The Role of Halogen Bonding in Controlling Assembly and Organization of Cu(II)-Acac Based Coordination Complexes

Abstract

In order to explore the use of non-covalent interactions in the deliberate assembly of metal-supramolecular architectures, a series of β-diketone based ligands capable of simultaneously acting as halogen-bond donors and chelating ligands were synthesized. The three ligands, L1, L2, and L3, carry ethynyl-activated chlorine, bromine, and iodine atoms, respectively and copper(II) complexes of all three ligands were crystallized from different solvents, acetonitrile, ethyl acetate, and nitromethane in order to study specific ligand-solvent interaction. The free ligands L2 and L3, with more polarizable halogen atoms, display C-X⋯O halogen bonds in the solid state, whereas the chloro-analogue (L1) does not engage in halogen bonding. Both acetonitrile and ethyl acetate act as halogen-bond acceptors in Cu(II)-complexes of L2 and L3 whereas nitromethane is present as a ‘space-filling’ guest without participating in any significant intermolecular interactions in Cu(II)-complexes of L2. L3, which is decorated with an iodoethynyl moiety and consistently engages in halogen-bonds with suitable acceptors. This systematic structural analysis allows us to rank the relative importance of a variety of electron-pair donors in these metal complexes.

Keywords

• halogen bonding
• coordination chemistry
• Cu-acac complexes
• supramolecular chemistry