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

The reactions of sodium malonate with CoII, CuII, or ZnII salts in the presence of adenine afforded the compounds [Co­(7H-ade-N9)2(H2O)4]­[Co­(κ2-mal)­(H2O)2]·4H2O (1), ∞1[Cu­(μ-mal)­(7H-ade-N9)­(μ2-H2O)] (2), and [Zn2(μ-mal)2(μ-7H-ade-N3,N9)2(H2O)2]·2H2O (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)­(H2O)]2 units bridged by malonate ligands, and 1D coordination polymeric chains are formed. Complex 3 is a centrosymmetric dimer, in which two ZnII 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) Å]. 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) Å. 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.