This invention relates to an improved method for making unsubstituted carborane anions and monosubstituted carborane anions of formula: (R—CBn—Hm′)− where n is an integer ranging from 5 to about 11 and m′ is an integer ranging from 5 to 16 where the relative values of n and m′ depend upon the exact structure of the carborane and the presence of a non-hydrogen substituent. m as used herein is an integer ranging from 5 to 16. When R is hydrogen the anion is unsubstituted. When R is a halogen, a phenyl, a substituted phenyl group, such as fluorophenyl group, or any other substituent, the carborane is substituted. The method is particularly useful for preparation of twelve-vertex carborane anions R—CB11H11−, where R is a defined above, and is specifically useful for preparation of the unsubstituted carborane CB11H12-??, where R is H.