Solution and solid state studies of three new supramolecular compounds of zinc(II), nickel(II) and uranium(VI) with chelidamic acid and 9-aminoacridine

Three new supramolecular compounds, (aacrH)2[Zn(hypydc)2]·4H2O 1, (aacrH)2[UO2(hypydc)2]·2DMSO 2, and (aacrH)2[Ni(hypydc)2]·4H2O 3, [where hypydcH2 = 4-hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid), aacr = 9-aminoacridine and DMSO = dimethyl sulfoxide] have been synthesized and characterized by elemental analysis, spectral (IR, UV–Vis, fluorescence), 1H NMR spectroscopy, thermal (TG/DTG/DTA) analysis and single crystal X-ray diffraction. All three compounds are proton transfer salts of the aminoacridinium cation and transition metal complex anions that crystallized from a solution of the dicarboxylic acid, aminoacridine, and metal nitrates as starting materials. The coordinating dicarboxylic acid is deprotonated at the carboxyl rather than the hydroxyl group, and the aminoacridine is selectively protonated at the pyridyl nitrogen but not at the amino group. In the crystal structures of 1–3 complex hydrogen bonding arrangements and π–π stacking play important roles. Water clusters (H2O)n [n = 2–4] are formed in compounds 1 and 3. The complexes are strongly luminescent at room temperature, exhibiting a sharp emission at 400 nm. The equilibrium constants of chelidamic acid (hypydc), 9-aminoacridine (aacr), proton transfer system as well as those of the complexes, were investigated by a potentiometric pH titration method.