New 3D supramolecular networks built from 1D and 2D frameworks via π–π and H-bonding interactions: Topology and catalytic properties

Two new metal-organic frameworks, {[Zn(dpe)(μ-OOCCH3)2](H2O)}n (1) and {[Zn3(dpe)4(μ-OOCC2H5)4](dpe)(ClO4)2}n (2) (dpe = 1,2-bis(4-pyridyl)ethene), have been prepared and investigated. Their structures were determined by X-ray crystallography. The different structures of both compounds indicate that the different steric constraints for a methyl group (acetato, compound 1) and an ethyl group (propionato, compound 2), as well as the counteranion effects (ClO4− for 2), play an important role in the formation and structure of these coordination polymers. Compound 1 exhibits a 1D zig–zag polymeric chain based on mononuclear secondary building units. The replacement of the acetate by propionate ligands, in the presence of additional ClO4− during the synthesis procedure, gives rise to a 2D network that is assembled from trinuclear secondary building units (compound 2). In addition, both compounds are further stabilized by π–π interactions and by hydrogen bonds to form intricate supramolecular frameworks. The 1D (1) and 2D (2) networks exhibit voids that contain guest water molecules for compound 1 and perchlorate/dpe for compound 2. Both coordination compounds have been structurally characterized and the thermal stability, potential cation-exchange and selected catalytic properties have been investigated. Interestingly, both Zn(II) compounds act as active heterogeneous catalysts for the high-yield cyanosilylation of acetaldehyde in dichloromethane and show highly size-selective properties for the substrate benzaldehyde. The metal sites in each compound have been studied in some more detail by using doped species with Mn(II) and Cu(II) and the EPR properties.