Raman and 29Si MAS NMR spectroscopy of framework materials containing three-membered rings

Raman and ²⁹Si MAS NMR spectroscopies are evaluated for the identification of three-membered rings (3MR) in framework oxide materials. Raman and ²⁹Si MAS NMR spectra from the 3MR-containing materials euclase, phenakite, clinohedrite, willemite, lovdarite, VPI-7, ZSM-18 and dipotassium zinc tetrasilicate are presented. The Raman spectra from these materials do not exhibit common bands representing vibrational modes assignable to individual 3MR. The dense beryllosilicate and zincosilicate minerals exhibit ²⁹Si MAS NMR resonances indicative of silicon positioned in 3MR while the molecular sieves lovdarite and VPI-7 give ²⁹Si MAS NMR resonances that can be assigned to silicons located at the center of “spiro-5” units that are constructed from two 3MR. Silicon atoms located in isolated 3MR in the molecular sieves ZSM-18 and dipotassium zinc tetrasilicate do not exhibit ²⁹Si MAS NMR resonances that can be distinguished from those assigned to silicons residing in 4MR and larger.The ²⁹Si MAS NMR spectra from the new materials VPI-8, VPI-9 and VPI-10 do not exhibit ²⁹Si MAS NMR resonances indicative of “spiro-5” units. The presence of isolated 3MR in these materials cannot be ruled out from the ²⁹Si MAS NMR spectroscopic results.