Chemically Robust, Cu-based Porous Coordination Polymer

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Functional Nanostructured Materials (including low-D carbon)

A Chemically Robust, Cu-based Porous Coordination Polymer Nanosheet for Efficient Hydrogen Evolution: Experimental and Theoretical Studies Bihang Zhou, Jia-Jia Zheng, Jingui Duan, Chun-Chao Hou, Yang Wang, Wanqin Jin, and Qiang Xu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b04471 • Publication Date (Web): 15 May 2019 Downloaded from http://pubs.acs.org on May 15, 2019

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ACS Applied Materials & Interfaces

A

Chemically

Robust,

Cu-based

Porous

Coordination Polymer Nanosheet for Efficient Hydrogen Evolution: Experimental and Theoretical Studies Bihang Zhou,† Jia-jia Zheng, ‡,∥Jingui Duan,†,* Chunchao Hou,§ Yang Wang,† Wanqin Jin,†,* and Qiang Xu§ †State

Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical

Engineering, Nanjing Tech University, Nanjing 211800, China ‡Institute

for Integrated Cell-Material Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto

606-8501, Japan §National

Institute of Advanced Industrial Science and Technology-Kyoto University Chemical

Energy Materials Open Innovation Laboratory, Yoshida, Sakyo-Ku, Kyoto 606-8501, Japan ∥

Fukui Institute for Fundamental Chemistry, Kyoto University, Nishi-hiraki cho, Takano, Sakyo-

ku, Kyoto 606-8103, Japan

ACS Paragon Plus Environment

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Keywords: Porous coordination polymer design, Ultrathin layer, Chemical stability, Cu2+ active site, Electrocatalytic hydrogen evolution, Mechanism study

Abstract: Due to extremely high number of accessible active sites and short diffusion path, porous coordination polymer (PCP) nanosheets have demonstrated a variety of promising applications, especially for energy conversion and mass transfer. However, the development of chemically stable PCP nanosheets with dense active sites and large lateral size is a great challenge in terms of feasible considerations. Herein, we firstly designed and prepared a kind of chemically stable PCP nanosheets via an integral strategy of bottom-up and top-down. Featuring densely exposed and periodic Cu2+ active sites (2.1×106 per μm2), as well as ultrathin nature (5 nm) and significant pore (18 Å), this nanosheet demonstrated remarkable performance of electrocatalytic hydrogen evolution. Further, one plausible process and the effect of Cu2+ active sites were proposed and validated by density functional theory (DFT) calculations.

Introduction Ultrathin two-dimensional (2D) materials, such as graphene/graphene oxide1, transition metal dichalcogenides2, metals/alloys3, phosphorene4 and boron nitride5, have attracted significant attention for their potential applications, derived from their unique structure and special 2D array. Thus far, worldwide efforts have been devoted to developing and creating new 2D materials6. Featuring the most versatile in structural design and accessibility of both inorganic and organic blocks at molecular level7, PCP nanosheets were believed to be the most promising media8-9. Beside successive advantages and functionalities from PCPs, the atomic or a few layered PCP nanosheets provide higher percentage of exposed surface atoms or active sites10-11. Further, along with the character of sharply shorten channel (accelerate molecule movement) and


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significant edge effect (enhanced chemical activity)12, PCP nanosheets have demonstrated more fascinating applications in gas separation, catalysis and energy storage/conversion8-9, 13-15. Recently, a few PCP nanosheets were prepared on flat metal surfaces16, created at air/liquid or liquid/liquid interfaces17, synthesized directly from corresponding precursors18 and exfoliated from their mother crystals8. However, none of them are stable in chemical solutions19-20. As well, the pore characters and active sites of these nanosheets were limited by few of known mother crystals and/or cycloaddition coordination reactions. Therefore, how to construct ultrathin PCP nanosheets with significantly chemical robustness, abundantly exposed active sites and large pores is an enormous challenge21-22. Inspired from reticular chemistry and graphene production, the integration of bottom-up assembly and top-down exfoliation was considered to be the rational strategy for expanding the diversity of newly functional and robust PCP nanosheets23. First, bottom-up crystal engineering of stable PCPs with 2D structure is highly possible that arise from pre-designed organic/inorganic blocks24. For example, inspired by the honeycomb net and the rule of the Shubnikov plane net, robust fes net with 4- and 2-fold rotation can be assessed from a 3connected linker and a 3-connected node, if stronger coordination bonds and lower energy state will be involved during the framework growth25-26. Secondly, the PCP nanosheets can be facilely exfoliated by a solvent/ultrasonic-assisted top-down technique, as the solvent with a surface energy matched to that of the PCP nanosheets will not only overcome the weak interaction between the layers but also avoid re-assembly of the produced nanosheets27. In this work, we firstly designed and prepared a kind of chemically stable PCP nanosheets through an integral strategy of bottom-up and top-down, where 1) designing and engineering a layered structure (named as NTU-33) by the coordination assembly of a plane-connected Cu2+


