Formation of a low-symmetry Pd 8 molecular barrel employing a hetero donor tetradentate ligand, and its use in the binding and extraction of C 70 .

The majority of reported metallo-supramolecules are highly symmetric homoleptic assemblies of M x L y type, with a few reports on assemblies that are obtained using multicomponent self-assembly or using ambidentate ligands. Herein, we report the use of an unsymmetrical tetratopic ligand (L un ) containing pyridyl and imidazole donor sites in combination with a cis -protected Pd(ii) acceptor for the formation of a low-symmetry M 8 L un 4 molecular barrel (UNMB). Four potential orientational isomeric (HHHH, HHHT, HHTT, and HTHT) molecular barrels can be anticipated for the M 8 L un 4 type metallo-assemblies. However, the formation of an orientational isomer (HHTT) of the barrel was suggested from single-crystal X-ray diffraction and 1 H NMR analysis of UNMB. Two large open apertures at terminals and the hydrophobic confined space surrounded by four aromatic panels of L un make UNMB a potential host for bigger guests. UNMB encapsulates fullerenes C 70 and C 60 favoured by non-covalent interactions between the fullerenes and aromatic panels of the ligand molecules. Experimental and theoretical studies revealed that UNMB has the ability to bind C 70 more strongly than its lower analogue C 60 . The stronger affinity of UNMB towards C 70 was exploited to separate C 70 from an equimolar mixture of C 70 and C 60 . Moreover, C 70 can be extracted from the C 70 ⊂UNMB complex by toluene, and therefore, UNMB can be reused as a recyclable separating agent for C 70 extraction.