Triangular Regulation of Cucurbit[8]uril 1:1 Complexes
Résumé
Triangular shapes have inspired scientists over time and are common in nature, such as the flower petals of
oxalis triangularis, or the triangular faces of tetrahedrite crystals or on the icosahedron faces of virus capsids. Supramolecular chemistry has enabled the construction of triangular assemblies, many of which possess functional features.
Among these structures, cucurbiturils have been used to build supramolecular triangles and we recently reported paramagnetic - cucurbit[8]uril (CB[8]) triangles but reasons of their formation remain unclear. Several parameters have now
been identified to explain their formation. At first sight, the radical nature of the guest appeared of prime importance to
get the triangles and we focused on extending this concept to biradicals for obtaining supramolecular hexaradicals. Two
sodium ions were systematically observed by ESI-MS in trimer structures and the presence of Na+
triggered or strengthened the triangulation of CB[8]:guest 1:1 complexes in solution. X-ray crystallography and molecular modelling have allowed proposing two plausible sites of residence for the two sodium cations. We then found that a diamagnetic guest
with an H bond acceptor function is equally good at forming CB[8] triangles. Hence, a guest molecule containing a ketone
function has been precisely triangulated thanks to CB[8] and sodium cations as determined by DOSY-NMR and DLS. A
binding constant for the triangulation of 1:1, to 3:3 complexes, is proposed. This concept has finally been extended to the
triangulation of ditopic guests toward network formation by reticulation of CB[8] triangles using dinitroxide biradicals.
Domaines
Chimie
Origine : Fichiers produits par l'(les) auteur(s)