Kinetically Controlled Fast Crystallization of M12L8 Poly-[n]-catenanes Using the 2,4,6-Tris(4-pyridyl)benzene Ligand and ZnCl2 in an Aromatic Environment

Abstract

Kinetic control in the presence of six aromatic solvents has been successfully applied in the synthesis of a poly-[n]-catenane composed of interlocked M12L8 icosahedral nanometric cages (i.e., internal voids of 2500 Å3). Using the exo-tridentate tris-pyridyl benzene ligand and ZnCl2 with appropriate templating molecules, due to good ligand aromatic interactions, the met-al-organic cages can be synthesized very fast, homogeneously and in large quantities as microcrystalline materials. Synchro-tron single crystal X-ray data (100 K) allowed the resolution of nitrobenzene guest molecules at the internal walls of the M12L8 nanocages while in the central part of the cages the solvent is highly disordered. The guest release occurs in two steps with the disordered nitrobenzene guests released in the first step (lower temperatures) due to the absence of strong cage-guest interactions. Density Functional Theory calculations provided a rationalization of these outcome and in particular, solid state approaches, showed theoretical evidence of the kinetic nature in the formation of the poly-[n]-catenane by the analysis of the packing energy in terms of monomeric and dimeric cages.