Microsoft Word - 2236618_File000003_38066724.docxof Zirconium-Based (Porphinato)Zinc(II) MOFs
Pravas Deria,* † ,a, b
Diego A. Gómez-Gualdrón †,c Idan Hod,a Randall Q. Snurr,* ,c Joseph T.
Hupp,* ,a Omar K. Farha*
,a, d
60208, United States.
b Department of Chemistry, Southern Illinois University, 1245 Lincoln Drive, Carbondale,
Illinois 62901, United States.
Illinois 60208, United States
d Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi
Arabia
S4. Molecular simulation details 8-10
S6. References 10
S1. Synthesis
PCN-222/MOF-545, which is based on the csq topology and has the molecular formula
Zr(µ-O)(µ-OH)(–OH)(–OH)(TCPP), was synthesized following published protocols
using solvothermal reactions of ZrOCl.8HO, TCPP and benzoic acid in the presence of ZnCl
in DEF to obtain the Zn(II)-metallated PCN-222. The as-synthesized material was dried without
further activation with HCl. The free-base variant of MOF-525[1] and NU-902 were metallated
with Zn(II) via post-synthesis metallation.[2]
S1A. Synthesis of PCN-222 [3] Zirconyl chloride octahydrate (97 mg; 0.30 mmol) and benzoic acid (2.7 g; 22 mmol) were
placed in a 6-dram vial (VWR) and dissolved in 10 mL N,N’-diethylformamide via sonication
(10 min). The resulting solution was incubated in an oven at 80 ºC for 1 h, and then cooled to
room temperature upon the addition of HTCPP (50 mg; 0.06 mmol) and ZnCl (50 mg; 0.37
mmol). The mixture was sonicated for 10 min (forming a clear solution) and then heated in an
oven at 100 ºC for 2 d. After cooling to room temperature and removing the mother liquor, the
microcrystalline MOF sample was centrifuged and washed with fresh DMF five times over the
course of three days. The solid was soaked (overnight) and washed with acetone (4×15 mL), and
finally dried in a vacuum oven (~100 torr) for 30 min at 50 °C to yield ~70 mg of MOF.
S3B. Synthesis of MOF-525[1]
Zirconyl chloride octahydrate (97 mg; 0.30 mmol) and benzoic acid (2.7 g; 22 mmol) were
mixed in 8 mL of DMF (in a 6-dram vial) and ultrasonically dissolved. The clear solution was
incubated in an oven at 80 °C for 2 hours. After cooling down to room temperature, 47 mg (0.06
mmol) of HTCPP was added to this solution and the mixture was sonicated for 20 min. The
purple suspension was heated at the bottom of an isotemperature gravity oven set at 70 °C for 24
hours. After cooling down to room temperature, the purple-red polycrystalline material was
isolated by filtration and washed 3 times with DMF. Subsequently, the solid residue was washed
with acetone three times and then soaked in acetone for additional 12 hours. MOF-525 was
filtered, briefly dried on a filter paper, and activated at 80 °C under vacuum for 12 hours.
S3
Figure SI-1. PXRD patterns for NU-902 (orange as-synthesized and green HCl-activated), showing good
agreement with the simulated PXRD pattern obtained for a computationally constructed model structure.
Diffraction appearing from 100 and 120 planes are marked with arrows to distinguish the diffraction pattern from a
closely related MOF structure, PCN-223. [4]
Figure SI-2. PXRD patterns for (a) MOF-525 and (b) PCN-222 (orange as-synthesized and green HCl-activated),
showing good agreement with simulated patterns.
S4
Figure SI-3. Partial ¹H NMR spectra of as-synthesized and HCl-activated NU-902. Two activated samples were
achieved by heating (100 °C) identical (~75 mg) NU-902 samples with 200 and 600 µL of 8M HCl(aq) into 10 mL
DMF. These data show that 200 µL HCl was enough to remove all the node-coordinated benzoates.
