Thermodynamics of solvent interaction with the metal-organic framework MOF-5

The inclusion of solvent in metal-organic framework (MOF) materials is a highly specific form of guest-host interaction. In this work, the energetics of solvent MOF-5 interactions has been investigated by solution calorimetry in 5 M sodium hydroxide (NaOH) at room temperature. Solution calorimetric measurement of enthalpy of formation (ΔH_f) of Zn₄O(C₈H₄O₄)₃·C₃H₇NO (MOF-5·DMF) and Zn₄O(C₈H₄O₄)₃·0.60C₅H₁₁NO (MOF-5·0.60DEF) from the dense components zinc oxide (ZnO), 1,4-benzenedicarboxylic acid (H₂BDC), N,N-dimethylformamide (DMF) and N,N-diethylformamide (DEF) gives values of 16.69 ± 1.21 and 45.90 ± 1.46 kJ (mol Zn₄O)^-1, respectively. The enthalpies of interaction (ΔH_int) for DMF and DEF with MOF-5 are -82.78 ± 4.84 kJ (mol DMF)^-1 and -89.28 ± 3.05 kJ (mol DEF)^-1, respectively. These exothermic interaction energies suggest that, at low guest loading, Lewis base solvents interact more strongly with electron accepting Zn₄O clusters in the MOF than at high solvent loading. These data provide a quantitative thermodynamic basis to investigate transmetallation and solvent assisted linker exchange (SALE) methods and to synthesize new MOFs.