Computational Structure Prediction of (4,4)-Connected Copper Paddle

Communication Cite This: Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Computational Structure Prediction of (4,4)-Connected Copper Paddle-wheel-based MOFs: Influence of Ligand Functionalization on the Topological Preference Sarawoot Impeng,†,§ Ruel Cedeno,† Johannes P. Dürholt,‡ Rochus Schmid,‡ and Sareeya Bureekaew*,† †

Department of Chemical and Biomolecular Engineering, School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology, Rayong 21210, Thailand ‡ Computational Materials Chemistry Group, Lehrstuhl für Anorganische Chemie 2, Ruhr-Universität Bochum, 150, D-44780 Bochum, Germany S Supporting Information *

ABSTRACT: The effect of linkers with extended π-system on the topological preference of (4,4)-connected copper paddlewheel-based metal−organic frameworks (MOFs) was investigated using the reverse topological approach (RTA) in which a genetic algorithm (GA) and the DFT-derived force field MOF-FF were used for ranking and predicting the most stable phase. Three tetracarboxylate linkers bearing different functionality, namely, phenylene (L1), naphthalene (L2), and anthracene (L3) groups, were studied. All potential topologies including nbo-b, ssa, ssb, pts, and lvt-b were considered. The computational results reveal that nbo-b is the most stable topology for all three investigated linkers. However, L2 is also formed in ssb according to experimental findings. Our simulation results show that the CH−π interactions with a Y-shaped configuration between naphthalene moieties of L2 stabilize the ssb framework. Unlike L2, CH−π interactions are not favorable for L1 and L3 because of unsuitable size of the π-system. The results of the RTA predictions are in agreement with experimentally reported data, suggesting the capability of RTA for accurate structural predictions of MOFs. More importantly, this work shows the exemption of reticular chemistry in which linker functionalization can result in alteration of the resulting topology, as found in the case of linker L2.

1. INTRODUCTION Since their discovery, metal−organic frameworks (MOFs) have become one of the most important classes of porous materials because of their striking properties such as high surface area, large internal pore volume, and tunable pore size.1−5 MOFs can be synthesized by the assembly of inorganic and organic building blocks via coordination bonds. To further improve their properties, efforts have been made to deliberately control their structures, especially pore size and network topology (net in short), with respect to specific applications including gas separation, energy storage, and catalysis.6−8 Reticular synthesis has become a useful strategy for the rational design of MOFs by providing an improved control of the pore size and topology.9−11 Unlike the conventional synthesis of organic compounds in which starting materials do not maintain their structures, reticular synthesis enables the assembly of judiciously designed building blocks that maintain their molecular shape throughout the reaction,12 an essential feature that enables systematic modulation of desired properties. Another important aspect of reticular synthesis relies on the idea that extending the length of the organic linker or its © XXXX American Chemical Society

functionality does not alter the topology of the desired MOFs. For example, varying the lengths of organic linker on the same inorganic building blocks yields a series of MOFs with the same topology but with different pore size called isoreticular MOFs (IRMOFs).13 In this case, the pore size corresponds to the lengths of the linkers. This concept has led to successful synthesis of various isoreticular MOFs, for example, MIL8814,15 and MIL-101 series16,17 and UiO-66 series,18 which highlights the significance of reticular chemistry on the rational design of MOFs. To facilitate the discovery of new MOFs, in-depth understanding and characterization of their structural architectures is necessary for the comparison of newly synthesized structures with the existing ones. Unfortunately, in several cases, single crystals are not accessible experimentally due to the poor crystallinity of some MOFs coupled with large unit cells or low symmetries. Consequently, structure solution is merely based Received: February 12, 2018 Revised: March 29, 2018 Published: April 5, 2018 A

DOI: 10.1021/acs.cgd.8b00238 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Figure 1. Schematic of augmented (4,4)-connected nets considered in this work.

