Effect of Halogenation on the Optical, Electrical, and Thermal Properties of the Model Compound [Me3(i-Pr)N]2[SnBr6]

Organic-inorganic hybrid lead halides have been extensively studied due to their outstanding physical properties and diverse compositional elements. However, environmentally benign tin-based hybrids with remarkable flexibility in bandgap engineering have been less investigated. Herein, we report the successful design and synthesis of three tin-based organic-inorganic hybrid compounds through precise molecular modification: [Me₃(i-Pr)N]₂[SnBr₆] (1), [Me₂CH₂Cl(i-Pr)N]₂[SnBr₆] (2), and [Me₂CH₂Br(i-Pr-Br)N]₂[SnBr₆] (3). Building on the prototype compound 1, the introduction of heavier halogen atoms in 2 (Cl) and 3 (Br) increased the potential energy barrier required for cationic flipping, thereby achieving a rise in the phase transition temperature from 335 K (1) to 355 K (2) and 375 K (3), which also perfectly coincides with the switchable dielectric anomalies and second harmonic generation (SHG) properties. Based on the two-dimensional fingerprint analysis of the Hirshfeld surface, with the introduction of halogens, the intermolecular interactions, including not only C-H···Br-Sn but also C-X···Br-Sn (X = Cl, Br) halogen···halogen interaction, lead to the higher phase transition temperatures in 2 and 3. Furthermore, UV-NIR-vis absorption spectra revealed that the optical bandgap varies with the substitution from H to Cl to Br, yet all belong to direct bandgap semiconductors. Based on the aforementioned properties, this work provides an effective molecular design strategy for exploring and constructing tin switchable materials with temperature-adjustable characteristics.