Considerations on the symmetry of pure silica ITQ-7 zeolite (ISV) derived from 29Si MAS NMR and Rietveld analysis

• 29Si MAS NMR spectroscopy reveals 16 non equivalent silicon sites for ITQ-7 zeolite.
• A lowering of the symmetry from P42/mmc to P42 is established.
• Space group P42 is confirmed from Rietveld refinement on PXRD data.

Pure silica ITQ-7 zeolite of topology ISV synthesized in fluoride media possesses a 3D 12-membered-rings pore system. Originally the structure of ITQ-7 zeolite was solved and refined from a calcined sample in the highest possible space group symmetry P42/mmc. This space group leads to only 5 independent silicon T sites for this structure. However, this high symmetry was not supported by solid state 29Si MAS NMR spectroscopy. In this short communication, we show from a revised 29Si solid state MAS NMR and Rietveld analyses, that lowering of the space group symmetry from P42/mmc to P42 consolidates structure model and experimental data, in particular, the number of non equivalent crystallographic T sites passing from 5 to 16, is in agreement with 29Si solid state NMR spectroscopy.

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