CrystEngComm

COMMUNICATION

Cite this: DOI: 10.1039/c8ce00455b

Received 23rd March 2018,Accepted 4th May 2018

DOI: 10.1039/c8ce00455b

rsc.li/crystengcomm

Revisiting the structural homogeneity of NU-1000,a Zr-based metal–organic framework†

Timur Islamoglu, *a Ken-ichi Otake,a Peng Li, a Cassandra T. Buru, a

Aaron W. Peters,a Isil Akpinar,a Sergio J. Garibaya and Omar K. Farha*ab

Synthesis and activation of phase-pure and defect-free metal–or-

ganic frameworks (MOFs) are essential for establishing accurate

structure–property relationships. Primarily suffering from missing

linker and/or node defects, Zr6-based MOFs can have polymorphs,

structures with the identical linker and node but different connec-

tivity, which can create multiple phases in a sample that compli-

cate the characterization. Here, we report the synthesis of phase-

pure NU-1000, a mesoporous Zr6-based MOF that typically con-

tains a significant secondary phase within the individual crystallites.

Large biomolecules and smaller inorganic molecules have been

installed in NU-1000 as probes to verify the near elimination of the

microporous secondary-phase. Obtaining structurally homoge-

nous MOFs will assist the design of new materials with distinct

structural features.

Introduction

In the last two decades, an ever growing interest in metal–or-ganic frameworks (MOFs), crystalline materials capable ofachieving permanent porosity composed of metal ions/clus-ters spaced with organic linkers, has led to the realization ofthousands of MOFs with unique properties.1 Among thereported MOFs, hexanuclear zirconium-based MOFs possesshigh chemical and thermal stability, making them extremelypopular candidates for multiple applications ranging fromgas storage to catalysis.2,3 Since the discovery of the first Zr6cluster based-MOF, UiO-66,4 many Zr6-based MOFs withlarger pore dimensions and geometries have beendesigned.2,5,6 Reticular chemistry7 allows control over the con-nectivity (i.e. the number of ligands coordinated to each Zr6

cluster) of the inorganic nodes ranging from 12-, 10-, 8-, or6-connected, resulting in a variety of topologies including, butnot limited to csq,8,9 scu,10–12 ftw,13–15 spn,16 reo17 and fcu.4

While structural irregularities or defects in these MOFs oftenindicate missing linkers and/or nodes, inhomogeneity is alsopossible if multiple phases can be constructed from identicalsecondary building units (SBUs, i.e. ligands and metalclusters).18–20 These phases are called polymorphs, and theresulting MOFs differ in crystal packing arrangements and/orconformations.2,17 For example, the combination of a tetra-topic porphyrin linker and a Zr6 cluster gives rise to at leastsix unique MOFs.12,15,21–23 The different connectivity of thevarious topologies manifests in distinctive physical (i.e. pore/aperture size/shape, morphology of crystal) and chemical (i.e.different number of reactive –OH sites) properties. Havingmultiple topologies in one sample significantly complicatesthe characterization and computational modelling of a mate-rial, where only phase-pure structures typically are consid-ered. Therefore, to establish strong structure–property rela-tionships, the studied MOFs should be close to phase-pure.Although using an excess amount of a monodentate modula-tor during the synthesis often suffices for isolating manyphase-pure Zr-MOFs,24–27 some systems require more effort toavoid polymorphs.

NU-1000, a Zr6-based MOF composed of Zr6IJμ3-OH)4IJμ3-O)4IJOH)4IJOH2)4 nodes and tetratopic pyrene-based linkers[TBAPy4−, 1,3,6,8-tetrakisIJp-benzoate)pyrene] with csq topol-ogy, possesses mesoporous 31 Å hexagonal channels andmicroporous 12 Å triangular channels with orthogonal 10 ×8 Å windows connecting the channels (Fig. 1A).8,28 Due to itshigh surface area, chemical and thermal stability, hierarchi-cal pore structure and relative ease of scalability, NU-1000has been heavily investigated for potential applications in-cluding catalysis and support materials on which to installadditional functionality.29–38 Phase purity in NU-1000 per-tains not to the bulk samples, but also to individual crystal-lites. In a typical synthesis of NU-1000 with benzoic acid as amodulator, NU-901 structural motifs are present in the