Figure 2. Schematic of the copper paddle-wheel cluster (Cu2(CO2)4) and three different tetracarboxylate linkers investigated in this work. Color code: gold, Cu; red, oxygen; black, carbon.

design and screening of MOFs for use in gas storage by Snurr et al.28,29 Initiated by the observation of two distinct MOF phases PCN-16 and PCN-16′ under different synthesis conditions,30 we have investigated isoreticular isomerism in the realms of nbo-b (4,4)-connected topology.31 Note that we used a minimum vertex topology, representing the organic tetracarboxylate linkers by a four-coordinated vertex. The GA search was able to predict all possible supramolecular isomers or phases. However, when considering all known copper paddlewheel MOFs with a tetracarboxylate linker there are few cases where a topology other than nbo is observed.32−35 In the current work, we thus extend the search space substantially and include further possible (4,4)-connected topologies including nbo-b, ssa, ssb, pts, and lvt-b, which are illustrated as augmented nets in Figure 1. The reason for selecting these topologies was based on synthetic accessibility as suggested in the literature.12,36 Again, we are focusing on minimum vertex topologies in order to leave the task of finding the orientation of the linker to the GA global search. Note that because of the two different vertices (Cu paddle-wheel and tetracarboxylic linker), the binary version of nbo and lvt (abbreviated as nbo-b and lvt-b), which are the nets with one kind of vertex, are used. Besides this enumeration of topologies

on indexation of powder X-ray diffraction (PXRD) patterns and some intuitive assumptions, which often carries insufficient information to fully elucidate the crystal structure. This instigates the need to develop efficient computational methods for structural prediction of MOFs.19 Recently, we proposed the top-down topology-based method for structural prediction of MOFs, which we called reverse topological approach (RTA).20,21 In this method, instead of deducing the network topology from the original structure, we used a known network topology as a starting point to predict and rank the possible structures. More specifically, the building blocks are mapped onto the given network topology or topological blueprint at the vertex position. The structure is then optimized via molecular simulations using a DFT-derived force field for MOFs such as MOF-FF,22 which was proven to be accurate for the study of the dynamic behavior of MOFs upon external stimulation such as temperature.23−25 In the calculations, we used our in-house developed computer software called weaver, which can perform automatic searching of the most stable structure for a given topology. Moreover, a genetic algorithm (GA) is applied for solving the global minimum problem. Our method has successfully predicted the structures of boron-based 3D covalent−organic frameworks.26,27 Furthermore, it has been implemented for the B



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Table 1. Relative Strain Energies (per Formula Unit), Space Groups, Lattice Parameters, and Accessible Surface Areas for All Investigated Network Topologies linker L1 ΔEstrain (kcal/mol) space group a/b/c α/β/γ S (m2/g)

nbo-b-L1

ssa-L1

0.0 R3̅m a = b = 18.698, c = 38.475 α = β = 90°, γ = 120° 3250

10.7 P6_3/mmc a = b = 28.838, c = 16.859 α = β = 90°, γ = 120° 3666

nbo-b-L2 ΔEstrain (kcal/mol) space group a/b/c α/β/γ S (m2/g)

ssa-L2

α/β/γ S (m2/g)

