A 'H Magic-angle spinning nuclear magnetic resonance investigation of large and uniform crystals of HZSM-5 type zeolites, synthesized either by means of TPA or without organic templates, shows that using TPA leads to a high concentration of defect centres within the ZSM-5 structure. Owing to non-intact Si-0-Si bonds, up to 8 % of the lattice Si were found to be present as Si-OH groups. A comparison of the 1H-2eSi cross-polarization spectra with the variation of the lH n.m.r. chemical shift of the Si-OH groups as well as with the results of ion-exchange experiments suggests a vicinal arrangement of the silanol groups. High concentrations of such structural defects within the crystals lead to a slight decrease of crystal sorption capacity for n-hexane and significantly reduce crystal hydrophobicity. Both the intracrystalline self-diffusion and the molecular reorientation of sorbed molecules as measured by means of the 'H n.m.r. pulsed field gradient technique and 13C n.m.r. lineshape analysis, respectively, show an enhanced molecular mobility of guest molecules within the defective ZSM-5 structure.

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