Thermodynamic stabilization in metal organic frameworks based on 1,3,5-benzenetricarboxylate linkers and rare earth metals

This work systematically investigates the thermodynamic stability in M-BTC metal organic frameworks, where M = Y, Eu, or La and BTC = (1,3,5-benzenetricarboxylate) linker. Enthalpies of formation obtained from calorimetric measurements of Y(BTC)·5.43(H₂O), Eu(BTC)·5.82(H₂O) and La(BTC)·4.85(H₂O) enable determination of the energetic landscape for metal substitution (Y, Eu, and La) in M-BTC materials. The enthalpies of formation from linker plus metal of La-BTC, Eu-BTC, and Y-BTC are − 3219.3 ± 3.4, 3.9 ± 2.0 and 713.3 ± 3.0 kJ mol^{− 1}_, respectively. The highly endothermic enthalpy of formation of Y(BTC)·5.43(H₂O) reflects a thermodynamic penalty for a change in the coordination environment of Y metal atoms in the BTC framework compared to Y₂O₃. The high thermodynamic stability of the M-BTC framework employing La metal confirms greater stabilization from the use of larger metal atoms in frameworks with oxygen-based linkers. The results from thermodynamic analysis suggest water is a stabilizing agent. Thus, the choice of metal atom and presence of guest water molecules can enthalpically stabilize the M-BTC materials by as much as ~ 3932 kJ mol^{− 1}. More broadly, the results indicate complex interplay among choice of metal, water content, and thermodynamic stability in M-BTC frameworks.