Supramolecular Metallacycles and Their Binding of Fullerenes

Abstract

The synthesis of a new triaminoguanidinium‐based ligand with three tris‐chelating [NNO]‐binding pockets and C3 symmetry is described. The reaction of tris‐(2‐pyridinylene‐N‐oxide)triaminoguanidinium salts with zinc(II) formate leads to the formation of cyclic supramolecular coordination compounds which in solution bind fullerenes in their spherical cavities. The rapid encapsulation of C60 can be observed by NMR spectroscopy and single‐crystal X‐ray diffraction and is verified using computation.

Anion Directed Selective Synthesis of Supramolecular Metallocycles and Related Coordination Dimers

“…ZnX 2 (dark blue) moieties occupy the twelve remaining [NNO] binding pockets. Chloride, bromide, thiocyanate and formate were already reported as co‐ligands X ‐ [18b] …”

“…As already mentioned, the ligand to zinc(II) ratio is 1 : 2 for binding motif I and 1 : 3 for binding motif II. However, the metallocycles in our earlier publication were obtained using a 1 : 3 ratio, which is why this ratio is kept for the following experiments, because it obviously does not influence the resulting structure type [18b] . The identification and characterization of coordination compounds is mainly related to the solid phase, because structural elucidation by single‐crystal X‐ray diffraction is most reliable and ultimately a solid product is desired.…”

“…9 was already published in our last work as an interesting host molecule for e. g. fullerenes. 1 H‐DOSY‐NMR spectroscopy already revealed neither decomposition nor aggregation of the metallocycles in solution [18b] . Their solubility is closely related to their co‐ligand occupation.…”

“…In contrast to chloride or bromide containing metallocycles, which all crystallize in monoclinic space groups, [18b] metallocycles crystallizing in tetragonal space groups possess channels through their cavities along the crystallographic c‐axis. Metallocycle 9 was already identified as excellent host for fullerene guests like C 60 and C 70 [18b] . The new metallocycles offer more opportunities for further host‐guest chemistry.…”

“…Our group recently introduced a new type of toroidal, supramolecular metallocycles whose cavities serve as excellent hosts for fullerenes C 60 and C 70 [18b] . They are synthesized by self‐assembly of pyridinyl‐derived triaminoguanidinium‐based ligands [H 3 L ]X with three tris ‐chelating binding pockets in presence of zinc(II) and suitable co‐ligands like chloride, bromide, thiocyanate or formate.…”