Influence of synthesis methods on the crystal structure and third-order nonlinear optical properties of calcium-based coordination polymers

This work investigates how different synthesis methods affect the crystal structure and third-order nonlinear optical (NLO) properties of coordination polymers formed from calcium chloride dihydrate and salicylic acid. Single crystals of the compounds were prepared using silica gel diffusion (CalSal) and slow evaporation (CalSalD) methods. In both cases, high-quality crystals were obtained at an optimal concentration of 0.5 M for both the metal salt and the ligand solutions. Single-crystal X-ray diffraction revealed that CalSalD possesses a novel crystal structure, while CalSal exhibits a previously known structure. However, this is the first report of CalSal being synthesised in a gel medium. The compounds were further characterised using FTIR spectroscopy, thermal analysis, and UV–visible spectroscopy. Third-order NLO studies using the Z-scan technique demonstrated distinct nonlinear optical properties for the two compounds, underscoring their potential in photonic and optoelectronic applications.