αEtGlytrz) with an iron salt from a MeOH/H2O medium affording: [Fe(αEtGlytrz)3](ClO4)2 (1); [Fe(αEtGlytrz)3](ClO4)2·CH3OH (2); [Fe(αEtGlytrz)3](NO3)2·H2O (3); [Fe(αEtGlytrz)3](NO3)2 (4); [Fe(αEtGlytrz)3](BF4)2·0.5H2O (5); [Fe(αEtGlytrz)3](BF4)2 (6); and [Fe(αEtGlytrz)3](CF3SO3)2·2H2O (7). Their spin transition properties were investigated by (57)Fe Mossbauer spectroscopy, superconducting quantum interference device (SQUID) magnetometry, and differential scanning calorimetry (DSC). The temperature dependence of the high-spin molar fraction derived from (57)Fe Mössbauer spectroscopy in 1 reveals an abrupt single step transition between low-spin and high-spin states with a hysteresis loop of width 5 K (Tc(↑) = 296 K and Tc(↓) = 291 K). The properties drastically change with modification of anion and/or lattice solvent. The transition temperatures, deduced by SQUID magnetometry, shift to Tc(↑) = 273 K and Tc(↓) = 263 K for (2), Tc(↑) = 353 K and Tc(↓) = 333 K for (3), Tc(↑) = 338 K and Tc(↓) = 278 K for (4), T(↑) = 320 K and T(↓) = 305 K for (5), Tc(↑) = 106 K and Tc(↓) = 92 K for (6), and T(↑) = 325 K and T(↓) = 322 K for (7). Annealing experiments of 3 lead to a change of the morphology, texture, and magnetic properties of the sample. A dehydration/rehydration process associated with a spin state change was analyzed by a mean-field macroscopic master equation using a two-level Hamiltonian Ising-like model for 3. A new structural-property relationship was also identified for this series of materials [Fe(αEtGlytrz)3](anion)2·nSolvent based on Mössbauer and DSC measurements. The entropy gap associated with the spin transition and the volume of the inserted counteranion shows a linear trend, with decrease in entropy with increasing the size of the counteranion. The first materials of this substance class to display a complete spin transition in both spin states are also presented.