In-Situ Ligand Formation-Driven Preparation of a Heterometallic Metal

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In-situ Ligand Formation-Driven Preparation of a Heterometallic Metal-Organic Framework for Highly Selective Separation of Light Hydrocarbons and Efficient Mercury Adsorption Yi Han, Hao Zheng, Kang Liu, Hongli Wang, Hongliang Huang, Lin Hua Xie, Lei Wang, and Jian Rong Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b08397 • Publication Date (Web): 22 Aug 2016 Downloaded from http://pubs.acs.org on August 23, 2016

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ACS Applied Materials & Interfaces

In-situ Ligand Formation-Driven Preparation of a Heterometallic Metal-Organic Framework for Highly Selective Separation of Light Hydrocarbons and Efficient Mercury Adsorption Yi Han,† Hao Zheng,† Kang Liu,† Hongli Wang,† Hongliang Huang,§ Lin-Hua Xie,‡ Lei Wang,*,† and Jian-Rong Li‡ †

Department Key Laboratory of Eco-chemical Engineering, Ministry of Education,

Inorganic Synthesis and Applied Chemistry, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, P. R. China. ‡

Beijing Key Laboratory for Green Catalysis and Separation and Department of

Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, P. R. China §

State Key Laboratory of Organic–Inorganic Composites, Beijing University of

Chemical Technology, Beijing 100029, P. R. China.

KEYWORDS: in-situ ligand formation • heterometallic metal-organic framework • sulfur decorating cages • light hydrocarbons separation • mercury adsorption

ACS Paragon Plus Environment


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ABSTRACT:

By

means

of

the

in-situ

ligand

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formation

strategy

and

Hard-Soft-Acid-Base (HSAB) theory, two types of independent In(COO)4 and Cu6S6 clusters were rationally embedded into the heterometallic metal-organic framework (HMOF) {[(CH3)2NH2]InCu4L4·xS}n (BUT-52). BUT-52 exhibits a three-dimensional (3D) anionic framework structure and has sulfur decorating the dumbbell-shaped cages with the external edges of 24 Å and 14 Å by the internal edges, respectively. Remarkably, due to the fact on the stronger charge-induced interactions between the charged MOF skeleton and the easily polarized C2 hydrocarbons (C2s), BUT-52 was used for C2s over CH4 and shows both high adsorption heats of C2s and selective separation abilities for C2s/CH4. Furthermore, BUT-52 also displays efficient mercury adsorption resulting from the stronger-binding ability beween the sulfur and mercury, and can remove 92% mercury from methanol solution even with the initial concentration as low as 100 mg/L. The results in this work indicate that feasibility of BUT-52 for the separation of light hydrocarbons and efficient adsorption/removal of mercury.

INTRODUCTION

Heterometallic

metal-organic

frameworks

(HMOFs)

based

on

distinct

metal-containing building units are a class of newly developed MOFs with a wide range of potential application, especially in adsorption/separation.1-2 This modular nature endows well tailored structures and the associated multiple functions within a single system. Compared with the efforts on the exploitation of suitable synthetic methods for


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the preparation of normal homometallic MOFs,3 the study of synthetic methodology on HMOFs is still at the early stage, a challenge yet. Post-synthetic coordination modification4 and direct/stepwise self-assembly5 based on mixed donor ligands, as well as metal ion/guest substitution6 are dominant strategies for the preparation of HMOFs thus far. Generally, hard Lewis acid of metal ions preferentially coordinate the carboxylate (harder donor) groups of a mixed donor ligand while the softer donor groups (pyridyl N- or sulfhydryl S-centers) are available to bind soft Lewis acid of metal ions. Specifically, self-assembly method refers to a routine process that one or two functional groups immobilize one type metal ions to in-situ form a polyfunctional metalloligand and further cross-link the remaining metal ions, resulting in the extended monomer- or cluster-based HMOF.7-12

The in-situ ligand formation, as one of the most powerful and efficient approach, has been widely used in the design and preparation of functional MOFs.13 It is worthy noting that, such approach denies the necessity of the ligand synthesis prior to the construction of MOFs. More importantly, it will decrease the reaction rate and further ensure the growth of single crystals sufficiently to allow single-crystal X-ray diffraction (SXRD). Among them, the reductive cleavage of the S-S bonds has been explored as an attractive route to functional ligands and new MOFs14 or molecular clusters.15 Nevertheless, this method based on the in-situ ligand formation is still not engaged in the preparation of HMOFs, to date.



