Diamondoid Frameworks via Supramolecular Coordination: Structural

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Diamondoid Frameworks via Supramolecular Coordination: Structural Characterization, Metallogel Formation, and Adsorption Study Liping Cao,*,†,# Pinpin Wang,†,# Xiaran Miao,§,# Honghong Duan,† Heng Wang,∥ Yunhong Dong,† Rui Ma,⊥ Ben Zhang,† Biao Wu,† Xiaopeng Li,∥ and Peter J. Stang‡

Inorg. Chem. Downloaded from pubs.acs.org by IDAHO STATE UNIV on 04/19/19. For personal use only.

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Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of Education, National Demonstration Center for Experimental Chemistry Education, College of Chemistry and Materials Science, Northwest University, Xi’an 710069, P. R. China ‡ Department of Chemistry, University of Utah, Salt Lake City, Utah 84112, United States § Shanghai Synchrotron Radiation Facility, Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, P. R. China ∥ Department of Chemistry, University of South Florida, Tampa, Florida 33620, United States ⊥ Xinjiang Laboratory of Phase Transitions and Microstructures in Condensed Matters, College of Physical Science and Technology, Yili Normal University, Yili 835000, P. R. China S Supporting Information *

ABSTRACT: Supramolecular coordination has been developed as an efficient tool to construct a variety of discrete metallacycles and metallacages with well-defined shapes and sizes. However, its application in framework construction has been barely exploited. In this paper, we report the direct synthesis of two diamondoid frameworks from a simple tetrahedral precursor, tetra(4-(4-pyridinyl)phenyl)methane, and two linear difunctional platinum(II) ligands via one-step supramolecular coordination. Controlled by the specific angularity and geometry of the tetrahedral and linear subunits, these frameworks possess a well-defined diamondoid topology with highly regulated periodicity and three-dimensional porosity. Moreover, these rigid frameworks can be directly changed into a metallogel when prepared in DMSO at high concentrations. Interestingly, these diamondoid frameworks exhibit a cationic nature and stimuli-responsive behavior, which potentially endow them with the selective adsorption and controlled release for anionic dyes and drugs in aqueous environments. Thus, this study demonstrates that supramolecular coordination is a facile and efficient approach for the preparation of functional framework materials containing predesigned and well-defined supramolecular coordination assemblies as molecular skeletons.

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INTRODUCTION Recently, three-dimensional framework materials (3D FMs), such as zeolite,1 metal−organic frameworks (MOFs),2,3 covalent organic frameworks (COFs),4 and supramolecular organic frameworks (SOFs),5−7 have been constructed via ionic interactions, coordination interactions, reversible covalent bonds, and noncovalent interactions, respectively. Given their high porosity with different shapes, sizes, and functionalized groups, these 3D FMs have been investigated for a variety of applications including gas storage and separation,8,9 heterogeneous catalysis,10 fluorescent materials (e.g., sensing and cell imaging),11 and drug delivery.12 In nature, diamonds possess several distinctive properties (e.g., extreme hardness, high stability and thermal conductivity, broad optical transparency, etc.),13 which partially stem from their tetrahedraloctahedral structure of carbon atoms with a Td symmetry. © XXXX American Chemical Society

Inspired by the carbon framework of diamonds, chemists and material scientists managed to build up their own 3D diamondoid frameworks, which have been constructed from molecular building blocks in a well-controlled manner.6,14−33 On the basis of the geometry and the topology of diamondoid frameworks, tetrahedral precursors have served as ideal structural nodes and, thus, have been used for directly constructing diamondoid frameworks. For example, Ermer discussed the diamondoid framework by demonstrating the self-assembly of adamantine-1,3,5,7-tetracarboxylic acid or methanetetraacetic acid through hydrogen bonds in the crystalline state.14 Recently, more and more diamondoid frameworks have been constructed via several different Received: February 19, 2019

