Anion binding with some 22- and 28-membered selenaaza macrocycles: Structural aspects and 77Se NMR studies

A series of macrocyclic adducts of the 22- and 28-membered selenaaza macrocycles (1 and 2, respectively) with different counter anions such as halides, sulfate, perchlorate, phosphate, trifluoroacetate and nitrate has been prepared. The adducts have been characterized by elemental analysis, IR, 1H NMR, 77Se NMR and ESI-MS analysis. The 77Se NMR spectrum of the SO42- adduct (7) shows an upfield shift compared to the parent macrocycle. The bromo (5), iodo (6), sulfate (7), trifluroacetate (10) adducts of the 22-membered selenaaza macrocycle and perchlorate (16), trifluroacetate (18) adducts of the 28-membered selenaaza macrocycle have been structurally characterized. The crystal structures show extensive hydrogen bonding networks. The molecular structures of all the compounds show the macrocycle to be fully protonated except the trifluroacetate adduct of the 22-membered macrocycle (10), which is only diprotonated. The binding constants of the neutral 22-membered selenaaza macrocycle towards, fluoride, bromide, iodide and sulfate ion have been determined by the NMR titration method.

Graphical abstractThe anion adduct formation properties of two selenaaza macrocycles of different ring sizes with various anions such as halides, SO42-, ClO4-, PO43-, CF3COO− and NO3- have been studied. The 77Se NMR spectrum of the sulfate adduct of the 22-membered selenaaza macrocycles shows a considerable upfield shift (difference ∼241 ppm) compared to the free ligand, indicating a strong interaction of the sulfate ion with the protonated macrocycle. The crystal structures of adducts show extensive hydrogen bonding between protonated macrocycles and the anions.Figure optionsDownload full-size imageDownload as PowerPoint slide