We report an investigation of the "missing-linker phenomenon" in the Zr-based metal-organic framework UiO-66 using atomistic force field and quantum chemical methods. For a vacant benzene dicarboxylate ligand, the lowest energy charge-capping mechanism involves acetic acid or Cl-/H2O. The calculated defect free energy of formation is remarkably low, consistent with the high defect concentrations reported experimentally. A dynamic structural instability is identified for certain higher defect concentrations. In addition to the changes in material properties upon defect formation, we assess the formation of molecular aggregates, which provide an additional driving force for ligand loss. These results are expected to be of relevance to a wide range of metal-organic frameworks.
Bibliographical noteFunding Information:
J.K.B is funded by the EPSRC (EP/G03768X/1). J.D.G thanks the Australian Research Council for funding under the Discovery Program, as well as the Pawsey Supercomputing Centre and NCI for the provision of computing resources. A.W. acknowledges support from the Royal Society. D.T. and K.L.S. are funded under ERC Starting Grant 277757 and J.M.S is funded under EPSRC Grant EP/K004956/1. Access to the ARCHER supercomputer was facilitated through membership of the HPC Materials Chemistry Consortium (EP/L000202). Data access statement: the parameter files and input configurations used in this work are available from http://dx.doi.org/10.4225/06/570D936A4B86F.
© 2016 American Chemical Society.