“…An interesting feature of fullerides is also the possibility of their polymerization at extreme conditions [ 237 , 238 , 239 , 240 ], which opens new synthetic strategies for obtaining carbon allotropes with entirely new physico-chemical properties. Polymerization can also be promoted by the intercalation of a wide range of electron donors (e.g., metals including Li, Na, K, Rb, or Mg), by entering the voids of the host fullerene lattice to form fully fledged solids [ 237 , 241 , 242 , 243 , 244 , 245 , 246 ].…”