Hybrid Triazine-Boron Two-Dimensional Covalent ... - ACS Publications

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Hybrid Triazine-Boron Two-Dimensional Covalent Organic Frameworks: Synthesis, Characterization, and DFT Approach to Layer Interaction Energies Krzysztof Gontarczyk,† Wojciech Bury,†,‡ Janusz Serwatowski,† Piotr Wieciński,† Krzysztof Woźniak,§ Krzysztof Durka,*,† and Sergiusz Luliński*,† †

Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warszawa, Poland Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland § University of Warsaw, Biological and Chemical Research Centre, Ż wirki i Wigury 101, 02-089 Warszawa, Poland

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‡

S Supporting Information *

ABSTRACT: The conversion of 2,4,6-tris(4′-bromophenyl)-1,3,5triazine to the respective triboronic acid was successfully accomplished by a simple triple Br/Li exchange followed by boronation. Further dehydrative condensation reactions with 2,3,6,7,10,11hexahydroxytriphenylene or 2,3,6,7-tetrahydroxy-9,10-dilalkylanthracenes (R = Me, Et) resulted in materials featuring good porosity and sorption properties with the nitrogen uptake exceeding 500 cm3/g (STP) and SBET up to 1267 m2/g (T = 77.2 K). In addition, simple dehydration of this compound was employed for the preparation of a hybrid 2D COF composed of triazine, boroxine, and benzene rings. The formation of materials was confirmed by the IR analysis and NMR studies on water-decomposed samples. All obtained COFs exhibit high thermal stability with decomposition temperatures in the range of 400−600 °C. They also show quite different morphology ranging from regular 0.5−4 μm spherical and ellipsoidal clusters to 5−12 μm bent rodlike particles. The PXRD studies supported by periodic DFT modeling in Crystal09 package revealed the formation of crystalline 2D honeycomb-type lattices with eclipsed stacking models. In addition, the differences between boroxine-triazine material and related COF-1 and CTF-1 structures were investigated by comparing layer interaction energies, work function values as well as atomic charges and electrostatic potential maps plotted on the electron density surfaces. It demonstrates that the interactions between layers are enhanced by the stacking of triazine and boroxine rings. Finally, we have investigated the upper limit to space accessible volume using a procrystal electron density approach. KEYWORDS: covalent-organic frameworks, two-dimensional materials, adsorption, periodic DFT calculations, interlayer energy, layer assembly, boron-triazine COFs

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INTRODUCTION

and Si[p-C6H4B(OH)2]4 for the construction of highly porous 3D COF-102 and COF-103 structures, respectively.9 The significant advantage of COF materials is that they often have a very low density, which drops below 0.2 g cm−3 for COF-102 and COF-103. In addition, COFs usually exhibit exceptional thermal stability (even up to 600 °C). The presented characteristics make COFs an attractive class of new porous materials. The building blocks of COFs do not undergo significant change in their overall geometry when incorporated into the material framework. This allows also for the design of COFs possessing desired composition, pore size, and aperture, which is very important from the practical point of view. Further development in the field is obviously coupled with the

Covalent organic frameworks constitute a class of porous organic materials composed of light elements such as carbon, boron, oxygen, nitrogen, silicon, and sulfur connected by strong covalent bonds.1−5 The seminal results regarding design of these materials were reported by Yaghi and co-workers. Their initial strategy was based on a simple dehydrative autocondensation of 1,4-phenyleneboronic acid and resulted in COF-1, which showed two-dimensional (2D) layer hexagonal architecture.6 Alternatively, they used the polycondensation reactions between the multiboronic acids and appropriate polyols (e.g., 2,3,6,7,10,11-hexahydroxytriphenylene, HHTP) to prepare various 2D organic frameworks showing improved sorption properties with respect to industrially and environmentally relevant gases such as H2, CH4, and CO2.6−8 The most impressive results were achieved for three-dimensional (3D) COFs based on tetraboronic acids C[p-C6H4B(OH)2]4 © 2017 American Chemical Society

Received: June 23, 2017 Accepted: August 23, 2017 Published: August 23, 2017 31129

DOI: 10.1021/acsami.7b09061 ACS Appl. Mater. Interfaces 2017, 9, 31129−31141

Research Article

ACS Applied Materials & Interfaces Scheme 1. Synthesis of Boronated Triazine 2

Figure 1. Molecular structure of (a) 2 and packing diagrams showing the hydrogen bond interaction patter within (b) (203) plane. Hydrogen bonds are marked as red dashed lines.

Scheme 2. Structures of the Polyols Used As Linkers for the Preparation of Triazine Boron-Based COFs

geometry of the pores with respect to classical boron-based COFs.

improvement of experimental and theoretical methods used for the characterization of these materials. Currently, the chemistry of COFs is no longer limited to boron-based monomers. Among various classes of these materials, systems comprising triazine rings are gaining recently a strong interest due to their promising properties. For instance, unlike the majority of boron COFs, the covalent triazine frameworks (CTFs) are hydrolytically stable, which was exploited for specific applications including surfactant adsorption,10 desalination,11 or even photocatalytic water splitting.12,13 They were also used as a platform in a Pd-based heterogeneous catalyst for cross-coupling reactions14 and other catalytic processes.15 It is already well-documented that CTFs show efficient and highly selective CO2 adsorption which can be used for gas separation.16−22 Considering the continued interest in boron COFs as well as the recent rapid growth of CTF chemistry, we present herein results of our work on novel boron-triazine 2D COFs (BTACOFs) obtained using 2,4,6-tris(4′-dihydroxyborylphenyl)1,3,5-triazine as a basic building block. They can be regarded as hybrid materials due to the presence of boron-based as well as triazine structural motifs. They exhibit high thermal stability and N2 sorption parameters comparable to those found for systems possessing similar topologies of 2D COF layers. However, it seems that the sheet stacking can be organized by specific boron−nitrogen interactions, resulting in a different

