Construction of Highly Porous Pillared Metal–Organic Frameworks

Jul 17, 2017 - Different from the conventional method to construct pillared-layer metal–organic frameworks (MOFs) by using mixed bipyridyl and dicar...
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Construction of Highly Porous Pillared Metal−Organic Frameworks: Rational Synthesis, Structure, and Gas Sorption Properties Hui-Fang Zhou,† Bo Liu,‡ Hai-Hua Wang,† Lei Hou,† Wen-Yan Zhang,† and Yao-Yu Wang*,† †

Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, College of Chemistry & Materials Science, Northwest University, Xi’an 710069, P. R. China ‡ College of Chemistry & Pharmacy, Northwest A&F University, Yangling 712100, P. R. China S Supporting Information *

ABSTRACT: Different from the conventional method to construct pillared-layer metal−organic frameworks (MOFs) by using mixed bipyridyl and dicarboxylate ligands, herein, we present a new approach to build pillared-layer frameworks based on the pyridyldicarboxylate ligands which were predesigned with a certain shape. As exemplified, the ligands of 3(2′,5′-dicarboxyphenyl)benzoic acid (H 3 dbba) and 3-(2′,5′dicarboxylphenyl)pyridine acid (H2dcpy) were selected and employed to construct three pillared-layer MOFs, [Zn3(dbba)2(bipy)(DMF)]·3DMF· 4H2O (1) (bipy = 4,4′-bipyridine), and a pair of crystal polymorphs of [Zn(dcpy)]·1.5DMF·1.5H2O (2 and 3), under solvothermal reactions, respectively. In the structures of 1−3, the [Zn2(COO)4] clusters are bridged by the terephthalate units of dbba3−/dcpy2− to form 2D layers; these layers are further pillared by bipy and the benzoate units of dbba3− or the pyridine units of dcpy2− to furnish the 3D frameworks. All of them possess high porosity characterized by N2 adsorption and exhibit high selective adsorption of C2H4 and CO2 over CH4.

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INTRODUCTION Crystalline metal−organic frameworks (MOFs), owing to the designability of the structure, high surface area, and chemical tunability, and exhibiting especially excellent performances in many fields, such as in gas adsorption, catalysis, sensing, and selective separation,1−3 have become one of the most popular porous materials in recent years. However, the reasonable construction of desired structures still exists as an intractable challenge, which significantly depends on not only synthetic factors, including solvents, temperatures, and pH values,4 but also the nature of the building blocks, such as metal ions, ligands, and possible templates.5 Pillared-layer structures, as one representative of MOFs, and the building method of these, is considered as one of the most valid and easily controlled strategies to build 3D porous frameworks.6 The synthetic protocol promises to generate various types of porous MOF materials, whose structures can be predicted through deliberate selection of linker components. Size-alterable organic linkers are employed to systematically adjust pore size and shape, and functional groups embedded in the ligands in pillars and/or layers could be introduced into the pore to modulate the pore surface toward the desired properties. For example, the incorporation of specific polar acylamide groups into the pillar ligand has been investigated to enhance CO2 capacity and CO2/CH4 selectivity at low pressure.7 Also, dynamic porous MOFs with “breathing effect” or “gate opening” pore characteristics can be prepared by using the designed flexible pillars.8 However, when lengthening the © 2017 American Chemical Society

pillar- or layer-ligands to expand the channel sizes, interpenetration usually occurs; this is also one key disadvantage for constructing highly porous frameworks of pillared-layer MOFs.6−9 Until now, the noninterpenerating framework with the extended linkers is rarely reported.10 Recently, a strategy to avoid interpenetration of pillared-layer MOFs via symmetry breaking at nodes through the introduction of three connectors into one network has been proposed, but it is difficult to get satisfactory crystals for single crystal structural determination.11 On the other hand, the geometry of a ligand is a crucial aspect in directing the structures of MOFs. Recently, we and other groups found that using the asymmetrical isomeric tritopic pyridyldicarboxylic acid ligands to build MOFs could effectively avoid interpenetration.12 Building on this content, we herein propose a strategy that designs a “⊥ ” type of pyridyldicarboxylatic ligand with double functional coordination units (carboxyl and pyridyl) to construct pillared-layer frameworks, wherein the rigid layers formed by the interconnection of carboxylates units and metal centers are pillared by pyridyl units to produce 3D frameworks. To illustrate this strategy, the solvothermal reaction of 3-(2′,5′dicarboxyphenyl)benzoic acid (H3dbba) and 4,4′-bipyridine (bipy) with Zn 2+ ion afforded a pillared-layer MOF [Zn3(dbba)2(bipy)(DMF)]·3DMF·4H2O (1). On the basis of the result of 1, the pyridyldicarboxylatic acid, 3-(2′,5′Received: May 11, 2017 Published: July 17, 2017 9147

