Halogen Bond Induced Structural and Photophysical Properties Modification in Organic-Inorganic Hybrid Manganese Halides.

The role of halogen bonding in organic-inorganic hybrid (OIH) halides was seldom investigated despite its potential to enhance the stability of the compound. In this context, we have synthesized (2-methylbenzimidazolium)MnCl 3 (H 2 O)·H 2 O (compound 1) crystallizing in a monoclinic space group P 2 1 / c with a 1D infinite chain of edge shared Mn octahedra. In contrast, the chloro-substituted derivative (5-chloro-2-methylbenzimidazolium) 2 MnCl 4 (compound 2) exhibits 0D Mn tetrahedra with a triclinic P 1̅ structure. This structural modification from 1D Mn octahedra to 0D Mn tetrahedra involves a unique type-II halogen bonding between organic chlorine (C-Cl) and inorganic chloride (Cl-Mn) ions. Compound 1 exhibits red emission, whereas compound 2 demonstrates dual-band emission, resulting from energy transfer from the organic amine to Mn centers. To rationalize this interesting modulation in structure and photophysical properties, the role of halogen bonding is explored in terms of quantitative electron density analysis and intermolecular interaction energies.