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

Janaka Gamekkanda,John Desper,Abhijeet Sinha,Marijana Ðaković,Christer Aakeröy

doi:10.3390/cryst7070226

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.

Highlights

Effective practical crystal engineering relies on the deceptively simple act of molecular recognition which [1], in turn, is achieved by balancing geometric compatibility with a multitude of reversible and relatively weak non-covalent forces [2,3,4,5]
We showed that two of three new ligands capable of simultaneous metal-chelation and directional halogen bonding presented have considerable potential as building blocks of extended 2-D
We demonstrated that the bromo- and iodo substituted ligands are capable of forming halogen bonds with several different solvent molecules that are capable of acting as halogen-bond acceptors such as acetonitrile and ethyl acetate

Summary

Introduction

Effective practical crystal engineering relies on the deceptively simple act of molecular recognition which [1], in turn, is achieved by balancing geometric compatibility with a multitude of reversible and relatively weak non-covalent forces [2,3,4,5]. The directed assembly of compositionally and structurally complex architectures requires a thorough understanding of the way in which complementary and competing forces eventually lead to a stable solid-state architecture [6,7]. Against this background, our goal was to establish reliable and robust avenues for the design and synthesis of crystalline metal-containing materials by encoding each building-block with structural-preferences that lead to “programmable” and predictable assembly [8,9,10]. Despite the relative frequent use of hydrogen bonds [28,29], Crystals 2017, 7, 226; doi:10.3390/cryst7070226 www.mdpi.com/journal/crystals

Objectives

Methods

Results

Discussion

Conclusion