CrystEngCommThis journal is © The Royal Society of Chemistry 2018

aDepartment of Chemistry, Northwestern University, 2145 Sheridan Road,

Evanston, Illinois 60208, USA. E-mail: timur.islamoglu@northwestern.edu,

o-farha@northwestern.edubDepartment of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah

21589, Saudi Arabia

† Electronic supplementary information (ESI) available. CCDC 1580411. For ESIand crystallographic data in CIF or other electronic format see DOI: 10.1039/c8ce00455b

Publ

ishe

d on

04

May

201

8. D

ownl

oade

d by

Nor

thw

este

rn U

nive

rsity

on

6/22

/201

8 3:

57:1

3 A

M.

View Article OnlineView Journal

CrystEngComm This journal is © The Royal Society of Chemistry 2018

middle of the crystallites.8 NU-901 (Fig. 1B) is a polymorphwhich crystallizes in the scu net and has higher density com-pared to the csq net NU-1000 (0.704 vs. 0.486 g cm−3).39 Singlecrystal X-ray diffraction (XRD) analysis revealed extra electrondensity with approximately 25% occupancy located in the cen-ter of the mesoporous channels of NU-1000.8 Coupled withcomputational models, this density is attributed to the NU-901 phase. Note, care must be taken to not eliminate the pos-sibility of secondary phases in single crystal X-ray diffractiondata by assuming the presence of solvent and using SQUEEZEto remove this electron density. Further evidence of this sec-ondary phase can be seen in scanning electron microscopy(SEM) images (Fig. 2A), where the center of the hexagonalrod-shaped crystal appears “rough”. Interestingly, the rest ofthe crystals shows six smooth rectangular facets forming thehexagonal rods, implying that secondary phase primarily ex-ists in the center of the crystal where seeding is thought to oc-cur. Several other experiments also confirm the presence of amicroporous regime in the center of the crystallites.40,41

Both NU-1000 and NU-901 are 8-connected, so the polymor-phism arises from the relative alignment of the C2 axes alongthe nodes (Fig. 1. Left). Nodes in the MOF with csq topology,NU-1000, are angled 120° to each other whereas in NU-901 withscu topology they are parallel. The alignment of the nodes isdictated by the conformation of adjacent benzoate groups onthe TBAPy4− linkers (Fig. 1. Right). Truhlar and coworkers re-cently calculated that introducing bulky groups (i.e. CF3 ortert-butyl) to the TBAPy4− at the 2- and 7-carbon positions (thecarbon atom between two benzoate groups) stabilizes therotamer present in NU-1000 and precludes the formation ofNU-901 phase.42 While this method could result in phase-purecsq net topology, the linker synthesis would be much morechallenging than TBAPy4− synthesis. As an alternative, Pennand coworkers employed biphenyl-4-carboxylic acid as themodulator instead of benzoic acid to induce a larger steric ef-fect around the node that prevented the formation of micropo-rous NU-901.39 However, the lengthy modulator can be prob-lematic when applying this method to other systems withchannels larger than that of NU-1000. For example, the iso-reticular expansion of NU-1000 to NU-1003 enlarges the

Fig. 1 (A) Schematic representations of the alternating Zr6 node resulting in csq topology NU-1000. (B) Schematic representations of the parallel Zr6node resulting in scu topology NU-901. Color code: carbon (gray), oxygen (red), zirconium (green). For clarity, hydrogen atoms have been omitted.

Fig. 2 SEM images of NU-1000 (A) and NU-1000-TFA (B) crystals.Scale bars are 2 micrometer.

Fig. 3 (A) Nitrogen isotherms of NU-1000 and NU-1000-TFA, (B) cor-responding pore size distribution.

CrystEngCommCommunication

Publ

ishe

d on

04

May

201

8. D

ownl

oade

d by

Nor

thw

este

rn U

nive

rsity

on

6/22

/201

8 3:

57:1

3 A

M.

View Article Online

CrystEngCommThis journal is © The Royal Society of Chemistry 2018

hexagonal channels to 44 Å and accommodates larger bio-molecules.40 Since the mesoporous channels are larger, NU-1003 would require a modulator lengthier than biphenyl-4-carboxylic, thereby limiting practical use in large-scale synthe-sis due to synthetic complexity and reduced solubility of lon-ger aromatic chain length ligands. Therefore, simplermethods for obtaining phase-pure NU-1000 are still needed.

