The synthesis of clathrate-II germanium square Ge-24(136) in an ionic liquid was recently discovered.(1) The key step in this process, the controlled oxidation of reactive precursor phases by a protic acid, was successfully applied to silicides M4Si4 (M = Na, K). Through this method, clathrate-I compounds of composition M8-xSi46 were obtained as crystalline products. The synthetic method demonstrates a mild oxidative route to a large class of metastable intermetallic compounds.