Hydrothermal stability of metal organic frameworks (MOFs) is critical for their application for hydrogen storage and other applications. The pKa values (in H2O) of the conjugated acids of carboxylate ligands and NBO charges (gas phase) of the ligands of MOF materials can reflect in their coordination abilities to metal ions and the strength of the resulted M-L bonds. The pKa values and NBO charges of 31 carboxylate ligands and 27 N-heterocyclic common multidentate ligands applied in the MOF syntheses were calculated at 273.15 K with B3LYP/6-31+G(d,p) level of calculations. Solvation Gibbs energies (?Gsolv) in aqueous solution are obtained using SMD modeling. NBO charges were calculated based on optimized structures in gas phase. We found the calculated pKa1 values have linear relationship with the experimental results of a few known bidentate ligands. We therefore only apply pKa1values and NBO charges to predict the coordination ability of the ligands. To our knowledge, systematic calculations of the pKa values and NBO charges of multidentate ligands have not been reported. Our work provides more quantitative comparisons of the coordination abilities of these ligands than just reasoning by substituent effects. The results can be used to predict whether a targeted MOF structure would be water and thermally stable. Some experimental results about water and thermal stability of MOF materials were successfully explained in terms of M-L bond strengths and polarity based on our calculated results, which are also useful to predict the stability of known MOFs, design new stable MOFs by choosing ligands with suitable coordination ability and provide guidance for the synthetic procedures based on the calculated pKa values. However, we are also aware that other factors such as steric effects, pore sizes and surface properties have effects on the hydrothermal stability of MOFs as reported by others.

What can pK<sub>a</sub> and NBO charges of the ligands tell us about the water and thermal stability of metal organic frameworks?

248th National Meeting (2014)

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What can pKa and NBO charges of the ligands tell us about the water and thermal stability of metal organic frameworks?

What can pK_a and NBO charges of the ligands tell us about the water and thermal stability of metal organic frameworks?