Ring statistics were computed using the R.I.N.G.S. code on the Zn-Im periodic graph obtained after identification of the building units. The definition of rings used in this work corresponds to the definition of "primitive rings" in the R.I.N.G.S. code (see Ref. 15 for an extended definition). We used a maximum search depth of 32, safely above the largest rings of the ZIF-4 crystal (16).