Mechanochemical and Solvent-Mediated Approach to Polymorphic Control in a Cu₃I₃ Luminescent Cluster: Combined Functional Studies and Theoretical Calculation

This work reports the controlled synthesis of eight polymorphs in a new Cu3I3(Xantphos)2 cluster system through solvent-directed crystallization and mechanochemical methods. Four distinct phases (α, β, γ, and δ) are fully characterized, exhibiting distinct Cu3I3 core geometries (F/B-type) and ligand arrangements (cis/trans). Polymorph selectivity is controlled by solvent polarity: acetonitrile (polar) stabilizes the high-dipole α-phase, whereas dichloromethane (nonpolar) preferentially forms the δ-phase. All polymorphs exhibit similar cluster-to-ligand charge transfer (CLCT) emissions (570-610 nm), as verified by spectroscopic and computational studies. We engineer the γ-phase into a high-performance volatile organic compound (VOC) sensor via silica dispersion, achieving rapid detection of pyridine vapor with a 52 ppm detection limit and 33-fold faster response than crystalline powder. This study establishes effective strategies for polymorph control in CuI clusters and highlights their potential for sensing applications, providing fundamental insights into structure-property relationships of luminescent coordination compounds.