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RESULTS AND DISCUSSION Synthesis and Characterization of COF Precursors. The synthesis of boronated triazine started from 4-bromobenzonitrile, which was subjected to trimerization in CHCl3 using triflic acid as a superacidic catalyst to give 2,4,6-tris(4bromophenyl)triazine 123−26 as a white solid in good yield (85%). In a consecutive reaction, an orange suspension of a respective trilithio reagent was generated using nBuLi in THF at −78 °C. Then an excess of B(Oi-Pr)3 was added, and the mixture was allowed to warm to room temperature. The mixture was quenched with aqueous H2SO4, and the final workup afforded 2,4,6-tris(4′-dihydroxyborylphenyl)-1,3,5-triazine 2 (Scheme 1). However, the boronic acid was isolated in a moderate yield (33%), presumably due to low solubility of precursor 1 in THF resulting in its incomplete conversion. Compound 2 was isolated as a white solid well soluble in wet acetone, and slow evaporation of a solution resulted in the formation of single crystals suitable for X-ray diffraction. Crystal structure determination showed that the molecule of 2 is essentially planar with a slight deviation of one phenyl group from the coplanar arrangement (Figure 1a). Molecules form hydrogen-bonded channelized layers parallel to the (203) crystal plane (Figure 1b). The channels are filled with water 31130


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ACS Applied Materials & Interfaces Scheme 3. Preparation of COFs Based on the Boronated Triazine 2

stoichiometric mixture of 2 and a polyol was stirred in a 1:1 mesitylene-1,4-dioxane mixture at 85 °C followed by repeated washing of a crude product with anhydrous THF and final drying under high vacuum (0.002 Torr) at 200 °C (Scheme 3). It is noticeable that using a higher initial concentration of substrates led to gelification of the obtained reaction mixture. The same approach was used to obtain BTA-COF4 via a dehydrative self-condensation of 2. The prepared materials are greyish (BTA-COF1−3) or white (BTA-COF4) powders. Their compositions were confirmed by recording 1H NMR spectra of respective solutions of samples subjected to hydrolytic degradation in DMSO-d6 with added D2O (Figure 2). At this point, we would like to stress that this process is slow and the obtained COF materials are in general quite stable under air. The 1H NMR analyses revealed that the obtained COFs contain significant amounts of mesitylene retained in materials dried at 85 °C under medium vacuum (0.1 Torr) for 24 h. Furthermore, BTA-COF2−3 are contaminated by significant amounts (ca. 1.5−2 equiv) of unreacted or partially reacted triazine triboronic acid 2. On the other hand, the

and acetone connected with triboronic acid molecules via hydrogen bonding interactions. We have decided to use two types of polyols for the condensation with 2: 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7-tetrahydroxy-9,10-dialkylanthracenes (9,10-dimethyl - THDMA and 9,10-diethyl THDEA) (Scheme 2). The synthesis of the latter ones involved the treatment of veratrole with ethanal or propanal, respectively, in the mixture of acetonitrile and concentrated H2SO4. This tandem electrophilic Friedel−Crafts-type substitution and subsequent oxidation of the initial cyclization products gave rise to tetramethoxy intermediates TMDMA and TMDEA, respectively. Subsequently, cleavage of methoxy groups with BBr3 afforded targeted tetrahydroxy linkers (Scheme 2).27−29 Synthesis and Characterization of COFs. The syntheses of materials BTA-COF1−3 were performed by dehydrative polycondensation reactions of 2 with 1 equiv of HHTP or 1.5 equiv of THDMA and THDEA, respectively (Scheme 3). A general protocol similar to those developed for the preparation of other boronate ester COFs was employed.1,2,6−9 Thus, a 31131


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ACS Applied Materials & Interfaces

