Carborane acid

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Ball-and-stick model of the carborane acid anion. (Acidic proton not displayed).

Colour scheme:
hydrogen − white,
chlorine − green,
boron − pink,
carbon − black.

Carborane acid H(CHB11Cl11) is a superacid [1] one million times stronger than sulfuric acid.[2][3] The reason for this high acidity is that the acid anion carborane (CHB11Cl11) is very stable and substituted with electronegative substituents (the chlorine atoms). H(CHB11Cl11) is the only acid known to protonate C60 fullerene without decomposing it.[4][5] Additionally, it is the only known anion capable of forming a stable, isolable salt with protonated benzene, C6H7+. In coordination chemistry carboranes can be used as unique bulky ligand scaffolds. It was recently demonstrated that the same carboranyl moiety can act either as strongly electron-withdrawing or electron-donating substituent, depending on the positional attachment of the cluster to the heteroatom.[6]


  1. ^ Note that the image the acidic proton is not the one bonded to the carborane but that it is the counterion not displayed
  2. ^ Olah, G. A.; Prakash, G. K. S.; Sommer, J.; Molnar, A. (2009). Superacid Chemistry (2nd ed.). Wiley. p. 41. ISBN 978-0-471-59668-4. 
  3. ^ That is, the concentration of H+ in a solution of the carborane superacid is a million times higher than in a solution of sulfuric acid.
  4. ^ Juhasz, M.; Hoffmann, S.; Stoyanov, E.; Kim, K.-C.; Reed, C. A. (2004). "The Strongest Isolable Acid". Angewandte Chemie International Edition 43 (40): 5352–5355. doi:10.1002/anie.200460005. PMID 15468064. 
  5. ^ Reed, C. A. (2005). "Carborane acids. New "strong yet gentle" acids for organic and inorganic chemistry" (pdf). Chemical Communications 2005 (13): 1669–1677. doi:10.1039/b415425h. PMID 15791295. 
  6. ^ Spokoyny, A. M.; Machan, C. W.; Clingerman, D. J.; Rosen, M. S.; Wiester, M. J.; Kennedy, R. D.; Stern, C. L.; Sarjeant, A. A.; Mirkin, C. A. (2011). "A coordination chemistry dichotomy for icosahedral carborane-based ligands". Nature Chemistry 3 (8): 590–596. Bibcode:2011NatCh...3..590S. doi:10.1038/nchem.1088. PMID 21778977. 

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