The structure of metal functionalized UiO-66 and UiO-67 Metal-Organic Frameworks (MOFs) were studied using Density Functional Theory with periodic boundary conditions in vacuum. The metalated structures were constructed by replacing the (μ3-OH) groups with (μ3-OMMe), where M is Mg or Zn. The synthesis of related complexes has been reported using UiO-69 and MgMe2. Different orientations of the Zr-nodes related to each other lead to different configurations that differ in the number of MMe groups pointing to each tetrahedral pore. There are three such unique configurations with either 4 and none (μ3-OMMe) groups, 3 and 1 (μ3-OMMe) groups, or 2 (μ3-OMMe) groups in each tetrahedral pore, which are defined with the notation, (4,0), (3,1) and (2,2), respectively. For the pristine material, (μ3-OH), all configurations have similar energies and are observed in the crystal. After functionalizing the bridging sites with MMe, (3,1) and (2,2) become unfavorable compared with (4,0). Calculations show that the unit cell of UiO-67 compresses with the introduction of MgMe into the tetrahedral pores relative to the pristine MOF. This is not the case for UiO-66. ZnMe binds differently to the bridging sites and does not affect the unit cell volume the same way as MgMe does. A closer look at the local geometry of the incorporated metals on the bridging sites reveals a three-fold coordination of Mg to oxygen, while Zn is only one-fold coordinated. Mg binds to two of the oxygen atoms belonging to the carboxylate of the linker, weakening the linker-Zr bond and causing the linker to bend. This bending may cause the volume compression by shortening the average length between the inorganic nodes.

Metal functionalization of UiO metal-organic frameworks

ACS Spring Meeting 2021

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