We show that dispersive interactions are important components in modelling zeolitic imidazolate frameworks (ZIF). Our comparative study of Zn-based and LiB-based zeolitic imidazolate frameworks reveals that, unexpectedly, both families exhibit a very similar structure-energy relationship, and exhibit a much larger energy spread than previously proposed. This finding suggests that from thermodynamic considerations, the diversity and synthesizability of LiB-based structures should be very similar to Zn-based ZIFs but very porous Zn- and LiB-ZIFs are predicted to be particularly challenging to synthesize. However, fewer unique LiB-based structure types have been synthesized thus far which suggests kinetic barriers may be more significant for LiB frameworks than Zn-based materials.