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 nanoreactorsWe 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-2011-0059PCT-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-2011StG-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 Ramon y Cajal contract. We thank Dr. Teodor Parella for fruitful discussions. We thank STR's from UdG for technical support, and we also acknowledge the computer resources, technical expertise, and assistance provided by the Barcelona Supercomputing Center Centro Nacional de Supercomputacion, and Centre de Serveis Cientifics i Academics de Catalunya (CESCA) for partial funding of computer tim