Here, we report the use of trifluoroacetic acid (TFA) as aco-modulator, along with benzoic acid, in the synthesis ofNU-1000 to help eliminate the NU-901 phase formation dur-ing the early stage of crystallization of NU-1000. While therole of the TFA is still under investigation, the presence ofTFA can inhibit the rate of H4TBAPy linker deprotonationsince TFA is much stronger acid (pKa = 0.3) than benzoic acid(pKa = 4.2). This suggests that the vast majority of the TFAwill be ionized while the majority of benzoic acid will be non-ionized at the reaction conditions (pH = ∼1.35). Additionally,Lewis acidity of the Zr6 node would be increased when TFA iscoordinated to the node instead of benzoic acid, which trans-lates into stronger ionic Zr–carboxylate bond.43 The resultingalteration of the coordination equilibrium during the crystalgrowth process yields nearly phase-pure NU-1000 crystals.

Results and discussion

SEM images of NU-1000 crystals synthesized using previouslyreported method yields crystals with “rough” surfaces in thecenter (Fig. 2A) while MOF crystals synthesized using TFA asco-modulator (referred as NU-1000-TFA) display hexagonalrods with six undisturbed rectangular facets throughout thecrystals (Fig. 2), suggesting the absence of the NU-901 phase.While the crystal morphology of MOFs can yield informationregarding the inner-structure of the material, further evi-dence is required to confirm a MOF's phase-purity. The N2

isotherm of NU-1000-TFA exhibits a larger mesoporous step,which translates to larger total pore volume compared to NU-1000 (Fig. 3, Table 1). Brunauer–Emmett–Teller (BET) theorycalculations reveal that NU-1000-TFA, NU-1000, and NU-901have similar surface areas (Table 1). Since NU-901 is a micro-porous MOF with a similar BET surface area compared toNU-1000, the elimination of NU-901 phase should have a pro-nounced effect on total pore volume but not on the specificsurface area. Additionally, the percent of micropore volumein the samples was reduced from 43 to 34% in NU-1000 toNU-1000-TFA (Table 1), which is consistent with the elimina-tion of the NU-901 phase.44

Despite the utility of powder X-ray diffraction (PXRD) pat-terns in determining phase-purity of solids, the diffractionanalysis of NU-1000-TFA was complicated because of similarunit cell dimensions of NU-1000 and NU-901, creating over-lap of the main diagnostic peaks for these MOFs. Instead, weemployed probe molecules to determine if the microporousNU-901 had been eliminated. First, dye (AlexaFluor-647) la-beled insulin (insulin647) was installed in NU-1000 and NU-1000-TFA by soaking the MOFs in a protein solution for 1day. Because of its size (13 Å × 34 Å), insulin easily diffusesthrough the large channels of NU-1000 while simultaneouslyrequiring much longer incubation times to diffuse throughthe microporous channels of NU-901. Confocal laser scan-ning microscopy (CLSM) images revealed a dark spot in thecenter of the NU-1000 crystals where insulin647 was not ableto diffuse, and this inhibited diffusion was attributed to thepresence of the microporous NU-901 phase. Contrastingly, ahomogeneous distribution of insulin647 was observedthroughout NU-1000-TFA (Fig. 4 and S4 and S5†).

The limited diffusion to the center of defective NU-1000can also be observed when the Keggin-type polyoxometalate(POM), H3PW12O40, an anionic metal oxide cluster composedof W ions bridged by oxygen atoms with ∼1 nm diameter,was employed as a probe molecule.41 Similar to insulin647,the POM's size encumbers diffusion through the microporesof NU-901. Both NU-1000-TFA and NU-1000 were soaked in asolution of POM for 3 days and then washed thoroughly prior

Table 1 Surface area, micropore and total pore volume of MOFs

MOFBET surfacearea (m2 g−1)

Micro/total porevolume (cm3 g−1)

Microporevolume (%)

NU-1000 2220 0.544/1.259 43NU-1000-TFA 2180 0.466/1.369 34NU-901 2100 0.677/0.780 87a

a Less than 100% micropore volume in NU-901 can be attributed tothe defects in the crystal.44

Fig. 4 (A) Confocal laser scanning microscopy (CLSM) images and (B)plots of fluorescence intensity of NU-1000 and NU-1000-TFA after in-stallation of insulin647 tagged with a fluorescent probe for 1 day atroom temperature.