loss (up to 5%) is observed at lower temperatures (up to ca. 150 °C). It can be associated with the removal of adsorbed gases and some volatile impurities (e.g., traces of water resulting from completion of condensation reactions). A more significant mass loss occurs in the temperature range of 150−300 °C. On the basis of the 1H NMR analyses of hydrolyzed samples, it can be assigned to the removal of remaining solvents (mostly mesitylene). Notably, the mass loss is much lower for BTACOF1 (ca. 10%), whereas it reaches 20−25% for BTA-COF2− 3, which is in agreement with the amounts calculated from 1H NMR analysis. This indicates the higher potential of BTACOF2−3 for penetration with mesitylene molecules due to the higher pore diameter of these 2D COFs. Further heating up to 450−500 °C does not result in any significant mass changes. Then a gradual decomposition starts as the total mass loss at 600 °C reaches 50% for BTA-COF3. To summarize, all obtained boronate ester COFs exhibit comparably high thermal resistance consistent with the exclusive presence of strong covalent bonds. This is also characteristic for many boron-based porous materials as well as for those featuring triazine rings.31−33 Unlike BTA-COF1−3, the boroxine BTA-COF4 shows a relatively flat TGA curve up to 400 °C (the mass loss reaches 11% at that temperature). This indicates that BTACOF4 does not incorporate substantial amounts of solvent molecules, which is naturally due to a smaller pore size. On the other hand, it seems to be slightly less stable in comparison with BTA-COF1−3 as it gradually starts to decompose at ca. 400 °C and 32% of the total mass is lost in the temperature range of 400−600 °C. The FT-IR spectra of the obtained COFs were recorded using the ATR technique. They feature strong bands of B−O stretching vibrations in the range of 1324−1344 cm−1. There are also intense bands in the range of 1505−1512 cm−1, which can be assigned to CN stretching vibrations in the triazine ring. In a recent study of IR spectral features of boron COFs,34 it was pointed out that a strong and sharp band in the range of ca. 1220−1240 cm−1 of C−O stretching vibrations is highly diagnostic of boronate ester formation. In the case of our materials, the bands which can be assigned to these vibrations were indeed observed but they were located slightly above the given region for BTA-COF1 (1242 cm−1), whereas a negative and stronger deviation was found for COFs based on anthracene tetraols (1208−1209 cm−1). Additional evidence for the boronate ester formation is the presence of a medium strong band at 645 cm−1. It has been noted previously35 that the vibrational mode between 633 and 658 cm−1 (involving out-of-plane displacements of boron atoms that are syn to outof-plane displacements of aryl hydrogen atoms) is diagnostic for boronate esters. On the other hand, the appearance of an analogous band at 679 cm−1 for BTA-COF1 is in agreement with the observation that the region from 677 to 714 cm−1 is diagnostic for boroxine rings. These out-of-plane vibrations are especially diagnostic in 2D COFs and COF-like assemblies. Nitrogen Sorption Properties of BTA-COF1−4. The porosity of obtained materials was investigated using N2 gas adsorption at 77 K. Prior to the measurements, samples were activated by heating at 200 °C under high vacuum (0.002 Torr) for 12 h to remove guest molecules. All recorded isotherms show a sharp increase of N2 uptake at low relative pressures (below 0.02 P/P0), which is a common feature of microporous materials (Figure 4), including classical boron COFs. In general BTA-COF1 and BTA-COF4 exhibit similar type-I sorption isotherms with relatively slow and almost constant increase of

Figure 2. Representative 1H NMR spectra of BTA-COF2 samples initially dried at 85, 250, and 300 °C and subjected to hydrolytic decomposition in wet DMSO-d6. The 1H NMR spectra of remaining COF materials are provided in the Supporting Information.

hydrolytic decomposition of BTA-COF1 leads to the recovery of starting materials in almost stoichiometric proportions. The further drying of all materials at 250 °C removed most of mesitylene, whereas its complete removal was observed at 300 °C (0.1 Torr). The performed 1H NMR analyses on samples dried at 300 °C prior to hydrolysis showed that starting materials are in almost stoichiometric proportions with no impurities, indicating that the boronic acid 2 can be efficiently removed from the mixture. This is due to observed decomposition of 2 to triphenyltriazine above 200 °C, which further sublimes from the mixture under these conditions. Finally, we have found that the activation of obtained COFs at 200 °C under high vacuum (0.002 Torr) for 12 h is sufficient to remove all volatiles prior to sorption measurements. This important observation should be taken into account when preparing other boronic COFs since residual molecules may significantly influence sorption properties. It is worth noting that BTA-COFs are synthesized using a general procedure applied for boron-based COFs, solvothermal conditions with heating at 85 °C, whereas the synthesis of pure CTF materials proceeds under harsh conditions (molten ZnCl2 at 400 °C). Furthermore, TGA analysis revealed that a significant (ca. 5 wt %) content of ZnCl2 resides in the material after purification.30 Thus, in our opinion, the approach based on a use of self-complementary building blocks can open new possibilities for various hybrid COF materials. The thermal stability of BTA-COF1−4 materials (dried only at 85 °C prior to analysis) was investigated under N 2 atmosphere by the TGA technique (Figure 3). A minor mass

Figure 3. TGA curves for BTA-COF1−4 recorded with the heating rate of 10 K/min. 31132


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Figure 4. Nitrogen sorption isotherms (T = 77 K) for BTA-COF1−4.

Table 1. Summary of Sorption Porosity Measurements, Pore Volumes, And Surface Areas Derived from Promolecular Density and Connolly Surface Approximations for Idealized Models of BTA-COF1-4 Structures sorption CrystalExplorera

Connolly surfacea a

SBET (m2 g−1) total pore volume (cm3 g−1) (P/P0 = 0.9) pore volume per unit cell (Å3) (% of the unit cell) surface area per gram/m2 g−1 pore volume per gram/cm3 g−1 pore volume per unit cell/Å3 (% of the unit cell) pore volume per gram/cm3 g−1

BTA-COF1

BTA-COF2

BTA-COF3

BTA-COF4

1 267 0.55 675 (48%) 1770 0.62 585 (42%) 0.54

1 013 0.67 4013 (69%) 2091 1.62 3782 (65%) 1.52

1 054 0.59 3905 (67%) 2042 1.41 3590 (62%) 1.30

611 0.37 171 (28%) 1605 0.27 131 (21%) 0.20

Values referred to DFT-optimized geometries of most stable models.

