Synthesis and characterization of a tripodal amide ligand and its binding with anions of different dimensionality

Synthesis and crystal structure of a tren-based amide, L-1, N, N', N ''- tris[(2-amino-ethyl)-3-nitro-benzamide] is reported. The crystallographic results show intramolecular hydrogen bonding and aromatic pi center dot center dot center dot pi stacking among tripodal arms which prevent opening of the receptor cavity. Intermolecular hydrogen bonding in L1 generates the sheetlike network in the solid state. The structural aspects of binding halides ( 1 and 2), nitrate ( 3), perchlorate ( 4), and hexafluorosilicate ( 5) with the protonated L1 are examined crystallographically. Protonation at the apical nitrogen of L1 in the presence of anions shows a structural transformation from sheet to bilayer network. Anion binding with multiple receptor units is observed via amide N - H center dot center dot center dot anion and aryl C - H center dot center dot center dot anion hydrogen-bonding interactions in all the complexes. The aryl group having nitro functionality that contributes to anion binding in complexes 1 - 5 through CH center dot center dot center dot anion interactions ( either para or meta to nitro C - H) is noteworthy. These studies also show higher anion coordination of chloride ( 8) and hexafluorosilicate ( 14) with L1H+.