Molecular and supramolecular recognition patterns in ternary copper(II) or zinc(II) complexes with selected...

Four ternary metal-complexes with Cu(II) or Zn(II), 2,6-pyridine-dicarboxylate (pdc) or glycyl-glycinate (GG) and the synthetic nucleoside 9-(2-hydroxyethyl)adenine (9heade) have been synthesized and studied by single-crystal X-ray diffraction and other physical methods. Relevant supramolecular assemblies found in the solid state structures have been further studied using density functional theory (DFT) calculations. In addition, the energetic features of the non-covalent interactions as well as the cooperativity effects have been calculated and characterized using the non-covalent interaction plot computational tool. Compounds trans-[Cu(pdc)(9heade)(H₂O)₂]·3H₂O (1a) and [Cu(pdc)(9heade)(H₂O)]·H₂O (1b), trans-[Zn(pdc)(9heade)(H₂O)₂] (2), share the same molecular recognition pattern consisting in the cooperation of the metal-N7(9heade) bond and an interligand (9heade)N6-H···O(pdc) interaction, regardless of the nature of the metal, the coordination environment and the water content. At a supramolecular level, these compounds exhibit pairs of complex molecules linked by H-bonds and interesting anion-π/π-π/π-anion assemblies (in 1a and 1b) or the unprecedented π-π interactions (in 2), involving the purine moieties or the exocyclic -⁶NH₂ purine groups, respectively. Compound 3, {[Cu(GG)(9heade)(H₂O)·Cu(GG)(μ₂-9heade)]·8H₂O}_n, consists in asymmetric dinuclear complex units (Cu···Cu 7.83 Å) that connect with adjacent ones by pairs of very weak Cu-O(carboxylate) bonds (Cu···Cu 3.81 Å) building a polymeric chain. The supramolecular transition from a single molecule to dinuclear units and finally a polymeric chain is also observed in the electron paramagnetic resonance spectra and discussed from a structural point of view as well as by DFT calculations. The unprecedented N7 and μ-N7,O(ol) metal binding patterns of 9heade differs from that recently reported (μ-N1,N7) in a Cd(II) polymer.