Figure SI-4. (a) Experimental N2 isotherms for NU-902 at 77 K. The red, green, dark red and pink isotherms are for
samples after treatment with various amounts of HCl in DMF during activation (benzoate removal), and the blue
isotherm is for the thermally dried as-synthesized material without HCl treatment. These isotherms show that 200
µL of 8M HCl (in 10 mL DMF) is sufficient to activate (i.e. completely remove all four benzoates from each node)
~ 75 mg NU-902 (see the corresponding ¹H NMR spectra in Fig SI-3). The isotherm predicted by molecular
simulation is shown in black. (b) Pore-size distribution obtained from the N isotherms for as-synthesized and HCl-
activated NU-902 samples. Note that upon HCl activation, a small mesoporous step at P/Po ~ 0.25 (panel a) was
observed. We ascribe this small mesoporous step to removal of a small fraction of the TCPP linker leading to defect
sites with large pore channels (30 ; panel b) in some regions of the MOF.
S5
Figure SI-5. DRIFTS plot of as-synthesized PCN-222 (Zn) (blue) with Zn-TCPP linker (note that the as-
synthesized PCN-222 (Zn) has benzoate decorated node) and NU-902 featuring free base TCPP. The activation
(benzoate removal) of NU-902 was carried out with various amounts of HCl. These data suggest that 200 µL 8M
HCl is enough to activate ~ 75 mg of NU-902 and that excess HCl does not damage the sample.
Figure SI-6. Absorption spectra of the Q-band region for free-base HTCPP starting materials (red) and the
as-synthesized PCN-222 featuring Zn-TCPP linker (black). (PCN-222 (Zn) sample was digested in 0.1 M NaOH.)
S6
Figure SI-7. SEM pictures of (a) NU-902, (b) MOF-525 after metalation with zinc(II), and (c) as-synthesized PCN-
222 (Zn). The corresponding relative elemental abundances for Zn to Zr were obtained from EDS experiments and
are presented in the right panel.
S7
S3. Kinetic data for acyl-transfer reactions.
Figure SI-8. Kinetic profiles for catalytic acyl transfer reaction as a function of MOF topology and regiochemistry
of pyridylcarbinol. (a, b) MOF-dependent plots of product concentration (M) vs time showing the rate of formation
of (a) 4-acetoxymethylpyridine (AMP) and (b) 2-AMP from N-acetylimidazole and corresponding pyridylcarbinols.
(c, d) Plots of product concentration vs time showing the rate of formation of various AMPs regiosiomers in (c)
MOF-525 and (d) PCN-222. All MOFs are based on Zn-TCPP linkers, and the experiments were carried out under
identical conditions. Solid lines are single exponential fits to the experimental data (symbols).
S8
S4 Details of the Molecular Simulations S4A. Computational construction of MOF structures
The structure of NU-902 is based on tetratopic porphyrinic organic linkers and zirconium
oxoclusters. The first prototype structural model of NU-902 was constructed in previous work
by some of us, [5]
where 204 zirconium-based hypothetical MOF structures were computationally
constructed and studied for methane storage. The construction method followed a top-down
approach, where MOF building blocks are mapped onto a topological blueprint. The resulting
structures then underwent structural optimization based on classical mechanics. Further details
can be found in ref [5]
, and Figure SI-9 briefly summarizes the MOF construction method.
Figure SI-9. Top row: topological blueprint and building blocks used in the construction of MOF NU-902. Bottom
row: Summary of steps for top-down construction of NU-902; from left to right: i) mapping inorganic node, ii)
mapping organic node, and iii) mapping spacer group. Oxygen: red, carbon: black, hydrogen: white, nitrogen: blue,
zirconium: aqua.
presented the following unit cell
parameters: a = b = 20.9 Å, c = 17.1 Å, α = β = 90, γ = 120. The simulated PXRD pattern of the
computational model of NU-902 agreed well with the experimental one, indicating that the
synthesis produced the desired structure. At this point, the unit cell of the computational model
of NU-902 was readjusted to match more closely the peak positions of the experimental PXRD
patterns, and the structure was re-optimized maintaining the unit cell dimension and shape fixed.
