Rare experimental evidence of direct metal–metal bonding between the often-overlooked rare earth elements

Fullerine gif with inner part

Source: © Royal Society of Chemistry

Theory had predicted a direct single bond between two yttrium centres but researchers had struggled to realise it experimentally. Now, scientists in China have become the first to make the elusive bond as part of an endohedral metallofullerene.

Xing Lu from Huazhong University of Science and Technology and colleagues used the stabilising effect of a fullerene cage to assist them in making the yttrium–yttrium bond. They prepared the metallofullerenes by arc discharge of a graphite/Y2O3 mixture and separated the resulting products by HPLC. This allowed the researchers to observe the encapsulated metals by x-ray crystallography.

Measured bond distances indicate that a single bond forms between two divalent yttrium sites. Interestingly, the direct yttrium–yttrium interaction was observed only in relatively small cages (C82) with yttrium carbide clusters forming in larger cages (C86-92).