3d Magnetically Ordered Open Supramolecular Architectures Based On Ferrimagnetic Cu/Adenine/Hydroxide Heptameric Wheels

The present work provides two new examples of supramolecular metal-organic frameworks consisting of three-dimensional extended noncovalent assemblies of wheel-shaped heptanuclear [Cu-7(mu-H2O)(6)(mu(3)-OH)(6)(mu-adeninato-kappa N3:kappa N9)(6)](2+) entities. The heptanuclear entity consists of a central [Cu(OH)(6)](4-) core connected to six additional copper(II) metal centers in a radial and planar arrangement through the hydroxides. It generates a wheel-shaped entity in which water molecules and mu-kappa N3:kappa N9 adeninato ligands bridge the peripheral copper atoms. The magnetic characterization indicates the central copper(II) center is anti-ferromagnetically coupled to external copper(II) centers, which are ferromagnetically coupled among them leading to an S = 5/2 ground state. The packing of these entities is sustained by pi-pi stacking interactions between the adenine nucleobases and by hydrogen bonds established among the hydroxide ligands, sulfate anions, and adenine nucleobases. The sum of both types of supramolecular interactions creates a rigid synthon that in combination with the rigidity of the heptameric entity generates an open supramolecular structure (40-50% of available space) in which additional sulfate and triethylammonium ions are located altogether with solvent molecules. These compounds represent an interesting example of materials combining both porosity and magnetic relevant features.