Tb3N@C84 :  An Improbable, Egg-Shaped Endohedral Fullerene that Violates the Isolated Pentagon Rule

Abstract.The structure of isomer 2 of Tb3N@C84 has been determined through single-crystal X-ray diffraction on Tb3N@C84·NiII(OEP)·2(C6H6). The carbon cage has a distinct egg shape due to the presence of a single pair of fused pentagons at one apex of the molecule. Thus, although 24 IPR structures are available to the C84 cage, Nature utilizes one of the 51 568 isomeric structures that do not conform to the IPR for this unusual molecule. The Tb3N portion of isomer 2 of Tb3N@C84 is strictly planar. One Tb atom is nestled within the fold of the fused pentagons, while the other Tb atoms are disordered over four pairs of sites.

Tb3N@C84 :  An Improbable, Egg-Shaped Endohedral Fullerene that Violates the Isolated Pentagon Rule, Beavers, Christine M., Zuo Tianming, Duchamp James C., Harich Kim, Dorn Harry C., Olmstead Marilyn M., and Balch Alan L. , Journal of the American Chemical Society, 09/2006, Volume 128, Issue 35, p.11352 - 11353, (2006)



BuckyEgg Tb3N@C84: image credit Mark Winter

Go to work on a terbium nitride buckyegg

BuckyEggBuckyEggAn egg-shaped fullerene, or "buckyball egg" has been made and characterized by chemists in America at UC Davis (California), Virginia Tech, and Emory and Henry College in Virginia. They were trying to encapsulate terbium atoms within fullerenes but instead encapsulated terbium nitride within an egg-shaped fullerene.1

The compound Tb3N@C84 was synthesized using an arc-discharge generator by vaporizing composite graphite rods containing a mixture of Tb4O7, graphite, and iron nitride as catalyst in a low-pressure He/N2atmosphere. This gave a complex mixture of products and chromatography gave seven terbium-containing fractions, the fourth fraction of which contained two isomers of Tb3N@C84. Crystallographc studies show the compound from one angle in particular seems very egg shaped! Remarkable! The Tb3N unit is clearly visible (terbium in green and nitrogen in blue).

Until the publication of this work it was normally accepted that no two pentagons can touch in a fullerene and are always surrounded by hexagons. However in this case there are two pentagons (the 8 atoms at the pointy part of the egg at the top of the attached image) linked as a bent pentalene fragment.

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Copyright 1993-2011 Mark Winter [The University of Sheffield and WebElements Ltd, UK]. All rights reserved.