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node and a T-shaped linker, and then 2) exfoliating ultrathin PCP nanosheets by optimal solvent/ultrasonic conditions (Scheme 1). Attractively, featuring densely exposed Cu2+ active sites (2.06×106 per μm2), significant pores (18 Å) and ultrathin nature (~5.0 nm), NTU-33 nanosheets demonstrated highly efficient electrocatalytic hydrogen evolution (HER) in an acid solution. Further, a plausible reaction mechanism, as well as the positive effect of Cu sites, were proposed and validated by DFT calculations.

Scheme 1. Illustration of design and preparation of chemically robust PCP nanosheet with abundant Cu active sites and significant pore via integral strategy of bottom-up assembly and top-down exfoliation. Results and discussion Inspired by the cycles of fes net and also our recent work28, a C2v symmetric and T-shaped ligand (5-(pyridin-4-yl)isophthalic acid: H2NL) was synthesized, since the nonuniform distances of the coordinating sites could benefit the formation of a semiregular framework with increased pore size, as well as stronger N-M coordination bonds (Figure S1). In addition, metalladithiolene chemistry revealed that d1 metal ions may form planar 3 or 4 connected coordination configuration29. Therefore, NTU-33 crystal was solvo-thermally synthesized from H2NL ligand along with CuBr2 in a water-led solvent system.


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Single crystal X-ray analysis revealed that NTU-33 crystallizes in the monoclinic space group with parameters of a = 20.091(5) Å, b = 19.410(5) Å, c = 13.624(4) Å and β = 90.1(8)° (Table S1). The asymmetric unit of NTU-33, with formula of [Cu2(NL)2·4H2O]·xSolvent, includes two crystallographically independent moieties, which are made up of two NL2- ligands, two isolated Cu2+ ions, and four coordinated water molecules (Figure S2). The coordination geometry of each Cu2+ ion in NTU-33 is a strongly distorted hexahedron that approaches to a square pyramid, such that the equatorial positions are occupied by two carboxylate O (η1 mode) from two ligands, a terminal water molecule, and a coordinated N atom from the pyridine moiety; the vertical position is occupied by another water molecule (Figure S3). As expected, each ligand is connected by three nodes (Figure S4). Therefore, the self-assembly of the NL2- ligand mediated by mononuclear Cu2+ ions leads to a 2D neutral network, possessing a 3,3,3,3-c net with an fes/Shubnikov plane topology. In addition, NTU-33 exhibits a uniform and circularstructural packing, which results in a large semiregular pore (~5×18 Å2) (Figure 1a). After the structural translation, the two crystallographically independent layers 1 and 4 produce layers 3 and 2, respectively (Figure 1b). Thus, the alternative packing of the four layers tailored the perforated pore into a smaller one with size of ~2×8 Å2 (Figure 1c, S5). Because of the π…π interactions and the involved hydrogen bond (Figure S6 and Table S2), the alternate layers grow together to form the bulk crystal of NTU-33 with a layer distance of 3.4 Å (Figure 1d). In addition, NTU-33 can be readily prepared in bulky, confirmed by powder X-ray diffraction(PXRD) patterns (Figure S7). From thermogravimetric (TG) analyses, NTU-33 is thermally stable up to 300oC (Figure S8).