Figure 5. Experimental (red solid line), Pawley refinement (green solid line), and Crystal09-derived simulated (blue solid line) PXRD patterns for the eclipsed structures of (a) BTA-COF1, (b) BTA-COF2, (c) BTA-COF3, and (d) BTA-COF4 together with corresponding SEM images.

sorption in the pressure range of 0.2−0.8 P/P0. The NLDFT pore size distribution (PSD) plot (Figure S9) for BTA-COF1 demonstrates two maxima at 11.7 and 16.7 Å, which is in

agreement with PXRD data (vide infra). Interestingly, the NLDFT PSD plot for BTA-COF4 shows only one major maximum below 10 Å, which also agrees well with its PXRD 31133


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Table 2. Comparison of BTA-COFs’ Parameters Derived from Experiment (Pawley Refinement) and Crystal09 Optimizations exptl

unit cell pmts (Å)

Crystal09

V (Å3) symmetry unit cell pmts (Å) V (Å3) d (g cm−3) pore size (Å)

BTA-COF1

BTA-COF2a

BTA-COF3a

BTA-COF4 AA-I

BTA-COF4 AA-II

a = 22.7 c = 3.5 1553 P̅6m2 a = 22.22 c = 3.27 1398 0.781 15.9

a = 43.7 c = 3.5 5822 P6/mmm a = 44.35 c = 3.41 5835 0.427 36.0

a = 43.7 c = 3.5 5822 P6/mmm a = 44.35 c = 3.41 5835 0.473 32.7

a = 15.7 c = 3.4 715 P3m a = 14.71 c = 3.28 614 1.046 8.5

a = 15.7 c = 6.7 1430 P̅3m a = 14.74 c = 6.53 1228 1.045 8.5

a

In BTA-COF2 and BTA-COF3 structures, the methyl/ethyl groups were replaced by chlorine atoms due to the problems with disordered hydrogen atoms resulting from the location of methyl/ethyl carbon atoms on the mirror plane elements of symmetry.

analysis. BTA-COF2 and BTA-COF3 show similar sorption behavior and both exhibit type-IV isotherm (Figure 4) typical for mesoporous 2D COFs.36 The BTA-COF2 demonstrates slightly higher gas uptake than BTA-COF3 in the range of 0.4− 0.8 P/P0, which might be a result of bulkier ethyl substituents present in the pores of BTA-COF3. In addition, desorption measurements revealed that the isotherms are almost reversible for BTA-COF1, whereas only a slight hysteresis was observed for remaining materials. It was pointed out previously that this is characteristic for materials containing hexagonally aligned one-dimensional (1D) mesopores with widths 300 °C. 1H NMR (300 MHz, acetone): δ 8.73 (d, J = 8.5 Hz, 1H), 8.10 (d, J = 8.5 Hz, 1H). 13C NMR (75 MHz, acetone): δ 172.4, 139.6, 138.0, 135.1, 128.4. Anal. Calcd for C21H18B3N3O6: C, 57.22; H, 4.12; N, 9.53. Found: C, 57.13; H, 4.30; N, 9.45. Synthesis of COFs. BTA-COF1. Compound 2 (0.44 g, 1 mmol) and HHTP (0.32 g, 1 mmol) were placed into a 100 mL Schlenk flask. Mesitylene (25 mL) and 1,4-dioxane (25 mL) were added, and the mixture was degassed under reduced pressure. Then the mixture was heated at 85 °C with stirring for 72 h. The obtained suspension was left to stand, and the supernatant solvent was carefully decanted with a syringe. THF (50 mL) was added, and the mixture was stirred overnight. The washing with THF was repeated twice in the same manner. The obtained slurry was dried in vacuo at 85 °C for 24 h to afford the product as a gray powder. Final removal of remaining guest molecules was accomplished by heating in vacuo at 200 °C for 12 h. Yield = 0.56 g (86%). BTA-COF2. It was obtained as a gray powder using the method described for BTA-COF1 from 2 (0.44 g, 1 mmol) and THDMA (0.41 g, 1.5 mmol). Yield = (0.44 g, 60%). BTA-COF3. It was obtained as a gray powder using the method described for BTA-COF1 from 2 (0.44 g, 1 mmol) and THDEA (0.45 g, 1.5 mmol). Yield = (0.60 g, 77%). BTA-COF4. It was obtained as a gray powder using the method described for BTA-COF1 from 2 (0.86 g, 1.94 mmol). However, the product was finally dried at lower temperature (200 °C) for 24 h. Yield = (0.60 g, 92%). Note: The reaction yields were calculated from samples dried at 200 °C. Single-Crystal X-ray Diffraction Analysis of 2. The single crystal of 2 was measured at 100 K on SuperNova diffractometer