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DOI: 10.1021/acs.inorgchem.9b00484 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 1. (a) Synthesis and Disassembly of Diamondoid Frameworks 3 and (b) Tetrahedral Unit 4

correction of errors under the conditions of assembly.38 Previously, we have reported a diamondoid supramolecular coordination framework (SCF) based on an adamantanoid supramolecular coordination cage as the tetrahedral node.39 Herein, we report a direct and simple approach to construct two different 3D diamondoid frameworks from a tetrahedral precursor as a central node and two different linear difunctional platinum(II) ligands as linkers. These new SCF materials feature 3D periodic and porous structures, which consist of one hexagon 1D channel along the [101] direction and three square 1D channels along a, b, and c axes, respectively. Additionally, we demonstrate that these 3D SCF materials exhibit a concentration-dependent formation and a stimuli-responsive disassembly process of a supramolecular coordination metallogel, as well as the ability of selective adsorption and controlled release for anionic molecules (e.g., dyes and drugs) in an aqueous environment.

approaches, including not only hydrogen bonds but also metal coordination, reversible covalent bonds, and other noncovalent interactions (e.g., host−guest interactions and halogen bonds). For example, Lin,20 Brammer,21 and Zaworotko22 reported a series of similar diamondoid MOFs, in which the metal ions [e.g., Zn(II), Cd(II), In(II), and Ni(II)] as the tetrahedral nodes were connected with linear organic linkers, respectively.20−23 Very recently, Yaghi,24,25 Wang,26−28 Wuest,29 and others utilized substituted tetraphenylmethane compounds as tetrahedral nodes to directly construct diamondoid COFs through reversible covalent bond forming reactions, such as the condensation of imines or the dimerization of azodioxides.24−33 They have exhibited excellent selective adsorption/ extraction ability,23 catalytic activity,26 chiral separation,32 and continuous-breathing behavior.22 However, the construction of specific 3D frameworks with a predesigned structure and controllable functionality is still a challenge. Coordination has proven to be a useful tool to construct supramolecular coordination complexes (SCCs), due to its high directionality and dynamic reversibility.34−36 In this approach, the metallic acceptors (e.g., Pt(II) and Pd(II) compounds) and ditopic bis(pyridine) donor ligands with different rigid binding angles (e.g., 60°, 90°, 108°, 127−149°, and 180°) can be precisely assembled to achieve a specific orientation, thereby generating a preprogrammed library of discrete 2D and 3D SCCs with a series of well-defined geometries.35,36 For example, Fujita and co-workers showed that a very small difference in the mean ligand bend angle results in a critical structural switch from lower- to higher-level coordination polyhedra.37 Moreover, compared to COFs, highly ordered frameworks via coordination are easier to obtain because of the dynamic coordination between the metal and the neutral pyridine linker, which allows for the rapid

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RESULTS AND DISCUSSION Synthesis and Characterization. Scheme 1a illustrates our synthetic approach to construct diamondoid frameworks. The tetrahedral precursor, tetra(4-(4-pyridinyl)phenyl)methane (1)40 with a bonding angle of nearly 108°, and two difunctional Pt(II) linkers with an angle of 180° each, bis[1,4(trans-Pt(PEt3)2OTf)]benzene (2a) and bis[4,4′-(trans-Pt(PEt3)2OTf)]biphenyl (2b),17 were prepared according to literature reports. When a solution of the tetrahedral precursor 1 in DMSO-d6 was added to the linear subunits 2a or 2b, respectively, under careful measuring the stoichiometry by 1H and 31P{1H} NMR, frameworks (3a and 3b) were isolated in the yield of 61% and 64%, respectively. Multinuclear (1H and 31P{1H}), 1H−1H correlated spectroscopy (COSY), and 2D diffusion-ordered spectroscopy B

DOI: 10.1021/acs.inorgchem.9b00484 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. Partial 1H NMR spectra (500 MHz, DMSO-d6, 298 K) recorded for (a): (i) 1, (ii) 2a, (iii) 3a, (iv) 3a + TBAB (1.0 equiv), and (b): (i) 1, (ii) 2b, (iii) 3b, (iv) 3b + TBAB (1.0 equiv). 31P{1H} NMR spectra (121.4 MHz, DMSO-d6, 298 K) recorded for (c): (i) 2a, (ii) 3a, (iii) 3a + TBAB (1.0 equiv), and (d): (i) 2b, (ii) 3b, (iii) 3b + TBAB (1.0 equiv). Here, primes (′) denote resonances for frameworks; asterisks (*) denote resonances for corresponding Pt-Br compounds.