DOI: 10.1021/acs.inorgchem.7b01197 Inorg. Chem. 2017, 56, 9147−9155

Article

Inorganic Chemistry dicarboxylphenyl)pyridine acid (H 2dcpy), was designed (Scheme 1), and two polymorphs of pillared-layer MOFs

Table 1. Details of Crystallographic Data of 1−3 formula Mr cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) F(000) Rint GOF on F2 R1a [I > 2σ(I)] wR2b (all data)

Scheme 1. Schematic Representation of Relation between H2dcpy and H3dbba and bipy

with the formula of [Zn(dcpy)]·1.5DMF·1.5H2O (2 and 3) were successfully synthesized. The synthesis, structures, and gas-adsorption properties were investigated.

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EXPERIMENTAL SECTION

Materials and Measurements. The reagents and solvents used in the experiments were purchased commercially and used directly. IR spectra using KBr pellets were carried out on a FT-IR 170 SX (Nicolet) spectrometer. Elemental analyses of carbon, hydrogen, and nitrogen were determined using a PerkinElmer 2400C automatic analyzer. Powder X-ray diffraction (PXRD) experiments were tested with a Bruker D8ADVANCE X-ray powder diffractometer (Cu K, 1.5418 Å). Thermogravimetric analyses (TGA) were measured with a heating rate of 5 °C min−1 on a Netzsch TG209F3 instrument. Gasadsorption isotherms were performed by using an ASAP 2020 M adsorption instrument. Synthesis of [Zn3(dbba)2(bipy)(DMF)]·3DMF·4H2O (1). Zn(NO3)2· 6H2O (59.5 mg, 0.2 mmol), H3dbba (26.2 mg, 0.1 mmol), and 4,4′bipyridine·2H2O (19.2 mg, 0.1 mmol) in DMF (5 mL) were sealed in a screw-capped vial (8 mL) in an oven at 105 °C for 48 h. Then, the reaction system was cooled to room temperature at a rate of 0.5 °C min−1. Colorless block crystals of 1 were collected by filtration and washed with DMF. Anal. Calcd for C52H58Zn3N6O20: C, 48.67; H, 4.56; N, 6.55%. Found: C, 48.80; H, 4.48; N, 6.71%. Synthesis of [Zn(dcpy)]·1.5DMF·1.5H2O (2). Zn(NO3)2·6H2O (59.5 mg, 0.2 mmol) and H2dcpy (24.3 mg, 0.1 mmol) in DMF (4 mL) were sealed in a screw-capped vial (8 mL) in an oven at 105 °C for 72 h. Then, the reaction system was cooled to room temperature at a rate of 0.5 °C min−1. Colorless block crystals of 2 were collected by filtration and washed with DMF. Anal. Calcd for C17.5H20.5N2.5O7Zn: C, 47.42; H, 4.66; N, 7.90%. Found: C, 47.96; H, 4.57; N, 8.12%. Synthesis of [Zn(dcpy)]·1.5DMF·1.5H2O (3). Zn(NO3)2·6H2O (29.7 mg, 0.1 mmol) and H2dcpy (24.3 mg, 0.1 mmol) in DMF (4 mL) were sealed in a 20 mL glass tube. The tube was then placed into a microwave reactor and heated to 105 °C; the reaction lasted for 2 h, followed by cooling to room temperature in 0.5 h. Needle microcrystalline precipitate crystals of 3 were obtained and washed with DMF. Anal. Calcd for C17.5H20.5N2.5O7Zn: C, 47.42; H, 4.66; N, 7.90%. Found: C, 47.81; H, 4.49; N, 8.05%. X-ray Crystallographic Measurements. The single crystal intensity data of 1 was conducted at 298 K on a Bruker-AXS SMART CCD area detector diffractometer under Mo Kα radiation (λ = 0.71073 Å) with ω rotation scans at a scan width of 0.3°. The single crystal intensity data of 2 and 3 were conducted on synchrotron beamline BL17B of SSRF with a wavelength of 0.65250 Å. All the structures were solved with direct methods and refined using SHELXL2014 and OLEX2 software suite. Partial lattice solvent molecules in the structures of complexes 1−3 were disordered and could not be modeled properly. Therefore, the intensity contributions from the lattice guests were removed by using the SQUEEZE operation of PLATON.13 The formulas were given by integrating the crystal structure, elemental microanalysis, IR, and TGA. Table 1 provides the details of crystallographic data of 1−3, and the selected bond lengths and angles are listed in Tables S1−S3 (see the

