Crystal and solution structures of the novel complex of sodium ketimide with two ketimine ligands [(tBu2C = NNa)4(HN = CtBu2)2]: stacking of complexed and uncomplexed (NNa)2 rings to give a highly distorted (NNa)4 cubane

Structure determinations of organometallic compounds of alkali metals often reveal new surprises: In the case of the sodium ketimide [(tBu2C = NNa)4(HN = CtBu2)2] 1, nonmetalated ketimine units function surprisingly as monodentate ligands for two of the four Na+ ions in the cubane-like (NNa)4 framework. This contrasts significantly with the well-known lithium ketimides such as (tBu2C = NLi)6, which in general resist complexation. Applying the ''ring-stacking principle'' from organolithium compounds, 1 can be interpreted as a twofold stack of (NNa)2 rings.