Coordination-driven self-assembly of discrete and polymeric copper(ii) and dicopper(ii) supramolecular structures based on oxacalix[2]benzene[2]pyrazines

Abstract

The reaction of oxacalix[2]benzene[2]pyrazines 1 and 2 with copper(II) nitrate, as well as dimeric copper(II) tetraacetate are presented. Ligands 1 and 2, both adopt 1,3-alternate conformation, with the two exo-Lewis basic sites spatially oriented outwards. Ligand 1 reacts with copper(II) ions generated a discrete molecular cage 3 by bridging two ligands via two Cu²⁺ ions in the equatorial region. While the reaction of 1 with dicopper(II) tetraacetate unit resulted in the formation of a discrete supramolecular complex 4 with 1 : 2 stoichiometry between the dicopper(II) unit and ligand 1, due to the larger size and axial coordination mode of the dicopper(II) unit. The conformationally flexible nature of ligand 2 facilitated the formation of coordination polymers 5 and 6 upon interaction with copper(II) and dicopper(II) units, respectively. Coordination polymer 5 featured a zigzag structure of alternating ligand 2 and Cu²⁺ ion, while in coordination polymer 6, ligand 2 serves as an axial 2-connected node, propagating the “paddlewheel” dicopper(II) unit along the polymeric chain.