Metallo-Supramolecular Structures by Self-Assembly through Weak Interactions in Mixed Ligand Metal Complexes of Adenine and Malonate

摘要

The reactions of sodium malonate with Co~(II), Cu~(II), or Zn~(II) salts in the presence of adenine afforded the compounds [Co(7H-ade- N9)_2(H_2O)_4][Co(κ~2-mal)(H_2O)_2]·4H_2O (1), ∞~1[Cu(μ-mal)(7H-ade- N9)(μ_2-H_2O)] (2), and [Zn_2(μ-mal)_2(μ-7H-ade-N3,N9)_2(H_2O)_2]·2H_2O (3), all of which have been characterized by elemental analyses, mass spectrometry, FT-IR, electronic and EPR spectroscopy, magnetic measurements, and single-crystal X-ray diffraction. Complex 1 is an ion-pair product managed by charge-assisted noncovalent interactions. Complex 2 is formed by binuclear [Cu(mal)(Hade)(H_2O)]2 units bridged by malonate ligands, and 1D coordination polymeric chains are formed. Complex 3 is a centrosymmetric dimer, in which two Zn~(II) ions are bridged by two adenine ligands coordinated by N3 and N9 atoms from a pair of head-to-tail Hade ligands to give a μ-N3,N9 coordination mode. The metallo-supramolecular crystal structures of 1?3 are essentially maintained by hydrogen-bonding and π,π-stacking interactions involving the adenine, the carboxylate groups, and water molecules of coordination and crystallization (in compounds 1 and 3). In these structures, the nature of the malonate coordination is dependent on the metal, whereas the hydrogen bonding and π- stacking capabilities of the adenine ligand influence the interactions observed in forming the three-dimensional structures. The magnetic properties of 2 were investigated in the temperature range of 2?300 K. Overall, weak antiferromagnetic behavior occurs (J = ?3 cm~(?1)) with a susceptibility maximum at 50 K, with the exchange pathway provided by aqua bridges [Cu?Cu separation of 3.3522(5) ?]. Very weak ferromagnetic interactions are also observed through the malonate ligand in an uncommon anti-skew noncoplanar coordination mode, with a copper?copper separation of 5.3828(5) ?. Magnetostructural comparisons with analogous compounds with oxo-bridged Cu(II) binuclear complexes are also provided. Spectroscopic and thermal stability data for all complexes are described in detail.