Synthesis and zero-dimensional structure of a new lead-free organic-inorganic[(C2H5)4N]3Bi2I9 compound: a promising material for optoelectronic devices.

A new lead-free organic-inorganic hybrid compound based on Bi(iii), namely tris(tetraethylammonium)nona-idodibismuthate(iii), [(C2H5)4N]3Bi2I9, has been successfully synthesized using a slow evaporation technique. The compound was characterized by single-crystal X-ray diffraction, Hirshfeld surface analysis, thermal analyses (DSC and TGA-DTA) and impedance spectroscopy. At room temperature, it crystallizes in the triclinic system with P1 space group. The crystal structure consists of discrete anionic dimers [Bi2I9]3-. These dimers are formed by two BiI6 octahedra sharing a triangular face. Charge balance is ensured by three [(C2H5)4N]+ cations. The organic and inorganic components are connected through C-H⋯I hydrogen bonds. These interactions lead to the formation of a stable three-dimensional supramolecular network. Hirshfeld surface analysis shows that H⋯I/I⋯H and H⋯H interactions dominate the intermolecular contacts. Weak I⋯I interactions also contribute to the structural cohesion. Thermal analyses (DSC and TGA/DTA) reveal a reversible phase transition in the temperature range of 331-340 K. No weight loss is observed during this transition. This behavior may affect the electrical properties of the compound and enhance its potential for temperature-dependent electronic applications. Nyquist plots display a single semicircular arc, which is characteristic of non-Debye relaxation. The AC conductivity follows Jonscher's universal power law. These results indicate thermally activated charge transport governed by the correlated barrier hopping (CBH) model.