Molecular and supramolecular recognition patterns in ternary copper(II) or zinc(II) complexes with selected rigid-planar chelators and a synthetic adenine-nucleoside

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)]center dot 3H(2)O (1a) and [Cu(pdc)(9heade)(H2O)]center dot 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 center dot center dot center dot 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-pi/pi-pi/ pi-anion assemblies (in 1a and 1b) or the unprecedented pi-pi interactions (in 2), involving the purine moieties or the exocyclic -(NH2)-N-6 purine groups, respectively. Compound 3, {[Cu(GG)(9heade)(H2O)center dot Cu(GG)(mu(2)-9heade)]center dot 8H(2)O}(n), consists in asymmetric dinuclear complex units (Cu center dot center dot center dot Cu 7.83 angstrom) that connect with adjacent ones by pairs of very weak Cu-O(carboxylate) bonds (Cu center dot center dot center dot Cu 3.81 angstrom) 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 mu-N7,O(ol) metal binding patterns of 9heade differs from that recently reported (mu-N1,N7) in a Cd(II) polymer.