Fig. 5 Tungsten EDS signal of NU-1000 and NU-1000-TFA crystalsafter [PW12O40]

3− loading. Black lines are smoothed (adjacent averag-ing) for clarity.

CrystEngComm Communication

Publ

ishe

d on

04

May

201

8. D

ownl

oade

d by

Nor

thw

este

rn U

nive

rsity

on

6/22

/201

8 3:

57:1

3 A

M.

View Article Online

CrystEngComm This journal is © The Royal Society of Chemistry 2018

to energy dispersive X-ray spectroscopy (EDS) analyses. Con-sidering the similar POM loading in both MOFs, the weakertungsten EDS signal at the center of PW12@NU-1000 crystalsuggests lower loading of POM at this location (Fig. 5). Onthe other hand, PW12@NU-1000-TFA exhibited a morehomogenous distribution of tungsten throughout the crystal.Limited diffusion of large probe molecules is not the onlytechnique to support the presence of the microporous sec-ondary phase in the center of the crystal. Installation of mo-lybdenum on the nodes of NU-1000 by atomic layer deposi-tion in MOFs (AIM) results in preferential deposition ofmolybdenum species in the center of the crystal, asevidenced from the lamda (Λ) shaped Mo EDS line profile(Fig. 6). This is the opposite trend of the observations whenlarger probes were installed in NU-1000. The molybdenumhexacarbonyl (MoIJCO)6) precursor is small enough to easilydiffuse in the micropores of the NU-901, so preferential exclu-sion by the secondary-phase should not occur. Since aggrega-tion of precursors under the ALD treatment conditions is sta-bilized by confinement,45 there is preferential growth ofmolybdenum clusters in the denser microporous region inthe center of the crystal. On the other hand, when thesecondary-phase is excluded from the center of crystals, uni-form distribution of molybdenum species is observed in thecase of NU-1000-TFA (Fig. 6).

While the use of probe molecules indirectly proves theprevention of the secondary-phase during the NU-1000-TFAgrowth, single crystal XRD analysis of large NU-1000-TFA crys-tals allows for a more quantitative evaluation of phase purity.

Fig. 7 shows the residual electron density maps of NU-1000and NU-1000-TFA crystals. In NU-1000-TFA, the electron den-sity in the mesopores resulting from the secondary-phase isapproximately 6% occupied, dramatically reduced from the25% occupancy in NU-1000, confirming the improvement inthe homogeneity of the crystals.8

Given the potential applications of NU-1000 as an atomi-cally ordered heterogeneous catalyst or catalyst support, wehave performed a multi-gram synthesis of NU-1000-TFA; theN2 isotherms, SEM images, and PXRD patterns confirm thepurity of the scaled-up batches (Fig. S1–S3†).

Conclusions

In conclusion, using TFA as a co-modulator in NU-1000 syn-thesis controls the crystal formation and can prevent the for-mation of NU-901 phase at the early stage of crystallization.We have utilized large biomolecules and inorganic moleculesas probes to demonstrate the elimination of secondary-phaseformation in NU-1000. Single crystal X-ray diffraction analysisconfirmed the significant enhancement in structural homo-geneity. We have also demonstrated that the synthesis proto-col developed here can be scaled-up easily to obtain multi-gram phase-pure NU-1000, which is crucial for industrial ap-plications. Currently, we are working on understanding therole of TFA as well as exploring the underlying kinetic andthermodynamic mechanism of NU-1000 growth.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

O. K. F. gratefully acknowledges support from DefenseThreat Reduction Agency (HDTRA1-18-1-0003) and Army Re-search Office-STTR (W911SR-17-C-0007). This work madeuse of the EPIC, Keck-II, and/or SPID facilities of North-western University's NUANCE Center, which has receivedsupport from the Soft and Hybrid Nanotechnology Experi-mental (SHyNE) Resource (NSF ECCS-1542205); the MRSECprogram (NSF DMR-1121262) at the Materials ResearchCenter; the International Institute for Nanotechnology(IIN); the Keck Foundation; and the State of Illinois,through the IIN.

