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

Abstract

By using the ligands 4-(4-bromobenzylideneamino)-4H-1,2,4-triazole (L₁) and 4-(4-iodobenzylideneamino)-4H-1,2,4-triazole (L₂), four different organic salts HL₁⁺·Cl⁻ (1), L₁·HL₁⁺·ClO₄⁻ (2), HL₂⁺·Cl⁻ (3), and L₂·HL₂⁺·ClO₄⁻ (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.