Up to 4 Cs or Rb atoms per 32 Si atoms can be incorporated into the channels of the all-silica (SiO 2 ) zeolites ITQ-4 and beta with effective oxidation states of zero. The optical properties and 29 Si MAS NMR spectra suggest partial or complete ionization within the channels to yield M + ions and relatively free electrons. This view is supported by a published structural model (
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