equipped with Atlas detector (Cu Kα radiation, λ = 1.54184 Å). Data reduction and analysis were carried out with the CrysAlisPro program.56 The structure was solved by direct methods using SHELXS-9757 and refined using SHELXL-2014.58 All non-hydrogen atoms were refined anisotropically. The structure is of moderate quality, which is due to the fact that sample crystallizes in a form of very tiny plates. The high values of R and wR factors result also from the presence of unrefinement residual electron density, which is located in the central part of channels. It can be attributed to the highly disordered solvent molecule (water and acetone). Crystallographic Information File (CIF) has been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. 1550182 (see SI CIF files 002.cif and 003.cif). 2: 2(C21H18B3N3O6)·4C3H6O·2(H2O), Mr (1 molecule of 2) = 441.06 au; T = 100 K; triclinic, P̅1, a = 15.255 (4) Å, b = 15.812 (7) Å, c = 16.019 (11)Å, α = 61.29 (6)°, β = 71.61 (4)°, γ = 83.00 (3)°, V = 3214 (3) Å3; dcalc = 1.184 g cm−3; μ = 0.725 mm−1; number of collected/independent reflection (Rint = 15.1%) = 13844/6968, R[F]/ wR[F] [I ≥ 3σ(I)] = 28.1%/65.0%, Δϱres(min/max) = −0.89/+1.99 e Å−3. PXRD Measurements. Powder X-ray diffraction (PXRD) analyses of BTA-COFs 1−4 were carried out on a BrukerAXS WAXS D8 powder diffractometer equipped with Cu radiation source (Cu Kα, λ = 1.54184 Å), a no background sample holder and a VÅNTEC detector. Data were collected over a 2θ range of 2.1°−35° in Bragg−Brentano geometry with a generator setting of 40 kV and 40 mA, step size of 0.02°, and exposure time per step of 3 s. TGA. Thermogravimetric analysis were performed on a TGA/ DSC1 (Mettler-Toledo) system under continuous flow of argon at the ramp rate of 10 K min−1 from 30 to 600 °C. The samples of 2−10 mg were prepared in covered ceramic crucibles. An empty crucible was used as a reference. α-Al2O3 was used for instrument calibration. Samples were measured after preliminary drying at 85 °C under 0.1 Torr for 24 h. Sorption Measurements. Micromeritics ASAP 2020 Surface Area and Porosity Analyzer was used to measure the nitrogen adsorption isotherms. Oven-dried sample tubes were evacuated and tared. The samples were transferred to the sample tubes, which were then capped by TranSeals. The samples were heated to 200 °C under a vacuum of 0.002 Torr for 12 h, at which point the outgas rate was less than 0.002 Torr/min. The evacuated sample tubes were weighed again, and the samples’ masses were determined by subtracting the mass of the previously tared tubes. N2 isotherms were measured using liquid nitrogen baths (77 K). Ultra high purity grade (99.999% purity) N2 and He, oil-free valves, and gas regulators were used for the free space correction and measurement. Relative pressure (P/P0) range for BET analysis was selected based on Rouquerol’s criteria.38 SEM Studies. In order to determine COFs morphology and size, scanning electron microscopy was applied. The samples were observed using SEM/STEM Hitachi s 5500 with maximal resolution of 0.4 nm at acceleration voltage of 30 keV and below 2 nm at 1 keV. The observation was performed using SE (secondary electron) signal. The microscope was equipped with Cold Field Emission gun. This type of electron source in the microscope ensures high resolution at relatively low beam current, which is important in the case of observation of sensitive materials like COFs. To minimize the effect of surface charging as well as to confine the structure damage by electrons, low beam current and low acceleration voltage (3 keV) were applied. Such observation conditions ensured enough brightness and resolution but were safe for the COFs samples. Additionally, low accelerating voltage allows one to observe surface morphology in detail, since the electrons penetrate lower thickness of the sample. Theoretical Calculations. All computations within the Crystal09 program package22 were performed at the DFT(B3LYP) level of theory. TZVP basis set proved to be sufficient for the purpose of the conducted calculations. Grimme dispersion correction59,60 was applied. The evaluation of Coulomb and exchange series was controlled by five thresholds, set to values of 10−7, 10−7, 10−7, 10−7, and 10−25. The condition for the SCF convergence was set to 10−7 on the energy difference between two subsequent cycles. Shrinking factor was equal to 4, which refers to 30−36 k-points (depending on space group 31138


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ACS Applied Materials & Interfaces ORCID

symmetry) in the irreducible Brillouin zone in the case of the studied systems and assures the full convergence of the total energy. First molecular geometries were obtained from data provided for related COF structures by replacing the boroxine nodes with triazine rings and modifying the structural symmetry. Then, all the structures including atom positions and unit cell parameters were fully optimized with Crystal09, and they served for the subsequent layer interaction energy calculations. For BTA-COF2 and BTA-COF3 structures, the methyl/ethyl groups were replaced by chlorine atoms due to the problems with disordered hydrogen atoms resulting from the location of methyl/ethyl carbon atoms on the mirror plane. Such replacement is justified by the fact that the CH3 group has a similar size to the Cl atom bound to the carbon atom (19 Å3 and 21 Å3, respectively). Consequently, the change of the crystal packing manner should be rather small. Crystal09 optimizations yielded more compact molecular packing which is especially reflected in lower interlayer stacking distances (2.9−3.2 Å vs 3.4 Å from PXRD). In the case of COF-1 AA eclipsed structure, the full optimization led to significant bending of the polymeric layers (global minimum). The flat geometry was found at local minimum, and this geometry was taken for further consideration. All obtained coordinates are placed in the Supporting Information. In the next step, the same set of coordinates were subjected to crystal interlayer energy computations. The calculation parameters were set identical as in the optimization procedure. The single layer was extracted from the crystal structures and p3m layered group of symmetry was set (SLAB option implemented in Crystal09 was used). The calculations include Grimme dispersion corrections and correction for the basis set superposition error. The latter one was calculated by using two upper and two lower layers as ghost functions. To allow for a direct comparison, the obtained interaction energy values are shown in two ways: they are scaled to the unit cell and are also related to the unit area of a given molecular slab. Electrostatic potentials mapped on the electron density surface (ρ = 0.0027 e Å−3) was calculated in Gaussian09 [B3LYP/6-31g(d,p) level of theory] on the fragment of the molecule including 174 atoms (13 aromatic and 6 triazine/boroxine rings) cut on the Car-B or Car-Ctriaz bonds and terminated with hydrogen atoms. Mulliken population analysis was derived from Crystal09 calculations (keyword PPAN). Following the procedure described on the Crystal Tutorial Project webpage,61 the work function was obtained as the difference of the energy of an electron at a large distance from the surface, minus the Fermi energy. As the potential at the large distance from the surface is almost zero, the work function was taken as negative Fermi energy. In order to elucidate Fermi energy, the keyword SMEAR (width = 0.01 hartree) was used. To accelerate, the convergence-modified Broyden scheme was used (keyword BROYDEN). The input file consisted of 5-layered slab representing (001) COF surface. To improve the description of the electrostatic potential, ghost functions were added in the vacuum region close to the surface (keyword GHOSTS).

