Abstract
Here we describe the formation of an unexpected and unique family of hollow six-stranded helicates. The formation of these structures depends on the coordinative flexibility of silver and the 2-formyl-1,8-napthyridine subcomponent. Crystal structures show that these assemblies are held together by Ag4I, Ag4Br, or Ag6(SO4)2 clusters, where the templating anion plays an integral structure-defining role. Prior to the addition of the anionic template, no six-stranded helicate was observed to form, with the system instead consisting of a dynamic mixture of triple helicate and tetrahedron. Six-stranded helicate formation was highly sensitive to the structure of the ligand, with minor modifications inhibiting its formation. This work provides an unusual example of mutual stabilization between metal clusters and a self-assembled metal–organic cage. The selective preparation of this anisotropic host demonstrates new modes of guiding selective self-assembly using silver(I), whose many stable coordination geometries render design difficult.
Highlights
We describe the formation of an unexpected and unique family of hollow six-stranded helicates
Self-assembly can produce complex metal−organic architectures from simple starting materials.[1−5] Such structures have been the subject of intense recent exploration, with applications spanning guest binding, stabilization of reactive species, biomolecular interactions, and chemical purification.[6−9] These applications often depend on binding a target in the pseudospherical cavity of a metal−organic cage
Zhao and co-workers have previously shown that nitrogen containing macrocycles can stabilize atomically precise silver clusters with defined geometries, supporting this hypothesis.[50,51]
Summary
We describe the formation of an unexpected and unique family of hollow six-stranded helicates. The introduction of flexible organic ligands[14−16] or metal coordination spheres[17−20] has led to the formation of new metal−organic cages, with nonspherical internal cavities, partially alleviating these limitations.[21−25] Silver(I), in combination with dipyridyl peptidic linkers, has recently been shown to generate a wealth of complex knotted architectures via self-assembly.[26−28] The strategy of incorporating a guest of interest into the architecture formed, as a template[29−31] or other structural element,[32,33] can enhance selectivity and sensitivity in guest binding.[34−36] if the guest is anionic,[37−39] the diverse coordination chemistry of anions can be used to effect the selective recognition[40−42] of targeted anions.[43]
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