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Figure 1. Structural view of NTU-33: (a) A significant pore (~5×18 Å2) and accessible Cu sites (blue polyhedron) from a monolayer; (b) Translation of the two crystallographically independent layers: from 1 to 3 and 2 to 4; (c) Packing view of four layers with a tailored pore (~2×8 Å2); (d) Side view of packed NTU-33, where the layer distance is 3.4 Å. The crystallographically independent layers was highlighted in blue and yellow, respectively. Structural stability of NTU-33 was investigated under ultrasonic condition within different solvents at first. From the PXRD patterns (Figure 2), we found that all peaks matched well with diffractions of the fresh sample. In addition, the framework stability was further evaluated under harsh conditions, in boiling chemical solutions with varied pH (2, 7, and 12). Despite not observing the diffraction of (0 2 0), (2 1 0) planes in all of them, the characteristic peaks at 15.2° and 25.9°(2θ) are consistent with that of the fresh sample. These results unambiguously revealed


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that NTU-33 could keep its original crystalline phase under a series of harsh conditions. Accordingly, the excellent stability here can be explained by the stronger Cu-N coordination bonds, and also water-induced stable energy state, similar as our previous stable and layered PCPs26.

Figure 2. Stability test: PXRD of sediments that collected from ultrasonic treated NTU-33 in various solvents (1h); PXRD of chemical treated NTU-33 at varied pH under 100°C for 24h. Instead of ball milling, solvent-assisted ultrasonic treatment was selected for PCP nanosheet exfoliation, as the soft force may be helpful for the plane integrity of generated nanosheets (Figure 3a). Before the exfoliation, vapor adsorption isotherms of water, ethanol, acetone, nbutanol, and n-hexane were collected on NTU-33. As shown in Figure S9, there were no uptakes of the vapors of ethanol, n-butanol, and n-hexane. Similarly, there are also no uptakes of the vapors of acetone and water at low pressure range. However, quick uptakes were found in them after the pressure reached to P/P0 = 0.5, indicating the guest inclusion between the layers. In others words, the water and acetone molecules can penetrate into the galleries of layered NTU33, and then reduce original π…π interaction of the face to face packed layers that benefits a lot


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for nanosheet exfoliation. Given the consideration of extra ultrasonic assistant and systemically varied surface tension (72.8 to 18.4 mN/m), NTU-33 crystals were soaked in these solvents and sonic-treated for 1 h. The suspensions were obtained after sedimentation of the delaminated suspension for a day. Further scanning electron microscopy (SEM) analysis was performed to confirm the successful exfoliation or not. As shown in Figure S10, very tiny particles were found in n-butanol and n-hexane suspension, whereas flat nanosheets sized 0.5-1 μm were observed in water. Moreover, the significantly large (4-8 μm) and flat nanosheets were found in acetone system. These results are consistent with the observation of vapor adsorption isotherms. Therefore, acetone is the optimal solvent for NTU-33 nanosheet exfoliation, as well as the protective agent for generated nanosheet. Further morphology analysis showed that the lateral dimension of the flat-layered NTU-33 nanosheets, collected from acetone solution, is mainly in the range of 4-8 μm (Figure 3b-g, S11). Thus, the lateral area of the nanosheet was around 25 to 30 μm2, which is far larger than that of all PCP nanosheets prepared by the top-down method30-32, and even larger than that of some porous organic sheets33. Atomic force microscopy (AFM) images were then used to detect the thickness of NTU-33 nanosheets. As shown in Figure 3g-h and S12, 2D objects were displayed clearly. The thickness between the flaky object and the substrate surface was uniformly 5.0 nm for the two separated nanosheets. In addition, the other nanosheets with thickness of 5.4 nm are shown in Figure 3i. Interestingly, the figure gives a step profile of two neighboring overlapping layers of the nanosheets, and the distance between the two adjacent layers is 0.69 nm, agreeing well with the thickness of two layers of NTU-33 (0.34 nm). Consistent with other reported colloidal suspensions of PCP nanosheets and organic nanosheets12, , Tyndall light scattering was also observed for the colloidal suspension of NTU-33 nanosheets in acetone (Figure 3j).