Notes and references

1 H. Furukawa, K. E. Cordova, M. O'Keeffe and O. M. Yaghi,The Chemistry and Applications of Metal-Organic Frame-works, Science, 2013, 341, 1230444.

2 Y. Bai, Y. Dou, L.-H. Xie, W. Rutledge, J.-R. Li and H.-C.Zhou, Zr-Based Metal–Organic Frameworks: Design,Synthesis, Structure, and Applications, Chem. Soc. Rev.,2016, 45, 2327–2367.

3 M. Rimoldi, A. J. Howarth, M. R. DeStefano, L. Lin, S.Goswami, P. Li, J. T. Hupp and O. K. Farha, Catalytic

Fig. 6 Molybdenum EDS signal of NU-1000 and NU-1000-TFA crys-tals after Mo-ALD process. Black lines are smoothed (adjacent averag-ing) for clarity.

Fig. 7 Fo–Fc contour maps in the ab plane of NU-1000 and NU-1000-TFA (before using SQUEEZE program). The electron densities due tothe secondary frameworks are visualized. Contours are from NU-1000−0.96 to 0.96 e A−3 in steps of 0.16 e A−3 and NU-1000-TFA −0.64 to0.64 e A−3 in steps of 0.16 e A−3, respectively. The contour maps werecalculated using ShelXle software.

CrystEngCommCommunication

Publ

ishe

d on

04

May

201

8. D

ownl

oade

d by

Nor

thw

este

rn U

nive

rsity

on

6/22

/201

8 3:

57:1

3 A

M.

View Article Online

CrystEngCommThis journal is © The Royal Society of Chemistry 2018

Zirconium/Hafnium-Based Metal–Organic Frameworks, ACSCatal., 2017, 7, 997–1014.

4 J. H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti, S.Bordiga and K. P. Lillerud, A New Zirconium InorganicBuilding Brick Forming Metal Organic Frameworks withExceptional Stability, J. Am. Chem. Soc., 2008, 130, 13850–13851.

5 J. Ma, L. D. Tran and A. J. Matzger, Toward TopologyPrediction in Zr-Based Microporous Coordination Polymers:The Role of Linker Geometry and Flexibility, Cryst. GrowthDes., 2016, 16, 4148–4153.

6 T.-F. Liu, N. A. Vermeulen, A. J. Howarth, P. Li, A. A.Sarjeant, J. T. Hupp and O. K. Farha, Adding to the Arsenalof Zirconium-Based Metal–Organic Frameworks: The Topol-ogy as a Platform for Solvent-Assisted Metal Incorporation,Eur. J. Inorg. Chem., 2016, 2016, 4349–4352.

7 O. M. Yaghi, M. O'Keeffe, N. W. Ockwig, H. K. Chae, M.Eddaoudi and J. Kim, Reticular Synthesis and the Design ofNew Materials, Nature, 2003, 423, 705.

8 J. E. Mondloch, W. Bury, D. Fairen-Jimenez, S. Kwon, E. J.DeMarco, M. H. Weston, A. A. Sarjeant, S. T. Nguyen, P. C.Stair, R. Q. Snurr, O. K. Farha and J. T. Hupp, Vapor-PhaseMetalation by Atomic Layer Deposition in a Metal–OrganicFramework, J. Am. Chem. Soc., 2013, 135, 10294–10297.

9 D. Feng, Z.-Y. Gu, J.-R. Li, H.-L. Jiang, Z. Wei and H.-C.Zhou, Zirconium-Metalloporphyrin Pcn-222: MesoporousMetal–Organic Frameworks with Ultrahigh Stability asBiomimetic Catalysts, Angew. Chem., Int. Ed., 2012, 51,10307–10310.

10 C. W. Kung, T. C. Wang, J. E. Mondloch, D. Fairen-Jimenez,D. M. Gardner, W. Bury, J. M. Klingsporn, J. C. Barnes, R.Van Duyne, J. F. Stoddart, M. R. Wasielewski, O. K. Farhaand J. T. Hupp, Metal–Organic Framework Thin FilmsComposed of Free-Standing Acicular Nanorods ExhibitingReversible Electrochromism, Chem. Mater., 2013, 25,5012–5017.