much lower, suggesting the formation of large supramolecular coordination assemblies in DMSO-d6. If we assume that 3a, 3b, and 4 are roughly spherical, then the ratio of the measured diffusion coefficients can be converted into ratios of molecular weights by the Stokes−Einstein equation,41 which in turn gives a degree of polymerization (n) of ∼37 for 3a and ∼122 for 3b. Moreover, dynamic light scattering (DLS) experiments on the DMSO solutions of 3a or 3b indicated an average size distribution of 21.0 nm for 3a and 58.8 nm for 3b (Figure S16). Both the DOSY and DLS results suggested that the length of the linkers can affect the size of the frameworks, likely because the longer linker may avoid the electrostatic repulsion and steric hindrance between the positively charged and highly branched building blocks as pillars in the framework structure. Structural Periodicity and Porosity. To gain further insight into the nature of these diamondoid frameworks, the microstructural aspects of samples of 3a and 3b in the solid state were examined by small-angle X-ray scattering (SAXS) and N2 sorption isotherm experiments. As shown in Figure 2a, two broad, but clear, scattering peaks corresponding to dspacings of about 4.2 and 2.0 nm were observed for 3a. We also simulated the 3D framework structures of 3 assuming the diamondoid topology using Material Studio 8.0. Indeed, a single adamantanoid fragment is observed as a basic structural unit in the diamondoid framework of 3a (Figure 2b and Table S1). When the SAXS results are compared with the simulated structures, the d-spacings match well with the calculated spacings of the average diameter of one hexagon 1D channel (∼4.3 nm) along the [101] direction (Figure 2c) and three square 1D channels (∼2.1 nm) along the a, b, and c axes (Figure 2d−f), thus providing evidence for the periodicity of this 3D framework material. The broad scattering peaks may be the result of the large numbers of branched PEt3 groups on the pillars of the framework structure, leading to a wide size distribution of these 1D channels. Moreover, the d-spacing of 4.2 nm along the [101] direction indicates that the porous

(DOSY) NMR of 3a and 3b in DMSO-d6 provided support for the formation of large diamondoid frameworks with high symmetry and uniformity. In the 1H and COSY NMR spectra of 3a (Figures 1a and S8), the protons on the pyridyl (Ha and Hb) and phenyl (Hc, Hd, and H1) rings exhibited downfield shifts compared to those of 1 (Δδ[Ha] = 0.16 ppm, Δδ[Hb] = 0.33 ppm, Δδ[Hc] = 0.16 ppm, and Δδ[Hd] = 0.05 ppm) and 2a (Δδ[H1] = 0.13 ppm), which is attributed to the coordination of the pyridine to the Pt center. Similar chemical shifts were also observed for the formation of 3b from 1 (Δδ[Ha] = 0.20 ppm, Δδ[Hb] = 0.37 ppm, Δδ[Hc] = 0.20 ppm, and Δδ[Hd] = 0.10 ppm) and 2b (Δδ[H1] = 0.15 ppm, and Δδ[H2] = 0.08 ppm) (Figures 1b and S9). Due to the similar, but subtly different, chemical environments of the PEt3 groups located in the interior or exterior of the designed framework structures, the 31P{1H} NMR spectra of 3a and 3b showed a broad singlet at δ = 14.31 ppm for 3a and δ = 14.94 ppm for 3b, with concomitant 195Pt satellites shifted upfield from those of the corresponding starting difunctional Pt(II) linkers 2a and 2b by Δδ = 5.56 and 5.67 ppm, respectively (Figure 1c,d). To further confirm the structure of the frameworks, the tetrahedral unit 4, as a fragment analogue in 3a and 3b, was synthesized in 79% isolated yield by mixing 1 and 2c in a ratio of 1:4 (Scheme 1b). Comparisons of the 1H and 31P{1H} NMR spectra of 3a, 3b, and 4 revealed that the chemical shifts in frameworks 3a and 3b are similar to those of the tetrahedral unit 4 (Figures S11 and S12), indicating that the tetrahedral features also exist in the framework structures of 3a and 3b. In the DOSY experiments of 3a, 3b, and 4, the observation of a single band confirmed that only a single product was formed. The diffusion coefficient was calculated as (9.974 ± 0.458) × 10−11 m2 s−1 for 3a, (6.722 ± 0.178) × 10−11 m2 s−1 for 3b, and (3.336 ± 0.097) × 10−10 m2 s−1 for 4, indicating the high uniformity of 3 and 4 (Figures S13−S15). Compared to that of unit 4, the diffusion coefficients of frameworks 3a and 3b are C

