Halogen-bonding contacts determining the crystal structure and fluorescence properties of organic salts

By using the ligands 4-(4-bromobenzylideneamino)-4 H -1,2,4-triazole ( L1 ) and 4-(4-iodobenzylideneamino)-4 H -1,2,4-triazole ( L2 ), four different organic salts H L1 + ·Cl − ( 1 ), L1 ·H L1 + ·ClO 4 − ( 2 ), H L2 + ·Cl − ( 3 ), and L2 ·H L2 + ·ClO 4 − ( 4 ) have been synthesized and structurally characterized through single-crystal X-ray diffraction ( L1 , L2 , 2 and 3 ) and PXRD ( 1 and 4 ) measurements. The results revealed that ligands L1 and L2 themselves exhibit a polymeric 1-D chain in a zigzag structure connected by C–Br⋯N and C–I⋯N halogen-bonding contacts, respectively. L1 in salt 2 was connected into a 3-D structure through N–H⋯O hydrogen-bonding contacts, while the interleaved 3-D network of L2 in salt 3 was mainly connected by C–I⋯Cl halogen-bonding contacts. As a result, the fluorescence properties of ligands L1 and L2 were reserved in halogen-bonding connected salts 1 and 3 , while there was a reduction in hydrogen-bonding connected salts 2 and 4 . Thus, the relationship between emission properties and halogen-bonding contacts can be proposed.