‘Pentadiamonds’ could reshape material engineering
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What’s harder than a diamond, a third lighter and could zip with electricity? A pentadiamond. A crystalline arrangement of carbon atoms that is made up mostly of pentagons. These don’t exist yet – they’ve only been created in computer simulations – but if one can be made, it could have a number of useful properties.
Carbon is one of the most versatile elements on the periodic table. Since each carbon atom can bond with up to four others, it is able to form intricate assemblies with different properties, such as ultra-hard diamond, semiconducting graphene and rope-like nanotubes.
Novel arrangements, or allotropes of carbon are being discovered all the time. As many as 1,000 different types are currently known. The search for additional allotropes is like “playing [with] LEGO blocks to create materials with fascinating shapes and structures,” said Susumu Okada, a condensed matter physicist at the University of Tsukuba in Japan.
Using state-of-the-art computer modelling, Okada and his colleagues decided to bring together two molecules – spiro[4.4]nona-2,7diene and [5.5.5.5]fenestratetraene – each of which contained a pentagonal ring of carbon atoms, to see if they might generate a potentially
Adam Mann
useful material. The simulations produced a carbon arrangement looking a bit like a typical football with several smaller footballs glued all around its exterior. The computer model was able to show that this pentadiamond, if it were synthesised in real life, would have some interesting properties.
Along with being stiffer than a standard diamond, which is one of the hardest substances known, pentadiamond would be slightly porous and could conduct electricity like the semiconductors used in electronic devices if chemical impurities were added.
If you held a pentadiamond in your hand it would likely feel lighter than a similar-sized diamond, though it wouldn’t be clear – rather a greyish colour like graphite. Because of its porous nature pentadiamond might be useful for storing gas, Okada said. Its lightness and hardness could make it useful for building the bodies of race cars, he added.
Purusottam Jena, a physicist at Virginia Commonwealth University, who was not involved in the work but has discovered other carbon allotropes, said the material is potentially quite exciting. “However, it needs to be experimentally synthesised,” he added, and until then remains strictly theoretical.