DOI: 10.1021/acs.inorgchem.9b00484 Inorg. Chem. XXXX, XXX, XXX−XXX

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cm3 g−1 N2 for framework 3b was adsorbed at 1.0 atm, and the pore-size distribution analysis revealed four main pores with 0.9, 1.3, 3.0, and 6.8 nm (Figure S21). The low N2 adsorption may be attributed to the fact that some of the OTf− counterions reside in the pores of these frameworks. Metallogel Formation. Metallogels are of interest not only for their gelation property but also for their application as catalysts, sensors, luminescent materials, functional polymers, and smart materials.42−44 Discrete coordination complexes (e.g., 2D polygons and foldamers), as cores or linkers, may selfassemble into flexible supramolecular networks or polymers that form metallogels via hydrogen bonding, host−guest interaction, π−π interactions, or metal−metal bonds, etc.45,46 In the present case, supramolecular coordination metallogels were directly obtained when the diamondoid frameworks were prepared from 1 and 2 in DMSO at high concentration (e.g., ∼30 mg mL−1) (Figure 3a). We performed concentration-

Figure 2. (a) Synchrotron small-angle X-ray-scattering profile of the solid sample of 3a. (b) The single adamantanoid fragment; the views of the diamondoid framework 3a along (c) the [101] direction and (d) a ([100]), (e) b ([010]), and (f) c ([001]) axes, respectivley. C, gray; N, blue; P, yellow; H, white; Pt, turquoise.

Figure 3. (a) Photographs of 1 (left), 3 (middle, 30.0 mg mL−1), and 3 + TBAB (right) in DMSO. Concentration-dependent (b) rheological characterization and (c) viscosity (T = 298 K) of 3b.

structure of the diamondoid framework in 3a is not part of an interpenetrated structure, unlike some other diamondoid frameworks.14−33 The electrostatic repulsions and steric hindrance between the positively charged and highly branched pillars in the framework structure may also be responsible for the lack of the interpenetration. The simulated framework structure of 3b also showed a similar adamantanoid fragment with calculated spacings of the average diameter of one hexagon 1D channel (∼5.1 nm) and three square 1D channels (∼2.4 nm), and the SAXS profile of 3b exhibited only weak and broad peaks corresponding to d-spacings of about 5.2 and 2.2 nm (Figure S17). The SAXS results indicate that 3b has a lower periodicity than 3a, perhaps because the longer linker in 3b has less rigidity than the shorter linker in 3a, which results in an interpenetrated structure.14−33,40 All the above data indicate that 3a and 3b have the expected diamondoid topology. The stability of 3a and 3b was examined by thermogravimetric analysis (TGA), which showed that 3a and 3b were stable up to 276 and 285 °C, respectively (Figures S18 and S19). The porosities of frameworks 3a and 3b were examined by measuring N2 sorption isotherm experiments at 77 K on the activated samples. Framework 3a displayed limited adsorption of 21.4 cm3 g−1 at 1.0 atm, and the pore-size distribution curve indicated four major pores with 1.4, 2.3, 3.9, and 6.7 nm (Figure S20). Owing to its interpenetrated structure, only 10.7

