Single-Site Bromination as a Minimal Structural Intervention for Drastically Enhanced Thermal Stability in Co(III) Schiff-Base Complexes

Abstract

Achieving a precise enhancement in the thermal stability of molecular materials without significantly compromising their inherent coordination architectures remains a formidable challenge, because conventional modifications often require extensive framework reconstruction. Herein, we demonstrate a minimal structural intervention strategy in which a single halogen perturbation drastically enhances the thermal robustness of Co(III)-Schiff-base complexes. By combining crystallographic analysis, variable-temperature X-ray diffraction, and extensive theoretical calculations, we evaluate the mechanistic impact of bromine substitution. The incorporation of a single bromine site remarkably delays the onset decomposition temperature from ca. 100 ℃ to 250 ℃ without altering the core coordination framework. Specifically, the high polarizability of bromine increases the global dispersion energy from -207.49 to -235.31 kcal/mol and significantly lowers the LUMO level, thereby creating an internal radical/hot-electron trap. This dual supramolecular and electronic stabilization raises the lattice-disruption energy to approach the cleavage energy of intramolecular covalent bonds. As a result, the thermal breakdown pathway shifts from stepwise dissociation to concerted collapse, offering a practical blueprint for the design of exceptionally stable molecular materials.

Keywords: Schiff-base complex, thermal stability, halogen substitution, weak interactions, dispersion stabilization, crystal engineering