Anion directed supramolecular architecture of benzimidazole-based receptor

The reaction of N,N,N′,N′-tetrakis-(1H,benzimidazol-2ylmethyl)ethane-1,2-diamine (L) with different inorganic as well as organic acid afford salts viz., LH44+·4ClO4−·4H2O (1), LH44+·4Br−·4(CH3)2SO (2), 2LH33+·3SiF62−·14H2O (3), LH44+·4H2PO4−·2H3PO4 (4) and L·2CH3COOH (5) with different structures. The X-ray crystallographic studies revealed that these compounds are all ionic in nature due to proton transfer except 5 and are stabilized in the solid state by networks of hydrogen bonds between their respective components as well as solvent molecules. It also demonstrates that different types of hydrogen bond between protonated ligand and the anions are responsible for the extensive supramolecular frame work. The three dimensional packing is mainly guided by well-balanced primary N–H⋯O, O–H⋯N, O–H⋯O hydrogen bonds and secondary C–H⋯O interactions between benzimidazole and acids. Moreover, the hydrogen bonds, π⋯π and C−H⋯π stacking interactions appear to be effective in stabilizing the crystal structures. The colorimetric test showed color change upon the addition of acids in solution of the ligand. The photo-physical experiments suggest that the ligand shows fluorescence properties in the presence of acids.