text: The "at" symbol is exclusively used in the chemical formula of these compounds.
full_question: The "at" symbol is exclusively used in the chemical formula of these compounds. In nanotweezers, these compounds reversibly bend inward when a voltage is applied across them. They are "doped" with potassium to make superconductors above 18 Kelvin. These molecules have mass of either 720 or 840 amus. They have two different bond lengths: those from 6-6 and 6-5 bonds. These materials dissolve in nonpolar solvents to turn bright (*) purple. These molecules can be synthesized by firing a laser at soot. When rolled into cylinders, they form single or double walls. They can hold entire metal atoms inside an icosahedral body. For 10 points, name these allotropes of carbon which forms soccer-ball shaped "buckyballs."
first_sentence: The "at" symbol is exclusively used in the chemical formula of these compounds.
raw_answer: fullerenes [or buckminsterfullerenes; prompt on buckyballs; prompt on carbon nanotubes]