Do molecules containing only carbon exist?

Why doesn't carbon form bonds with itself to form a molecule? Carbon shows the property of catenation, so why doesn't it form a cyclic molecule such as:



```
 C = C 
 ‖   ‖ 
 C = C 

```



They do form. Besides [fullerenes](https://en.m.wikipedia.org/wiki/Fullerene), there are carbon molecules with varying numbers of atoms [around some stars](http://adsabs.harvard.edu/full/1987ApJ...314..352K). Such molecular forms are, of course, less stable than the macromolecular structures we more commonly see under ambient conditions.


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