Organic-inorganic hybrid materials with high phase transition temperatures regulated by halogen substitution

Halogen-substituted morpholine-based organic-inorganic hybrid compounds have attracted attention in phase transition and optoelectronics due to their tunable structural and electronic properties. In this work, a series of crystals, [C₆H₁₄NO]₂CdI₄, [C₆H₁₄NO]₂CdBr₄, and [C₆H₁₄NO]₂CdCl₄, were synthesized and characterized. All exhibit reversible solid-solid phase transitions at 406 K, 419 K, and 422 K, respectively, and semiconducting behavior with tunable band gaps of 3.298-4.398 eV. Supercell and Hirshfeld surface analyses reveal that progressive halogen substitution (I → Br → Cl) strengthens C-H⋯X hydrogen bonds, increases lattice confinement, and raises the rotational potential of organic cations, providing a structural basis for high-temperature phase transitions. This work demonstrates that halogen modulation in the inorganic framework is an effective strategy for designing multifunctional organic-inorganic hybrid materials with controllable thermal and optoelectronic properties.