Structural Phase Transition in 0D (3,5-DMP)₂Bi_1-SbCl₅ Metal Halides: Expression of the Lone Pair Effect and...

Low-dimensional Bi/Sb-based organic-inorganic metal halides (OIMHs) have attracted immense attention from the research community because of their structural diversity and efficient luminescence properties. Further understanding of the relationship between the structure and luminescence properties of these materials is of utmost importance for tuning the luminescence properties for various practical applications. Herein, we have synthesized two lead-free Bi/Sb-based novel OIMHs, (3,5-DMP)₂BiCl₅ and (3,5-DMP)₂SbCl₅ [(3,5-DMP) = 3,5-dimethylpiperidine], with zero-dimensional (0D) structures and crystallizing in triclinic (P$$ space group) and monoclinic (P2₁/c space group) crystal systems, respectively. Both the compounds behave as typical semiconductors with indirect optical band gaps of 3.34 and 3.36 eV for pristine Bi and Sb compounds. These compounds exhibit higher environmental and thermal stability at ambient conditions. Gradual substitution of Sb at the Bi site in (3,5-DMP)₂Bi_1-SbCl₅ resulted in the introduction of structural strain due to the significant expression of the lone pair effect, thus leading to a structural transition from the triclinic to monoclinic phase. The effect of the structural phase transition on the optical properties is also studied in (3,5-DMP)₂Bi_1-SbCl₅. This work may offer new direction and guidance for exploring various 0D hybrid metal halides and tuning the structures for improvement in the luminescence properties.