Synthesis and structure of [Na11(O^tBu)10(OH)]: 1H NMR shift of a hydroxide ion encapsulated in a 21-vertex alcoholate cage

[Na11(O^tBu)10(OH)], a hydroxide enclosing 21-vertex cage compound, was found to crystallize from mixtures of sodium tert.butanolate with sodium hydroxide. Its structure can be derived from the known (NaOtBu)6-hexaprismane by replacing one butanolate unit with OH– and capping the latter with five additional units of NaO^tBu. The hydroxide shows a signal at –3.21 ppm in the 1H NMR spectrum.