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Krzysztof Woźniak: 0000-0002-0277-294X Krzysztof Durka: 0000-0002-6113-4841 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by National Science Centre (Poland) within the framework of the project DEC-UMO-2016/21/B/ ST5/00118. PXRD X-ray measurements were undertaken in the Crystallographic Unit of the Physical Chemistry Laboratory at the Chemistry Department of the University of Warsaw. Authors thank Prof. J. Lewiński for providing access to a physisorption analyzer, Prof. P. Parzuchowski for his assistance in FTIR (ATR) spectroscopy measurements, Dr. D. Pociecha for providing access to the PXRD diffractometer, and Dr. T. Płociński from the Faculty of Materials Science and Engineering WUT for providing an access to SEM. Computational facilities were provided by the Wrocław Centre for Networking and Supercomputing. We gratefully acknowledge the Aldrich Chemical Co., Milwaukee, WI, for a long-term collaboration.

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(1) Feng, X.; Ding, X.; Jiang, D. Covalent Organic Frameworks. Chem. Soc. Rev. 2012, 41, 6010−6022. (2) Ding, S.-Y.; Wang, W. Covalent Organic Frameworks (COFs): from Design to Applications. Chem. Soc. Rev. 2013, 42, 548−568. (3) Waller, P. J.; Gándara, F.; Yaghi, O. M. Chemistry of Covalent Organic Frameworks. Acc. Chem. Res. 2015, 48, 3053−3063. (4) Xiang, Z.; Cao, D.; Dai, L. Well-defined Two-dimensional Covalent Organic Polymers: Rational Design, Controlled Syntheses, and Potential Applications. Polym. Chem. 2015, 6, 1896−1911. (5) Huang, N.; Wang, P.; Jiang, D. Covalent Organic Frameworks: a Materials Platform for Structural and Functional Designs. Nat. Rev. Mater. 2016, 1, Article no. 16068, 10.1038/natrevmats.2016.68. (6) Côté, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Porous, Crystalline, Covalent Organic Frameworks. Science 2005, 310, 1166−1170. (7) Furukawa, H.; Yaghi, O. M. Storage of Hydrogen, Methane, and Carbon Dioxide in Highly Porous Covalent Organic Frameworks for Clean Energy Applications. J. Am. Chem. Soc. 2009, 131, 8875−8883. (8) Côté, A. P.; El-Kaderi, H. M.; Furukawa, H.; Hunt, J. R.; Yaghi, O. M. Reticular Synthesis of Microporous and Mesoporous 2D Covalent Organic Frameworks. J. Am. Chem. Soc. 2007, 129, 12914− 12915. (9) El-Kaderi, H. M.; Hunt, J. R.; Mendoza-Cortés, J. L.; Côté, A. P.; Taylor, R. E.; O’Keeffe, M.; Yaghi, O. M. Designed Synthesis of 3D Covalent Organic Frameworks. Science 2007, 316, 268−272. (10) Bhunia, A.; Dey, S.; Bous, M.; Zhang, C.; von Rybinski, W.; Janiak, C. High Adsorptive Properties of Covalent Triazine-based Frameworks (CTFs) for Surfactants from Aqueous Solution. Chem. Commun. 2015, 51, 484−486. (11) Lin, L.-C.; Choi, J.; Grossman, J. C. Two-dimensional Covalent Triazine Framework as an Ultrathin-film Nanoporous Membrane for Desalination. Chem. Commun. 2015, 51, 14921−14924. (12) Jiang, X.; Wang, P.; Zhao, J. 2D Covalent Triazine Framework: a New Class of Organic Photocatalyst for Water Splitting. J. Mater. Chem. A 2015, 3, 7750−7758. (13) Bi, J.; Fang, W.; Li, L.; Wang, J.; Liang, S.; He, Y.; Liu, M.; Wu, L. Covalent Triazine-Based Frameworks as Visible Light Photocatalysts for the Splitting of Water. Macromol. Rapid Commun. 2015, 36, 1799−1805. (14) Lin, S.; Hou, Y.; Deng, X.; Wang, H.; Sun, S.; Zhang, X. A New Triazine Functionalized Luminescent Covalent Organic Framework for Nitroaromatic Sensing and CO2 Storage. RSC Adv. 2015, 5, 41017−41024.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b09061. Details of TGA, PXRD and N2 sorption analyses, additional SEM images, copies of FTIR and NMR spectra of starting materials and hydrolyzed COFs samples, NLDFT pore size distribution, details of theoretical calculations (PDF) CIF structure (CIF) CIF structures (CIF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. 31139