11 J. Pang, S. Yuan, J. Qin, C. Liu, C. Lollar, M. Wu, D. Yuan,H.-C. Zhou and M. Hong, Control the Structure of Zr-Tetracarboxylate Frameworks through Steric Tuning, J. Am.Chem. Soc., 2017, 139, 16939–16945.

12 P. Deria, D. A. Gómez-Gualdrón, I. Hod, R. Q. Snurr, J. T.Hupp and O. K. Farha, Framework-Topology-DependentCatalytic Activity of Zirconium-Based (Porphinato)ZincIJIi)Mofs, J. Am. Chem. Soc., 2016, 138, 14449–14457.

13 T. C. Wang, W. Bury, D. A. Gómez-Gualdrón, N. A.Vermeulen, J. E. Mondloch, P. Deria, K. Zhang, P. Z.Moghadam, A. A. Sarjeant, Q. R. Snurr, J. F. Stoddart, T. J.Hupp and O. K. Farha, Ultrahigh Surface Area ZirconiumMofs and Insights into the Applicability of the Bet Theory,J. Am. Chem. Soc., 2015, 137, 3585–3591.

14 T.-F. Liu, D. Feng, Y.-P. Chen, L. Zou, M. Bosch, S. Yuan, Z.Wei, S. Fordham, K. Wang and H.-C. Zhou, Topology-GuidedDesign and Syntheses of Highly Stable MesoporousPorphyrinic Zirconium Metal–Organic Frameworks withHigh Surface Area, J. Am. Chem. Soc., 2015, 137, 413–419.

15 W. Morris, B. Volosskiy, S. Demir, F. Gándara, P. L. McGrier,H. Furukawa, D. Cascio, J. F. Stoddart and O. M. Yaghi,

Synthesis, Structure, and Metalation of Two New HighlyPorous Zirconium Metal–Organic Frameworks, Inorg. Chem.,2012, 51, 6443–6445.

16 H. Furukawa, F. Gándara, Y.-B. Zhang, J. Jiang, W. L. Queen,M. R. Hudson and O. M. Yaghi, Water Adsorption in PorousMetal–Organic Frameworks and Related Materials, J. Am.Chem. Soc., 2014, 136, 4369–4381.

17 V. Bon, I. Senkovska, I. A. Baburin and S. Kaskel, Zr- and Hf-Based Metal–Organic Frameworks: Tracking Down the Poly-morphism, Cryst. Growth Des., 2013, 13, 1231–1237.

18 T. D. Bennett, A. K. Cheetham, A. H. Fuchs and F.-X.Coudert, Interplay between Defects, Disorder and Flexibilityin Metal–Organic Frameworks, Nat. Chem., 2016, 9, 11.

19 Z. Fang, B. Bueken, D. E. De Vos and R. A. Fischer, Defect-Engineered Metal–Organic Frameworks, Angew. Chem., Int.Ed., 2015, 54, 7234–7254.

20 M. J. Cliffe, W. Wan, X. Zou, P. A. Chater, A. K. Kleppe,M. G. Tucker, H. Wilhelm, N. P. Funnell, F.-X. Coudert andA. L. Goodwin, Correlated Defect Nanoregions in a Metal–Organic Framework, Nat. Commun., 2014, 5, 4176.

21 D. W. Feng, Z. Y. Gu, Y. P. Chen, J. Park, Z. W. Wei, Y. J.Sun, M. Bosch, S. Yuan and H. C. Zhou, A Highly StablePorphyrinic Zirconium Metal–Organic Framework with Shp-a Topology, J. Am. Chem. Soc., 2014, 136, 17714–17717.

22 H. L. Jiang, D. W. Feng, K. C. Wang, Z. Y. Gu, Z. W. Wei, Y. P.Chen and H. C. Zhou, An Exceptionally Stable, Porphyrinic ZrMetal–Organic Framework Exhibiting Ph-Dependent Fluores-cence, J. Am. Chem. Soc., 2013, 135, 13934–13938.

23 D. W. Feng, W. C. Chung, Z. W. Wei, Z. Y. Gu, H. L. Jiang,Y. P. Chen, D. J. Darensbourg and H. C. Zhou, Constructionof Ultrastable Porphyrin Zr Metal–Organic Frameworksthrough Linker Elimination, J. Am. Chem. Soc., 2013, 135,17105–17110.