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Figure 3. Preparation process and characterization of NTU-33 nanosheets: (a) a schematic view for nanosheet preparation via acetone-assisted ultrasonic exfoliation; (b-f) SEM images; (g) Side length distribution, calculated from SEM images; (h-i) Thickness analysis; (j) Tyndall effect (~0.1-0.2 mg/mL) in acetone. To validate the structure and crystallinity of NTU-33 nanosheets, infrared (IR) spectra and PXRD were collected. As shown in Figure S13, the absorption peaks, especially the one at 1617 cm-1, of this nanosheet are identical to that of its bulky crystal. To perform the PXRD, 20 mL NTU-33 nanosheets solution (~0.1-0.2 mg/mL) was dropped on top of the Al2O3 disk, forming a re-stacked layer after solvent evaporation. As shown in Figure S14, the weak diffraction of the (0 0 4) plane were observed. Therefore, both of these characterizations showed negligible influence of the exfoliation process on coordinated bonds and local crystallinity of NTU-33.


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Figure 4. HRTEM and SAED analysis of NTU-33 nanosheet: (a-b) HRTEM images at different resolutions. The arrangement of bright spots is consistent with the pore packing from the single crystal data; (c-d) SAED patterns of NTU-33 nanosheet. Distinct electron diffraction spots were found in d. Despite these observations, detailed structure of NTU-33 nanosheets was investigated by highresolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) (Figure 4 and S15). Because of the high porosity and instability of PCPs under an electron beam, very few studies have reported direct imaging of PCP lattices34. As shown in Figures 4a and S16, the extremely high-resolution data were obtained for three NTU-33 nanosheets. By looking closely at the HRTEM image (Figure 4b and S16), the pore can be clearly identified as bright spots. The arrangement of the spots matches the single crystal data well. Notably, these layers exhibited distinctive electron diffraction spots that correspond to the diffraction pattern of planes of the nanosheet (Figure 4c, d and S17). The simulated SAED


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pattern matched well with the experimental results, reconfirming the crystallinity of exfoliated NTU-33 nanosheets. Therefore, we are sure that NTU-33 nanosheet, a kind of chemically robust and ultrathin nanosheet with local crystallinity and larger lateral size, was finely exfoliated. Given the ultrathin nature, densely exposed active sites, as well as significant pore, electrocatalytic HER activity of NTU-33 nanosheets was evaluated in a typical three-electrode system. The electrocatalytically activated NTU-33 nanosheets (10 h electrolysis of NTU-33 nanosheets) and NTU-33 nanoparticles (obtained from sonic treatment with a size of 0.5 to 3 μm, Figure S18) were also assessed for comparison. The corresponding polarization curves are shown in Figure 5a. The onset potential of NTU-33 nanosheets for HER was about -0.38 V vs. a reversible hydrogen electrode (RHE) with an operating potential of -0.56 V vs. RHE at 10 mA·cm-2, which was lower than that of the NTU-33 nanoparticles. The operating potential of electrocatalytically activated NTU-33 nanosheet shifted to -0.43 V at 10 mA·cm-2 after 10 h electrolysis of NTU-33 nanosheets, similar to the electrocatalytic performance of the 2D Co6O(dhbdc)2 layer30, which indicates a self-transformation process. Thus, the performance of activated NTU-33 nanosheet catalyst is better than those of HKUST-1, NENU-5, NENU-499, Cu(II) complex35-36, CNT-supported molecular catalysts37, and N- or P-doped graphene38, and also comparable to other reported Ni/Fe based PCP nanosheet catalysts (NiTHT: -0.33 V39 and Ni-Fe-MOF: 0.255 V40), MoO2/MoS2 nanostructures41-42, and WS2 nanosheets43. In addition, the Tafel slope was another important parameter for evaluating the kinetic activity of the catalysts, which is depicted in Figure 5b. The value of the Tafel slope for electrocatalytically activated NTU-33 nanosheets was 129 mV·dec-1, which is far below those of the NTU-33 nanosheet (158 mV·dec-1) and NTU-33 nanoparticles (153 mV·dec-1). Furthermore, the HER kinetics at the electrode/electrolyte interface was further investigated by electrochemical impedance


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spectroscopy (Figure 5c). NTU-33 nanosheets and activated NTU-33 nanosheets display a smaller series resistance (Rs) and charge transfer resistance (Rct) than NTU-33 particles, indicating a faster reaction rate and easier electron transfer and charge transportation. More importantly, a long-term electrochemical process (10 h) showed that the NTU-33 nanosheet is a durable and efficient catalyst in such an acidic system (Figure 5d).