a

1

2

3

C43H29Zn3N3O13 991.86 monoclinic C2/c 24.8170(10) 22.64(4) 26.737(8) 90 91.937(7) 90 15014(27) 8 0.878 4016 0.0914 1.092 0.1138 0.3296

C13H7ZnNO4 306.59 monoclinic P21/c 16.262(3) 24.374(5) 18.172(8) 90 118.27(2) 90 6344(3) 12 0.963 1848 0.0694 1.001 0.0628 0.1817

C13H7ZnNO4 306.59 trigonal R3c 36.625(5) 36.625(5) 17.487(4) 90 90 120 20314(7) 36 0.902 5543 0 1.034 0.0219 0.0602

R1 = ∑|Fo| − |Fc|/∑|Fo|. bwR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2.

Supporting Information). CCDC reference numbers for 1−3 are 1548968−1548970.

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RESULTS AND DISCUSSION Synthesis. Solvothermal reaction of Zn(NO3)2·6H2O with H3dbba and bipy in DMF under 105 °C for 48 h gave rise to colorless crystals of 1. Notably, for the reaction of Zn(NO3)2· 6H2O with H2dcpy in DMF under 105 °C, the crystals of both 2 and 3 occurred in one step with various heating times (6, 12, 24, or 48 h). Systematic synthesis reactions were subsequently carried out; the pure phase of 2 can be obtained with a longer reaction time and higher concentration of Zn salt, while the pure phase of 3 can be synthesized quickly by using a microwave method for 2 h. Crystal Structure of 1. Compound 1 crystallizes in the monoclinic space group C2/c, which contains three independent Zn2+ ions, two dbba3−, one bipy, and one coordinated DMF molecule in its asymmetric unit (Figure 1a). Two types of paddle-wheel Zn2 units are found in 1. As shown in Figure 1b, a regular paddle-wheel [Zn2(COO)4N2] cluster is formed on the basis of two Zn1 and four μ2-COO− groups, and two pyridyl Ndonors are bonded to the axial position. Neighboring Zn2 and Zn3 are connected by three μ2-COO− groups, and one pyridyl N-donor and one monodentate COO− group are further bonded to the axial position to generate an irregular paddlewheel [Zn2(COO)4N] cluster, where one coordinated DMF molecule is bonded to the Zn3 center (Figure 1c). For a clearer understanding on the structure of 1, the dbba3− can be divided into two parts: the terephthalate unit and the benzoate unit. As shown in Figure 1d, the [Zn2(COO)4N2] and [Zn2(COO)4N] clusters are bridged by terephthalate and 1/2 benzoate units of dbba3− to give a 2D layer that expands along the bc crystal plane, and those layers are pillared by bipy and 1/2 benzoate units of dbba3− to furnish a 3D porous framework with solventaccessible voids of 63.3% (9501.8 Å3 out of the 15014.0 Å3 per unit cell volume) (Figure S1). The framework contains rectangular channels along the [100] direction with opening sizes of about 10.6 × 12.2 Å2 (the distances of C18···C19 and C4···C10, respectively, in the opposite position of the channel) (Figure 1e). 9148

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Figure 1. (a) Coordination environment of Zn2+ ions in 1. (b) [Zn2(COO)4N2] cluster. (c) [Zn2(COO)4N] cluster. (d) The [Zn2(COO)4N2] and [Zn2(COO)4N] clusters are bridged by terephthalate and 1/2 benzoate units of dbba3− to give a 2D layer. (e) 3D structure of 1 with open channels.

