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Abstract
We examine the pressure dependence of the spin-crossover transition in [Fe(pap-5NO2)2] that occurs near room temperature. We employ a combination of high-pressure calorimetry and powder X-ray diffraction measurements, conducted both under variable-pressure and variable temperature conditions. Both methods indicate that the spin-crossover transition shifts linearly to higher temperatures with increasing pressure, while simultaneously exhibiting an increase in the width of the thermal hysteresis. We report a giant barocaloric effect, revealing isothermal entropy changes in the 70.2-79.1 J kg-1 K-1 range and adiabatic temperature changes between 19.6 and 25.9 K for a pressure change of 2 kbar. Although the effect diminishes under reversible conditions, it remains substantial, with values of 70.2 J kg-1 K-1 and 13.5 K, respectively.
Supplementary materials
Title
Supplementary Material
Description
See the Supplementary Material for the experimental and calculated XRPD patterns of [Fe(pap-5NO2)2] (Fig. S1); magnetic properties of [Fe(pap-5NO2)2] in the presence/absence of thermal grease Apiezon H (Fig. S2); evolution of the HS and LS molar fractions with pressure at 310 and 330 K (Fig. S3); unit-cell parameters pressure dependence at 320 K (Fig. S4); and a representative thermogram, showcasing the irreversibility between the first and second thermal cycle (Fig. S5).
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