lvt-b-L1

pts-L1

11.1 Imma a = 19.295, b = 16.88, c = 27.0 α = β = γ = 90° 3700

23.4 P4/mmm a = b = 19.341, c = 8.59 α = β = γ = 90° 3659

ssb-L2

lvt-b-L2

pts-L2

0.0

12.9

1.0

12.4

24.8

R3m ̅ a = b = 18.648, c = 38.647 α = β = 90°, γ = 120° 2714

P6_3/mmc a = b = 28.83, c = 16.859 α = β = 90°, γ = 120° 3959

I4/mmm a = b = 19.04, c = 27.332 α = β = γ = 90° 2487 linker L3

Imma a = 16.601, b = 16.90, c = 21.767 α = β = γ = 90° 3575

P4/mmm a = b = 19.446,,c = 8.581 α = β = γ = 90° 3649

nbo-b-L3 ΔEstrain (kcal/mol) space group a/b/c

ssb-L1 2.0 I4/mmm a = b = 19.02, c = 27.228 α = β = γ = 90° 3020 linker L2

ssa-L3

ssb-L3

lvt-b-L3

pts-L3

0.0

54.3

1.4

12.9

27.8

R3m ̅ a = b = 18.603, c = 38.702 α = β = 90°, γ = 120° 2266

P6_3/mmc a = b = 27.231, c = 16.98 α = β = 90°, γ = 120° 3393

I4/mmm a = b = 18.964, c = 27.265 α = β = γ = 90° 1966

Imma a = 16.9, b = 19.211, c = 22.014 α = β = γ = 90° 3264

Cmmm a = 36.37, b = 40.615, c = 8.602 α = β = γ = 90° 3503

2. COMPUTATIONAL DETAILS

the same building blocks, is compared to each other in order to rank and find the lowest-energy structure. Accessible geometric surface areas of the final structures were computed by sampling the surface, accessible by a spherical probe molecule with the kinetic diameter of nitrogen (3.64 Å). For this purpose, the ZEO++ code has been used.40,41 In addition, the final structures were analyzed by detecting the space group and the conventional unit cell parameters using the program library spglib. Only those atoms belonging to the inorganic building block were used in the symmetry analysis in which a rather loose threshold (symprec ≤ 1.0) was employed.

Figure 1 shows the network topologies that were used as the topological templates for constructing the hypothetical MOFs with (4,4)-connected network from copper paddle-wheel (Cu2(CO2)4) cluster and L1, L2, and L3 linkers (see Figure 2). All topological templates were taken from the MOF+ Web site.37 We employed the weaver code to automatically insert those inorganic and organic building blocks into the given topologies. All periodic structures were then optimized with P1 symmetry (no symmetry constraint) using the MOF-FF force field. Molecular simulations were performed using our pydlpoly code based on DL_poly Classic with a Python scripting interface. The periodic box size of all systems was greater than twice the van der Waals (vdW) cutoff, which was 12 Å. The shifted force method introduced by Fennell and Gezelter38 was used for truncating the electrostatic interactions. Instead of point charges, Gaussian type charge distributions were employed. A GA was employed to locate the most stable phase of each topology. The genetic algorithm was run for maximal 200 generations with a population size varying between 100 and 200 individuals. The best individual of each generation was maintained, while twins were discarded to maintain diversity. To select the best candidate structure for crossover, a tournament selection was applied, and the mutation rate was 0.05. We performed molecular dynamics (MD) simulations in the NVT ensemble to allow proper arrangement of the extended π-system of the linkers making the proper arrangement for CH−π interactions. All MD simulations were carried out at 500 K and 1 atm using the Nose− Hoover thermostat.39 Like in previous work,20,21,27,31 the strain energy per formula unit of all possible networks, which were constructed from

3. RESULTS AND DISCUSSION 3.1. MOFs with Copper Paddle-wheel and Linker L1 Building Blocks. The relative strain energies and crystallographic data of the hypothetical MOFs constructed from the combination of Cu2(CO2)4 and linker L1 in the studied nets (denoted as nbo-b-L1, ssb-L1, ssa-L1, lvt-b-L1, and pts-L1) are collected in Table 1. The corresponding optimized geometries are illustrated in Figure 3. Considering the relative strain energies, it was found that the nbo-b results in the lowest energy structure. The next stable topology is ssb, which is 2.0 kcal/mol less stable in energy than nbo-b. In addition, ssa-L1, lvt-b-L1, and pts-L1 are less stable than the nbo-b-L1 with relative energy of 10.7, 11.1, and 23.4 kcal/mol, respectively. Comparing the computational results to available experimental data, the predicted nbo-b-L1 was successfully synthesized and reported as NOTT-101 by Lin et al.35 This result suggests that the structural preference depends on the thermodynamic stability of the framework. Other network topologies (ssb, ssa, lvt-b, and pts) have not yet been prepared, to the best of our knowledge, probably because of their lower thermodynamic stability. Figure 4a shows the PXRD pattern of nbo-b-L1, which matches very well with the PXRD pattern of NOTT-101. Overall, these results indicate the capability of RTA for accurate prediction of the topological preference of MOFs.

and thus screening of topological isomers, we still use the GA global search to identify the lowest energy isoreticular isomers. The computational results are compared to the related experimental data. In addition, the theoretical analysis could lead to better insights into the molecular origins of the observed linker-induced topological preference, which could be used to control the target topology by proper selection of organic linkers.

