“Shake ‘n Bake” Route to Functionalized Zr-UiO-66 Metal–Organic Frameworks

We report a novel synthetic procedure for the high-yield synthesis of metal–organic frameworks (MOFs) with fcu topology with a UiO-66-like structure starting from a range of commercial ZrIV precursors and various substituted dicarboxylic linkers. The syntheses are carried out by grinding in a ball mill the starting reagents, namely, Zr salts and the dicarboxylic linkers, in the presence of a small amount of acetic acid and water (1 mL total volume for 1 mmol of each reagent), followed by incubation at either room temperature or 120 °C. Such a simple “shake ‘n bake” procedure, inspired by the solid-state reaction of inorganic materials, such as oxides, avoids the use of large amounts of solvents generally used for the syntheses of Zr-MOF. Acidity of the linkers and the amount of water are found to be crucial factors in affording materials of quality comparable to that of products obtained under solvo- or hydrothermal conditions.

25.9 mg of desolvated MOF was digested. In the 1 H NMR spectrum, the four signals of internal standard 2-fluorobenzoic acid (FBA) fall between 7.00 and 7.60 ppm and account for one proton each. The signal of AcOH falls at 1.82 ppm and accounts for three protons.
Thus, in order to have a quantitative comparison of the two species, the integral of AcOH (0.184) must be divided by three, giving 0.061. In the 19 F NMR spectrum, the signal of internal standard FBA falls at -116.2 ppm and accounts for one proton. The signal of F4-BDC falls at -143.7 ppm and accounts for four protons. Thus, in order to have a quantitative comparison of the two species, the integral of F4-BDC (2.654) must be divided by four, giving 0.664. This leads to calculate a F4-BDC/AcOH ratio of 10.9. Assuming the general formula Zr6O4(OH)4(F4-BDC)6x (AcOH)2 x , the following can be written: 6− 2 = 10.9 (equation S1) Solving equation S1, a value of 0.26 for x is determined, leading to the following proposed formula: Zr6O4(OH)4(F4-BDC)5.74(AcOH)0.52, having formula weight (FW) of 2063 g mol -1 .
The absolute concentration of AcOH in solution is obtained by multiplying its normalised integral (0.061) times the concentration of FBA (0.11 M), obtaining 0.0067 M. The absolute amount (in mg) of AcOH in the MOF can be derived by multiplying the concentration times volume of the solution (1.0 mL) and the molecular weight of the acetate anion (59 g mol -1 ), obtaining 0.40 mg. This leads to derive an experimental wt% of 1.54% for AcOH in the desolvated MOF. The absolute concentration of F4-BDC in solution is obtained by multiplying its normalised integral (0.664) times the concentration of FBA (0.11 M), obtaining 0.0730 M. The absolute amount (in mg) of F4-BDC in the MOF can be derived by multiplying the concentration times volume of the solution (1.0 mL) and the molecular weight of the F4-BDC dianion (236 g mol -1 ), obtaining 17.22 mg. This leads to derive an experimental wt% of 66.50% for F4-BDC in the desolvated MOF. According to the proposed formula Zr6O4(OH)4(F4-BDC)5.74(AcOH)0.52, the calculated wt% of AcOH is 1.49%, while that of F4-BDC is 65.65%. The good agreement between experimental and calculated wt% suggests that the proposed formula is correct and that the analysed MOF does not contain impurities. 11 Figure S8. 1 H (top) and 19 F (bottom) NMR spectra of F4-UiO-66 50 L water.
24.8 mg of desolvated MOF was digested. In the 1 H NMR spectrum, the four signals of internal standard 2-fluorobenzoic acid (FBA) fall between 7.00 and 7.60 ppm and account for one proton each. The signal of AcOH falls at 1.82 ppm and accounts for three protons.
Thus, in order to have a quantitative comparison of the two species, the integral of AcOH (0.187) must be divided by three, giving 0.062. In the 19 F NMR spectrum, the signal of internal standard FBA falls at -116.2 ppm and accounts for one proton. The signal of F4-BDC falls at -143.7 ppm and accounts for four protons. Thus, in order to have a quantitative 12 comparison of the two species, the integral of F4-BDC (2.506) must be divided by four, giving 0.627. This leads to calculate a F4-BDC/AcOH ratio of 10.1. Assuming the general formula Zr6O4(OH)4(F4-BDC)6x (AcOH)2 x , the following can be written as the same way of eq. S1: 21.2 mg of desolvated MOF was digested. In the 1 H NMR spectrum, the four signals of internal standard 2-fluorobenzoic acid (FBA) fall between 7.00 and 7.60 ppm and account for one proton each. The signal of AcOH falls at 1.82 ppm and accounts for three protons.
