Methylation of HNEt3[NB11H11] by Me triflate gave MeNB11H11 (I) which added MeOH to give H[MeNB11H11(OMe)] (II). II in CH2Cl2 in the presence of excess MeOH completely dissocd. Although the free acid II could not be isolated, [(Ph3P)2N][MeNB11H11(OMe)] (III) was isolated and characterized by NMR and x-ray structural anal. III is orthorhombic, space group Pca21, Z = 4, R = 0.058, Rw = 0.066. The anion of III has a nido structure. This nido structure is thermodn. very stable and is not solvolyzed in H2O or alcs. [MeNB11H11R]- (R = Me, Me3CO, F) were also formed from I and LiMe/tetramethylethylenediamine, KOCMe3/18-crown-6 and KF/18-crown-6, resp.