Synthesis and structure of the Interchain Expanded Interrupted Zeolites ZEO-4A and ZEO-4B Fig. illustrates the interchain expanded reaction process and the structure of the obtained zeolites, which were solved and refined by combining state-of-the-art 3D electron diffraction (3D ED) and synchrotron powder X-ray diffraction data (SPXRD). The reactions that introduce silicon between the chains of ZEO-2 (Fig. ) are carried out in acidic ethanolic solution using either dimethyldichlorosilane (DCDMS, containing a single Si per molecule) or 2,4,6,8tetramethylcyclotetrasiloxane (TMCTS, a single 4-ring, S4R, containing four Si per molecule with methyl and H substituents at each Si corner). The reaction results in the intercalation of new silicon atoms in between adjacent chains connecting them together in a new stable crystalline zeolite (PXRD shown in Fig. ). The resulting materials, which we call ZEO-4A (Fig. ) and ZEO-4B (Fig. ), respectively, depending on the silylating agent used, DCDMS or TMCTS respectively, maintain the needle like morphology of ZEO-2 (Fig. ). While our previous ZEO-1 to ZEO-3 materials were all developed and patented by the Anhui ZEO New Material Technology Co., China, the materials reported in this work have been developed in the ICMM-CSIC, Spain, but the same ZEO nomenclature has been used for convenience. The interchain expansion concept by insertion of DCDMS or TMCTS and the knowledge of the 29 Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) in Fig. of ZEO-4A (D 2 + Q 4 ) and ZEO-4B (T 3 + Q 4 ), respectively, see below, allowed us to model build the corresponding structures of both zeolites followed by optimization by density functional Tight Binding (TB) methods (see details in the supplementary information). Nonetheless, the single-crystal structure of both ZEO-4A and ZEO-4B was successfully solved ab initio by using continuous rotation electron diffraction (cRED). Thanks to the high-quality cRED data (Fig. -S4, Tables , and S5), the positions of silicon and oxygen atoms on the framework structure of ZEO-4A and ZEO-4B were located directly from the observed electron density maps (Fig. ), while some dangling Si-CH 3 groups were observed from the difference electron density map during the refinement against cRED data (Fig. ). The resulting ZEO-4 materials contain nominally extra-large 20×16×16 MR pores and present two structurally different variants of the interchain expanded interrupted zeolite because of the different silylating reagents used. With DCDMS the silylating agent contains two methyl groups per Si and can connect only to the silica chains and not among them in ZEO-4A (Fig. ). However, TMCTS contains only a single methyl group per Si so the newly introduced Si atoms connect not only to the chains but are also interconnected in pairs through oxygen bridges in ZEO-4B (Fig. ). The final configuration of the newly introduced Si in ZEO-4B implies the breaking of the TMCTS ring in the acid alcohol solution. In both ZEO-4 materials, the dangling Si-CH 3 groups should effectively reduce the pore apertures and provide a four-lobed shape of the windows along [001] further reducing the effective entrance (Fig. ). To obtain more accurate atomic positions, the structures of ZEO-4A and ZEO-4B, including the position of the dangling Si-CH 3 groups, were subsequently Rietveld refined against SPXRD (Fig. , Table indicating that the originally abundant Q 3 [i.e. Si(OSi) 3 OH or Si(OSi) 3 O -] species in ZEO-2 have essentially all been connected to the newly inserted Si. Additionally, C MAS NMR shows mainly resonances assigned to the methyl groups at -3 and -8 ppm for ZEO-4A and ZEO-4B (Fig. ), respectively, and only in ZEO-4B trace amounts of ethanol can be deduced by the presence of very small resonances at 16 (-CH 3 ) and 58 (-CH 2 OH) ppm. Furthermore, no 31 P MAS NMR signal is detected in ZEO-4A or ZEO-4B (Fig. ), showing that all the organic structure-directing agent (OSDA) in the starting ZEO-2 material has been removed from the zeolite during the IChEZ reaction. This is corroborated by the C and 31 P liquid NMR of the filtrate solution (Fig. ), which shows that the OSDA can be recovered intact, which opens the way to its recycling. Self-supported FT-IR spectra on ZEO-4 also proved the silylation and OSDA removal during the IChEZ procedure (Fig. ). (ZEO-4A, yellow curve) or T 3 (ZEO-4B, orange curve) in addition to Q 4 but not Q 3 . By contrast, ZEO-5 (B) coming from either ZEO-4A (blue curve) or ZEO-4B (violet curve) is a fully connected zeolite containing mainly Q 4 and just a minor concentration of Q 3 connectivity defects, highlighted by the grey vertical line, as proved by the poor intensity enhancement under cross-polarization (CP, black curves).