Tripodal tris(diamide) receptor having H-bond donors and acceptors on trindane platform for H2PO4− recognition

A new C3v-symmetric tris(diamide) receptor 2 possessing both H-bond donor and acceptor sites was synthesized and characterized by various spectral data. The anion recognition ability of receptor 2 was investigated by 1H NMR in DMSO-d6. Among the tested anions (F−, Cl−, Br−, I−, NO3−, HSO4− and H2PO4−), the receptor 2 shows high selectivity towards H2PO4− anion. The amide-NH protons peaks of receptor 2 at δ 10.42 and δ 8.23 ppm were broadened and shifted to downfield region in the presence of H2PO4−. The appended arms with tris(diamide) H-bond donors and pyridine H-bond acceptors of receptor 2 provide a preorganized cavity to encapsulate the H2PO4− through multiple hydrogen bonds. The 1H NMR titration measures the binding constant (Ka) of 293 M−1 for the host–guest complex formed between receptor 2 and H2PO4−. Further, the possible 3D structure of receptor 2 and its complex with H2PO4− anion was proposed through density functional theory method.