Dedicated to Professor Guy Ourisson on the occasion of his 70th hirtlidaj.Helicates, metal complexes that form double" -41 or triple in solution and/or in the solid state, are generated by self-assembly of two or three ligand strands around suitable metal ions. Whereas the double helix of DNA results from the assembly of two complementary chains of nucleotides through hydrogen bonding, helicates form spontaneously from linear ligands composed of a series of discrete binding subunits through metal ion coordination. The process may be considered as resulting from the operation of a programmed system, in which the steric and interactional information stored in the ligands is read out by the metal ions following the algorithm detined by their coordination geometry.[31 Thus homostranded d~u b l e [ ' .~,~I and t r i~l e [~.~] helicates have been obtained from chains of 2,T-bipyridine (bpy) or 2,2 : 6',2"-terpyridine (terpy) groups connected by short covalent bridges, and metal ions having tetrahedral or octahedral coordination geometry. Recently, a heteroduplex helicate based on a tris-bpy strand, a tris-terpy strand, and pentacoordinated Cu" ions has been described.['] The DNA double helix is usually acyclic but can also be closed into a cyclic structure, a circular DNA, as found in some viruses. By analogy, it would be of great interest to devise means of generating closed, circular helicates. We describe herein the self-assembly of such a supramolecular architecture. The trisbpy ligand L and iron(i1) chloride have been found to form spontaneously and quantitatively a circular double helicate, cH (Fig. I), in other words, a double helicate closed into a ring, as indicated by 'H N M R spectroscopy and mass spectrometry as well as by X-ray crystal structure determination.

Die einfache Reaktion eines Tris‐bpy‐Liganden mit FeCl2 führt durch Selbstaufbau zu dem einzigartigen Komplexkation 1 ‐ einem Torus aus fünf Liganden, die in Form einer Doppelhelix um fünf FeII‐Ionen gewunden sind; im Zentrum des Torus befindet sich ein Chlorid‐Ion. Dies fünffache, zirkulare Helicat ist ein Analogon der zirkularen DNA.magnified image

The polytopic linear 4 and circular 5 ligands undergo self-assembly with copper(i) and silver(i) ions to generate the large inorganic entities 2 and 3 containing, two and three internal cavities, respectively. The process amounts to the spontaneous assembly of a total of 15 and 19 particles to yield multicompartmental architectures. The crystal structures of two such complexes have been determined. They confirm the nature of the entities formed and show that in addition several substrate species (anions and solvent molecules) are contained in the cavities. The generation of architectures 2 and 3 presents several important features: it represents a multicomponent mixed-ligand self-assembly process involving self-compartmentalisation with simultaneous inclusion (and selection) of multiple substrate species. Such features are of interest for both the analogies with biological processes and the potential applications in nanoscience. They also amount to a further step in the design of systems of increasing structural and functional complexity.

COMMUNICATIONS 15a, R' = H, R2 = H 154 R' = H, R2 = tBu 1% R' = tBu, RZ = H 15d, R1 = tBu, R2 = tBu OR1 ORZ F n o c -I l e -S e r -G l y -I l e -S e r -G l y -I l e -G l y -[~A )~~~ I I OH OH HO HO I H O P 16b HO HO 'OH HO .OH HO ,OH Bz-Ile -Se r-Gly-Ile-d r-Gly-Ik -Gly-OMe Bz-IleSe r-Gly-Ile-~r-Gly-Ile-Gly-OMeSelf-assembly processes offer a particularly attractive method for preparing nanosized supramolecular devices in that the required structural complexity of such entities can be accessed in

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