Recent advances in the construction and applications of heterometallic macrocycles and cages

Self-Assembly with 2,6-Bis(1-(pyridin-4-ylmethyl)-1H-1,2,3-triazol-4-yl)pyridine: Silver(I) and Iron(II) Complexes

A new "click" ligand, 2,6-bis(1-(pyridin-4-ylmethyl)-1H-1,2,3-triazol-4-yl)pyridine (L) featuring a tridentate 2,6-bis(1,2,3-triazol-4-yl)pyridine (tripy) pocket and two pyridyl (py) units was synthesized in modest yield (42%) using the copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The coordination chemistry of the ligand with silver(I) and iron(II) ions was examined using a battery of solution (¹H and DOSY (diffusion ordered spectroscopy) nuclear magnetic resonance (NMR), infrared and absorption spectroscopies, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS)), and solid state (X-ray crystallography, elemental analysis) techniques. When treated with silver(I) ions, the ligand forms discrete [Ag(L)]⁺ (X-, where X- = BF₄-, NO₃- or SbF₆-) complexes in dimethyl sulfoxide (DMSO) solution but these complexes crystallize as coordination polymers. The addition of [Fe(H₂O)₆](BF₄)₂ to an acetonitrile solution of the ligand forms the expected monomeric octahedral [Fe(L)₂]2+ complex and treatment of the iron(II) complex with AgBF₄ generates a heterometallic linear coordination polymer.

Homochiral Emissive Λ8 - and Δ8 -[Ir8 Pd4 ]16+ Supramolecular Cages

Synthetic self-assembly is a powerful technique for the bottom-up construction of discrete and well-defined polyhedral nanostructures resembling the spherical shape of large biological systems. In recent years, numerous Archimedean-shaped coordination cages have been reported based on the assembly of bent monodentate organic ligands containing two or more distal pyridyl rings and square-planar PdII ions. The formation of photoactive PdII metallamacrocycles and cages, however, remain rare. Here we report the first examples of emissive and homochiral supramolecular cages of the form [Ir8 Pd4 ]16+ . These cages provide a suitably sized cavity to host large guest molecules. Importantly, encapsulation and energy transfer have been observed between the blue-emitting NBu4 [Ir(dFppy)2 (CN)2 ] guest and the red-emitting Δ8 -[Ir8 Pd4 ]16+ cage.

Integrative self-sorting of coordination cages based on 'naked' metal ions

Coordination-driven self-assembly of metal ions and organic ligands has been extensively utilised over the past four decades to access a variety of nano-sized cage assemblies, with functions ranging from sensing and catalysis to drug delivery. Many of the reported examples, however, are highly symmetric architectures that contain one type of organic ligand carrying not more than a single functionality. This contrasts significantly with the level of structural and functional complexity encountered in biological macromolecular hosts, which are able to bind and chemically convert smaller molecules in their highly-decorated internal cavities. To address this disparity, rational approaches that facilitate heteroleptic assembly by regulating integrative self-sorting of metal ions and multiple ligand components have emerged. Among these, routes to access coordination cages from 'naked' metal cations that offer more than two coordination sites are still in early development, as the complexity of the self-sorted products in terms of composition and stereochemistry presents an entropic challenge. This feature article highlights recent progress in controlling integrative self-sorting of multi-component cage systems with a focus on structures composed of 'naked' metal cations and two different ligands. Once heteroleptic self-assembly strategies find a wider implementation in supramolecular design, the resultant interplay between tailored combinations of precisely positioned substituents promises enhanced functionality in nanoscale structures.

Stepwise construction of discrete parallelogram- and prism-shaped organometallic architectures based on half-sandwich rhodium fragments

Using a versatile pyridyl-substituted imidazole-4,5-dicarboxylate proligand, together with half-sandwich rhodium fragments, a series of discrete organometallic complexes with parallelogram and trigonal prism shapes were constructed stepwise.

Molecular and crystalline architectures based on HgI2: from metallamacrocycles to coordination polymers

We report the synthesis and X-ray characterization of three metallamacrocycles and one coordination polymer obtained by using coordination driven self-assembly of the HgI₂ salt with four different ligands.

Selective synthesis of iridium(iii)-derived molecular Borromean rings, [2]catenane and ring-in-ring macrocycles via coordination-driven self-assembly

Unprecedented iridium(iii) derived molecular Borromean rings, 2[catenane] and ring-in-ring metallacycles were synthesizedviacoordination driven self-assembly using an iridium(iii)-based acceptor and dipyridyl donors.

Metallosupramolecular 3D assembly of dimetallic Zn4[RuL2]2 and trimetallic Fe2Zn2[RuL2]2

A 3D trismetallo-macromolecule was assembled with a stepwise synthesized key metallo-organic ligand, which was created by a reaction on complex strategy.