Mechanochemical one-pot synthesis of Fe(ii) Schiff-base complexes exhibiting spin crossover

Spin crossover (SCO) compounds, can reversibly switch between low-spin and high-spin states in response to external stimuli such as temperature, pressure, or light. These transitions involve pronounced changes in magnetic, optical, and structural properties. Consequently, SCO materials are attractive candidates for molecular switches and have recently gained attention as promising solid-state barocaloric cooling materials due to their large and reversible entropy changes. In this context, SCO systems offer a promising, viable, and sustainable solution for next-generation solid-state cooling technologies. The development of environmentally benign technologies must be accompanied by equally sustainable synthetic methodologies. To enable large-scale production and practical implementation, mechanochemistry has emerged as a green approach that minimizes solvent use, reduces reaction times, and facilitates scalability. Here, we investigate the mechanochemical synthesis of three Fe(ii) Schiff-base complexes featuring N4O2 coordination spheres. Reaction parameters and conditions have been optimised, and all three complexes were successfully synthesised via a one-pot mechanochemical route. The mechanochemically obtained materials closely match those produced by conventional solution-phase methods and retain their characteristic SCO behavior. Two compounds exhibit abrupt spin transitions near room temperature, while the third shows a more gradual transition. Comprehensive characterization was performed using powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and vibrating sample magnetometry (VSM). Overall, these results highlight mechanochemistry as a viable and environmentally friendly strategy for screening and producing new promising SCO materials for barocaloric applications, providing a solid foundation for the development of sustainable solid-state refrigeration technologies.