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

The majority of reported metallo-supramolecules are highly symmetric homoleptic assemblies of M L 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) containing pyridyl and imidazole donor sites in combination with a -protected Pd(ii) acceptor for the formation of a low-symmetry ML molecular barrel (UNMB). Four potential orientational isomeric (HHHH, HHHT, HHTT, and HTHT) molecular barrels can be anticipated for the ML type metallo-assemblies. However, the formation of an orientational isomer (HHTT) of the barrel was suggested from single-crystal X-ray diffraction and H NMR analysis of UNMB. Two large open apertures at terminals and the hydrophobic confined space surrounded by four aromatic panels of L make UNMB a potential host for bigger guests. UNMB encapsulates fullerenes C and C 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 more strongly than its lower analogue C. The stronger affinity of UNMB towards C was exploited to separate C from an equimolar mixture of C and C. Moreover, C can be extracted from the C⊂UNMB complex by toluene, and therefore, UNMB can be reused as a recyclable separating agent for C extraction.