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Figure 3. Optimized structures of the most stable phase for all investigated network topologies. Color code: gold, Cu; red, oxygen; black, carbon; white, hydrogen.

As shown in our previous work20 and elsewhere,33 the linker deformation in the network topology reflects the stability of the framework. A closer analysis of the geometry of linker L1 in all studied topologies reveals that the carboxylate group is apparently rotated out of the phenyl plane in the case of ssa, ssb, lvt-b, and pts. However, the carboxylate rotation is not seen in nbo-b (see Figure 5). These results exemplify the effect of linker deformation on the stability of the framework, verifying that it can be attributed to the deformation of the linker.20,33 To comprehend the influence of linker deformation on the stability of framework, we performed single-point energy calculations of the L1 taken from nbo-b and ssb, using both MOF-FF and DFT at the B3LYP/def-SV(P) level of theory. For DFT calculations, the TURBOMOLE program was used, and the details of calculations are provided in the Supporting Information. Note that we focus on only the case of nbo-b and ssb topologies because they are small in energy difference of 2.0 kcal/mol (Table 1). It is anticipated that the energy difference between the two geometries is close to the energy difference of

the frameworks. The single-point energy calculations show that the L1 geometry taken from ssb is less stable than the corresponding structure taken from nbo-b with an energy of 2.4 kcal/mol. These results clearly demonstrate the effect of linker deformation on the stability of the network topology. Note that calculations with MOF-FF and DFT give a similar energy difference of 2.4 kcal/mol. In order to verify that the linker deformation, with the carboxylate moiety rotating out of the aromatic ring plane, plays a key role in the structural stability, we performed DFT calculations using benzoate as a molecular model. As demonstrated in Figure S1, which shows the plot of energy versus torsion angle between carboxylate and phenyl ring, the most stable conformation is found for a torsion angle of 0°. The rotation of this dihedral angle destabilizes the system. Altogether, these results show the influence of local linker deformations on the overall stability of MOFs, and the assembly of Cu2(CO2)4 and L1 lead to the formation of D



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Figure 4. XRD patterns of predicted MOFs compared with the corresponding experimental one: (a) nbo-b-L1, (b) nbo-b-L2, (c) ssb-L2, and (d) nbo-b-L3.

b-L2, ssb-L2, ssa-L2, lvt-b-L2, and pts-L2) are again shown in Table 1, and their corresponding optimized geometries are illustrated in Figure 3. Similar to what was found for the assembly of Cu2(CO2)4 and linker L1, nbo-b-L2 is the most stable structure among all studied topologies. The next stable topology is ssb, which is 1.0 kcal/mol energetically less preferred. Moreover, the systems of lvt-b, ssa, and pts are thermodynamically less stable than nbo-b by 12.4, 12.9, and 24.8 kcal/mol, respectively (see Table 1). Considering the topological stability of MOFs made from L1 and L2, it can be estimated that the stability of hypothetical MOFs increases similarly in the order pts < ssa ≈ lvt-b < ssb < nbo-b. Interestingly, the energy difference between nbo-b and ssb of L2 is significantly decreased by a factor of one half with respect to that of L1. Due to the small energy difference, it is expected that both nbo-b-L2 and ssb-L2 are possible to be synthesized. Experimentally, the two predicted MOFs from L2 in nbo-b and ssb (denoted as nbo-b-L2 and ssb-L2) were successfully obtained as ZJU-7 and NOTT-109 MOFs by Cai et al.32 and Schröder et al.,35 respectively. As shown in Figure 4b,c, the simulated PXRD patterns of nbo-b-L2 and ssb-L2 match well with the patterns of ZJU-7 and NOTT-109, respectively. Note that the different conditions such as solvent and reaction time were used for the preparations of ZJU-7 and NOTT-109. Therefore, it can be concluded that the assembly of Cu2(CO2)4 and linkers L2 can be formed in either nbo-b or

Figure 5. Geometries of L1 taken from the optimized structures of nbo-b-L1 and ssb-L1, and their relative energies calculated with MOFFF (with DFT).