Figure 5. Electrochemical performance of NTU-33 catalysts: (a) Polarization curves of various catalysts in 0.5 M H2SO4; (b) Corresponding Tafel plots of the polarization curves; (c) Electrochemical impedance spectroscopy of series of catalysts; (d) Time dependence of current density under a static overpotential for 10 h. The reaction mechanism was further investigated by DFT calculations using a cluster model (M1), where both of several steps of one-electron reduction and protonation were considered. As shown in Figure 6, the calculations here indicate that M1 firstly undergoes one-electron reduction followed by protonation to afford [M1-H], in which the Cu(II) atom is converted to


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Cu(I) having a tetrahedral-like coordination structure and the proton (H+) is bound to the O atom of one carboxylate ligand (Figure S19). In the next step, the protonation occurs first to afford [M1-2H]+, in which the other carboxylate is protonated. The one-electron reduction of [M1-H] to [M1-H]– is more endothermic than the protonation by 27.7 kcal mol-1 (Figure S19). This is reasonable because the unstable Cu0 species would be formed by the second one-electron reduction of [M1-H] but the Cu(I) is maintained in [M1-2H]+. The next one-electron reduction of [M1-2H]+ affords [M1-2H], in which one proton is bound with the O atom of one carboxylate ligand like that in [M1-1H] and the other H migrates from the O atom of the other carboxylate to the Cu(I) in [M1-2H]+ via the hydrogen bonding network to form a Cu(II)-H species. Then, we investigated the H2 formation through coupling between the protons and hydride-like H atom and found that this reaction occurred via a reasonable cyclic transition state [M1-TS1]. However, the Gibbs energy of activation (ΔGº‡) was very large (47.2 kcal mol-1). It is concluded that this H2 formation from [M1-2H] is difficult to occur. In [M1-2H], the Cu has +II oxidation state in a formal sense, which suggests that one-electron reduction can occur to afford a Cu(I) species [M1-2H]-. Actually, this one-electron reduction occurs with moderate exergonicity of 2.0 kcal mol-1, as shown in Figure 6. Because two carboxylate ligands coordinate with one Cu(I) and one of them is protonated in [M1-2H]-, it is likely that the other carboxylate can be protonated by the third proton (H+) to form [M1-3H] (Figure 6). This process, [M1-2H]-  [M1-3H], is calculated to be exothermic. Starting from [M1-3H], H2 is generated through a transition state [M1-TS2] with ΔGº‡ of 17.7 kcal mol-1. This is the rate-determining step of this catalytic reaction and the moderate ΔGº‡ is consistent with the excellent catalytic activity of NTU-33 for HER. The H-H bond formation in [M1-3H] is understood to be the reverse of the heterolytic H-H s-bond activation44.


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Figure 6. The Gibbs energy profile for the hydrogen gas (H2) evolution (pH = 0 and E = 0 V). Detailed structures in the reaction process are shown in Figure S19. Numbers below compound name represent the Gibbs energy (in kcal mol-1). Conclusions In summary, we have developed an integral strategy of bottom-up and top-down for fine design and facile synthesis of chemically robust and ultrathin PCP nanosheet with densely exposed Cu activate sites and larger lateral size. We have shown that the electrocatalytic hydrogen evolution of NTU-33 in an acidic solution significantly outperforms traditional bulky PCPs and its micropowders in terms of activity, by exposing dense Cu2+ active sites and reducing


