Anion-assisted formation of discrete homodimeric and heterotetrameric assemblies by benzene based protonated heteroaryl receptors

Abstract

Anion-assisted formation of discrete homodimeric and heterotetrameric assemblies by benzene based protonated heteroaryl receptors L¹–L⁶ have been studied thoroughly by single crystal X-ray diffraction studies. Crystallographic results elucidate the fact that protonated tripodal receptor L¹ formed staggered homodimeric capsular assemblies 2 and 3 with CF₃COO^– and ClO₄^– ions, respectively. Protonation of L³ with trimesic acid also showed the formation homodimeric assembly, 6. In all these cases the anions are hydrogen bonded to the receptor molecules and show remarkable influence on the outcome of the self-assembly process to form discrete capsules. The necessity of the alkyl substitution on the benzene platform has been established from complexes 8, 9, and 10, which were obtained upon protonation of L⁶ with HNO₃, HI, and HClO₄, respectively. Interestingly, when a 1:1 mixture of L¹ (tripodal) and L⁵ (dipodal) were treated with HClO₄ and HBF₄, discrete heterotetrameric assemblies have been isolated as complexes 11 and 12. The detailed solid state structural analysis of these complexes revealed the formation of heterotetrameric assemblies assisted by anion–water clusters. Correlation of these solid state structural assemblies with our previously reported complexes 1, 4, 5, and 7 has also been described. The role of anionic templates in assisting the formation of discrete capsular assemblies from receptors possessing heteroaryl units and 1,3,5-methyl substituted benzene platform has been established.