MOF with the nbo-b, as verified by good agreement between computational and experimental results. 3.2. MOFs with Copper Paddle-wheel and Linker L2 Building Blocks. In this section, we intend to investigate the impact of ligand functionalization and especially extended πsystems on the topological preference of MOFs. To investigate this effect, linker L2 decorated with a naphthalene group (Figure 1) was employed. Cu2(CO2)4 and linker L2 were mapped onto all possible network topologies and then structurally optimized in order to rank and predict the most stable geometry with the lowest strain energy. The relative energies and crystallographic data of hypothetical MOFs (nboE



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Figure 6. Orientation of L2 and L3 found in ssb-L2 and ssb-L3. Less bulky L2 is allowed for rearranging the orientation to maximize the CH−π interaction without violation of the geometry of the ligand. When the more bulky L3 rearranges to achieve CH−π interaction, with the limit of space, geometry deformation of L3 is observed.

ssb, respectively (Table 1). The energy difference between the two topologies is 1.4 kcal/mol, which is energetically between those values of L1 and L2. In addition, the pts, lvt-b, and ssa are less stable than nbo-b with energy of 27.8, 12.9, and 54.3 kcal/mol, respectively. These energy differences become higher with respect to those values in the case of L1 and L2. Due to the bulky anthracene moiety, L3 could not fit into the topological template, resulting in structural deformation of building units and, consequently, poor stability. Considering the optimized geometry of the ssb made from L3, the intermolecular CH−π interactions between the linkers are observed in a similar fashion as for L2. Having a larger π system, ssb-L3 was expected to possess more CH−π interactions than ssb-L2 to stabilize the system; consequently, energy difference of nbo-b-L3 and ssb-L3 should be less than that of nbo-b-L2 and ssb-L2 (1.0 kcal/mol). However, as mentioned above, the energy difference between nbo-b-L3 and ssb-L3 is 1.4 kcal/mol, less favorable than the expectation. Forming CH−π interaction requires space for the arrangement of aromatic moieties to maximize the interaction. In the case of ssb-L2, the framework affords enough space allowing for four CH−π interactions from four adjacent L2. However, in the case of ssb-L3, due to the bulkiness of the linker and the limit of space, framework-stabilizing CH−π interactions and framework-destabilizing steric repulsion mutually occur (Figure 6). In addition, the forming CH−π interaction induces geometry deformation of L3, resulting in less stable conformation. It can thus be implied that in the case of linker L3, the bulkiness violates the stability of the ssb structure and probably raises the energy difference between the nbo-b and ssb. Nevertheless, the energy difference between nbo-b-L3 and ssb-L3 (1.4 kcal/mol) is 0.6 kcal/mol smaller than that in the case of L1 (2.0 kcal/ mol). This is due to the presence of CH−π interactions between anthracene moieties of L3 in the ssb framework. Altogether, these results indicate the effect of an extended πsystem in the tetracarboxylate linker on the structural preference of MOFs. The influence of functionalized linker on framework stability and gas adsorption in MOFs has been experimentally reported as well.42−45 Next, we compared our computational results with available experimental data. Experimentally, the predicted MOF from linker L3 with the nbo-b net (denoted as nbo-b-L3) was successfully prepared and reported as PCN-14 by Ma et al.46 The XRD pattern of nbo-b-L3 is similar to that of PCN-14 as

