Accordingly, the 29 Si MAS NMR spectra (Fig. ) contain only Q 4 silicon resonances and are essentially identical irrespective of the starting material, apart from minor differences in peak broadening and resolution (blue and violet curves). The small concentration of Q 3 resonances is demonstrated by the poor intensity enhancement under 29 Si{ 1 H} cross polarization (CP) conditions (black curves). A resonance at -98.6 ppm in the direct irradiation spectra (blue and violet curves), which is not enhanced under cross polarization, is at an unusually low field for a Q 4 Si site in SiO 2 zeolites (at least 6 ppm at a lower field than previous reports) but this is just due to the very sharp Si-O-Si angles at the responsible Si site, corresponding to an average angle of 126.3º according to the experimental relationship of Thomas et al. The single-crystal structure of ZEO-5 was also solved ab initio by using cRED. The cRED data were collected on the calcined crystals of both variants of ZEO-4 separately, and both resulted in C-centered monoclinic symmetry with a resolution of ~0.80 Å and more than 95% completeness (Fig. , Tables S3-S4, and S6). The structures of calcined ZEO-5A and ZEO-5B were solved directly in the space group C2/c. Again, all the atoms, both silicon and oxygen, in the framework of the calcined materials were located directly from the observed electron density maps (Fig. ). As stated above, the structure of the calcined zeolite, ZEO-5 (Fig. ), is unique irrespective of the starting ZEO-4 material and contains two fused double four-ring units that we call triple 4R (T4R). Such a structural unit has never been seen before in a zeolite, either natural or synthetic, regardless of chemical composition. The existence of T4R in ZEO-5 was double checked in the difference electron density map during the refinement against the high-quality cRED data (Fig. ). The framework of ZEO-5 was refined anisotropically against the cRED data, and the refinement converged to an unweighted residual factor (R 1 ) value of 0.1139 and 0.1268 for the material obtained from ZEO-4A and ZEO-4B, respectively (Table ). Further Rietveld refinement of the structure of ZEO-5 against SPXRD data was performed to obtain more precise bond lengths and angles (Fig. , Tables ). With the precise structural model in hand, we assign the -98.6 ppm resonance mentioned above to the Si atoms in the central 4R of the T4R (Si12 and Si13 with average Si-O-Si angles in the Rietveld refined structure of 137.5° and 137.0°, respectively). These average angles are less acute than expected according to the experimental equation mentioned above (126.3°) but it must be taken into account that these angles and chemical shifts are very much outside the range of experimental data used in determining the equation. The structural models derived by cRED and Rietveld refinement have been confirmed by STEM imaging (Fig. ).