Variable Cooperative Interactions in the Pressure and Thermally Induced Multistep Spin Transition in a Two-Dimensional Iron(II) Coordination Polymer

Abstract

Two types of experiments conducted to investigate the effect of pressure on the spin crossover (SCO) properties of the 2D Fe­(II) coordination polymer formulated {Fe­[bipy­(ttr)2]} n are reported, namely, (1) magnetic measurements performed at variable temperature and at fixed pressure and (2) visible spectroscopy at variable pressure and fixed temperature. The magnetic experiments carried out under a hydrostatic pressure constraint of 0.04, 0.08, and 0.8 GPa reveal a two-step spin transition behavior. The characteristic critical temperatures of the spin transition are shifted upward in temperature as pressure increases. The slope of the straight-line of the T c vs P plot, dT c/dP, is 775 K/GPa and 300 K/GPa, for the high temperature and the low temperature steps, respectively. These values are remarkably large and denote the extreme sensitivity of the material to the application of pressure. Indeed, the visible spectroscopic measurements performed at 293 K show that a complete spin transition is induced at pressures as low as 0.4 GPa. Moreover, the pressure-induced spin transition is reversible and shows an asymmetric hysteresis. An analysis of the cooperative interactions of the thermal- and pressure-induced spin transition in the framework of the model of elastic interactions reveals that the elastic energy of the lattice as well as the interaction parameter between the SCO centers change during the course of the spin transition. Consequently, the character of the spin transition varies from abrupt for the high temperature step to continuous for the low temperature step.

The joint effect of elasticity, interaction energy and entropy on behavior of pressure- and temperature-induced electronic bistability in a family of two-dimensional Hofman-like coordination polymers

“…36 More precisely, it denotes the change from the poorly absorbing HS state, characterized by the 5 T 2g -5 E g electronic transition in strict O h symmetry to the highly absorbing LS state, characterized by two absorption bands, corresponding to the following electronic spin transitions: 1 A 1g -1 T 1g and 1 A 1g -1 T 2g . 22,23,48 Then, from its intensity, the pressure dependences of the high spin state fraction for FpzPd and FpzNi were obtained and are shown in Fig. 5(c) and Fig.…”

Expansion of the multifunctionality in off-stoichiometric manganites using post-annealing and high pressure: physical and electrochemical studies

“…The pressure was measured using the pressure dependence of the superconducting transition temperature of high-purity lead. 47…”

Pressure-Induced Mixed States Caused by Spin-Elastic Interactions during First-Order Spin Phase Transition in Spin Crossover Compounds

“…9,34,43−45 Under pressure, the transition temperature moves to high temperature, and the steepness of the transition decreases and becomes inclined. 21,37,41,42 These features are also presented in Figure 2. The displacement of the transition and its steepness depends on the composition and pressure.…”

“…The presented data on the study of TIST in the case of a first-order phase transition demonstrate sharp transitions with a rectangular hysteresis. ,,− Under pressure, the transition temperature moves to high temperature, and the steepness of the transition decreases and becomes inclined. ,,, These features are also presented in Figure . The displacement of the transition and its steepness depends on the composition and pressure.…”

“…Among all types of spin transition (ST), the first-order spin crossover, which has a large hysteresis width and a transition temperature T 1/2 at room temperature, has the most potential for application. Since most ST cannot directly meet the actual application, it is an urgent task to study the possibility of precise regulation of ST. − The use of both various external physical stimuli, such as temperature, pressure, − ,− light, − magnetic field, , and X-ray radiation, and chemical, such as the structural modification and replacement of coordinated metal ligands, organic radicals, or metals, − can change the properties of the complex in a wide range and then regulate the ST phenomenon.…”