Bifunctional Hybrid Dual‐Metal Halides: Simultaneous Tuning of Melting Point and Photoluminescence for Intelligent Anti‐Counterfeiting Applications

Hybrid metal halides exhibit extraordinary structural diversity and tunable physicochemical properties. 20 new Sb‐ and rare earth ( RE )‐based hybrid chlorides are reported here, namely the RE ( L ) n [SbCl 6 ] ( L = 1,3‐dimethylurea (DMU) and 1‐methylurea (MU) ligands). RE metals form cationic complexes with neutral ligands L , exhibiting coordination numbers of 6 or 8. In MU‐based compounds, RE ‐ligand interactions dictate melting temperatures ( T m ), enabling thermochromic anti‐counterfeiting. Ligand substitution on RE sites imposes tunable chemical pressure on [SbCl 6 ] 3− octahedra, altering their symmetry and distortion. Photoluminescence (PL) studies and theoretical calculations reveal an unusual broad dual‐band emission in DMU compounds. This originates from triplet radiative recombination within [SbCl 6 ] 3− , with Jahn‐Teller interactions splitting the triplet excited states. Emission peaks, Stokes shifts, and PL quantum yields are tunable via structural and chemical engineering. This work demonstrates the first systematic control of T m in RE hybrid halides and tunable PL in dual‐metal systems and showcases the strong potential of these materials for anti‐counterfeiting applications.