("extra-large pore zeolites" have pore apertures formed by rings of at least 14 T atoms). The materials IM-12 (UTL), ITQ-33 (ITT), ITQ-37 (-ISV), ITQ-44 (IRR), ITQ-54 (-IFU), and CIT-13 (*CTH) fall in this category. Systems containing Ge-rich d4r units have received particular attention due to the possibility to selectively remove Ge from the framework. Selective Ge removal forms the basis of the so-called ADOR (assembly -disassembly -organisation -reassembly) mechanism, a versatile strategy to prepare new frameworks that are unavailable through direct synthesis. Finally, several phosphate-based zeotypes with d4r cages have been synthesised in fluoride-containing media, among them the extra-large pore gallophosphate (GaPO) cloverite (-CLO) and LTA-type aluminophosphates (AlPOs). While practical applications of cloverite are severely limited due to its low stability, AlPO4-LTA has been employed in membrane-based separations and in thermal energy storage. X-ray diffraction investigations of as-synthesised samples prepared via the "fluoride route" have typically located the fluoride anions at, or close to, the centre of the d4r cage in all-silica zeolites like octadecasil, ITQ-7, ITQ-12, and ITQ-13, and in GeO2 zeotypes like ASU-7 (ASV), ASU-9 (AST), FOS-5 (BEC), ITQ-21, and IM-10 (UOZ). In AlPO4 and GaPO4 zeotypes, somewhat different locations have been reported for different structures: While the fluoride anions are situated at the centre of the cage in AlPO4-16 (AST) and in cubic LTA-type AlPO4 and GaPO4, off-centre displacements were observed in rhombohedrally distorted AlPO4-LTA and in the gallophosphate cloverite. This off-centre displacement, which coincides with a distortion of the d4r cages, leads to a certain variation in the distances between fluoride and the Al/Ga atoms at the corners, with Al-F distances in rhombohedral AlPO4-LTA ranging from 2.52 to 2.82 Å, and Ga-F distances from 2.29 to 2.65 Å in cloverite. The propensity of fluoride to form Al-F/Ga-F bonds, often occupying a bridging position between two such atoms, is well known. Such bonding environments are found, for example, in AlPO4 and GaPO4 zeotypes with "ring-opened" d4r (sti cage) units (SSZ-51, GaPO4-ZON ) and in CHA-and GIS-type fluoroaluminophosphates. With typical Al-F distances of ~1.85 to 2.0 Å, and Ga-F distances of ~1.9 to 2.2 Å, the distances observed in these zeotypes are shorter than those found in d4rcontaining systems, pointing to a different bonding character. The isotropic displacement parameters of F atoms located inside d4r cages are often considerably larger than those of the framework atoms. On the one hand, this can be plausibly explained with the considerable mobility of the encapsulated fluoride anions in the absence of a localised bond to any of the surrounding T atoms. On the other hand, it might also point to a disorder over different positions within the cage. If only powder samples are available, as is typically the case for synthetic zeolites and zeotypes, it is challenging to resolve such disorder with diffraction methods.