Comprehensive structural and DFT analysis of a newly synthesized bismuth-based organic–inorganic hybrid material: in-depth insights into vibrational, optical, and photoluminescence properties of (C8H14N2)2[Bi2Br10]·2H2O

Abstract

A newly synthesized bismuth-based organic–inorganic hybrid material, (C₈H₁₄N₂)₂[Bi₂Br₁₀]·2H₂O, was synthesized using a slow evaporation technique and thoroughly characterized to explore its structural, vibrational, optical, and electronic properties. Single-crystal X-ray diffraction confirmed its monoclinic crystal system with a centrosymmetric P2₁/c space group, featuring edge-sharing [Bi₂Br₁₀]⁴⁻ dimers interconnected via non-covalent interactions. Hirshfeld surface analysis and fingerprint plots revealed dominant H⋯Br and H⋯H interactions, highlighting the role of hydrogen bonding in stabilizing the crystalline architecture. Vibrational studies using FTIR and Raman spectroscopy provided detailed assignments of molecular vibrations, corroborated by density functional theory (DFT) calculations. The optical properties were investigated through UV-vis spectroscopy in solution and diffuse reflectance spectroscopy (DRS) in the solid state, revealing an indirect band gap of 2.9 eV (solid-state) and 3.086 eV (solution), validated by theoretical electronic structure calculations. Photoluminescence (PL) studies demonstrated a strong blue and rose emission, supported by CIE chromaticity analysis, positioning this material as a promising candidate for optoelectronic applications. Additionally, advanced DFT analyses, including electron localization function (ELF), localized orbital locator (LOL), reduced density gradient (RDG), and non-covalent interaction (NCI) analyses, provided deep insights into electronic charge distribution, weak intermolecular interactions, and structural stability. These findings establish (C₈H₁₄N₂)₂[Bi₂Br₁₀]·2H₂O as a bismuth-based hybrid material with significant potential in optoelectronics, luminescent materials, and functional optical applications.