Self-assembled tetragonal prismatic molecular cage highly selective for anionic π guests

The metal-directed supramolecular synthetic approach has paved the way for the development of functional nanosized molecules. In this work, we report the preparation of the new nanocapsule 3⋅(CF3SO3)8 with a A4B2 tetragonal prismatic geometry, where A corresponds to the dipalladium hexaazamacrocyclic complex Pd-1, and B corresponds to the tetraanionic form of palladium 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (2). The large void space of the inner cavity and the supramolecular affinity for guest molecules towards porphyrin-based hosts converts this nanoscale molecular 3D structure into a good candidate for host–guest chemistry. The interaction between this nanocage and different guest molecules has been studied by means of NMR, UV/Vis, ESI-MS, and DOSY experiments, from which highly selective molecular recognition has been found for anionic, planar-shaped π guests with association constants (Ka) higher than 109 M−1, in front of non-interacting aromatic neutral or cationic substrates. DFT theoretical calculations provided insights to further understand this strong interaction. Nanocage 3⋅(CF3SO3)8 can not only strongly host one single molecule of M(dithiolene)2 complexes (M=Au, Pt, Pd, and Ni), but also can finely tune their optical and redox properties. The very simple synthesis of both the supramolecular cage and the building blocks represents a step forward for the development of polyfunctional supramolecular nanovessels, which offer multiple applications as sensors or nanoreactors.We are grateful for financial support from the MICINN of Spain (CTQ2009-08464/BQU to M.C., CTQ2011-25086/BQU, CTQ2011-23156/BQU, PhD grant AP2010-2517 to M.G.B, INNPLANTA- INP-2011-0059-PCT-420000-ACT1 and Consolider-Ingenio CSD2010-00065), the FEDER fund (European Fund for Regional Development) for the grant UNGI08-4E-003, the European Research Council for Project ERC-2011- StG-277801 to X.R. and ERC-2008-StG-29910 to M.C., and the Generalitat de Catalunya (2009SGR637, 2009SGR528, and a Ph.D. grant to C.G.S.). X.R. and M.C. thank ICREA-Academia awards. I.I. thanks MINECO for a Ramón y Cajal contract.Peer Reviewe