Refrigeration through Barocaloric Effect Using the Spin Crossover Complex {Fe[H2B(pz)2]2(bipy)}

Abstract

Spin crossover complexes have a very striking signature of a huge volume change coupled with low–high spin conversion around a critical temperature, which can be pressure tuned in a large temperature interval. Herein, the barocaloric effect is reported in the spin crossover complex {Fe[H2B(pz)2]2(bipy)} (bipy = 2,2′‐bipyridine) from theoretical and applied points of view. The experimental data reveal a giant barocaloric effect, through the isothermal entropy change (ΔST = 83 J kg−1 K−1) around T = 273 K, upon moderated hydrostatic pressure variation (ΔP = 2 kbar). The high and linear behavior in the pressure dependence of the phase transition temperature (19 K kbar−1) leads to a huge relative cooling power (RCP = 7296 J kg−1) upon ΔP = 3 kbar, which is discussed using Ericsson's cooling cycle. Theoretical results, obtained from a microscopic model, updated with the vibration modes from density functional theory (DFT) calculation, show remarkable agreement with the experimental data.