ssb, depending on the synthetic conditions used. Since the energy difference of both is rather small, 1.0 kcal/mol, careful optimization of the synthesis method is strongly recommended; otherwise, mixed phase can be formed. Note that our computational calculations consider only thermodynamic effects, excluding kinetic and solvent effects. However, the computational results of the RTA structure predictions are in good agreement with the experimental observations, namely, that the two most theoretically stable MOFs were successfully synthesized using distinct solvothermal conditions. In structural preference of the MOF aspect, one can say that thermodynamic effects dominate over kinetic and solvent effects. The structure of NOTT-109 was first erroneously reported35 to be a pts, and it was later recognized to be a ssb. Here the topological analysis is based on considering both Cu2(CO2)4 and linker L2 as 4-connected vertices. As suggested by Yaghi and O’Keeffe,12 a 4-connected vertex in a crystal structure can be considered as two linked 3-connected vertices. Therefore, the ssb-L2 predicted MOF, which is structurally similar to NOTT-109, can be considered as a (3,4)-connected stx derived from the minimum vertex (4,4)-connected ssb. As we discussed above, the energy difference between nbo-bL2 and ssb-L2 decreases by one half compared to that of L1. Considering the optimized geometry of ssb-L2, the framework provides sufficient space allowing for the rearrangement of the naphthalene ring to form CH−π interactions with Y-shaped configuration showing an intermolecular distance of ∼2.7 Å (see Figure 6). Note that for CH−π interactions with Y-shaped configuration, two hydrogen atoms from one aromatic molecule are pointing toward the plane of another aromatic molecule. However, in the case of L1 these intermolecular interactions are almost absent because of the smaller size of the extended π-system L1, as compared to that of L2. The CH−π interactions stabilize ssb, which is the reason why the energy difference between nbo-b and ssb of L2 becomes one half of that of L1. 3.3. MOFs with Copper Paddle-wheel and Linker L3 Building Blocks. To verify and comprehend the influence of linkers with extended π-system on the topological preference, a larger extended π-system, L3 with an anthracene backbone, was further studied. Considering the relative strain energies of hypothetical MOFs, constructed from the assembly of Cu2(CO2)4 and L3 (nbo-b-L3, ssb-L3, ssa-L3, lvt-b-L3, and pts-L3), the two most stable topologies are again nbo-b and F



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shown in Figure 4d. Even though ssb is 1.4 kcal/mol less stable than nbo-b, so far, it has not yet been successfully synthesized. These results show again the ability of RTA for accurate prediction the structural preference of MOFs.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.8b00238.

