The energy landscapes of zeolitic imidazolate frameworks (ZIFs): towards quantifying the presence of substituents on the imidazole ring

The energy landscapes of isoelectronic zeolitic imidazolate frameworks (ZIFs)-Zn(2-fluoroimidazolate)(2) and Zn(2-methylimidazolate)(2)-were studied by density-functional-theory total energy calculations. The incorporation of the methyl-group was shown to make the system highly polymorphic in contrast to the fluoro-group which selects at most three favourable framework types. The inter-ligand interactions are discussed as a key to target a particular network topology. The importance of dense network types (zni and coi) in ZIF systems is emphasized.