In Situ Capture of a Ternary Supramolecular Cluster in a 58-Nuclei Silver Supertetrahedron

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2022In Situ Capture of a Ternary Supramolecular Cluster in a 58-Nuclei Silver Supertetrahedron Zhi Wang, Meng-Die Li, Jia-Yang Shi, Hai-Feng Su, Jia-Wei Liu, Lei Feng, Zhi-Yong Gao, Qing-Wang Xue, Chen-Ho Tung, Di Sun and Lan-Sun Zheng Zhi Wang Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, State Key Laboratory of Crystal Materials, Shandong University, Ji'nan 250100 , Meng-Die Li Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, State Key Laboratory of Crystal Materials, Shandong University, Ji'nan 250100 , Jia-Yang Shi Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, State Key Laboratory of Crystal Materials, Shandong University, Ji'nan 250100 , Hai-Feng Su State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 , Jia-Wei Liu Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, State Key Laboratory of Crystal Materials, Shandong University, Ji'nan 250100 , Lei Feng Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, State Key Laboratory of Crystal Materials, Shandong University, Ji'nan 250100 , Zhi-Yong Gao School of Chemistry and Chemical Engineering, Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, Henan Normal University, Xinxiang 453007 , Qing-Wang Xue Shandong Provincial Key Laboratory of Chemical Energy Storage and Novel Cell Technology, School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252000 , Chen-Ho Tung Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, State Key Laboratory of Crystal Materials, Shandong University, Ji'nan 250100 , Di Sun *Corresponding author: E-mail Address: [email protected] Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry and Chemical Engineering, State Key Laboratory of Crystal Materials, Shandong University, Ji'nan 250100 and Lan-Sun Zheng State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 https://doi.org/10.31635/ccschem.021.202100880 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Although inorganic anion templates are highly appreciated in the synthesis of nanosized silver clusters, supramolecular clusters used as templates to mold silver nanoclusters remain as-yet-unknown due to their existence as volatile forms in solution. Here, we report the synthesis of a novel silver-thiolate nanocluster ( SD/Ag58a), comprising an outer tetrahedral cage of 58 silver atoms and a central supramolecular cluster [CH3[email protected](SO4)4(H2O)6]8− (hereafter abbreviated as CS4H6). Ternary CS4H6 cluster was constructed from an (SO4)4 tetrahedron encaging one CH3OH molecule inside and six water molecules sitting between paired SO42− ions to form the [SO4···H2O···SO4] hydrogen bonds (H-bonds). Also, the CS4H6 could coordinate to the inner wall of the Ag58 cage by forming Ag–O bonds, exerting templating effect on the formation of SD/Ag58a. Moreover, SD/Ag58a showed a photocurrent response upon visible light irradiation and emitted luminescence in the near-infrared (NIR) region at a cryogenic temperature. This work exemplifies the ternary supramolecule templating effect in the construction of silver nanocluster and facilitates understanding of the structure of complex solvated anion cluster in atomic precision. Download figure Download PowerPoint Introduction Coinage-metal nanoclusters have long been of great interest to researchers in both chemistry and materials fields due to their aesthetically appealing structures and the distinct physicochemical properties across luminescence, catalysis, chirality, electrochemistry, and so on.1–11 Historically, a plethora of atom-precise coinage-metal nanoclusters with thiolates, phosphines, and alkynes have been documented as protecting ligands, especially among the silver nanocluster family.12–16 Some prominent examples are Ag44,17 Ag62,18 Ag180,19 Ag374,20 and Ag490,21 with the central metal valances of +1 or between 0 and +1. Due to the high complexity of the coordination-driven assembly system, obtaining novel silver nanoclusters with ordered arrangements for both metal cores and ligand shells is still a major challenge. To solve this thorny issue, an anion template, mostly oxo-anion, was introduced as a guiding agent in the assembly of silver nanoclusters.22,23 Simple inorganic anions such as spherical Cl−, triangular CO32−, tetrahedral SO42−, and even larger polyoxometallates (POMs) have been witnessed to demonstrate huge success