size of 13.7 × 16.3 Å2 (measured between the centers of two SBU1 and two SBU2, respectively), while the hexagonal loop is composed of two SBU1, four SBU2, and eight terephthalate units with the size of 16.3 × 24.4 Å2 (measured between the centers of two SBU2 and two SBU1, respectively). These 2D layers are joined together by pyridine units to generate a 3D pillared-layer framework (Figure S2). There is an open square channel along the c axis with the size of about 11.5 × 11.5 Å2 (Figure 2e), and the other smaller open square channel with the size of about 9.7 × 9.7 Å2 can be viewed along the [101] direction. The effective volume is estimated to be 54.3% (3441.7 Å3 out of the 6343.0 Å3 per unit cell volume). Crystal Structure of 3. Compound 3 adopts the trigonal space group R3c, and the asymmetric unit consists of two independent Zn2+ ions and two dcpy2− ligands (Figure 3a). Both Zn2+ ions with similar tetragonal pyramid geometries are connected by four μ2-COO− groups to produce a paddle-wheel [Zn2(COO)4] unit, and two pyridyl N-donors occupy the axial position to finish the [Zn2(COO)4N2] cluster (Figure 3b). The same as 2, the dcpy2− ligand in 3 can be segmented as the combination of terephthalate and pyridine units. As shown in Figure 3c, the paddle-wheel clusters are linked via terephthalate units to extend along the ab plane to form a Kagome-type layer, pillared by pyridine units, leading to a 3D pillared Kagomelayer framework containing two types of channels running along the c axis (Figure 3d and Figure S3). The size of the

Crystal Structure of 2. Notably, the benzoate units of dbba3− play the role of pillar in 1, showing the similar function as that of diamine ligands in the construction of the pillarlayered framework. Herein, using pyridine units to replace the benzoate units, the ligand of H2dcpy was designed and used to construct a pillar-layered MOF. As we expected, under synthetic conditions similar to those of 1, a new 3D pillarlayered framework of 2 was synthesized. Compound 2 crystallizes in the monoclinic space group P21/c, and there are three independent Zn2+ ions and three dcpy2− ligands in the asymmetric unit (Figure 2a). Similar to 1, there are also two kinds of Zn2 units in the structure of 2. Zn1 displays a tetragonal pyramid geometry, and four COO− groups of four different dcpy2− species connect two Zn1 ions to generate a paddle-wheel [Zn2(COO)4N2] cluster (SBU1) (Figure 2b). Zn2 exhibits distorted tetragonal pyramid geometries defined by four COO− O atoms and one N atom of four dcpy2−, while Zn3 is four-coordinated by three COO− O atoms and one N atom. The neighboring Zn2 and Zn3 connect with dcpy2− to give an interesting [Zn2(COO)4N2] cluster (SBU2) (Figure 2c). The dcpy2− ligand in 2 can also be segmented as the combination of terephthalate and pyridine units. As shown in Figure 2d, the two different [Zn2(COO)4N2] clusters are connected by terephthalate units to give a 2D layer, which contains two types of loops. The parallelogram loop is made up by two SBU1, two SBU2, and four terephthalate units with the 9149

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Figure 2. (a) Coordination environment of Zn2+ ions in 2. (b) [Zn2(COO)4N2] cluster. (c) [Zn2(COO)4N2] cluster. (d) The [Zn2(COO)4N2] clusters are bridged by terephthalate of dcpy2− to form a 2D layer. (e) 3D structure of 2 with open channels.

exhibits an obvious weight loss of 30.7% below 150 °C, which is ascribed to the loss of 1.5DMF and 1.5H2O per formula unit (calcd 30.8%), and a plateau is observed until the collapse of the framework at 350 °C (Figure S8). Interestingly, the TGA curve of 3 is very similar to that of 2, which shows the weight loss of 30.0% below 200 °C corresponding to 1.5DMF and 1.5H2O per formula unit (calcd 30.8%), and a plateau is observed until the collapse of the framework at 350 °C, suggesting that both frameworks of 2 and 3 possess similar thermal stability. In addition, the lattice and coordinated solvent in 1 can be fully removed by directing activation at 170 °C for 8 h under vacuum (Figure S7), while the guest molecules located in the channels of 2 and 3 can be fully removed by soaking the as-synthesized samples in acetone for 3 days and subsequently drying the material overnight at 120 °C under vacuum (Figures S9 and S10). PXRD patterns demonstrate the framework integrity of the desolvated samples for 1−3 (Figures S4−S6). Sorption Properties. To evaluate the pore character of 1− 3, N2 sorption isotherms were investigated at 77 K (Figure 4). The reversible type-I N2 sorption isotherms of 1−3 show the microporous property. The Brunauer−Emmett−Teller (BET) and Langmuir surface area reach 2078 and 2344 m2 g−1 for 1, 1386 and 1474 m2 g−1 for 2, and 2095 and 2188 m2 g−1 for 3,

