In order to span the conformational landscape involved in the ZIF nucleation process, we have computed the formation free energies of a broad ensemble of large Zn clusters with either imidazolate or 2-methylimidazolate. Specifically, 42 Zn z Im l clusters and 20 Zn z mIm l clusters, with z ranging from 1 to 6 and l ranging from 1 to 18 have been characterized. The corresponding energies obtained from thermodynamic cycle computations are listed in Table and Table , respectively. These calculations are expected to shed some light on the observation that mIm -leads readily to (only) the formation of ZIF-8, while Im -leads to other topologies.