Influences of Temperature, Pressure, and Lattice Solvents on the Spin Transition Regime of the Polymeric Compound [Fe(hyetrz)₃]A₂·3H₂O (hyetrz = 4-(2‘-hydroxyethyl)-1,2,4-triazole and A^- = 3-nitrophenylsulfonate)

Abstract

[Fe(hyetrz)3](3-nitrophenylsulfonate)2·3H2O (1 · 3H 2 O), with hyetrz = 4-(2‘-hydroxyethyl)-1,2,4-triazole, has been synthesized, and its physical properties have been investigated with several techniques, including optical and Mössbauer spectroscopies, magnetism at different pressures up to ca. 9 kbar, thermogravimetry, calorimetry, and X-ray powder diffraction. At room temperature, 1 · 3H 2 O is in the low-spin (LS) state and the color is pink. As the compound is heated, the three noncoordinated water molecules are released, and the Fe2+ sites now undergo a transition from low-spin (LS, S = 0) to high-spin (HS, S = 2) states. This transformation, denoted as 1 · 3H 2 O (LS) → 1 (HS), is irreversible in a normal atmosphere and is accompanied by a change of color between pink and white. Depending on the rate of increasing temperature, it is possible to observe compound 1 in the metastable LS state. The thermal transformation from this metastable state to the stable HS state is then extremely abrupt, occurring within ca. 1 K. Compound 1 has been found to exhibit a spin transition in the low-temperature range, with T 1/2 around 100 K. This transition is cooperative around T 1/2, with a thermal hysteresis of about 10 K, but already begins immediately below room temperature. At 4 K, about 15% of the Fe2+ sites have been found to remain in the HS state. The pressure dependence of the LS ⇔ HS transition for 1 has been investigated. A pronounced effect has been observed; the transition temperature is shifted from 100 to 270 K as the pressure varies from 1 bar up to 8.9 kbar.

Synthesis, Crystal Structure, Spectroscopic and Magnetic Properties of an Unprecedented Three-Dimensional CuII Coordination Compound of 1,2-Bis(1,2,4-triazol-4-yl)ethane

“…[11b,12,13,16Ϫ20,23Ϫ29] This has been confirmed by an X-ray crystallographic study for [Cu(4-amino-1,2,4-triazole) 3 ](ClO 4 )2·0.5H 2 O. [34] Using alkyl [21,30,31,35] or hydroxyalkyl substituents [8,22,32,33] of different sizes, this triply bidentate N1,N2 bridging of the 4-substituted 1,2,4-triazole ligand has again uniquely been found. In the absence of coordinating anions, this yields linear trinuclear compounds [21,30,31,35] or infinite linear chains.…”

“…In the absence of coordinating anions, this yields linear trinuclear compounds [21,30,31,35] or infinite linear chains. [8,21,22,32,33] On the other hand, taking 4-phenyl-substituted derivatives under the same experimental conditions only led to the formation of linear trinuclear species having triple N1,N2-1,2,4-triazole bridges. [36] Surprisingly, with 4,4Ј-bis(1,2,4-triazole) (abbreviated as btr) this N1,N2 bridging coordination mode has not yet been observed.…”

Solution and solid state properties of Fe(III) complexes bearing N-ethyl-N-(2-aminoethyl)salicylaldiminate ligands

“…This included the discovery of several new examples of SCO compounds [3,[9][10][11], the explanation of different types of SCO profiles [4,12] and the modification of SCO compounds to increase cooperativity and to direct their application into materials science [13]. Scientists have developed SCO networks [14][15][16], frameworks [17][18][19], gels [20][21][22], liquid crystals [23][24][25], nanoparticles and nanocrystals [26][27][28][29], nanowires [30], thin films [31][32][33] and have also applied patterning techniques to fabricate SCO devices [34]. Among complexes displaying SCO, [Fe(salEen) 2 ] + derivatives (salEen = N-ethyl-N-(2-aminoethyl)salicylaldiminate) are known to undergo thermal SCO sensitive to unit cell contents and supramolecular packing in the crystal [35].…”

Counterion Effect on the Spin‐Transition Properties of the Cation [Fe(btzx)3]2+ (btzx=m‐Xylylenebis(tetrazole))

“…Triazole-based materials have been intensively studied, and the influence of the different chemical "pieces" constituting the compound on the spin-transition properties has been thoroughly investigated. [37][38][39][40][41][42] In the case of spherical counterions, the smallest ion leads to the highest transition temperature. [23] The greater electrostatic pressure generated on the cation by the smaller anions, stabilises the LS state over the HS state.…”