dependent rheological experiments at room temperature for these frameworks with the concentration ranging from 5.0 to 30.0 mg mL−1. The data show that the storage modulus (G′) is much larger than the loss modulus (G′′) for both 3a (≥25.0 mg mL−1) and 3b (≥20.0 mg mL−1), and both (G′ and G′′) are independent of the angular frequency (ω), thus indicating the formation of metallogels (Figures 3b, S23, and S24). The increase of viscosity versus shear rate (γ̇) from the solution state (e.g., 5.0−20.0 mg mL−1 for 3a; 5.0−15.0 mg mL−1 for 3b) to the gel state (e.g., 25.0−30.0 mg mL−1 for 3a; 20.0− 30.0 mg mL−1 for 3b) further confirmed their concentrationdependent gelation property (Figures 3c, S23, and S24). The rheological results also demonstrate that the higher degree of polymerization of 3b resulted in a lower critical gelation concentration of 3b than that of 3a. Besides the concentration, other factors may also affect the formation of these supramolecular coordination metallogels. For example, bromide ion (Br−) is an effective competitor for the coordination between Pt and pyridine to give a more stable Pt-Br compound.47 The 1H and 31P{1H} NMR spectra of mixtures of 3a or 3b with tetrabutylammonium bromide (TBAB), respectively, indicated the free protons of 1 and a sharp 31P singlet at δ = 13.21 or 14.29 ppm, respectively, corresponding D

DOI: 10.1021/acs.inorgchem.9b00484 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 4. SEM images of 3a (a, d) and 3b (b, e) prepared from the corresponding solutions (2.5 mg mL−1) and gels (30.0 mg mL−1) in DMSO, respectively. (c) Schematic illustration for the possible mechanism of the self-assembled cuboids formed from 3.

to Pt-Br compounds (Scheme 1a and Figure 1), demonstrating that the addition of TBAB led to the disassembly of the frameworks, and a transition from gel to solution (Figure 3a). We also investigated the morphologies of the self-assembled samples from the solutions and gels of 3 by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM images of the samples prepared from a solution of 3 (2.5 mg mL−1) in DMSO by evaporation at 50 °C indicated that both 3a and 3b can self-assemble into supramolecular coordination cuboids with a length of 1.60 ± 0.39 μm for 3a and 277 ± 22 nm for 3b (Figure 4a−d). The thickness of these cuboids as determined by AFM was 1.06 ± 0.04 μm for 3a and 551 ± 37 nm for 3b, thus confirming the 3D nature of these selfassembled cuboids (Figure S25). Therefore, in these cases, we surmised that 3 in DMSO could further self-assemble or crystallize orderly into the large and regular cuboids controlled by their intrinsic cubic lattice structures in the evaporation process (Figure 4c). In contrast, the morphologies of gelated frameworks 3 (30.0 mg mL−1), which were prepared by a freeze-drying methodology, revealed interconnected gelation structures, further illustrating that 3D diamondoid frameworks play a key role in the formation of metallogels (Figure 4d,e). Adsorption Study. The adsorption ability of 3D framework materials for guest molecules is mainly determined by the framework−guest interactions, which are located not only at the interior pores or spaces but also on the exterior surfaces of the framework walls.48 Therefore, compared to neutral frameworks, 3 with cationic framework walls and mobile anions may have the ability to absorb anionic guests via electrostatic interaction through an ion-exchange process between solid and solution phases. The capacity and selectivity of 3a and 3b for extracting guests (e.g., dyes and drugs) from aqueous solutions was evaluated at 298 K by using ultraviolet− visible (UV−vis) spectroscopy (Figures S26−S34). Anionic Dye-1 to Dye-3 and cationic Dye-4 and Dye-5 with different shapes, sizes, and functional groups were chosen as models for exploring the adsorption behavior of 3a and 3b (Chart 1). For anionic Dye-1 to Dye-3, their adsorption profiles showed fast adsorption rates and a large adsorption equilibrium (qe) (Figure 5a,b and Table S2). The amounts of Dye-1 adsorbed by 3a and 3b are 139.9 and 203.5 mg g−1, respectively. In contrast, for cationic Dye-4 and Dye-5, both 3a and 3b showed very poor adsorption from their aqueous solution due to the electrostatic repulsion between the cationic frameworks and guests. Therefore, 3a and 3b may be useful for the

