Self-assembled M2L4 coordination cages: Synthesis and potential applications

• An overview on various metal-mediated self-assemblies of formula M2L4 is provided.
• Cage structures and their capacity to encapsulate guest molecules is discussed.
• Remarkable properties of host–guest systems and their applications are highlighted.

Metal-mediated self-assemblies of the general formula MxLy (M = metal ion, L = ligand) have emerged as a promising research area of supramolecular chemistry because of their applicability in various fields such as molecular recognition, catalysis and drug delivery. The focus of this review is on discrete coordination cages of the type M2L4 using square-planar, square-pyramidal or octahedral coordinated metal ions (e.g. Pd, Pt, Co, Cu, Ni or Zn) and bis(monodentate) N-ligands. The synthesis and characterization of these metallocages is discussed, and special attention is given to the molecular structures with well-defined internal cavities and the molecular recognition properties. The self-assembled M2L4 cages are capable to encapsulate anionic, neutral or cationic guest molecules within their cavity. Therefore, some of these M2L4 host–guest systems are certainly promising for application in medical diagnostic, drug delivery, catalytic reactions, environmental analytics, material science and chemosensing.

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