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REFERENCES

(1) Ferey, G. Hybrid porous solids: past, present, future. Chem. Soc. Rev. 2008, 37, 191−214. (2) Horike, S.; Shimomura, S.; Kitagawa, S. Soft porous crystals. Nat. Chem. 2009, 1, 695−704. (3) Murray, L. J.; Dinca, M.; Long, J. R. Hydrogen storage in metalorganic frameworks. Chem. Soc. Rev. 2009, 38, 1294−1314. (4) Kreno, L. E.; Leong, K.; Farha, O. K.; Allendorf, M.; Van Duyne, R. P.; Hupp, J. T. Metal−organic framework materials as chemical sensors. Chem. Rev. 2012, 112, 1105−1125. (5) Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M. The chemistry and applications of metal-organic frameworks. Science 2013, 341, 1230444. (6) Collins, D. J.; Zhou, H.-C. Hydrogen storage in metal-organic frameworks. J. Mater. Chem. 2007, 17, 3154−3160. (7) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Metal-organic framework materials as catalysts. Chem. Soc. Rev. 2009, 38, 1450−1459. (8) Li, J.-R.; Ma, Y.; McCarthy, M. C.; Sculley, J.; Yu, J.; Jeong, H.-K.; Balbuena, P. B.; Zhou, H.-C. Carbon dioxide capture-related gas adsorption and separation in metal-organic frameworks. Coord. Chem. Rev. 2011, 255, 1791−1823. (9) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Reticular synthesis and the design of new materials. Nature 2003, 423, 705−714. (10) O’Keeffe, M.; Peskov, M. A.; Ramsden, S. J.; Yaghi, O. M. The Reticular Chemistry Structure Resource (RCSR) database of, and symbols for, crystal nets. Acc. Chem. Res. 2008, 41, 1782−1789. (11) Tranchemontagne, D. J.; Mendoza-Cortes, J. L.; O’Keeffe, M.; Yaghi, O. M. Secondary building units, nets and bonding in the chemistry of metal-organic frameworks. Chem. Soc. Rev. 2009, 38, 1257−1283. (12) Li, M.; Li, D.; O’Keeffe, M.; Yaghi, O. M. Topological analysis of metal−organic frameworks with polytopic linkers and/or multiple building units and the minimal transitivity principle. Chem. Rev. 2014, 114, 1343−1370. (13) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Systematic design of pore size and functionality in isoreticular MOFs and their application in methane storage. Science 2002, 295, 469−472. (14) Serre, C.; Mellot-Draznieks, C.; Surblé, S.; Audebrand, N.; Filinchuk, Y.; Férey, G. Role of solvent-host interactions that lead to very large swelling of hybrid frameworks. Science 2007, 315, 1828− 1831. (15) Surble, S.; Serre, C.; Mellot-Draznieks, C.; Millange, F.; Ferey, G. A new isoreticular class of metal-organic-frameworks with the MIL88 topology. Chem. Commun. 2006, 3, 284−286. (16) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.; Dutour, J.; Surble, S.; Margiolaki, I. A chromium terephthalate-based solid with unusually large pore volumes and surface area. Science 2005, 309, 2040−2042. (17) Sonnauer, A.; Hoffmann, F.; Fröba, M.; Kienle, L.; Duppel, V.; Thommes, M.; Serre, C.; Férey, G.; Stock, N. Giant pores in a chromium 2,6-naphthalenedicarboxylate open-framework structure with MIL-101 topology. Angew. Chem., Int. Ed. 2009, 48, 3791−3794. (18) Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability. J. Am. Chem. Soc. 2008, 130, 13850−13851. (19) Maurin, G. Role of molecular simulations in the structure exploration of metal-organic frameworks: illustrations through recent advances in the field. C. R. Chim. 2016, 19, 207−215. (20) Amirjalayer, S.; Tafipolsky, M.; Schmid, R. Exploring network topologies of copper paddle wheel based metal−organic frameworks with a first-principles derived force field. J. Phys. Chem. C 2011, 115, 15133−15139. (21) Bureekaew, S.; Schmid, R. Hypothetical 3D-periodic covalent organic frameworks: exploring the possibilities by a first principles derived force field. CrystEngComm 2013, 15, 1551−1562.

4. CONCLUSION The reverse topological approach (RTA) was employed to investigate the influence of ligand functionalization on the structural preference of (4,4)-connected MOFs constructed from paddle-wheels Cu2(CO2)4 and three different tetracarboxylic linkers decorated with benzene, naphthalene, and anthracene groups (denoted as L1, L2, and L3, respectively). A DFT-derived force field MOF-FF and a generic algorithm (GA) were used in order to rank and locate the lowest-energy structure. All possible topologies including nbo-b, ssa, ssb, pts, and lvt-b were considered based on (4,4)-connected network topology. The computational results show good agreement with experimental data in which nbo-b is the most stable topology among all the topologies for all investigated linkers. In addition, in the case of L2, ssb topology is also possible to be formed because it is only 1.0 kcal/mol less stable in energy than nbo-b. It is evident that ssb framework is stabilized by the CH−π interactions between naphthalene groups of L2. However, these interactions are less favorable for L1 and L3 because of the size of extended π-system on linkers, which is too small and bulky for L1 and L3, respectively. Altogether, these results reveal that the ligand functionalization significantly affects the topological stability of MOFs. Moreover, this work is not only providing insight into understanding the linkerinduced topological preference but also demonstrating the exemption of reticular chemistry.

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DFT calculations and energy profile for rotation of carboxylate plane (dihedral angle) in benzoate (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Sareeya Bureekaew: 0000-0001-9302-2038 Present Address

§ National Nanotechnology Center (NANOTEC), National Science and Technology Development Agency, Pathumthani 12120, Thailand.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS S.I. acknowledges financial support from Vidyasirimedhi Institute of Science and Technology (VISTEC) through a postdoctoral fellowship. J.P.D. is grateful for the financial support by the Funds of the Chemical Industry. S.B. is grateful for financial support through Thailand Research Fund (TRF) grant number RSA6080068. G



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Computational Structure Prediction of (4,4)-Connected Copper Paddle

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