While zeolites typically crystallize as three-dimensional (3D) fully connected framework materials, called tectosilicates when silica based, there exist examples of layered zeolite precursors that only form the final zeolite by a postsynthetic 2D-3D topotactic condensation.[ ] The 2D layered precursors have been shown to also offer the opportunity to produce expanded versions of the corresponding zeolite by an intralayer expansion reaction of the layered precursor with a silylating agent.[ ] This reaction introduces Si atoms between the layers, thus increasing the number of Si members in the ring limiting the pores. The obtained materials are called Interlayered Expanded Zeolites (IEZ), although we propose to use a different acronym, ILEZ, for reasons that will be obvious below. ILEZ materials are interrupted frameworks rather than true zeolites because dangling Si-R or Si-OH groups remain in the final as-made and calcined materials, respectively.[ ] Very recently, we have reported the first case of a 1D-to-3D topotactic condensation of a complex chain silicate zeolite precursor (ZEO-2) into the extra-large pore ZEO-3 zeolite, which was at that time the silica polymorph of lowest density ever reported. ZEO-3 has a 3D system of pores open through rings containing 16, 14, and 14 tetrahedra (16×14×14 membered ring, MR). Here we report that it is possible to introduce silicon between the chains of ZEO-2, resulting in what we call Interchain Expanded Zeolites (IChEZ). The resulting zeolites have a 3D system of extra-large 20, 16, and 16 MR and after calcination contains no dangling bonds, so it is a true fully connected tectosilicate zeolite that, additionally, contains triple 4-ring (T4R) units never observed before. Introduction of Ti in ZEO-5 results in an extra-large pore catalyst for the selective oxidation of alkenes.