In this work, we provide an unprecedentedly detailed analysis of the possible pre-nucleation building units for a large series of ZIFs, considering the influence of the solvent and of counterions on the pre-nucleation mechanisms. We conducted DFT calculations on a large ensemble of cluster configurations, based on Imidazolate (Im -) and 2-methyl-Imidazolate (mIm -) linkers, considering the presence of solvent and counterions to closely account for experimental conditions. mIm -is the linker in ZIF-8, the prototypic ZIF with cubic sodalite (SOD) topology. Remarkably, mIm -does not lead to the crystallization of ZIFs with other topologies. In contrast, ZIFs based on Im -have been prepared with a wide range of topologies, such as BCT, DFT, GIS, MER, zec, zni, AFI, and CAN. Porous Zn-Im-ZIFs are typically obtained either with very low yields or with the aid of added templating molecules. We therefore study a large set of clusters using Zn and Im -/mIm -ligands, devoting efforts both to examine the pre-nucleation stages of formation of clusters of a few Zn atoms and to explore efficient methods to scale the computation to large clusters entering the nucleation regime, with tens to hundreds of Zn atoms.