Room-temperature barocaloric effect in [Fe(pap 5NO2)2] spin-crossover material

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.