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Very recently, a 3D nanotubular Co2+/Na+-based HMOF (BUT-51, BUT = Beijing University of Technology) was synthesized in our group and used in dye selective adsorption and separation.16 And in this work, by means of elaborate choice of reactants and Hard-Soft-Acid-Base (HSAB) theory, we implement the in-situ ligand formation strategy and successfully synthesized an intriguing monomer- and cluster-based HMOF (Scheme 1), with the formula of {[(CH3)2NH2]InCu4L4·xS}n (BUT-52, H2L = 6-mecaptopyridine-3-carboxylic, S represents unassigned free solvent molecules), which comprises classic In(OOC)4 monomers and unique Cu6S6 clusters. It was found that the in-situ synthesized trifunctional H2L17 is originated from 6,6'-dithiodinicotinic acid resulting from the cleavage S-S bond during the solvothermal reaction,18-20 and further benefits the synthesis of BUT-52. Remarkably, due to the charged nature of BUT-52 and easily polarized C2 hydrocarbons (C2s), we further performed the charged HMOF for highly selective separation of C2s from C1 (CH4), where BUT-52 exhibits both high adsorption heats of C2s and selective separation abilities for C2H2/CH4, C2H4/CH4, C2H6/CH4 by the enhanced host-guest interactions through charge-induced forces. In addition, given the characterization of sulfur decorating the dumbbell-shaped cages, BUT-52 also shows efficient mercury adsorption due to the stronger-binding ability beween the sulfur and mercury.


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Scheme 1. Illustration of the rational design of BUT-52 based on In3+, Cu+ and the in-situ synthesized ligand involving carboxylate, pyridyl and thiol groups.

RESULTS AND DISCUSSTION

Synthesis, characterization, crystal structure, and N2 adsorption property of BUT-52. Dark red polyhedral single crystals of BUT-52 were successfully prepared by heating the mixture of InCl3, CuI and 6,6'-dithiodinicotinic acid in a 1:4:2 molar ratio in DMA/EtOH mixed solution at 120 oC for 12 h. The resultant framework formula of {[(CH3)2NH2]InCu4L4·MeCN·H2O}n was defined from TGA and elemental analysis (EA) after thorough treatment with CH3CN (see experimental section). The anionic feature of the framework of BUT-52 was further confirmed by dye adsorption



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experiments. As expected, BUT-52 can rapidly adsorb cationic dye Methylene Blue (MB), but does not adsorb the anionic dye, Methyl Orange (MO) (Figure S13). In addition, PXRD confirms that dye uptake occurs with the retention of the framework of BUT-52. Significantly, H2L and [(CH3)2NH2]+ should be generated from the decomposition of 6,6'-dithiodinicotinic acid and DMA, respectively. Furthermore, the synthesis of BUT-52 relies on subtle control over various experimental parameters, particularly the starting materials. For example, reaction of In(NO3)3, CuI, and 6,6'-dithiodinicotinic acid could not form BUT-52, and the similar result occurs in the combination of InCl3, Cu(ClO4)·4MeCN, and 6,6'-dithiodinicotinic acid. However, direct treatment of H2L, InCl3 and CuI could only produce unidentified amorphous solid. The results prove that the in-situ ligand formation strategy based on slow formation of H2L via decomposition of 6,6'-dithiodinicotinic acid is critical for the synthesis of BUT-52. TGA of BUT-52 after thorough treatment with CH3CN revealed an initial weight loss of 6.1% up to 124 °C that are consistent with the loss of lattice CH3CN and H2O molecules. Above this temperature, a series of decomposition steps commence (Figure S2).


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Figure 1. (a) Highlighted the coordination environment of L2- ligand. (b) 4-connected In(COO)4 monomer and unique Cu6S6 cluster. (c) The novel formed hexadentate metalloligand based on one Cu6S6 cluster and six L2- ligands. Color scheme: In, green; Cu, brown; S, yellow; N, blue; C, black; O, red. H atoms were omitted for clarity.

