Giant and Reversible Barocaloric Effect in Trinuclear Spin‐Crossover Complex Fe₃(bntrz)₆(tcnset)₆

Abstract

A giant barocaloric effect (BCE) in a molecular material Fe3(bntrz)6(tcnset)6 (FBT) is reported, where bntrz = 4‐(benzyl)‐1,2,4‐triazole and tcnset = 1,1,3,3‐tetracyano‐2‐thioethylepropenide. The crystal structure of FBT contains a trinuclear transition metal complex that undergoes an abrupt spin‐state switching between the state in which all three FeII centers are in the high‐spin (S = 2) electronic configuration and the state in which all of them are in the low‐spin (S = 0) configuration. Despite the strongly cooperative nature of the spin transition, it proceeds with a negligible hysteresis and a large volumetric change, suggesting that FBT should be a good candidate for producing a large BCE. Powder X‐ray diffraction and calorimetry reveal that the material is highly susceptible to applied pressure, as the transition temperature spans the range from 318 at ambient pressure to 383 K at 2.6 kbar. Despite the large shift in the spin‐transition temperature, its nonhysteretic character is maintained under applied pressure. Such behavior leads to a remarkably large and reversible BCE, characterized by an isothermal entropy change of 120 J kg−1 K−1 and an adiabatic temperature change of 35 K, which are among the highest reversible values reported for any caloric material thus far.

Colossal and reversible barocaloric effect in liquid-solid-transition materials n-alkanes

“…In the literature, adiabatic temperature changes were measured either by the direct method (Δ T d ), or by the quasi-direct method (reversible adiabatic temperature changes Δ T r and nonreversible adiabatic temperature changes Δ T ir ) 6 . For C 16 H 34 and C 18 H 38 , (i.e., the maximum value of |Δ T d |) increases almost linearly with pressure up to 400 MPa and is larger than that of all reported materials excluding FBT 18 , which exhibits comparable (i.e., the maximum value of |Δ T r |) values below 200 MPa. In regard to (i.e., the maximum value of |Δ S r |), C 16 H 34 and C 18 H 38 show better performance.…”

Pressure Tunable Electronic Bistability in Fe(II) Hofmann-like Two-Dimensional Coordination Polymer [Fe(Fpz)2Pt(CN)4]: A Comprehensive Experimental and Theoretical Study

“…The compressibility of the lattice parameters in the HS and LS phases was also established. To record full ( T , P ) diagrams of SCO compounds is of high importance in view of their potential implementation in fridges, taking advantage of the barocaloric effect observed in SCO materials with large entropy changes upon ST. 62 , 63 …”

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

“…The presence of hysteresis reduces the efficiency of the refrigeration cycles and recently this subject was discussed for the barocaloric effect, in spin crossover materials. [ 45 ] Also, SCO compounds show a great potential to present interesting multicaloric properties. In particular, simultaneous application of both magnetic field and pressure were discussed on SCO compounds by some of us.…”