Chemistry Nexus

Image credit Mark Winter

An 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. [http://dx.doi.org/10.1021/ja063636k]
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.

Abstract:[http://dx.doi.org/10.1021/ja063636k] 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.

References