Potentiometric measurements and crystal structures of three supramolecular metal-organic compounds, MIIA(CaII, SrII, BaII)-pyridine-2,6-dicarboxylic acid-2-aminopyridine, have been investigated. On the basis of crystallographic data, three supramolecular coordination compounds, [Ca(pydc)(μ-H2O)(H2O)2]n (1), (2-apyH)2[Sr(pydc)2(H2O)3]·5H2O (2), and (2-apyH)2[Ba(pydc) 2(H2O)3]·5H2O (3) (pydc = pyridine-2,6-dicarboxylate, 2-apy = 2-aminopyridine), were prepared. These compounds form a 3-D structure by a variety of noncovalent interactions such as extensive O–H⋯O, N–H⋯O, C–H⋯O hydrogen bonds, C–O⋯π, N–H⋯π, C–H⋯π, and π⋯π interactions. The equilibrium constants for the pydc-2-apy adduct and the stoichiometry and stability of complexation of this adduct with Ca(II), Sr(II) and Ba(II) in aqueous solution were investigated by potentiometric pH titration method. The stoichiometry of the complexes in solution was compared to the crystalline metal ion complexes
