Natural systems such as enzymes and antibodies possess strong and selective host–guest binding using multiple noncovalent interactions which inspire supramolecular chemists to design water soluble synthetic receptors (covalent cages, and coordination cages) that can accommodate guest inside its cavity.1 The confined nano-space present in selected receptors has been exploited for host-guest chemistry and intriguing functions.2 In the seminar, discussion will be focus on design, synthesis and application of water-soluble cationic Pd6L'6L3 type trigonal molecular prism (MP), 13 and Pd8L'8L4 type molecular cuboid (MC), 2 where L' and L stand for tmeda and tetradentate nonchelating ligand, respectively. The Pd(II) ions are located at the vertices of the coordination cages/architectures. The coordination cages 1 and 2 have been synthesized by complexation of cis-Pd(II)(tmeda)(NO3)2 with designer tetra-pyridyl ligands L1 and L2 in separate reactions. The approximate dimension of the molecular prism (1) is 8 x 14 A in terms of basal length and height whereas for the molecular cuboid (2) it is 12 x 13 x 13 A. The cage molecules could encapsulate hydrophobic guest molecules in a size/shape selective manner in water medium. The guest binding preference the prismatic cage 1 qualitatively follows the order nonpolar polar anionic. The aromatic walls of cage 1 protect encapsulated radical initiators like AIBN and HMPP from decomposition even after deliberate irradiation of the host-guest complexes with UV light. The bigger cage 2 shows encapsulation certain polyaromatic guest molecules in water, that the cage 1 could not accommodate due to size restriction. In fact, the cage 2 could even bind larger supramolecular compounds like selected crown ethers and cryptands. Binding of one unit of selected crown ethers by cage 2 and intriguing Cs+ induced conformational alteration of encapsulated crown ether as well as change in host-guest stoichiometry will be discussed. The nano-space of cage 2 was considered as a suitable molecular reaction vessel in view of its large size. Knoevenagel condensation reactions of selected aromatic aldehydes and active methylene compounds were successfully performed in the cavity of 2 using water as solvent. A mononuclear diamagnetic Ni(II) complex upon encapsulation by cage 2 showed ferromagnetic behaviour probably due to some cage induced confinement effect. Alteration of physical/chemical properties of guest molecules when bound in the coordination cage is a notable theme of discussion of the seminar.

1. Stank, A.; Kokh, D. B.; Fuller, J. C.; Wade, R. C. Acc. Chem. Res. 2016, 49, 809–815.
2. Takezawa, H.; Fujita, M. Bull. Chem. Soc. Jpn. 2021, 94, 2351-2369.
3. Ray, M.; Krishnaswamy, S.; Pradhan, A. K. Chand, D. K. Chem. Mater. 2023, 35, 6702- 6712. (Cover Page)