Thus, in order to have a quantitative comparison of the two species, the integral of AcOH (0.156) must be divided by three, giving 0.052. In the 19 F NMR spectrum, the signal of internal standard FBA falls at -116.2 ppm and accounts for one proton. The signal of F4-BDC falls at -143.7 ppm and accounts for four protons. Thus, in order to have a quantitative comparison of the two species, the integral of F4-BDC (2.188) must be divided by four, giving 14 0.547. This leads to calculate a F4-BDC/AcOH ratio of 10.5. Assuming the general formula Zr6O4(OH)4(F4-BDC)6x (AcOH)2 x , the following can be written:  12.6 mg of desolvated MOF was digested. The signal of internal standard fumaric acid (FumA) falls at 6.40 ppm and accounts for two protons. The signals of NO2-BDC fall at 8.38, 8.06 and 7.42 ppm and account for one proton each. The NO2-BDC signal at higher chemical shift displays a slightly lower integral than the other signals, probably due to incomplete relaxation, therefore the integral of NO2-BDC is taken as the mean between the integrals of the signals at 8.06 and 7.42 ppm, giving 0.178. The signal of AcOH falls at 1.80 ppm and accounts for three protons. Thus, in order to have a quantitative comparison of the three species, the integral of FumA (1.000) must be divided by two, giving 0.500, whereas the integral of AcOH (0.046) must be divided by three, giving 0.015. This leads to calculate a NO2-BDC/AcOH ratio of 11.5. Assuming the general formula Zr6O4(OH)4(NO2-BDC)6x (AcOH)2 x , the following can be written:   The absolute amount (in mg) of NO2-BDC in the MOF can be derived by multiplying the concentration times the volume of the solution (1.0 mL) and the molecular weight of the corresponding dianion (209 g mol -1 ), obtaining 10.53 mg. This leads to derive an experimental wt% of 54.56% for NO2-BDC in the desolvated MOF. The absolute concentration of AcOH in solution is the ratio between its normalised integral (0.028) and 0.500, multiplied by the concentration of FumA (0.10 M), obtaining 0.0056 M. The absolute amount (in mg) of AcOH in the MOF can be derived by multiplying the concentration times volume of the solution (1.0 mL) and the molecular weight of the acetate anion (59 g mol -1 ), obtaining 0.33 mg. This leads to derive an experimental wt% of 1.71% for AcOH in the desolvated MOF. According to the proposed formula Zr6O4(OH)4(NO2-BDC)5.68(AcOH)0.64, the calculated wt% of NO2-BDC is 62.39%, while that of AcOH is 1.98%. The fact that slightly less NO2-BDC and AcOH than expected are found suggests that there could be a small amount of impurity, probably of inorganic nature, in the product. The larger discrepancy found in this sample, compared to those prepared in the presence of less water, suggests that a larger amount of water leads to formation of more impurities. 27.6 mg of desolvated MOF was digested. The signal of internal standard fumaric acid (FumA) falls at 6.37 ppm and accounts for two protons. The signals of Br-BDC fall at 7.90, 7.66 and 7.24 ppm and account for one proton each. The Br-BDC signal at higher chemical shift displays a slightly lower integral than the other signals, probably due to incomplete relaxation, therefore the integral of Br-BDC is taken as the mean between the integrals of the signals at 7.66 and 7.24 ppm, giving 0.299. The signal of AcOH falls at 1.78 ppm and accounts for three protons. Thus, in order to have a quantitative comparison of the three species, the integral of FumA (1.000) must be divided by two, giving 0.500, whereas the integral of AcOH (0.330) must be divided by three, giving 0.110. This leads to calculate a Br-BDC/AcOH ratio of 2.7. Assuming the general formula Zr6O4(OH)4(Br-BDC)6x (AcOH)2 x , the following can be written: According to the proposed formula Zr6O4(OH)4(Br-BDC)5.06(AcOH)1.88, the calculated wt% of NO2-BDC is 52.39%, while that of AcOH is 5.50%. The good agreement between experimental and calculated wt% suggests that the proposed formula is correct and that the analysed MOF does not contain impurities. The absolute amount (in mg) of PyDC in the MOF can be derived by multiplying the concentration times the volume of the solution (1.0 mL) and the molecular weight of the corresponding dianion (165 g mol -1 ), obtaining 11.29 mg. This leads to derive an experimental wt% of 48.03% for PyDC in the desolvated MOF. If the formula Zr6O4(OH)4(PyDC)6.00 is proposed (FW = 1668 g mol -1 ), the calculated wt% of PyDC is 59.35%, a value much in excess of the experimental one.
Given the use of concentrated HNO3 in this synthesis, it is reasonable to expect that the MOF could contain the PyDC linker with the pyridine nitrogen in protonated form and nitrate 24 as the counterion. Chromatographic analysis of the digested MOF revealed that it contained 1.67 mmol g -1 of NO3 -(10.29 wt%). Thus, a PyDC/NO3ratio of 1.75 can be derived.
Assuming the formula Zr6O4(OH)4(PyDC)6x (HPyDC) x (NO3) x , the following can be written: Solving this simple equation, a value of 3.43 for x is determined, leading to the following formula: Zr6O4(OH)4(PyDC)2.57(HPyDC)3.43(NO3)3.43, having FW of 1884 g mol -1 . According to this formula, the calculated wt% of PyDC is 52.55%, while that of NO3is 11.29%. Thus, the proposed formula overestimates the wt% of both PyDC and NO3 -. This could be due either to the presence of some impurity or to the presence of defects, compensated in this case by the hydroxide/water couple often reported in the literature. In the latter case, the formula Zr6O4(OH)4(PyDC)2.21(HPyDC)2.95(NO3)2.95(OH -/H2O)1.68 (FW = 1774 g mol -1 ) can be proposed, which leads to calculated wt% of PyDC (48.00%) and NO3 -(10.31%) in excellent agreement with the experimental ones.  (black line) and the same synthesis kept sealed into the reactor for 24h (red line).