hexagonal channel is about 16.7 Å (the distance of the two centers of opposite phenyl rings). For the triangular channel, it can accommodate an imaginary spheroid with a diameter of 3.4 Å. The effective volume is estimated to be 55.4% (11249.2 Å3 out of the 20314.0 Å3 per unit cell volume). Remarkably, as a special kind of pillared-layer MOF, a pillared Kagome network features larger channels and higher porosity, particularly in which interpenetration is avoided because it is non-self-duals.14 A classical approach to building pillared Kagome-layer frameworks is that using dicarboxylates to connect [M2(RCOO)4] clusters to form rigid layers, which are then further pillared by bipyridyl to construct 3D networks (Scheme 2). Since the first 3D pillared Kagome-layer MOF [Zn2(bdc)2(dabco)]n was synthesized by Chun and Moon,15 MOFs with Kagome nets are still rarely reported because of the difficulty of selective synthetic control; for example, the framework isomerism of pcu net is easily formed.16 PXRD and TGA. The experimental PXRD patterns of 1−3 agree well with their simulated ones (Figures S4−S6), indicating the phase purity. The TGA result of 1 exhibits an obvious weight loss of 28.2% below 205 °C, which is attributed to the release of 4DMF and 4H2O per formula unit (calcd 28.4%), and a plateau is observed until the collapse of the framework at 330 °C (Figure S7). Similarly, the TGA plot of 2 9150

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Inorganic Chemistry

Figure 3. (a) Coordination environment of Zn2+ ions in 3. (b) Zn2(COO)4N2 cluster. (c) The [Zn2(COO)4N2] clusters are bridged by terephthalate of dcpy2− to give a 2D layer. (d) 3D structure of 3 with open channels.

Scheme 2. 3D Pillared Kagome-Layer Frameworks Based on [Zn2(COO)4N2] Clusters, Diazabicyclo[2,2,2]octane and Benzenedicarboxylate (Previous Work), and H2dcpy (This Work)

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Figure 4. N2 sorption isotherms at 77 K of (a) 1, (b) 2, and (c) 3, respectively (the inset shows the pore size distribution incremental pore volume (V) vs pore width).

Figure 5. C2H4, CO2, and CH4 sorption isotherms of (a) 1, (b) 2, and (c) 3 at 273 and 298 K. Solid symbols: adsorption. Open symbols: desorption.

respectively. The total microporous volumes are 0.84, 0.55, and 0.82 m3 g−1 for 1−3, respectively, demonstrating high porosity. The measured pore size distribution (PSD) curves based on the density-functional theory (DFT) method show the main pore sizes of 9.3 Å, 10.0 Å, and 9.3 and 12.7 Å for 1, 2, and 3, respectively (inset to Figure 4). These values conform to the Xray analysis if the van der Waals radii of the atoms are excluded. The establishment of porosity of 1−3 encouraged us to explore their potential applications for C2H4, CO2, and CH4 capture at ambient temperature. Accordingly, we systematically measured C2H4, CO2, and CH4 sorption isotherms at 273 and 298 K up to 1 atm. As shown in Figure 5, all complexes show high adsorption capacities of C2H4 and CO2 (Table 2), while only a small amount of CH4 uptakes, indicating the significant selective capture of C2H4 and CO2 over CH4. Moreover, different from the C2H4 sorption isotherms at 273 K for 2 and 3, the sigmoid isotherm for 1 may be ascribed to framework flexibility, presumably because of framework deformation caused by the gas molecules entering the pores.17 On the other hand, though 1 and 3 possess larger pore channels and

