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Cage Keeps C60 Captive In The Solid State

Molecular cage captures fullerene guests, even in the absence of solvent

by Bethany Halford
July 26, 2010 | A version of this story appeared in Volume 88, Issue 30

Credit: Nat. Chem.
The new molecular cage catches C60 (orange) in its cuboctahedral voids.
Credit: Nat. Chem.
The new molecular cage catches C60 (orange) in its cuboctahedral voids.

Molecular cages can be the rudest of hosts. Guests are welcome as long as there’s plenty of solvent around, but removing the cages from solution and close packing keeps visitors out. Now, chemists in Japan have created a molecular cage capable of capturing fullerene guests, even in the solid state (Nat. Chem., DOI: 10.1038/nchem.742). The University of Tokyo’s Makoto Fujita, Yasuhide Inokuma, and Tatsuhiko Arai created a “crystalline molecular sponge” from a network of octahedral M6L4 cages, where the metal complex M is Co(NCS)2 and the ligand L is 2,4,6-tris(4-pyridyl)-1,3,5-triazine. The material has three distinct cage structures, possessing vast interstitial voids with the cuboctahedral cage structures M12L8 and M12L24, which are capable of capturing C60 and larger fullerenes. When crystals of the molecular cage were soaked in a saturated toluene solution of C60, they absorbed an impressive 35% of the material’s weight in the fullerene, gradually turning black in the process. Furthermore, when the crystals were placed in a solution that was equal parts C60 and C70, the material preferentially absorbed the larger fullerene, which, according to the authors, could lead to new methods for enrichment and isolation.


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