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ACS Applied Materials & Interfaces (15) Niu, F.; Tao, L.; Deng, Y.; Gao, H.; Liu, J.; Song, W. A Covalent Triazine Framework as an Efficient Catalyst for Photodegradation of Methylene Blue under Visible Light Illumination. New J. Chem. 2014, 38, 5695−5699. (16) Sekizkardes, A. K.; Altarawneh, S.; Kahveci, Z.; Islamoğlu, T.; ElKaderi, H. M. Highly Selective CO2 Capture by Triazine-Based Benzimidazole-Linked Polymers. Macromolecules 2014, 47, 8328− 8334. (17) Gu, C.; Liu, D.; Huang, W.; Liu, J.; Yang, R. Synthesis of Covalent Triazine-based Frameworks with High CO2 Adsorption and Selectivity. Polym. Chem. 2015, 6, 7410−7417. (18) Gomes, R.; Bhanja, P.; Bhaumik, A. A Triazine-based Covalent Organic Polymer for Efficient CO2 Adsorption. Chem. Commun. 2015, 51, 10050−10053. (19) Gao, Q.; Bai, L.; Zhang, X.; Wang, P.; Li, P.; Zeng, Y.; Zou, R.; Zhao, Y. Synthesis of Microporous Nitrogen-Rich Covalent-Organic Framework and Its Application in CO2 Capture. Chin. J. Chem. 2015, 33, 90−94. (20) Saleh, M.; Baek, S. B.; Lee, H. M.; Kim, K. S. Triazine-Based Microporous Polymers for Selective Adsorption of CO2. J. Phys. Chem. C 2015, 119, 5395−5402. (21) Puthiaraj, P.; Cho, S.-M.; Lee, Y.-R.; Ahn, W.-S. Microporous Covalent Triazine Polymers: Efficient Friedel−Crafts Synthesis and Adsorption/Storage of CO2 and CH4. J. Mater. Chem. A 2015, 3, 6792−6797. (22) Dey, S.; Bhunia, A.; Esquivel, D.; Janiak, C. Covalent Triazinebased Frameworks (CTFs) from Triptycene and Fluorene Motifs for CO2 Adsorption. J. Mater. Chem. A 2016, 4, 6259−6263. (23) Pang, J.; Tao, Y.; Freiberg, S.; Yang, X.-P.; D’Iorio, M.; Wang, S. Syntheses, Structures, and Electroluminescence of New Blue Luminescent Star-shaped Compounds Based on 1,3,5-Triazine and 1,3,5-Trisubstituted Benzene. J. Mater. Chem. 2002, 12, 206−212. (24) Tanaka, H.; Shizu, K.; Nakanotani, H.; Adachi, C. Twisted Intramolecular Charge Transfer State for Long-Wavelength Thermally Activated Delayed Fluorescence. Chem. Mater. 2013, 25, 3766−3771. (25) Naik, S.; Kumaravel, M.; Mague, J. T.; Balakrishna, M. S. Novel Trisphosphine Ligand Containing 1,3,5-Triazine Core, [2,4,6C3N3{C6H4PPh2-p}3]: Synthesis and Transition Metal Chemistry. Inorg. Chem. 2014, 53, 1370−1381. (26) Hermer, N.; Stock, N. The New Triazine-based Porous Copper Phosphonate [Cu3(PPT)(H2O)3]·10H2O. Dalton Trans. 2015, 44, 3720−3723. (27) Chung, Y.; Duerr, B. F.; McKelvey, T. A.; Nanjappan, P.; Czarnik, A. W. Structural Effects Controlling the Rate of the RetroDiels-Alder reaction in Anthracene Cycloadducts. J. Org. Chem. 1989, 54, 1018−1032. (28) Shklyaev, Yu. V.; Yeltsov, M. A.; Rozhkova, Yu. S.; Tolstikov, A. G.; Dembitsky, V. M. A New Approach to Synthesis of 3,3-Dialkyl-3,4dihydroisoquinoline derivatives. Heteroat. Chem. 2004, 15, 486−493. (29) Balaban, T. S.; Eichhöfer, A.; Krische, M. J.; Lehn, J.-M. Hierarchic Supramolecular Interactions within Assemblies in Solution and in the Crystal of 2,3,6,7-Tetrasubstituted 5,5′-(Anthracene-9,10diyl)bis[pyrimidin-2-amines]. Helv. Chim. Acta 2006, 89, 333−351. (30) Kuhn, P.; Antonietti, M.; Thomas, A. Porous, Covalent Triazine-based Frameworks Prepared by Ionothermal Synthesis. Angew. Chem., Int. Ed. 2008, 47, 3450−3453. (31) Tao, L.-M.; Niu, F.; Zhang, D.; Wang, T.-M.; Wang, Q.-H. Amorphous Covalent Triazine Frameworks for High Performance Room Temperature Ammonia Gas Sensing. New J. Chem. 2014, 38, 2774−2777. (32) Sakaushi, K.; Antonietti, M. Carbon- and Nitrogen-Based Porous Solids: A Recently Emerging Class of Materials. Bull. Chem. Soc. Jpn. 2015, 88, 386−398. (33) Sakaushi, K.; Antonietti, M. Carbon- and Nitrogen-Based Organic Frameworks. Acc. Chem. Res. 2015, 48, 1591−1600. (34) Smith, M. K.; Northrop, B. H. Vibrational Properties of Boroxine Anhydride and Boronate Ester Materials: Model Systems for the Diagnostic Characterization of Covalent Organic Frameworks. Chem. Mater. 2014, 26, 3781−3795.

