An elegant study by O'Keefe and Yaghi linked the possibility to form zeolite structures containing Ge, Si or both, to the geometric preference of various bond angles for Ge and Si in Si 8-n Ge n O 20 cubic subunits. Villaescusa et al. subsequently synthesised the D4R subunit analogue, Ge 8 O 12 (OH) 8 F -. Such idealised views of the D4R as an isolated, Ge-rich subunit, while beneficial as models, do not, however, capture the effects of confinement within the zeolite framework.