SXRD analysis reveals that BUT-52 is a three-dimensional (3D) anionic framework structure and crystallizes in the cubic space group Pn-3m with cell parameters a = 22.0484(2) Å, V = 10718.43(17) Å3. The crystallographically asymmetric unit contains 1/8 In3+ ions, 1/2 Cu+ ions, 1/2 L2- ligands as shown in Figure S1. The In3+ center exhibits an eight-coordinated distorted tetrahedral geometry, binding with eight O atoms from four independent L2- ligands, the In-O bond lengths are ranging from 2.218(3) to 2.314(3) Å. Cu+ ion is trigonal coordinated by one pyridyl N atom and two S atoms from three independent L2- ligands, where the observed Cu-S and Cu-N bond lengths are 2.251(10) and 2.052(4) Å, respectively. In the coordination environment of tri-functional L2- ligand, it utilizes the carboxylate group to chelate an eight-coordinated In3+ ion to constitute a classic 4-connected In(COO)4 moiety; while it takes its remaining N- and S-donor centers to link three Cu+ ions to make up a unique Cu6S6 cluster (Figure 1a and 1b), which is very different from the reported analogues.21-28 The combination of one Cu6S6 and six L2- can be thus viewed as a novel hexadentate carboxylic ligand, typically a metalloligand (Figure 1c). The solvent-accessible volume in BUT-52 estimated by PLATON29 is 67.4% of the total volume (potential solvent area volume = 7221.3 Å3; per unit cell volume = 10718.4 Å3), after removing all of the guest solvent molecules and [(CH3)2NH2]+. It should be noted



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that there are disordered [(CH3)2NH2]+ accommodating the extra-large solvent accessible voids, which keep the charge-balance. In this 3D structure (Fig. 2c), the interconnections of 12 [In(COO)4] moieties and 8 Cu6S6 clusters via 28 L2- ligands define the sulfur decorating dumbbell-shaped cage, and the approximate sizes were observed of 24 Å by the external edges of two opposite Cu6S6 clusters, and 14 Å by the internal edges of two opposite pyridine rings, respectively (Figure 2a and 2b). Topologically, the [In(COO)4] moiety serves as a 4-connected node, whereas [Cu6S6L6] metalligand can act as a 6-connecting node, by means of SYSTRE30 analysis thus leading to a (4,6)-connected toc net with a Schläfli symbol of (44.62)(46.66.83) (Figure 2d).

Figure 2. (a) and (b) Top and side view of the dumbbell-shaped cage in BUT-52 (the radius of caged sky-blue sphere is 7 Å). (c) 3D cage-based structure of BUT-52. (d)


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The simplification of the polymeric network in BUT-52 to the (4,6)-connected toc topology.

The permanent porosity of BUT-52 was evaluated by N2 adsorption experiment at 77 K. After solvent-exchange with acetone, BUT-52 was activated and degassed under vacuum at 50 °C for 12h and exhibits Type-I N2 isotherm, being characteristic of microporous nature with the saturated uptake of 126.2 cm3 g–1 (at P/P0 = 0.95), and Brunauer-Emmett-Teller (SBET) and Langmuir (SLangmuir) surface area are 358 m2 g−1 and 522 m2 g−1, respectively (Figure S3). The BET surface area of BUT-52 is 358 m2 g–1, probably due to the partially blocked voids induced by electrostatic attraction between disordered [(CH3)2NH2]+ cations and anionic framework.16 Clearly, after N2 adsorption, BUT-52 keeps the intact structure skeleton, which was confirmed by PXRD (Figure 3). Also, the CO2 uptake capacities are 57.9 and 26.5 cm3 g−1 at 273 and 298 K, respectively. At zero loading, the enthalpy of CO2 adsorption (Qst) is 25.1 kJ mol−1, as estimated from the sorption isotherms at 273 and 298 K using the virial equation (Figure S4).31-33



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Figure 3. PXRD patterns of BUT-52 after various treatments.

