Intramolecular halogen bonding: Enantiomer induced by 'rhombic-shape' intramolecular halogen bonding

Programmable supramolecular materials assembled from chiral components are receiving increasing attention. Herein, we report a self-assembled racemic based on a halogenated Schiff base complex, [Cu3L2Cl2(H2O)] (L = N, N'-bis (3-Bromosalicylidene) ethylene-1,3-diaminopropane). Structural analysis reveals that the disappearance of molecular symmetry is closely related to the unique intramolecular 'rhombic-shape' halogen bonding of the compound. To the best of our knowledge, this is the first example of 'rhombic-shape' halogen bonding within a single molecule. To gain deeper mechanistic insight into the formation of this peculiar structure, we performed a series of structural analyses and theoretical calculations on the reported compound. The results suggest that the 'rhombic-shape' halogen bonding structure formed among the four Br atoms is asymmetric. This asymmetry structural feature further affects the molecular symmetry and serves as the primary factor inducing the special chirality in the molecule.