24 A. Schaate, P. Roy, A. Godt, J. Lippke, F. Waltz, M. Wiebckeand P. Behrens, Modulated Synthesis of Zr-Based Metal–Or-ganic Frameworks: From Nano to Single Crystals, Chem. –

Eur. J., 2011, 17, 6643–6651.25 R. J. Marshall, C. L. Hobday, C. F. Murphie, S. L. Griffin,

C. A. Morrison, S. A. Moggach and R. S. Forgan, AminoAcids as Highly Efficient Modulators for Single Crystals ofZirconium and Hafnium Metal–Organic Frameworks,J. Mater. Chem. A, 2016, 4, 6955–6963.

26 Z. Hu, I. Castano, S. Wang, Y. Wang, Y. Peng, Y. Qian, C.Chi, X. Wang and D. Zhao, Modulator Effects on the Water-Based Synthesis of Zr/Hf Metal–Organic Frameworks: Quan-titative Relationship Studies between Modulator, SyntheticCondition, and Performance, Cryst. Growth Des., 2016, 16,2295–2301.

27 F. Drache, V. Bon, I. Senkovska, J. Getzschmann and S.Kaskel, The Modulator Driven Polymorphism of Zr (Iv)Based Metal–Organic Frameworks, Philos. Trans. R. Soc., A,2017, 375, 20160027.

28 T. C. Wang, N. A. Vermeulen, I. S. Kim, A. B. Martinson, J. F.Stoddart, J. T. Hupp and O. K. Farha, Scalable Synthesis andPost-Modification of a Mesoporous Metal–Organic Frame-work Called Nu-1000, Nat. Protoc., 2016, 11, 149–162.

CrystEngComm Communication

Publ

ishe

d on

04

May

201

8. D

ownl

oade

d by

Nor

thw

este

rn U

nive

rsity

on

6/22

/201

8 3:

57:1

3 A

M.

View Article Online

CrystEngComm This journal is © The Royal Society of Chemistry 2018

29 T. Islamoglu, S. Goswami, Z. Li, A. J. Howarth, O. K. Farhaand J. T. Hupp, Postsynthetic Tuning of Metal–OrganicFrameworks for Targeted Applications, Acc. Chem. Res.,2017, 50, 805–813.

30 J. E. Mondloch, M. J. Katz, W. C. Isley Iii, P. Ghosh, P. Liao,W. Bury, G. W. Wagner, M. G. Hall, J. B. DeCoste, G. W.Peterson, R. Q. Snurr, C. J. Cramer, J. T. Hupp and O. K.Farha, Destruction of Chemical Warfare Agents UsingMetal–Organic Frameworks, Nat. Mater., 2015, 14, 512–516.

31 A. Atilgan, T. Islamoglu, A. J. Howarth, J. T. Hupp and O. K.Farha, Detoxification of a Sulfur Mustard Simulant Using aBodipy-Functionalized Zirconium-Based Metal–Organic Frame-work, ACS Appl. Mater. Interfaces, 2017, 9, 24555–24560.

32 P. Li, J. A. Modica, A. J. Howarth, E. Vargas, P. Z.Moghadam, R. Q. Snurr, M. Mrksich, J. T. Hupp and O. K.Farha, Toward Design Rules for Enzyme Immobilization inHierarchical Mesoporous Metal-Organic Frameworks, Chem,2016, 1, 154–169.

33 T. Islamoglu, M. A. Ortuño, E. Proussaloglou, A. J. Howarth,N. A. Vermeulen, A. Atilgan, A. M. Asiri, C. J. Cramer andO. K. Farha, Presence Versus Proximity: The Role of PendantAmines in the Catalytic Hydrolysis of a Nerve AgentSimulant, Angew. Chem., 2018, 130, 1967–1971.

34 R. J. Drout, K. Otake, A. J. Howarth, T. Islamoglu, L. Zhu, C.Xiao, S. Wang and O. K. Farha, Efficient Capture ofPerrhenate and Pertechnetate by a Mesoporous Zr Metal–Organic Framework and Examination of Anion BindingMotifs, Chem. Mater., 2018, 30, 1277–1284.

