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

Abstract

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.