Hosting of [Cs(crown ether)] type host-guest complexes by a nano-sized molecular cuboid.

Encapsulation of a guest by host-forming (G-in-H)-type host-guest complexes is the central theme of supramolecular chemistry. Binding of typical hosts (H) in the cavity of a larger host (H) to form (H-in-H) type assemblies is also known. However, the incorporation of host-guest complexes in a larger host to form [(G-in-H)-in-H] type assemblies, where (G-in-H) is composed of one guest and one host is relatively unexplored. A recent report describes the binding of host-guest complexes consisting of one guest and two hosts in a larger host molecule. In the present work, we have prepared a nano-sized polycationic molecular cuboid of the type Pd(L')(L) as the H, which is capable of encapsulating two units of H such as dibenzo[3]crown- (where ranges from 6 to 8). The molecular cuboid is found to selectively recognize the larger-sized dibenzo[24]crown-8 and dibenzo[21]crown-7 over the smaller-sized dibenzo[18]crown-6. The polycationic molecular cuboid can bind a family of [Cs(crown ether)] type cationic host-guest complexes composed of one unit of a guest (Cs) and two units of the H (crown ether). All these complexes are prepared self-assembly in a water medium; the surrogate nuclear waste Cs is deeply internalized, being encapsulated by two units of crown ether, which are in turn sheltered by the molecular cuboid. All the [G-in-(H)-in-H] type assemblies are characterized using spectroscopic techniques and single-crystal structures. The relative orientation of the pair of crown ethers around the Cs ion is found to be different in the native form compared to the encapsulated form in the molecular cuboid.