Hexanuclear coordination cages of the formula [(C5Me4R)M(C7H3NO 4)]6 (M = Rh, Ir; R = Me, H) were obtained by stepwise reaction of [(C5Me4R)M(μ-Cl)Cl]2 with, first AgOAc and then pyridine-3,5-dicarboxylic acid. Crystallographic analyses show that the cages adopt a distorted octahedral geometry with the pyridine-3,5-dicarboxylates functioning as dianionic bridging ligands, each of which connects three different (C5Me4R)M fragments. The cages act as exoreceptors for large alkali metal cations K+ and Cs+, as well as NH4+, but show low affinity for Na+. Crystallographic and NMR spectroscopic analyses indicate that two metal ions can be coordinated to the surface of the cages. The respective binding sites comprise three carbonyl O-atoms from the bridging pyridine-3,5-dicarboxylate ligands. Novel supramolecular architectures were obtained by reacting the dinuclear macrocycle [(cymene)Ru(μ-C12H12O4)(H 2O)]2 with different N-donor ligands. A tetranuclear assembly was obtained with 1,2-di(4-pyridyl)ethylene, whereas hexanuclear complexes were formed with 2,4,6-tris(4-pyridyl)triazine and 1,3,5-tris(4-pyridylethynyl)benzene. The reaction with 5,10,15,20-tetra(4-pyridyl)porphyrine, on the other hand gave tetra- or octanuclear complexes, depending on the stoichiometry that was employed. The 2,4,6-tris(4-pyridyl)triazine complex was shown to act as a host for polycyclic aromatic compounds such as pyrene, triphenylene and coronene. A hexanuclear coordination cage has been formed by self-assembly of three elongated [(cymene)Ru(μ-C14H10O6)] 2 dinuclear macrocycles and two equivalents of 2,4,6-tris(4-pyridyl)triazine. The twisted coordination prism with a height of 3.5 Å (bottom to top) could be untwined by addition of coronene to – for half-sandwich complex-based cages – unprecedented size of 10.8 Å (bottom to top). Crystallographic and NMR spectroscopic analyses indicate that two coronene molecules can be encapsulated inside this cage.
Kay Severin, Farzaneh Fadaei Tirani, Damien Wen Chen, Jean Charles Edouard de Montmollin, Atena-Bianca Solea