volumes than those of 2, the adsorption capacities of 1 and 3 for C2H4 and CO2 at 298 K are comparable or even less than that of 2, which indicates that the appropriate pore structure is important for C2H4 and CO2 capture.18 To predict the adsorption selectivities of C2H4 and CO2 over CH4 in 1−3 for the C2H4−CH4 and CO2−CH4 binary mixtures, the ideal adsorbed solution theory (IAST)19 was employed on the basis of the adsorption curves of C2H4, CO2, and CH4 at 298 K (Figures S14−S16). As shown in Figure 6, under the equimolar mixtures (the mole rations of 50:50) of C2H4−CH4 and CO2− CH4 systems, the C2H4/CH4 selectivities calculated at 1 atm for 1−3 are 7, 10, and 7, respectively, and all the CO2/CH4 selectivities are about 4. The values of the selectivities of C2H4 and CO2 with respect to CH4 in 1−3 are comparable with those known MOFs that possessed good C2H4/CH4 and CO2/ CH4 selectivity.20 In addition, to estimate the strength of the framework with C2H4 and CO2 interactions, the isosteric heat of adsorption (Qst) was calculated via the virial method by fitting the sorption curves collected at 273 and 298 K (Figures S17−S19). The Qst values of C2H4 and CO2 at initial coverage 9152

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Inorganic Chemistry Table 2. Adsorption Data for 1−3 273/298 Kb BET 1 2 3 a

a

2196 1386 2095

C2H4

CO2

CH4

S(C2H4/CH4)c

S(CO2/CH4)c

Qst(C2H4)d

Qst(CO2)d

168/95 123/85 97/64

105/49 93/52 78/47

24/14 28/17 29/16

7 10 7

4 4 4

20.3 22.9 27.8

21.2 19.7 22.7

Surface area, m2 g−1. bAdsorptive capability, cm3 g−1. cSelectivity sorption at 298 K. dIsosteric heat of adsorption, kJ mol−1.

Figure 6. IAST adsorption selectivity of (a) 1, (b) 2, and (c) 3 for C2H4/CH4 and CO2/CH4 at equimolar mixtures.

Figure 7. Adsorption enthalpies of C2H4 and CO2 for (a) 1, (b) 2, and (c) 3, respectively.

are 20.3 and 21.2 kJ mol−1 for 1, 22.9 and 19.7 kJ mol−1 for 2, and 27.8 and 22.7 kJ mol−1 for 3, respectively (Figure 7). Notably, for 1, the Qst value of C2H4 is lower than that of CO2 at initial coverage. The reason may be the stronger interactions of CO2 with the open zinc sites after the coordinated DMF molecule was removed from the desolvated framework of 1 than C2H4, as for CO2 (4.30 × 1026 esu cm2) that has a large quadrupole moment compared to C2H4 (1.50 × 1026 esu cm2). The larger Qst values of C2H4 and CO2 for 3 than those of 1 and 2 should be due to the existence of small open channel in the framework of 3 which makes the pore surface come in

closer contact with gas molecules, leading to the strong interactions.21 Furthermore, the intermediate adsorption enthalpies for all 1−3 imply the low-energy consumption for the material regeneration, an advantage for energy saving.

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CONCLUSION In summary, a new proposal to build pillared-layer frameworks based on the pyridyldicarboxylate ligands was proposed. Three pillared-layer MOFs with highly porous volumes were successfully synthesized by employing a mixed bipyridyl and tricarboxylic system to pyridyldicarboxylate ligands. In addition, 9153

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Inorganic Chemistry

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all materials possess high C2H4 and CO2 uptake capacities, as well as good selectivity for C2H4 and CO2 over CH4 gases. The results open a new blueprint on the synthetic design of pillaredlayer MOFs for future applications.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b01197. Supplementary structural figures; PXRD, TGA, and FTIR spectra of 1−3; and sorption isotherms fitting (PDF) Accession Codes

CCDC 1548968−1548970 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Lei Hou: 0000-0002-2874-9326 Yao-Yu Wang: 0000-0002-0800-7093 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the staff from the BL17B beamline of NFPS at the Shanghai Synchrotron Radiation Facility, for assistance during data collection. This work was supported by the NSF of China (21531007, 21371142, 21471124, and 21601145).

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REFERENCES

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DOI: 10.1021/acs.inorgchem.7b01197 Inorg. Chem. 2017, 56, 9147−9155

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DOI: 10.1021/acs.inorgchem.7b01197 Inorg. Chem. 2017, 56, 9147−9155