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 [Cu7(μ-H2O)6(μ3-OH)6­(μ-adeninato-κN3:κN9)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 μ–κN3:κN9 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 π–π 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.