Transitioning Formamide Solvothermal Syntheses of MOFs to Less Toxic Solvents

Metal-organic frameworks (MOFs) are most commonly synthesized in toxic formamide solvents. Though some progress has been made for certain classes, zinc carboxylate MOFs are particularly reliant on formamide solvents. Transitioning away from these solvents is difficult because they serve multifaceted roles in MOF formation chemistry and phase direction. Herein, the synthetic factors required for the effective removal of formamide solvents across various classes of MOFs are investigated. Complete formamide removal is achieved for IRMOF-5, IRMOF-3, HKUST-1, and Zn-MOF-74. The function of formamide solvents in MOF synthesis is replicated using a system comprising tetrahydrofuran (THF) and a base additive. When designing MOF syntheses without formamide solvents, the solubility of both the organic linker and metal salt, along with the use of a base possessing sufficient pKa to deprotonate multitopic linkers, emerge as critical determinants of successful MOF formation. These insights provide a foundation for designing new sustainable MOF syntheses.