The Low-Pressure-Driven Barocaloric Effect at Room Temperature in the Two-Dimensional Hofmann-Type Coordination Polymer {Fe II (pdz) ₂ [Pt(CN) ₄ ]}

The two-dimensional Hofmann-type coordination polymer {Fe(pdz) 2 Pt(CN) 4 } (pdz = pyridazine) was investigated under ambient and applied hydrostatic pressure using magnetic susceptibility, Raman, infrared (IR), and X-ray diffraction techniques. The spin transition of the compound is characterized by enhancing hysteresis width and abruptness with increasing pressure. This unconventional behavior is attributed to an elevated ratio of interaction energy (Γ) to elastic energy (Δ elastic ) within the elastic interaction framework. Pressure-dependent Raman and IR spectroscopies revealed an inhomogeneous pressure distribution within the framework, manifesting as differential responses in vibrational modes. The barocaloric performance, evaluated via high-pressure differential scanning calorimetry, yields a large isobaric entropy change of 115 J kg –1 K –1, an isothermal entropy change of 58 J kg –1 K –1, and an adiabatic temperature change of 14 K at 1 kbar, positioning the material as a competitive candidate among spin-transition compounds for room-temperature solid-state cooling applications.