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diffusion constraints. More importantly, this work promises to open up a platform that is highly amenable to the engineering of robust PCP nanosheet and modeling of functional sites, which means that even better-performing PCP nanosheets across a wider range of energy conversion could be within reach. EXPERIMENTAL SECTION Synthesis of NTU-33 crystal. A mixture of CuBr2 (170 mg, 0.76mmol), 5-(pyridin-4-yl) isophthalic acid (27 mg, 0.11 mmol), HBr (0.54 mL) and H2O/DMF = 4:1 (18 mL) was stirred for ca. 20 min in air, then transferred and sealed in a 25 ml Teflon-lined autoclave, which was heated at 75°C for 24h and then 80°C for two days. After cooling down to room temperature, blue crystals were obtained with good yield (~60%: based on ligand). Water stability tests. For stability test, fresh sample was soaked (~30 mg for each) into three bottles (10 ml). HCl and NaOH were used to turn solution pH. After 24h treatment at 100oC, the wet samples were evaluated by PXRD. Preparation of NTU-33 nanosheets and nanoparticles. After washing by DMF (5 mL×3) and acetone (5 mL×3) for three times each, NTU-33 crystals (~30 mg) were dispersed in acetone (50 mL) and treated in an ultrasonic bath (KQ5200DE) with 40% power for 1 h. After freestanding for 1 day to removal the large particles (NTU-33 nanoparticles), the suspension was transferred to a glass tube (50 mL) with 17 mm of inner diameter for further free-standing for at least 15 days. Finally, NTU-33 nanosheets suspension was obtained from the top 20 mL solution. Electrochemical Measurements. Electrochemical experiments were conducted on a CHI7088E electrochemical station in a standard three electrodes cell in 0.5 M H2SO4 at room temperature. A glass carbon electrode (GCE, 3 mm in diameter), an Ag/AgCl with 3.5 M KCl and a graphite rod were used as the working electrode, reference and counter electrode,


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respectively. 2 mg of the catalyst and 2 mg active carbon (MSP-20X) were dispersed in 1 mL of water/ethanol/Nafion (460/500/40, v/v) by sonication to form a homogeneous ink. Typically, 4 L well-dispersed catalysts were covered on the glassy carbon electrode and then dried in an ambient environment for measurements. Linear sweep voltammetry (LSV) was tested with a scan rate of 10 mV s-1. EIS measurements were carried out from 1000 HZ to 100 mHz with an amplitude of 10 mV. The potential was converted to the reversible hydrogen electrode (RHE) via the Nernst equation. ERHE  EAg/AgCl + 0.059 + EAg/AgCl. Computational Details. A cluster model (M1) was constructed using one Cu atom and three 5-(pyridin-4-yl) isophthalate ligands to mimic the experimental structure of NTU-33, as shown in Figure S19. In NTU-33, the isophtalate ligand coordinates to two Cu atoms. Because the outside N and O atoms of the isophtalate coordinate with the other Cu atom, their positions were fixed in M1 during geometry optimization; this is not unreasonable because their positions do not change very much by the reaction. Considering that the catalytic reaction was performed in acidic water solvent, we added four water molecules to M1 because four water molecules take reasonable positions in M1 forming hydrogen bonding network with carboxylate moieties of the isophtahlate. Then, one proton was added to M1, the geometry optimization of which leaded to the protonated carboxylate and the formation of hydrogen bond between the protonated carboxylate and neighbouring H2O. DFT calculations were performed with the Gaussian 16 program package45. The geometry optimizations followed by frequency calculations were carried out using the dispersioncorrected46 B3LYP-D3 functional47-50, where the LANL2DZ basis set with the effective core potentials (ECPs) 51 were used for Cu and the 6-31G(d) basis sets52-53 were used for other atoms. To evaluate potential energy at better level, a larger (311111/22111/411/11) basis set with ECPs