Hydrocarbon adsorption isotherms, calculations of selectivities based on the Henry's law, selectivity and isosteric heats of gas adsorption (Qst). Natural gas, consisting mainly of CH4 is a clean alternative energy source used in the chemical industry, and purification is prerequisite. The major impurities facing natural gas are C2s (C2H2, C2H4 and C2H6). So, highly efficient separation of C2s over C1 (CH4) is required. Compared to traditional energy-intensive separation technologies,34-35 adsorptive separation using microporous MOF materials is widely considered as a more environment-friendly and energy-efficient alternative.36-43 Inspired by the robust nature and permanent porosity of BUT-52, we further investigated the uptake capacity of this MOF for light hydrocarbons. The maximal sorption values at ambient pressures for pure C2H2, C2H4, C2H6, and CH4 are 86.7, 56.9, 71.6 and 13.2 cm3 g-1 at 273 K and are 71.6, 37.9, 40.7, and 7.7 cm3 g-1 at 298 K, respectively (Figure 4a). Although the adsorbed amount of C2H2 in BUT-52 at 298 K is lower than those with high-density of


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open-metal sites such as Cu-BTC (201 cm3 g-1),44 PCN-16 (176 cm3 g-1)38 and Zn-MOF-74 (122 cm3 g-1),45 the C2H2 uptake of BUT-52 at 298 K is comparable with MIL-53 (72 cm3 g-1),41 ZJU-31 (71.1 cm3 g-1)46 and Cu(etz) (70 cm3 g-1),47 and is much higher than UTSA-36 (57 cm3 g-1),42 MOF-5 (26 cm3 g-1)44 and M’MOF-20 (21 cm3 g-1).48 The systematical adsorption capacities to CH4 than those of C2H2, C2H4 and C2H6 at both 273 and 298 K further imply that BUT-52 may be a good candidate material for the separation of C2s from CH4.

To evaluate the adsorption selectivity of light hydrocarbons, the separation ratios of C2s over CH4 are calculated by the Henry’s Law. Henry's law selectivity for gas component i over j at a specific temperature is calculated based on the following equation: Sij = KHi/KHj Henry's law constants were calculated directly from the adsorption isotherms. The results show that the selectivities for C2H2/CH4, C2H4/CH4 and C2H6/CH4 at 273 K, respectively, are 36.4, 20.5, and 15.5, and at 298 K are 23.5, 14.4, and 13.7. Notable, BUT-52 displays a great separation ratio of C2H2/CH4, in excess of 23 at 298 K, which is much higher than those of MOFs with high-density open-metal sites UTSA-33a (17.1),49

Cu(BDC-OH)

(9.3),50

and

(H3O)4[Ni6(µ3-O)2(µ2-OSC2H6)2(SO4)2(TATB)8/3]·4C2H6O·13H2O (14.1),51 and is comparable to that of ZJU-31 (23.4)46 (Some virial parameters are summarized in Table



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S3). In addition, the separation ratios of CO2 versus CH4 and N2 are also given, and the detailed information is provided in Figure S9-11.

Figure 4. (a) C2H2, C2H4, C2H6 and CH4 sorption isotherms at 273 and 298 K. (b) The isosteric heats of adsorption of C2H2, C2H4, C2H6 and CH4 on BUT-52. To illuminate why BUT-52 shows selective separation for light hydrocarbons, the isosteric heat of adsorption, Qst, defined as

was determined using the pure component isotherm fits. The isosteric heats (Qst) values of C2H2, C2H4, C2H6 and CH4 at zero coverage are 35.5, 27.3, 31.8 and 19.0 kJ mol-1, respectively (Figure 4b). The calculated results show the hierarchy of adsorption capacity is commonly CH4 < C2H4 < C2H6 < C2H2, indicating that feasibility of BUT-52 for the separation of light hydrocarbons. The systematically higher adsorption heats of C2s and selectivies of C2s/CH4 can be probably attributed to the stronger charge-induced van der Waals interactions between the charged framework skeleton of BUT-52 and the easily polarized C2s.33,

52-56

These results confirm the promising


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separation of CH4 from mixtures containing C2H2, C2H4 and C2H6 species, that is, potential application for BUT-52 in the purification of natural gas.

Procedure and characterization of mercury adsorption. Due to the advantages of the stronger-binding ability between sulfur atoms and diverse metal ions, the incorporating of the very reactive sulfur atoms into MOFs becomes very popular and often studied for efficient metal ions removal/separation applications,57-61 especially for mercury adsorption. Notably, Xu and co-workers utilized thioether-anchored Zn4O·(L)3·(DMF)4·(H2O)4 (H2L = 2,5-Bis(2-(methylthio)ethylthio)terephthalic acid) to take up HgCl2 from an ethanol solution at a concentration as low as 84 mg/L.57 Shortly

afterwards,

the

thiol-laced

2,5-dimercapto-1,4-benzenedicarboxylic

acid)

Zr-DMBD crystals

(H2DMBD

lowering

the

= Hg2+

concentration in water below 0.01 ppm and effectively taking up Hg from the vapor phase was reported in the same group.58 Based on the characterization of sulfur decorating the dumbbell-shaped cages in BUT-52, the exploration of its application for mercury adsorption seems to be promising.



