MOFs based on Zr6-nodes have received considerable interest due to their exceptional thermal, chemical and mechanical stability. Two of the most representative examples are the UiO-66 and NU-1000 MOFs.1, 2 Both frameworks are constructed from Zr6Ox nodes that are connected via carboxylate ligands. In UiO-66, the Zr6 node has 12 points of extension, whereas in NU-1000, it has only 8 points of extension. As a consequence, the remaining coordination sites of NU-1000 are occupied by coordinated aqua and hydroxyl ligands, giving rise to a unique mixed proton topology.3 This unique H-bonded pattern has significant importance in catalysis, acid/base chemistry and deposition of metal atoms on the nodes of the framework. In this work, we investigate the dehydration process of NU-1000, by means of Density Functional Theory (DFT). Reaction (free) energies and transition state barriers are calculated for the proton migration to the hydroxyl groups and the subsequent water formation. Due to the complex proton topology, multiple pathways have to be explored. Based on experimental results, it is suggested that the Zr6Ox nodes undergo structural distortions upon heating. We try to assign the structural distortions in NU-1000 and compare with the phase transitions in bulk zirconia. A mixed computational approach is used3, where we utilize ab-initio molecular dynamics simulations and DFT results from periodic models and molecular clusters. References: (1) Valenzano, L.; Civalleri, B.; Chavan, S.; Bordiga, S.; Nilsen, M. H.; Jakobsen, S.; Lillerud, K. P.; Lamberti, C. Chem. Mater. 2011, 23, 1700. (2) Mondloch, J. E.; Bury, W.; Fairen-Jimenez, D.; Kwon, S.; Demarco, E. J.; Weston, M. H.; Sarjeant, A. A.; Nguyen, S. T.; Stair, P. C.; Snurr, R. Q.; Farha, O. K.; Hupp, J. T. J. Am. Chem. Soc. 2013, 135, 10294. (3) Planas, N.; Mondloch, J. E.; Tussupbayev, S.; Borycz, J.; Gagliardi, L.; Hupp, J. T.; Farha, O. K.; Cramer, C. J. J. Phys. Chem. Lett. 2014, 5, 3716.

Computational study of the dehydration process of the NU-1000 MOF

251st National Meeting (2016)

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