Poly-halogen-induced enhanced thermal stability in Co(III) Schiff-base complexes: structural and theoretical insights

Peripheral poly-bromination can significantly enhance the thermal stability of discrete coordination compounds. Here, we compare a pair of strictly isostructural Co(III)-Schiff base complexes that differ only by the presence of 3,5-dibromo substituents on the ligands. Thermogravimetric analysis shows that the onset decomposition temperature increases from approximately 100 °C in the unhalogenated complex to approximately 220 °C in the brominated analogue, accompanied by a shift from multistep to a sharper, more cooperative decomposition profile. Variable-temperature X-ray diffraction indicates improved structural persistence in the brominated crystal. Hirshfeld surface analysis, together with NCI, IGMH, QTAIM, and dispersion calculations, reveals that bromination strengthens the non-covalent interaction network, particularly through increased Br···H contacts and enhanced dispersion forces. Frontier orbital analysis shows a modest lowering of the LUMO energy level. These supramolecular and electronic changes collectively correlate with the observed improvement in thermal stability. This work demonstrates that peripheral poly-bromination offers a practical strategy to enhance the thermal robustness of discrete Co(III)-Schiff base complexes while preserving the core coordination structure.