Some small weakly coordinating anions based on carboranes.

The intrinsic gas-phase acidities of CB4XnH5-n and CB5XnH6-n (X ≡ F, Cl or CF3) were calculated using the DFT B3LYP method at the 6-311+G** level. For comparison also the 6-31+G* basis set was used for fluorinated species. The results of the two calculation levels correlated satisfactorily. As the most favourable protonation site of these anions, the facet on the opposite side from the carbon-peaked polyhedron was found. When ordering the substituent groups in terms of increasing acidity of the carboranes, the order F < Cl < CF3 was obtained. [ABSTRACT FROM AUTHOR]