Comprehensive studies of non-covalent interactions within four new Cu(II) supramolecules

Abstract

This work investigates the supramolecular aggregation of Cu(II) complexes based on a combination<br><br>of the heterocyclic N-donor ligand 2-aminopyrimidine (2-apym) and a variety of different carboxylate<br><br>ligands, like salicylic acid (H2SAL), maleic acid (H2MAL), and glycine (HGLY). Four new Cu(II)<br><br>complexes [Cu(HSAL)2(2-apym)2](I), [Cu(HSAL)2(2-apym)2]? (H2SAL)2(2-apym) (I\\'), {(H2-apym)[Cu(GLY)(m-Cl)2Cl]}n (II) and [Cu(m-MAL)(2-apym)]n (III) have been synthesized and<br><br>characterized by elemental analyses, FT-IR spectra, and X-ray structural analyses. I and I9 appear as<br><br>molecular clusters whereas II is a 1-D coordination polymer with weak axial Cu–Cl interactions.<br><br>However the last one shows a 2-D coordination polymer with trigonal bipyramidal geometry for<br><br>Cu(II) ion. The two last cases have no molecular fragments packed with non-covalent interactions. In<br><br>these new supramolecular compounds, existent species join together with the cooperation of multiple<br><br>inter/intra-molecular classical O–H…O/N, N–H…O/N, and non-classical N–H…Cl hydrogen bonds<br><br>(H-bonds), offset face to face p…p, edge to face C/N–H…p, and lp…p stacking interactions in the<br><br>form of various homo/hetero-synthons leading to architecturally different structures. DFT<br><br>calculations were used to estimate the binding energy of the involved non-covalent interactions and<br><br>whole stabilization energy of related network of I, I9, and II. Theoretical calculations facilitate the<br><br>comparison of intermolecular interactions, which demonstrate that for all of I–II, N–H…N and N–<br><br>H…O H-bonds govern the network formation. The equilibrium constants for the three proton-transfer systems including SAL/2-apym, GLY/2-apym, MAL/2-apym, the stoichiometry and stability<br><br>of complexation of these systems with Cu2+<br><br>ion in aqueous solution were investigated by<br><br>potentiometric pH titration method. The stoichiometries of the most complex species in solution was<br><br>compared to the crystalline Cu2+<br><br>ion complexes with the cited proton-transfer systems.