Binary Solvent System Composed of Polar Protic and Polar Aprotic Solvents for Controlling the Dimensionality of MOFs in the Solvothermal Synthesis

Abstract

The ample choice of organic ligand and series of available metal ions offer a library of metal–organic frameworks (MOFs) to be designed, synthesized, and applied for various interesting applications. However, the way to achieve complete control over the formation of desired architectures and properties is still an elusive goal. Several factors often directly or indirectly influence the synthesis of MOFs such as nature of solvent, pH, temperature, reactant stoichiometry, concentration of precursors, counterions, etc. These parameters are crucial for the formation of the crystalline product in the first place and also dictate the overall network dimension or topology. Herein, we have synthesized six Zn(II)/ Co(II)/ Cu(II) based MOFs and rationalized the effect of the presence of polar protic solvents like water/ethanol in directing the overall network dimension. The presence of polar protic solvents like ethanol/water resulted in the formation of secondary building units (SBUs) that directs the network to extend on a plane while the absence/scarcity of such solvents leads to a different SBU that facilitate propagation of the network in three dimensions. Such variation was attributed to the competitive coordination ability of such solvents and the extent of hydrogen bonding with the ligand.