Chart 1. Dyes and Drugs Used in This Study

selective adsorption of anionic guests. We also investigated the adsorption of anionic drugs (Drug-1 to Drug-4) in aqueous solution. As seen in Figure 5c,d, the drug uptake was complete in several days with considerable loading capacity. For example, the loading capacity for Drug-1 is 80.2 and 115.0 mg g−1 for 3a and 3b, respectively (Table S2). In all cases, framework 3b exhibited a higher qe for these dyes and drugs than 3a, likely because 3b has a bigger pore size and therefore more framework space. To test the stability and release behavior, the solid samples of guest-adsorbed 3a and 3b were immersed in water at room temperature. These dye and drug molecules can remain in the frameworks for several days in pure water (Figure S35). However, when excess TBAB was added to the aqueous solution, the dye molecules were readily released from guestadsorbed 3a and 3b (Figure 5e,f).49 The percentages of dyes Dye-1 to Dye-3 released from adsorbed samples of 3a in about 10 h were 97.6%, 83.2%, and 98.5%, respectively (Figure 5e). Similarly, the release of Dye-1 to Dye-3 from the solid samples of guest-adsorbed 3b can also be triggered by TBAB, resulting in quantitative release (Figure 5f). As determined by NMR (Figure 1), the drug releases were triggered by Br− ions via breakage of the coordination bonds between Pt and pyridine. E

DOI: 10.1021/acs.inorgchem.9b00484 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 5. The amount of dyes (Dye-1 to Dye-5) and drugs (Drug-1 to Drug-4) adsorbed by 3a (a, c) and 3b (b, d) against time from corresponding aqueous solutions. The percentage of dyes (Dye-1 to Dye-3) released from adsorbed samples of 3a (e) and 3b (f) with the addition of TBAB in water.

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Compounds 139 and 2a−c40,50 were prepared according to the literature procedures. NMR spectra were recorded on a Varian Unity 300 or 500 MHz spectrometer. 1H NMR chemical shifts are reported relative to residual solvent signals, and 31P{1H} NMR chemical shifts are referenced to an external unlocked sample of 85% H3PO4 (δ = 0.0). Mass spectra were recorded on a Micromass Quattro II triple quadrupole mass spectrometer using electrospray ionization with a MassLynx operating system. Dynamic light scattering (DLS) experiments were performed on a Zetasizer Nano ZS90. Rheological data were collected by a TA AR-G2 at different concentrations. The scanning electron microscope (SEM) images were obtained on a Hitachi SU8010 microscope. AFM images were obtained on a Multi Mode 8 instrument. After replacing the DMSO solvent with CH2Cl2, thermal gravimetric analysis (TGA) experiments of the solid samples were performed on a NETZSCH STA 449C Simultaneous Thermal Analyzer over the temperature range of 30−800 °C in a nitrogen-gas atmosphere, and N2 sorption isotherms were measured by an AUTOSORB IQ instrument. UV−vis spectra were measured using an Agilent Cary-100 spectrophotometer. Small-angle powder diffraction experiments were recorded on BL16B1 at Shanghai Synchrotron Radiation Facility (SSRF) (λ = 0.124 nm, photo flux ≈ 1 × 1011, beam size ≤ 0.4 mm × 0.8 mm). Samples were held in evacuated 1 mm capillaries. Sample-to-detector distance was 2010 mm (corrected by bull tendon). A MarCCD 165 detector was used to collect the data.

CONCLUSION Over the past few years, supramolecular coordination is an efficient approach to construct not only supramolecular coordination complexes (SCCs)34,35 with well-defined shapes and sizes but also supramolecular coordination frameworks (SCFs)39 with a predesigned structure and controllable functionality. In the present work, we have demonstrated the construction of two diamondoid frameworks from tetra(4-(4pyridinyl)phenyl)methane as the central node and two linear difunctional platinum(II) ligands as the linkers via supramolecular coordination. Like MOFs and COFs, these 3D framework materials possessed well-defined periodicity and porosity. Furthermore, the selective adsorption, high adsorption capacity, and controlled release of these cationic diamondoid frameworks for anion dyes and drugs could be utilized in biological and medical applications, such as drug delivery. Given the potential applications in the construction of framework materials, we also expect this approach to stimulate interesting new designs for 2D and 3D framework structures with a specific and sophisticated topology.