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by the Stuttgart-Dresden-Bonn group54-55 was employed for Cu and the 6-311+G(2d,p) 56 basis sets were used for the other atoms. Solvation effect (H2O) was evaluated with polarized continuum model (PCM). The translational entropy in solution was corrected by the method developed by Whitesides et al57. To calculate the Gibbs energy change of M1 with different numbers of protons and electrons, we employed the chemical potentials of proton and electron, as follows: (H+) = –11.721 eV and (e–, E) = (e–, SHE) – E, where (H+) was estimated at pH = 0 using the empirical method25, e(SHE) was taken as difference in free energy between 1/2H2 and H+ according to the definition of standard hydrogen electrode (SHE), and E is the onset potential versus SHE, on the basis of the works recently reported58. Several (2 ~ 5) small imaginary frequencies (below 30i cm-1) were found in the optimized geometry because we fixed some atoms in the geometry optimizations, as mentioned above. Considering the presence of those artificial frequencies, the smallest five frequencies were omitted in the free energy calculations. ASSOCIATED CONTENT

Supporting Information. The Supporting Information is available free of charge on the ACS Publications website: Experimental details, synthesis and characterization of H2NL, singlecrystal X-ray study, perspective drawings of crystal diagrams, detailed characterization, crystallographic data for NTU-33 and calculation model (pdf). Crystallographic data of NTU-33 have been deposited in the Cambridge Crystallographic Data Centre (CCDC: 1864692) (CIF). AUTHOR INFORMATION

Corresponding Author *Email: [email protected] (J. D.); [email protected] (W. J.).


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Author Contributions J. D. conceived the idea of this work. B.Z., C. H. and Y. W. carried out the experiments. J. Z. did the calculation. J. D. wrote the paper. All authors gave valuable comments for paper writing. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT

We thank the financial support of National Natural Science Foundation of China (21671102), National Natural Science Foundation of Jiangsu Province (BK20161538), Innovative Research Team Program by the Ministry of Education of China (IRT-17R54), The Six Talent Peaks Project in Jiangsu Province (JY-030), State Key Laboratory of Materials-Oriented Chemical Engineering (ZK201803) and the Young and Middle-aged Academic Leader of Jiangsu Provincial Blue Project. In addition, we kindly thank TEM measurement by Prof. Yinong Lv. REFERENCES (1) Chen, L.; Shi, G. S.; Shen, J.; Peng, B. Q.; Zhang, B. W.; Wang, Y. Z.; Bian, F. G.; Wang, J. J.; Li, D. Y.; Qian, Z.; Xu, G.; Liu, G. P.; Zeng, J. R.; Zhang, L. J.; Yang, Y. Z.; Zhou, G. Q.; Wu, M. H.; Jin, W. Q.; Li, J. Y.; Fang, H. P. Ion Sieving in Graphene Oxide Membranes Via Cationic Control of Interlayer Spacing. Nature 2017, 550, 415-418. (2) Langer, F.; Schmid, C. P.; Schlauderer, S.; Gmitra, M.; Fabian, J.; Nagler, P.; Schüller, C.; Korn, T.; Hawkins, P. G.; Steiner, J. T.; Huttner, U.; Koch, S. W.; Kira, M.; Huber, R. Lightwave Valleytronics in a Monolayer of Tungsten Diselenide. Nature 2018, 557, 76-80. (3) Duan, H.; Yan, N.; Yu, R.; Chang, C.-R.; Zhou, G.; Hu, H.-S.; Rong, H.; Niu, Z.; Mao, J.; Asakura, H.; Tanaka, T.; Dyson, P. J.; Li, J.; Li, Y. Ultrathin Rhodium Nanosheets. Nat. Commun. 2014, 5, 3093-3100. (4) Li, L.; Yu, Y.; Ye, G. J.; Ge, Q.; Ou, X.; Wu, H.; Feng, D.; Chen, X. H.; Zhang, Y. Black Phosphorus Field-Effect Transistors. Nat. Nanotechnol. 2014, 9, 372-377. (5) Mannix, A. J.; Zhou, X.-F.; Kiraly, B.; Wood, J. D.; Alducin, D.; Myers, B. D.; Liu, X.; Fisher, B. L.; Santiago, U.; Guest, J. R.; Yacaman, M. J.; Ponce, A.; Oganov, A. R.; Hersam, M. C.; Guisinger, N. P. Synthesis of Borophenes: Anisotropic, Two-Dimensional Boron Polymorphs. Science 2015, 350, 1513-1516.


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Graphic Abstract


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Chemically Robust, Cu-based Porous Coordination Polymer

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