(35) Rambo, B. M.; Lavigne, J. J. Defining Self-Assembling Linear Oligo(dioxaborole)s. Chem. Mater. 2007, 19, 3732−3739. (36) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Reporting Physisorption Data for Gas/Solid Systems with Special Reference to the Determination of Surface Area and Porosity. Pure Appl. Chem. 1985, 57, 603−619. (37) Thommes, M. In Nanoporous Materials Science and Engineering; Lu, G. Q., Zhao, X. S., Eds.; Imperial College Press: London, U.K., 2004; Chapter 11. (38) Rouquerol, J.; Llewellyn, P.; Rouquerol, F. Is the BET Equation Applicable to Microporous Adsorbents? Stud. Surf. Sci. Catal. 2007, 160, 49−56. (39) Dogru, M.; Sonnauer, A.; Gavryushin, A.; Knochel, P.; Bein, T. A Covalent Organic Framework with 4 nm open pore. Chem. Commun. 2011, 47, 1707−1709. (40) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B: Condens. Matter Mater. Phys. 1988, 37, 785−789. (41) Peintinger, M. F.; Vilela Oliveira, D.; Bredow, T. Consistent Gaussian basis sets of triple-zeta valence with polarization quality for solid-state calculations. J. Comput. Chem. 2013, 34, 451−459. (42) Dovesi, R.; Orlando, R.; Civalleri, B.; Roetti, R.; Saunders, V. R.; Zicovich-Wilson, C. M. CRYSTAL: A Computational Tool for the Ab Initio Study of the Electronic Properties of Crystals. Z. Kristallogr. Cryst. Mater. 2005, 220, 571−573. (43) Dovesi, R.; Saunders, V. R.; Roetti, R.; Orlando, R.; ZicovichWilson, C. M.; Pascale, F.; Civalleri, B.; Doll, K.; Harrison, N. M.; Bush, I. J.; D’Arco, P.; Llunell, M. CRYSTAL09; University of Torino: Torino, 2009. (44) Spackman, M. A.; Jayatilaka, D. Hirshfeld Surface Analysis. CrystEngComm 2009, 11, 19−32. (45) Spackman, M. A.; Byrom, P. G. A Novel Definition of a Molecule in a Crystal. Chem. Phys. Lett. 1997, 267, 215−220. (46) Spackman, M. A. Molecules in Crystals. Phys. Scr. 2013, 87, 048103. (47) Spackman, M. A.; McKinnon, J. J.; Jayatilaka, D. Electrostatic Potentials Mapped on Hirshfeld Surfaces Provide Direct Insight into Intermolecular Interactions in Crystals. CrystEngComm 2008, 10, 377−388. (48) Spitler, E. L.; Koo, B. T.; Novotney, J. L.; Colson, J. W.; UribeRomo, F. J.; Gutierrez, G. D.; Clancy, P.; Dichtel, W. R. A 2D Covalent Organic Framework with 4.7-nm Pores and Insight Into its Interlayer Stacking. J. Am. Chem. Soc. 2011, 133, 19416−19421. (49) Liu, X.-H.; Guan, C.-Z.; Wang, D.; Wan, L.-J. Graphene-Like Single-Layered Covalent Organic Frameworks: Synthesis Strategies and Application Prospects. Adv. Mater. 2014, 26, 6912−6920. (50) Wang, P.; Jiang, X.; Zhao, J. Bottom-up Design of 2D Organic Photocatalysts for Visible-Light Driven Hydrogen Evolution. J. Phys.: Condens. Matter 2016, 28, 034004. (51) Stegbauer, L.; Schwinghammer, K.; Lotsch, B. V. A HydrazoneBased Covalent Organic Framework for Photocatalytic Hydrogen Production. Chem. Sci. 2014, 5, 2789−2793. (52) Uijttewaal, M. A.; de Wijs, G. A.; de Groot, R. A. Ab; Initio. and Work Function and Surface Energy Anisotropy of LaB6. J. Phys. Chem. B 2006, 110, 18459−18465. (53) Uijttewaal, M. A.; de Wijs, G. A.; de Groot, R. A. Generalised Coexistence of a Low Work Function and a Stable Surface: CaAl4 and BaAuIn3. Surf. Sci. 2006, 600, 2495−2500. (54) Uijttewaal, M. A.; de Wijs, G. A.; de Groot, R. A.; Coehoorn, R.; van Elsbergen, V. L.; Weijtens, C. H. Interrelation of Work Function and Surface Stability: The Case of BaAl4. Chem. Mater. 2005, 17, 3879−3882. (55) Attema, J. J.; Uijttewaal, M. A.; de Wijs, G. A.; de Groot, R. A. Work Function Anisotropy and Surface Stability of Half-Metallic CrO2. Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 165109. (56) CrysAlis Pro; Oxford Diffraction Ltd.: Oxford, U.K., 2010. (57) Sheldrick, G. M. A Short History of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. 31140


Research Article

ACS Applied Materials & Interfaces (58) Sheldrick, G. M. Crystal Structure Refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8. (59) Grimme, S. Accurate Description of van der Waals Complexes by Density Functional Theory Including Empirical Corrections. J. Comput. Chem. 2004, 25, 1463−1473. (60) Grimme, S. Semiempirical GGA-type Density Functional Constructed with a Long-Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787−1799. (61) Doll, K. Metals, metallic surfaces and adsorption thereon, Crystal Tutorial Project. http://www.theochem.unito.it/crystal_tuto/ mssc2013_cd/tutorials/metals/index.html (accessed March 24, 2015).

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