Influence of Anions in Silver Supramolecular Frameworks: Structural Characteristics and Sorption Properties

The complexation of a preorganized thioether-functionalized bis(pyrazolyl)methane ligand (L) with silver precursors produces supramolecular structures organized at two hierarchical levels: [AgL]6(X)6 metal–organic cyclic hexamers and their organization in 3D architectures. The cyclic toroidal hexamers of 22–26 Å external diameter are found to be stable already in solution before self-assembly into the crystalline state. In the 3D lattice, the hexameric building block are arranged in different highly symmetric space groups as a function of a variety of anions (cubic Fd3̅ with PF6– or BF4– and rhombohedral R3̅ with CF3SO3– or NO3–) and form cavities with the geometrical shapes of Platonic solids (tetrahedron and octahedron) that can be occupied by a variety of solvent molecules. Upon evacuation, cubic crystals can produce stable frameworks with permanent porosity, which can absorb reversibly several vapors, CO2 and CH4.