One large gap in research related to hybrid org./inorg. frameworks pertains to the inability to rationally design materials with targeted structural features and hence properties, a problem that stems from a lack of knowledge of their crystn. processes. Little is known, for example, about how specific reaction conditions relate to framework crystn. or whether frameworks are derived from the addn. of single metal-ions or larger aggregates of metal-ions and ligands that first form in soln. Thus, materials synthesis cannot keep pace with computational efforts aimed at structure and property prediction. In recent work we have demonstrated that binary solvothermal conditions used in synthesis may result in partitioning of the solvent's around growing MOF crystallites, based upon the relative hydrophobicity of the crystallite and of the two solvents (Figure 1). The current work, which is a combined exptl. and theor. study, is examg. how solvent organization and solvation free energy changes for two MOF's made of the same building blocks, but with different topologies. For instance, MOF-235 and MIL-101 contain the same triangular Fe3O core interlinked by 1, 4 benzene dicarboxylate ligands. While MOF-235 is a cationic framework with charge balancing anions in the channels that render it effectively nonporous, MIL-101 is neutral mesoporous framework, 3.4 nm, with surface areas over 3000 m2/g. Of specific interest is whether the solvation favorability of the two frameworks influences the final product outcome, or whether a specific reaction pathway during crystn. is essential for control of which MOF is produced.