35 A. W. Peters, Z. Li, O. K. Farha and J. T. Hupp, AtomicallyPrecise Growth of Catalytically Active Cobalt Sulfide on FlatSurfaces and within a Metal–Organic Framework Via AtomicLayer Deposition, ACS Nano, 2015, 9, 8484–8490.

36 M. C. Simons, M. A. Ortuño, V. Bernales, C. A. Gaggioli, C. J.Cramer, A. Bhan and L. Gagliardi, C–H Bond Activation onBimetallic Two-Atom Co-M Oxide Clusters Deposited on Zr-Based Mof Nodes: Effects of Doping at the Molecular Level,ACS Catal., 2018, 8, 2864–2869.

37 A. Van Wyk, T. Smith, J. Park and P. Deria, Charge-Transferwithin Zr-Based Metal–Organic Framework: The Role of Po-lar Node, J. Am. Chem. Soc., 2018, 140, 2756–2760.

38 W. Zhang, Y. Ma, I. A. Santos-López, J. M. Lownsbury, H. Yu,W.-G. Liu, D. G. Truhlar, C. T. Campbell and O. E. Vilches,Energetics of Van Der Waals Adsorption on the Metal–Organic Framework Nu-1000 with Zr6-Oxo, Hydroxo, andAqua Nodes, J. Am. Chem. Soc., 2018, 140, 328–338.

39 S. P. Desai, C. D. Malonzo, T. Webber, J. X. Duan, A. B.Thompson, S. J. Tereniak, M. R. DeStefano, C. T. Buru, Z. Y.Li, R. L. Penn, O. K. Farha, J. T. Hupp, A. Stein and C. C. Lu,Assembly of Dicobalt and Cobalt-Aluminum Oxide Clusterson Metal-Organic Framework and Nanocast Silica Supports,Faraday Discuss., 2017, 201, 299–314.

40 P. Li, S.-Y. Moon, M. A. Guelta, L. Lin, D. A. Gómez-Gualdrón,R. Q. Snurr, S. P. Harvey, J. T. Hupp and O. K. Farha, Nanosizinga Metal–Organic Framework Enzyme Carrier for AcceleratingNerve Agent Hydrolysis, ACS Nano, 2016, 10, 9174–9182.

41 C. T. Buru, P. Li, B. L. Mehdi, A. Dohnalkoya, A. E. Platero-Prats, N. D. Browning, K. W. Chapman, J. T. Hupp and O. K.Farha, Adsorption of a Catalytically AccessiblePolyoxometalate in a Mesoporous Channel-Type Metal-Or-ganic Framework, Chem. Mater., 2017, 29, 5174–5181.

42 W.-G. Liu and D. G. Truhlar, Computational Linker Designfor Highly Crystalline Metal–Organic Framework Nu-1000,Chem. Mater., 2017, 29, 8073–8081.

43 B. Van de Voorde, I. Stassen, B. Bueken, F. Vermoortele, D.De Vos, R. Ameloot, J.-C. Tan and T. D. Bennett, Improvingthe Mechanical Stability of Zirconium-Based Metal-OrganicFrameworks by Incorporation of Acidic Modulators, J. Mater.Chem. A, 2015, 3, 1737–1742.

44 H. Noh, C.-W. Kung, T. Islamoglu, A. W. Peters, Y. Liao,P. Li, S. J. Garibay, X. Zhang, M. R. DeStefano, J. T.Hupp and O. K. Farha, Room Temperature Synthesis ofan 8-Connected Zr-Based Metal–Organic Framework forTop-Down Nanoparticle Encapsulation, Chem. Mater.,2018, 30, 2193–2197.

45 L. C. Gallington, I. S. Kim, W.-G. Liu, A. A. Yakovenko, A. E.Platero-Prats, Z. Li, T. C. Wang, J. T. Hupp, O. K. Farha,D. G. Truhlar, A. B. F. Martinson and K. W. Chapman,Regioselective Atomic Layer Deposition in Metal–OrganicFrameworks Directed by Dispersion Interactions, J. Am.Chem. Soc., 2016, 138, 13513–13516.

CrystEngCommCommunication

Publ

ishe

d on

04

May

201

8. D

ownl

oade

d by

Nor

thw

este

rn U

nive

rsity

on

6/22

/201

8 3:

57:1

3 A

M.

View Article Online