Thermally Induced FeII Spin Crossover Hybrid Complex Incorporating Para-Sulfocinnamic Acid

Anion-Driven Light-Induced Spin Change (AD-LISC) enables multifunctional materials to switch magnetic states with light, enhancing potential applications in data storage, sensors, and molecular electronics, by improving spin state control by integrating photoactive anions. In this study, we report the synthesis and characterization of new mononuclear Fe^II coordination complex, [Fe(3-bpp)₂](psca)₂ ⋅ solvent (1 ⋅ X) as determined by single-crystal X-ray diffraction. The structure incorporates para-sulfocinnamic acid (psca), non-coordinated anion as well as unidentified disorded solvent molecules (X). TGA analysis confirmed the presence of 2.5 water molecules as solvent in the crystal lattice after exposure to air. Moreover, ⁵⁷Fe Mössbauer spectroscopy and magnetic susceptibility measurements (SQUID) reveals a mixture of high-spin and low-spin states in 1 ⋅ 2.5H₂O, with a predominance of low-spin sites at room temperature. The desolvated form 1 shows a gradual spin crossover behaviour centred around the room temperature region. Additionally, single crystal X-ray diffraction, evaluated according to Schmidt's criteria for [2+2] photodimerization, revealed that 1 ⋅ X does not satisfy the spatial requirements for photodimerization; accordingly, no colour change was noticed upon UV light exposure.