Neighboring Cage Participation for Assisted Construction of Self-Assembled Multicavity Conjoined Cages and Augmented Guest Binding.

A set of PdL, PdL, and PdL-type single-, double-, and triple-cavity cages are prepared by complexation of Pd(NO) with designer bis-monodentate (), tris-monodentate (), and tetrakis-monodentate () ligands. The PdL cage exists in equilibrium with a PdL cage; the equilibrium shifted to PdL at 70 °C or upon addition of pyrazine--dioxide (PZDO). The PdL cage binds a PZDO molecule using electrostatic, bifurcated H-bonding and overcoordinated H-bonding interactions. The discrete PdL and PdL compounds are conjoined cages comprising of unequal sized PdL cages (bigger and smaller). The bigger unit of PdL cage selectively binds a PZDO, and the smaller one binds a nitrate, fluoride, chloride, or bromide. The PdL cage, having a central bigger PdL cavity and two smaller peripheral PdL cavities, binds one PZDO and two nitrate, fluoride, chloride, or bromide. The smaller cavity can be prepared individually from Pd(II) and bis-monodentate ligand (), however, in the presence of template like a nitrate, fluoride, chloride, or bromide; otherwise, it forms an oligomeric mixture. Notably, the conjoined PdL and PdL cages could be prepared with (preferably) or without using a template for smaller cavity, and the bigger PdL is formed by sacrificing the possibility of the PdL moiety. Thus, the conjoined cages are formed in a symbiotic manner where the neighboring cages participate in the formation of each other. The binding of PZDO shows that the presence of one neighboring cage (as in PdL) augments the binding affinity and that is further augmented in the presence of two neighboring cages (as in PdL).