Isolated pentagon rule
Sir Harry Kroto believed C60 was stable because it was the smallest cage which could be constructed with five and six membered rings, in which all the pentagons were isolated.
Kroto continued to wonder when this Isolated Pentagon Rule requirement was satisfied again, and found that he could not make one between C60 and C70. He believed that if C60 was a stable truncated icosahedron, as they had proposed, then C70 must be the next special structure.
As he had seen that C70 was the next special structure experimentally, Kroto thought this was the most convincing circumstantial evidence for the validity of their buckminsterfullerene structural proposal, prior to its isolation in 1990.
Sir Harry Kroto wanted to publish an image of their mass spectrum showing C28 dominant but the request was denied.
Kroto also believed that Multiplet IPR metastability criteria (MIPR) might operate for fullerenes smaller than C60 such as C50.
I knew that the Galveston group had the quantum chemistry experience to verify my conjecture that no IPR structure existed between C60 and C70. I called them up on the telephone.
Tom Schmalz told me that they had reached the same conclusion and said they had almost completed the proof of this conjecture.
Sir Harry Kroto
Kroto continued, "So, the IPR was developed simultaneously and independently by the Galveston group which furthermore proved it elegantly. They also proved the MIPR concept in their comprehensively exhaustive theoretical study.
"Our recent work at FSU/Maglab has confirmed these early observations and shown that C28 is very special indeed. It can satisfy its tetravalency by trapping a tetravalent individual atom such as Ti, Zr or U."
Icosahedral carbon particles
A simple model building exercise led to the conclusion that closed large fullerenes would have quasi-icosahedral structures. This project was initially an arts project as Kroto wanted to build a large fullerene structure as a sculpture.
To my surprise it was not round like Buckminster Fuller’s Montréal dome. As all the curvature was focused around the pentagons, the surface is essentially flat between them. This resulted in an explanation of why spheroidal carbon particles have the quasi-icosahedral structures that had been observed. This is a nice example of an arts project resulting in a science breakthrough. An unusual situation!
Sir Harry Kroto
Articles
IPR and C28 paper (PDF, 566KB)
The smallest stable fullerene, M@C28 (M = Ti, Zr, U): stabilisation and growth from carbon vapor
The formation of quasi-icosahedral spiral shell carbon particles
The formation of quasi-icosahedral spiral shell carbon particles (PDF, 513KB)