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Figure 5. The Raman spectra of as-synthesized sample of BUT-52 (dark red) and HgCl2 treated BUT-52 sample (brown yellow). To assess the mercury adsorption capacity, freshly prepared BUT-52 crystal sample (～15 mg) was immersed in a methanol solution of HgCl2 (0.1 M, 3.0 mL). After being stirred for about 12 hours at room temperature, the crystals turned from dark red into brown yellow (Figure 5 insert). The solid was then isolated by centrifugation and further thoroughly washed with methanol to remove residual HgCl2 on the surface of sample. Energy-dispersive X-ray spectroscopy (EDS) revealed that both the elements of Hg and Cl are obviously located in the resulting sample (denoted as BUT-52·HgCl2) (Figure S14). Inspired by this, the chemical composition and In/Cu/Ag ratio of BUT-52·HgCl2 were further determined by EA, TGA and AAS analysis, leading to a molecular

formula

of

{[(CH3)2NH2]InCu4L4·1.28HgCl2·2MeOH·0.5H2O}n.

In

addition, after mercury adsorption, BUT-52 keeps its original framework skeleton, which was confirmed by PXRD (Figure 3). Further to this, the adsorptive mechanism


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was revealed by Raman spectrum of BUT-52·HgCl2, showing a strong characteristic band at 353 cm-1, consistent with the stretch of Hg-S bond (355 cm-1),57 which is absent in the spectrum of BUT-52 (Figure 5). Notably, other metal ions (Pb2+ , Cu2+, Pd2+ and Ag+) having stronger binding abilities with sulfur atoms do not affect the dark red color of the crystal samples after a 12 hours stirring (The crystals of BUT-52 are decomposed in a methanol solution of Ag+). EDS demonstrated that negligible contents of Pd and Pb are in the resulting samples, respectively (Figure S15). In addition, AAS analysis revealed an approximately In/Cu ratio of 1:4 in the final sample in a methanol solution of Cu2+, indicating that there is no obvious uptake toward Cu2+ as well. These results may show a mercury-exclusive adsorption in BUT-52, and further suggest no effects of other metal ions on the removal of mercury.

Furthermore, we performed the effective capture of mercury in a low concentration from methanol. An as-prepared BUT-52 sample (～15 mg) was added in a dilute methanol solution (3 mL) of HgCl2 with the initial concentration of 100 mg/L. After the mixture was stirred at RT for 12 h, the residual amount of HgCl2 in the solution was decreased to ～ 8 mg/L, indicating over 92% of the HgCl2 was thus removed by BUT-52. Although the removal efficiency of BUT-52 is lower than that of Zr-DMBD with thiol function (>99.9%),58 which is comparable with thioether-anchored Zn4O·(L)3·(DMF)4·(H2O)4 (>94%).57 The above results indicate that BUT-52 may be a good candidate for efficient mercury adsorption and removal.

CONCLUSIONS



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In summary, by means of the in-situ ligand formation strategy and HSAB theory, a novel anionic HMOF of BUT-52 with sulfur decorating the dumbbell-shaped cages was rationally designed and synthesized. It was found that this MOF exhibits high adsorption heats of C2s and selective separation of C2s over CH4, the mechanism of which might be due to the enhanced host-guest electrostatic interactions between the charged HMOF framework and more polarized C2s. In addition, BUT-52 shows efficient mercury adsorption by the stronger-binding ability beween the sulfur and mercury. These realizations in this work initiate the extensive exploration of the emerging aspects towards unique synthesis approach and potential applications of HMOFs. A research endeavor toward the rational design and synthesis of functional HMOFs for adsorption and separation is in progress.

