Design and multifunctional characterization of bis[4-carbomethoxypyridinium] hexabromostannate(IV): A new organic–inorganic hybrid for nonlinear optical and dielectric applications

A new organic–inorganic hybrid, bis[4-carbomethoxypyridinium] hexabromostannate(IV) (4CPHBS), was synthesized and structurally characterized. Single-crystal X-ray diffraction revealed that the compound crystallizes in the monoclinic system (space group P2₁/n) with nearly ideal octahedral [SnBr₆]^2- anions stabilized by extensive hydrogen-bonding and π–π stacking interactions with organic cations. Hirshfeld surface analysis confirmed dominant Br···H contacts along with significant H···O and π–π interactions, highlighting the role of supramolecular forces in crystal stabilization. Vibrational spectra (FT-IR and Raman) identified characteristic modes of the pyridinium, carbomethoxy, and hexabromostannate groups. NMR studies supported protonation of the pyridinium ring, while optical measurements revealed a direct band gap of 3.17 eV and a sharp photoluminescence emission at 491 nm. Thermal analysis indicated stability up to ∼160 °C, and SEM–EDS/XRF/XPS confirmed phase purity and composition. Nonlinear optical (Z-scan) studies demonstrated reverse saturable absorption and self-defocusing with χ⁽³⁾=7.23×10^–11 esu, while dielectric and AC conductivity measurements exhibited strong frequency and temperature dependence. These multifunctional features highlight 4CPHBS as a promising candidate for optoelectronic and dielectric applications.