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

Abstract

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(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 2 O)] 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 πstacking 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.

1D and 3D supramolecular structures exhibiting weak ferromagnetism in three Cu(II) complexes based on malonato and di-alkyl-2,2’-bipyridines

“…Malonate has been extensively studied regarding its role as a magnetic-exchange passageway in Cu(II) complexes, polynuclear compounds and coordination polymers [36][37][38]. In most cases, malonato ligand promotes ferromagnetic coupling.…”

“…In most cases, malonato ligand promotes ferromagnetic coupling. In previous studies about the magnetostructural correlations of malonato-based Cu(II) complexes and extended systems [37][38][39][40], it was concluded that the parameter that rules, primarily, the magnetic interaction between metal ions is the relative position of the carboxylato bridge of the malonate ligand related to the Cu(II) ions: equatorial-equatorial (strong interaction), equatorial-apical (weak interaction) and apical-apical (negligible interaction). According to their supramolecular structures, 1, 2, and 3 form chains with a regular alternation of the corresponding complex units, which are linked as a bidentate (η 5 -chelation) + monodentate (1), bidentate (η 5 -chelation) + mono-dentate (2), bidentate (η 5 -chelation) + bis(monodentate) (3) ligand through two carboxylate oxygens of the malonate, via hydrogen-bonding interactions, with the antisyn coordination mode (figures 2, 4, and 5), which correspond to the equatorial-apical carboxylate bridge in the solid-state supramolecular structures.…”

In-Situ Self-Assembly of Zinc/Adenine Hybrid Nanomaterials for Enzyme Immobilization

“…It also has been demonstrated that some CPs are capable of adsorbing and entrapping a broad range of molecules, due to their good biocompatibility and porosity [34,39]. Adenine, as an important naturally occurring nitrogen heterocycle present in nucleic acids [40], has multiple possible metal-binding modes [41][42][43]. It has been reported that adenine could coordinate with Zn [44], Au [45], Ag [46], Co [47] or Cu [48] to form CPs with diversified morphology and structure.…”

Variation in crystalline architectures through supramolecular interactions in copper(II) complexes with tridentate N2O donor Schiff bases

“…The most commonly used approach for engineering the crystal structure of such complexes employ non-covalent intermolecular forces (hydrogen bonding, aromatic ring stacking, etc.) [11,12]. However, although there have been many reports on supramolecular systems, it still remains a difficult job to explore several complexes with different topological networks.…”