EXPERIMENTAL SECTIONS

Materials and instruments. All reagents and solvents were commercially available and used without further purification. IR spectra were recorded from KBr pellets in the range 4000~400 cm–1 on a Shimadzu IR435 spectrometer. A FLASH EA 1112 analyzer was performed for the elemental analysis. Thermogravimetric analysis (TGA) was recorded on a Netzsch STA 449C thermal analyzer between 30 and 800 °C and a heating rate of 10 °C min–1 in atmosphere. Powder X-ray diffraction (PXRD) data were measured on the PANalytical X′Pert PRO diffractometer using Cu-Kα radiation (λ = 1.541874 Å). Energy-dispersive X-ray spectrometry (EDS) was performed on a Bruker ISMNM 761 scanning electron microscope. A Z28000 graphite-oven atomic


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absorption spectrophotometer (AAS) was employed to determine the amount of metal ions. Raman spectra were acquired on a Renishaw inVia system. N2, CO2, CH4, C2H2, C2H4 and C2H6 adsorption/desorption data were measured on an ASAP 2020 surface area analyzer.

Synthesis of {[(CH3)2NH2]InCu4L4·MeCN·H2O}n (BUT-52). A mixture of InCl3·4H2O (15 mg, 0.05 mmol), CuI (38 mg, 0.2 mmol), and 6,6'-dithiodinicotinic acid (31 mg, 0.1 mmol) dissolved in DMA (2 mL) and EtOH (2 mL) was heated at 120 °C for 12 h. Dark red polyhedral crystals of BUT-52 in 56% yield (based on InCl3·4H2O) accompanied unreacted CuI were harvested. As-synthesized BUT-52 should be immersed in CH3CN for 3 days (change fresh CH3CN every 12h), and thoroughly washed by CH3CN to remove excess CuI. BUT-52 was found to be insoluble in common organic solvents, but decomposed in water. EA calcd (%) for C28H25Cu4InN6O9S4: C, 30.94; H, 2.32; N, 7.73. Found: C, 31.17; H, 2.02; N, 7.82.

Activation of the sample. The procedures were performed following our recently published work,16 except the as-synthesized sample of BUT-52 was firstly immersed and thoroughly washed by fresh CH3CN.

Mercury adsorption. Freshly prepared BUT-52 sample (15 mg) was immersed in a methanol solution of HgCl2 (0.1 M, 3.0 mL). After being stirred for about 12 hours at room temperature, the crystals turned from dark red into brown yellow. The resulting crystals

formulated

as

{[(CH3)2NH2]InCu4L4·1.28HgCl2·2MeOH·0.5H2O}n

(designated as BUT-52·HgCl2) was isolated by centrifugation and thoroughly washed



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by methanol remove residual HgCl2 on the surface of sample. AAS analysis revealed an approximately In/Cu/Hg ratio of 1:4:1.28 [In, Cu and Hg concentrations found: 57.1 mg/g, 132.4 mg/g and 125.7 mg/g, respectively]. Elemental analysis calcd (%) for C29H30Cu4InHg1.28N6O10.5S4Cl2.56: C, 23.61; H, 3.05; N, 5.70. Found: C, 23.97; H, 3.97; N, 5.43.

Single-crystal X-ray crystallography. Data collection for BUT-52 was carried on a an Agilent Technologies SuperNova Single Crystal Diffractometer using Cu Kα radiation (λ = 1.54178 Å) at 100 K. The structure was solved using SHELXS-97 and refined with SHELXL-97.62 The hydrogen atoms were included in the structure-factor calculations at idealized positions by using a riding model and were refined isotropically. The contributions of guests were removed by using the “SQUEEZE” as implemented in PLATON29. CCDC-1057212 (BUT-52) contains the supplementary crystallographic data for this paper. Crystal data and the selected bond lengths and angles for BUT-52 are summarized in Table S1 in Table S2.

ASSOCIATED CONTENT

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org.

Additional structural figures, PXRD patterns, TGA curves, N2 and CO2 sorption isotherms and adsorption enthalpies, fittings for adsorption isotherms, FT-IR spectra, photographs and UV-vis spectra, EDS spectra, and tables (PDF)


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CIF file for BUT-52 (CIF)

AUTHOR INFORMATION Corresponding Author E-mail: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (Nos. 51372125, 21571112, and 51572136), the Scientific and Technical Development Project of Qingdao (No. 13-1-4-184-jch) and Doctoral Fund of QUST (No: 010022733 and 010022728).

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In-Situ Ligand Formation-Driven Preparation of a Heterometallic Metal

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