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

Abstract

Synthesis and crystal structure of a tren-based amide, L₁,N,N‘,N‘‘-tris[(2-amino-ethyl)-3-nitro-benzamide] is reported. The crystallographic results show intramolecular hydrogen bonding and aromatic π···π 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···anion and aryl C−H···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···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⁺.