Structure–property relationships in tris(2-amino-5-methylpyridinium) hexabromobismuthate monohydrate with a focus on optical and electrical behavior for optoelectronics applications

Abstract

The hybrid compound (C₆H₉N₂)₃[BiBr₆]H₂O was synthesized via slow evaporation and structurally characterized using single-crystal X-ray diffraction. It crystallizes in the monoclinic C2/c space group and adopts a zero-dimensional architecture composed of isolated [BiBr₆]³⁻ octahedra, protonated organic cations (C₆H₉N₂)⁺, and water molecules. These components are interconnected through hydrogen bonding and π–π interactions. Optical absorption measurements reveal a direct band gap of 2.81 eV, confirming the semiconducting nature of the material. Impedance spectroscopy, performed over a frequency range of 0.4 Hz to 3 MHz and a temperature range of 318 K to 363 K, reveals separate contributions from grains and grain boundaries. These were modeled using an equivalent circuit, indicating non-Debye relaxation behavior. The DC conductivity follows an Arrhenius-type behavior with activation energies of 0.96 and 0.51 eV. AC conductivity obeys Jonscher's power law, and the temperature-dependent decrease in the frequency exponent (s) supports the correlated barrier hopping (CBH) mechanism. The material exhibits enhanced dielectric permittivity, suggesting promising potential for optoelectronic and energy storage applications.