This work investigates the supramolecular aggregation of Cu(II) complexes based on a combination of the heterocyclic N-donor ligand 2-aminopyrimidine (2-apym) and a variety of different carboxylate ligands, like salicylic acid (H 2 SAL), maleic acid (H 2 MAL), and glycine (HGLY). Four new Cu(II) complexes [Cu(HSAL) 2 (2-apym) 2 ] (I), [Cu(HSAL) 2 (2-apym) 2 ]?(H 2 SAL) 2 (2-apym) (I9), {(H2apym)[Cu(GLY)(m-Cl) 2 Cl]} n (II) and [Cu(m-MAL)(2-apym)] n (III) have been synthesized and characterized by elemental analyses, FT-IR spectra, and X-ray structural analyses. I and I9 appear as molecular clusters whereas II is a 1-D coordination polymer with weak axial Cu-Cl interactions. However the last one shows a 2-D coordination polymer with trigonal bipyramidal geometry for Cu(II) ion. The two last cases have no molecular fragments packed with non-covalent interactions. In these new supramolecular compounds, existent species join together with the cooperation of multiple inter/intra-molecular classical O-H … O/N, N-H … O/N, and non-classical N-H … Cl hydrogen bonds (H-bonds), offset face to face p … p, edge to face C/N-H … p, and lp … p stacking interactions in the form of various homo/hetero-synthons leading to architecturally different structures. DFT calculations were used to estimate the binding energy of the involved non-covalent interactions and whole stabilization energy of related network of I, I9, and II. Theoretical calculations facilitate the comparison of intermolecular interactions, which demonstrate that for all of I-II, N-H … N and N-H … O H-bonds govern the network formation. The equilibrium constants for the three protontransfer systems including SAL/2-apym, GLY/2-apym, MAL/2-apym, the stoichiometry and stability of complexation of these systems with Cu 2+ ion in aqueous solution were investigated by potentiometric pH titration method. The stoichiometries of the most complex species in solution was compared to the crystalline Cu 2+ ion complexes with the cited proton-transfer systems.

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The title compound, (C6H9N2)2[Cu(C6H2N2O4)2(H2O)2]·6H2O, consists of a mononuclear trans-[Cu(pzdc)2(H2O)2]2− dianion (pzdc is pyrazine-2,3-dicarboxyl­ate) and two [ampyH]+ cations (ampy is 2-amino-4-methyl­pyridine) with six water mol­ecules of solvation. The CuII atom is hexa­coordinated by two pzdc groups and two water mol­ecules. The coordinated water mol­ecules are in trans-diaxial positions and the pzdc dianion acts as a bidentate ligand through an O atom of the carboxyl­ate group and the N atom of the pyrazine ring. There are diverse hydrogen-bonding inter­actions, such as N—H⋯O and O—H⋯O contacts, which lead to the formation of a three-dimensional supra­molecular architecture.

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