This invention relates to an improved method for making unsubstituted carborane anions and monosubstituted carborane anions of formula: (R--CB.sub.n--H.sub.m').sup.- 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--CB.sub.11H.sub.11.sup.-, where R is a defined above, and is specifically useful for preparation of the unsubstituted carborane CB.sub.11H.sub.12-??, where R is H.