This optimization was done using the Forcite module of Material Studio. [6]
The obtained
structure was then used for simulation of nitrogen adsorption and other calculations. Interatomic
interactions during optimization were described using the Universal Force Field. [7]
A similar
procedure was used to obtain the structures of MOF-525 and PCN-222, where the computational
structures of these two MOFs were also obtained from ref [5]
and readjusted to match the
experimental unit cell dimensions. Note that no cif files for MOF-525 and PCN-222 were
provided in the original publication, so we opted to create the structures in the computer under
the constraint of matching the reported unit cell experimental values
S9
S4B. Nitrogen adsorption simulation in NU-902
Nitrogen adsorption in NU-902 was calculated via grand canonical Monte Carlo simulations
using the multipurpose simulation code RASPA. [8] Intermolecular interactions were described
using a Lennard Jones (LJ) plus Coulomb potential. The σ and ε LJ parameters of NU-902 atoms
were assigned according to the Universal Force Field, [7]
and no Coulombic charges were
assigned to these atoms. The σ and ε LJ parameters and Coulombic charges of nitrogen
molecules were assigned according to the TraPPE model for nitrogen [9]
as illustrated below:
Adsorption simulations were done at 77 K for pressures up to 1 bar. Each GCMC simulation
used 20,000 cycles for equilibration and 20,000 cycles for data collection. In a cycle, N Monte
Carlo moves are performed, where N is the maximum between 20 and the number of molecules
in the system. Random equal-probability insertion, deletion, translation and rotation moves were
performed for nitrogen molecules, whereas NU-902 remained fixed during simulation.
A 2 x 2 x 2 supercell was used along with a 12.8 Å cutoff to truncate LJ interactions. No tail
corrections for LJ interactions were used, and the Ewald sum technique was used to compute
Coulombic interactions. The gas-phase nitrogen fugacity was calculated using the Peng-
Robinson equation of state.
S4C. Optimization of NAI and PC on porphyrins (quantum mechanics)
To perform computationally affordable quantum mechanics calculations, we reduced the number
of atoms involved in the simulation. Thus for our quantum mechanics calculations, we only used
the “ball and stick” atoms shown in Figure SI-10 for each MOF. These atoms represent the
porphyrin pairs 1, 4 and 8 from PCN-222, NU-902 and MOF-525, respectively. Furthermore,
given the similarities between pairs 1 and 4, we only performed quantum calculations on pairs 1
and 8. Of the atoms representing the MOFs, carbon atoms were maintained fixed, whereas
hydrogen, nitrogen and zinc atoms were allowed to relax during optimizations.
S10
Figure SI-10. Illustrations of atoms used in quantum mechanics calculations representative of each MOF. The used
atoms are shown in “ball and stick” representation and correspond to the porphyrin pairs 1 (in the triangular channel
of PCN-222 (csq), 4 (in the diamond channel of NU-902 (scu)), and 8 (in the cubic cage of MOF-525 (ftw)).
Oxygen: red, carbon: gray, hydrogen: white, nitrogen: blue, zirconium: aqua.
In our quantum calculation we wanted to focus on how 2-PC, 3-PC, and 4-PC bind along with
AIM on the different porphyrin pairs to obtain insights into how their concerted binding could
potentially facilitate the formation of a transition state in the different MOFs. Note that in the
transition state presented in Scheme 1 in the main text, the hydroxyl oxygen of PC approaches
the carbonyl carbon of NAI, and the hydroxyl hydrogen of PC is transferred to the carbonyl
oxygen of NAI. Thus for the initial configuration in our calculations we anchored NAI and PC
to one porphyrin each, making NNAI-Zn and NPC-Zn both equal to 2.0 Å, and oriented NAI and
PC so that the hydroxyl oxygen and hydrogen of PC were as close as possible to the carbonyl
carbon and oxygen of NAI, respectively. One consideration, however, was to try to have NAI
and PC as perpendicular as possible with respect to the porphyrins. NAI and PC atoms were all
allowed to relax. The optimized configurations are shown in Figure 6 in the main text. The
optimizations were performed using density functional theory (DFT) with the three-parameter
Becke gradient-corrected exchange [10]
The LANL2DZ basis set [11]
was used for Zn atoms, and the 6-31+G* [12]
basis set was used for all
other atoms.
S11
References
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2015, 5, 6302-6309.
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