 Based on spectroscopy, substitutions have been reported with boron (borafullerenes), nitrogen (azafullerenes), oxygen, arsenic, germanium, phosphorus, silicon, iron, copper, nickel, rhodium  and iridium.Reports on isolated heterofullerenes are limited to those based on nitrogen  and oxygen.The C60 fullerene dimerizes in a formal [2+2] cycloaddition to a C120 bucky dumbbell in the solid state by mechanochemistry (high-speed vibration milling) with potassium cyanide as a catalyst.