Abstract

Hybrid halide compounds of formula A2BX4 represent a promising class of materials for tuning structural and electronic properties via halide substitution. Here, we report the synthesis and comprehensive characterization of the (CH3NH3)2ZnX4 (X = Cl, Br, I) series, including the first full structural resolution of the iodide analogue. Single-crystal X-ray diffraction revealed a halide-driven transition from a three-dimensional monoclinic structure (P21/c) for Cl and Br to a layered orthorhombic structure (Pbca) for I. Raman spectroscopy showed redshifts in lattice phonons and N-H stretching broadening along the series, indicating weaker hydrogen bonding and enhanced vibrational coupling with heavier halides. Thermal analysis confirmed phase transitions associated with CH3NH3+ dynamics, followed by complete decomposition below 300 degrees C, largely independent of halide identity. Diffuse reflectance spectroscopy revealed wide bandgap semiconducting behavior, with values decreasing systematically from 5.55 eV (Cl) to 4.25 eV (I). These findings establish a clear structure-property correlations in the (CH3NH3)2ZnX4 family and provide a foundation for future bandgap and lattice engineering in hybrid halide systems.