Colossal and Reversible Barocaloric and Solvent-Caloric Effects in a TC-Adjustable Spin-Crossover Complex

Barocaloric effects (BCE) represent an appealing refrigeration technology and have attracted great interest recently. However, most BCE materials still cannot meet real-world refrigeration requirements because of their fixed phase transition temperature TC and the significantly high pressure required to drive a wide cooling temperature span. Here, we address these bottlenecks by engineering molecular channels in a SCO complex, Fe[L2]. Besides the observation of colossal and reversible BCE in Fe[L2], the designed molecular channels allow fast commutation of H2O and CH3OH, which enables the tunability of TC and creates a refrigeration window as wide as 80 K by simply altering the solvent atmosphere, as confirmed by SC-XRD, P-DSC, PXRD, Raman, and DFT calculations. Inspired by the proposed "solvent-caloric" effect, the refrigeration capacity at ambient pressure can be 9 times higher than that achieved at 100 MPa using conventional BCE methods, greatly boosting the universality for different BCE refrigeration scenarios. Our results demonstrate that the designed molecular channels in SCO complexes can influence the SCO transition properties and thereby bring forth singular caloric phenomena, offering new routes for orchestrating novel cooling materials.