Abstract
Progress in metallo-supramolecular chemistry creates potential to synthesize functional nano systems and intelligent materials of increasing complexity. In the past four decades, metal-mediated self-assembly has produced a wide range of structural motifs such as helicates, grids, links, knots, spheres and cages, with particularly the latter ones catching growing attention, owing to their nano-scale cavities. Assemblies serving as hosts allow application as selective receptors, confined reaction environments and more. Recently, the field has made big steps forward by implementing dedicated functionality, e.g. catalytic centres or photoswitches to allow stimuli control. Besides incorporation in homoleptic systems, composed of one type of ligand, desire arose to include more than one function within the same assembly. Inspiration comes from natural enzymes that congregate, for example, a substrate recognition site, an allosteric regulator element and a reaction centre. Combining several functionalities without creating statistical mixtures, however, requires a toolbox of sophisticated assembly strategies. This review showcases the implementation of function into self-assembled cages and devises strategies to selectively form heteroleptic structures. We discuss first examples resulting from a combination of both principles, namely multicomponent multifunctional host–guest complexes, and their potential in application in areas such as sensing, catalysis, and photo-redox systems.
Highlights
Coordination cages are constructed from single metal nodes or, sometimes, small metal clusters that are bridged by multitopic ligands
In the following discussion we focus on four different approaches that have been used for the controlled assembly of non-statistical heteroleptic coordination cages: (a) coordination sphere engineering (CSE), (b) shape complementary assembly (SCA), (c) non-symmetric ligands and (d) backbone-centred steric hindrance (Fig. 2)
The eld of metallo-supramolecular assembly has shown that a large variety of complex nano structures can be synthesized from available organic building blocks and metal cations from the main or transition group elements
Summary
The self-assembly of discrete nanoscale host architectures such as rings, cages and spheres has evolved into a vibrant sub eld of supramolecular chemistry over the last decades.[1,2,3,4] Routes to assemble such compounds can be primarily subclassi ed into hydrogen-bonded,[5,6] dynamic-covalent[7,8,9,10,11,12] and metal-mediated approaches.[13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28] In the latter category, most systems are built up from a combination of two major components: metal centres acting as nodes, and organic ligands serving as bridges to join the nodes into a regularly shaped, 3-dimensional object with an accessible cavity. In particular when comparing self-assembled cages to their o en-called natural paradigms – protein-based enzymes – one realizes that their complexity differs vastly.[33,34] Cavities around the active sites of enzymes are of low symmetry, chiral, and contain a mix of different chemical functionalities such as recognition sites, catalytic groups and conformational switches. Functionalized ligands of otherwise same shape and dimensions can certainly be mixed and subjected to metal-mediated (or dynamic covalent) assembly This usually leads to complex product mixtures governed by a statistical distribution of the components within the structures.[35,36,37] In contrast, in this review we focus on strategies for the rational introduction of multiple building blocks into metal-mediated architectures. As we could not cover all so far reported studies comprehensively, we apologize for what might not have found entry into this selection and refer to further reviews in this direction.[26,39,40,41,42,43]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
