The organic precursor of the seminal experiment for the generation of C 18 is the cyclocarbon oxide molecule C 18 -(CO) , and the preparation process is to remove the masking carbonyl groups (-CO) from it sequentially . Two other novel carbon-rich molecules with cyclic skeleton, C 18 -(CO) and C 18 -(CO) 2 , are usually emerged as chemical intermediates, and the final all-carboatomic C 18 ring can be formed in one or more steps. It was found from some experimental explorations that C 18 -(CO) 6 is an easily synthesized and relatively stable species under ambient conditions , and researchers even determined its crystal structure by X-ray diffraction very early .