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EXPERIMENTAL SECTION

Materials and Methods. Starting materials were purchased from commercial suppliers and used without further purification. F

DOI: 10.1021/acs.inorgchem.9b00484 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Synthesis of Diamondoid Framework 3a. To a solution of 1 (20.3 mg, 32.3 μmol) in DMSO (6 mL) was added 2a (80.0 mg, 64.7 μmol), and the reaction mixture was stirred at room temperature for 24 h. Then, the mixture was poured into ethyl ether (10 mL) with shaking to give a white precipitate, which was washed with Et2O (10 mL) and centrifuged. The precipitate was dried under high vacuum to give white powder 3a (61.6 mg, 61%). 1H NMR (500 MHz, DMSOd6, n is the number of repeated tetrahedral fragments in diamondoid framework): 8.80 (s, 8nH), 8.30−7.80 (m, 16nH), 7.70−7.30 (m, 8nH), 7.20−6.60 (m, 8nH), 1.50−1.20 (m, 48nH), 1.20−0.80 (m, 72nH). 31P{1H} NMR (121.4 MHz, DMSO-d6): 14.31 (s, 195Pt satellites, 1JPt‑P = 2716.4 Hz). Synthesis of Diamondoid Framework 3b. To a solution of 1 (13.0 mg, 20.7 μmol) in DMSO (5 mL) was added 2b (54.4 mg, 41.4 μmol), and the reaction mixture was stirred at room temperature for 24 h. Then, the mixture was poured into ethyl ether (10 mL) with shaking to give a white precipitate, which was washed with Et2O (10 mL) and centrifuged. The precipitate was dried under high vacuum to give white powder 3b (48.1 mg, 64%). 1H NMR (500 MHz, DMSOd6, n is the number of repeated tetrahedral fragments in diamondoid framework): 8.83 (s, 8nH), 8.20−7.90 (m, 16nH), 7.65−7.50 (m, 8nH), 7.50−7.20 (m, 16nH), 1.45−1.25 (m, 48nH), 1.20−0.95 (m, 72nH). 31P{1H} NMR (121.4 MHz, DMSO-d6): 14.94 (s, 195Pt satellites, 1JPt‑P = 2663.3 Hz). Synthesis of Tetrahedral Unit 4. To a solution of 1 (3.8 mg, 6.0 μmol) in CH2Cl2 (3 mL) was added 2c (16.0 mg, 24.3 μmol), and the reaction mixture was stirred at 50 °C for overnight. The mixture was concentrated by N2 flow, and then poured into ethyl ether (5 mL) to give a white precipitate, which was washed with Et2O (5 mL) and centrifuged. The precipitate was dried under high vacuum to give white powder 4 (15.6 mg, 79%). 1H NMR (500 MHz, DMSO-d6): 8.82 (d, J = 5.8 Hz, 8H), 8.06 (d, J = 5.8 Hz, 8H), 8.03 (d, J = 8.3 Hz, 8H), 7.52 (d, J = 8.3 Hz, 8H), 7.32 (d, J = 7.4 Hz, 8H), 7.04 (t, J = 7.4 Hz, 8H), 6.92 (t, J = 7.4 Hz, 4H), 1.35−1.20 (m, 48H), 1.10−0.95 (m, 72H). 31P{1H} NMR (121.4 MHz, DMSO-d6): 14.87 (s, 195Pt satellites, 1JPt‑P = 2682.2 Hz). ESI-TOF-MS: m/z 1479.9772 for [4 − 2OTf]2+ (calcd. 1479.9525); 936.9029 for [4 − 3OTf]3+ (calcd. 936.9893).

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Normal University) and Prof. Donghua Xu (Changchun Institute of Applied Chemistry) for performing the rheology experiment.

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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.9b00484. Experimental details including synthesis, NMR, ESI-MS, UV−vis spectra, SEM, and DLS data (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Liping Cao: 0000-0002-1747-6107 Biao Wu: 0000-0002-0724-4150 Xiaopeng Li: 0000-0001-9655-9551 Peter J. Stang: 0000-0002-2307-0576 Author Contributions #

These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (21771145 and 21472149). L.C. thanks Prof. Dongxu Xue (Shaanxi Normal University) for performing N2 sorption isotherm experiment; Prof. Kaiqiang Liu (Shaanxi G

DOI: 10.1021/acs.inorgchem.9b00484 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.9b00484 Inorg. Chem. XXXX, XXX, XXX−XXX