Uncovering Structural Opportunities for Zirconium Metal–Organic Frameworks via Linker Desymmetrization

Abstract The discovery of metal–organic frameworks (MOFs) mimicking inorganic minerals with intricate topologies requires elaborate linker design guidelines. Herein, the concept of linker desymmetrization into the design of tetratopic linker based Zr‐MOFs is applied. A series of bent tetratopic linkers with various substituents are utilized to construct Zr‐MOFs with distinct cluster connectivities and topologies. For example, the assembly between a bent linker L‐SO2 with C 2v symmetry and an 8‐connected Zr6 cluster leads to the formation of an scu topology, while another flu topology can be obtained by the combination of a novel 8‐connected Zr6 cluster and a bent linker L‐O with C 1 symmetry. Further utilization of restricted bent linker [(L‐(CH3)6)] gives rise to a fascinating (4, 6)‐c cor net, originated from the corundum lattice, with an unprecedented 6‐c Zr6 cluster. In addition, the removal of toxic selenite ions in aqueous solution is performed by PCN‐903‐(CH3)6 which exhibits rapid and efficient detoxification. This work uncovers new structural opportunities for Zr‐MOFs via linker desymmetrization and provides novel design strategies for the discovery of sophisticated topologies for practical applications.

(1) 4,4'-sulfonylbis(2,6-dibromoaniline) 4,4'-sulfonyldianiline (2.48 gm, 0.01 mole) was dissolved in glacial acetic acid (15 ml), followed by the addition of bromine in acetic acid (32ml, 0.01 mol, 20% bromine in acetic acid). The mixture was kept stirred overnight at room temperature, followed by dilution with excess cold water. The solid product was filtered, washed with cold water, dried and recrystallized from ethyl acetate. Yield 85%. 1 [1] (2) Tetramethyl 5',5''''-sulfonylbis(2'-amino-[1,1':3',1''-terphenyl]-4,4''-dicarboxylate) 4,4'-sulfonylbis(2,6-dibromoaniline) (2.82 g, 5 mmol), methyl 4-boronobenzoate (4.32 g, 24 mmol), Pd(PPh 3 ) 4 (0.3 g, 0.26 mmol) and K 3 PO 4 (10.64 g, 40 mmol) were S4 placed in a 500 ml two-necked round bottom flask under N 2 atmosphere. The flask was further charged with 200 mL dry 1,4-dioxane, and heated for 48 h. After cooling down to room temperature, the solvent was removed followed by the addition of water. The water phase was washed with CH 2 Cl 2 . The mixed organic phase was then dried by MgSO 4 . After the solvent was removed, the crude product was purified by column chromatography with CH 2 Cl 2 as the eluent. Yield 90%. 1 Figure S4. 1   to room temperature, the solvent was removed followed by the addition of water. The water phase was washed with CH 2 Cl 2 . The mixed organic phase was then dried by MgSO 4 . After the solvent was removed, the crude product was purified by column chromatography with CH 2 Cl 2 as the eluent. Yield 86%. 1       down to room temperature, the solvent was removed followed by the addition of water. The water phase was washed with CH 2 Cl 2 . The mixed organic phase was then dried by MgSO 4 . After the solvent was removed, the crude product was purified by column chromatography with CH 2 Cl 2 as the eluent. Yield 88%. 1   M NaOH aqueous solution. The mixture was stirred at 50 C overnight. The organic phase was removed, while the aqueous phase was acidified with diluted hydrochloric acid. The yellow precipitate was further filtered and washed with water for several S10 times. Yield 98%. 1   (1) Bis(3,5-dibromo-2,4,6-trimethylphenyl)methane Bromine (2.0 mL, 40 mmol) was added to dimesitylmethane (2.52 g, 10 mmol) in acetic acid (50 mL) at room temperature. The reaction was stirred at 35 °C for 5 min and then poured into cold water (200 mL). The crude product was filtered off and purified on silica gel column with n-hexane/ethyl acetate (6:1) as the mobile phase.
Yield: 3.85 g, 7.5 mmol, 75%. 1   for 48 h. After cooling down to room temperature, the solvent was removed followed by the addition of water. The water phase was washed with CH 2 Cl 2 . The mixed organic phase was then dried by MgSO 4 . After the solvent was removed, the crude product was purified by column chromatography with CH 2 Cl 2 as the eluent. Yield

S3. Single Crystal X-ray Crystallography
All as-synthesized crystals were taken from the mother liquid without further treatment, transferred to oil and mounted on to a loop for single crystal X-ray data collection. All crystals data were collected with a SuperNova diffractometer equipped with mirror Cu-Kα radiation (λ = 1.54184 Å) and an Eos CCD detector at 150 K. The data was collected with a ω-scan technique and an arbitrary φ-angle. Data reductions were performed with the CrysAlisPro package, and an analytical absorption correction was performed. All the structures were solved by the direct method using the SHELXS program of the SHELXTL package and refined by the full-matrix least-squares method with SHELXL. 2 The structures were treated anisotropically, whereas the aromatic and hydroxyl hydrogen atoms were placed in calculated ideal positions and refined as riding on their respective carbon or oxygen atoms. Structure was examined using the Addsym subroutine of PLATON to assure that no additional symmetry could be applied to the models. Crystal data collection are summarized in  Figure S12.

S18
Computational Methods. To interpret the relationship between linker rigidness and the resulting topology, a density functional theory (DFT) study was performed by using DMol3 module of Material Studio program package. [3][4] The generalized gradient approximation (GGA) of the Perdew, Burke, Ernzerhof (PBE) functional and DNP 4.4 basis were employed for all calculations. 5 Grimme method was applied for DFT-D correction. To simulate the states of the linkers in PCN-901, -902 and -903, torsions between two lateral phenyl rings of ligands were constrained. For comparison, the energies of a given linker fragment in different conformations were normalized by subtracting the energy of its unconstrained structure. The calculated energies of linker fragments are listed in Table S2.

S6. Gas Sorption Isotherm
Before gas sorption experiment, as-synthesized sample was washed with DMF and immersed in CH 2 Cl 2 and hexane for one day, during which the solvent was decanted and freshly replenished three times. The solvent was removed under vacuum at 100 o C, yielding a porous material. Gas sorption measurements were then conducted using a Micrometritics ASAP 2020 system.