in constructing silver nanoclusters with different nuclearity and geometry.24–37 Moreover, organic anion such as squarate recently surfaced in this field, being used as a template to build an Ag24 cluster.38 During the studies on anion-templated silver nanoclusters,39–42 we noticed the strong electrostatic interactions between anion and surrounding solvent molecules, forming some supramolecular clusters through hydrogen bonds (H-bonds), and then acted as a potential template using remaining lone-paired electrons to direct the assembly of silver nanoclusters. In fact, solvated anions, as a body, have rarely been trapped in the silver nanoclusters. Recently, our group43 isolated and characterized two silver nanoclusters encapsulating a pair of the binary supramolecular cluster [(CO3)2H2O]4−, making the supramolecule templated silver nanoclusters go a big step forward. However, achieving ternary supramolecule templated silver clusters is still rare. Anion solvated by multiple solvents will produce complex supramolecular clusters, carrying rich binding sites and diverse spatial arrangement of functional groups, which have great potential as template to create a wealth of silver cluster based functional material treasures. In turn, the confined solvated anions can be characterized expediently by X-ray crystallography to understand the nucleation mechanism of solvated anions. Herein, we described the synthesis, crystal structure, and some essential properties of a silver-thiolate nanocluster [CH3[email protected](SO4)4(H2O)6@Ag58(iPrC6H4S)40(CF3COO)6(H2O)10]·4CF3COO ( SD/Ag58a). The fabricated SD/Ag58a contained a tetrahedral Ag58 cage and a ternary supramolecular cluster [CH3[email protected](SO4)4(H2O)6]8− ( CS4H6). This is the first case of a ternary supramolecular cluster trapped into a silver nanocluster. The distinct templating effect of CS4H6 was verified, comparing it with previously reported Ag37.44 Experimental Methods Experimental details, including the synthesis, isolation, single-crystal X-ray diffraction (SCXRD), infrared (IR), UV-vis ( Supporting Information Figure S6), energy-dispersive X-ray spectroscopy (EDS; Supporting Information Figure S8), and powder X-ray diffraction (PXRD; Supporting Information Figure S9), are shown in the Supporting Information. Briefly, SD/Ag58a was synthesized by a simple stirring method at ambient temperature. Typically, 6 mL CH3OH/CH2Cl2/CH3CN (v/v/v = 1/1/1) containing (iPrC6H4SAg)n and Na2SO4 was stirred for 2 h, then 0.5 mL dimethylformamide (DMF) solution of CF3COOAg was added and stirred for another 4 h (Scheme 1). It should be noted that the feeding sequence of Na2SO4 and CF3COOAg could not be reversed, and precipitates were formed at the bottom in abundance. The solution was filtered by filter paper, and the yellow filtrate was let alone for cultivating crystals. After 2 weeks, colorless rod crystals of SD/Ag58a were isolated and characterized by SCXRD. Other tetrahedral anion templates such as MoO42−, WO42−, PO43−, and ClO4− did not work in this system, possibly due to the nonmatched size or coordination ability to that of SO42−. Scheme 1 | Synthetic route for SD/Ag58a. Download figure Download PowerPoint Results and Discussion Having determined the molecular structure of SD/Ag58a by SCXRD analysis, we found that it crystallized in an orthorhombic space group Pnnn; the asymmetric unit consisted of a quarter of the Ag58 cluster. Selected details of the data collection and structure refinements are listed in Supporting Information Table S1. SD/Ag58a can be described as a ternary supramolecular cluster CS4H6 enwrapped by the outer Ag58 shell, consisting of 58 Ag atoms arranged into a supertetrahedron surrounded by 40 iPrC6H4S−, 6 CF3COO−, and 10 water ligands (Figure 1a). The 40 iPrC6H4S− ligands could be divided into two categories based on their coordination regioselectivity: 28 covering four triangular faces and 12 riding on the six edges of the Ag58 supertetrahedron (Ag–S distances: 2.28–2.76 Å). On each triangular face, seven iPrC6H4S− ligands exhibited two kinds of coordination modes (one in μ3 and six in μ4 mode, Figure 1b). Two iPrC6H4S−, one μ2-η1:η1 CF3COO− and one water ligand, riding on each edge of Ag58 supertetrahedron. The residual four water molecules were tied to four vertexes of supertetrahedron to accomplish the total coordination of the Ag58 shell (Ag–Owater distances: 2.33–2.76 Å). The 58 Ag atoms distributed on the outer surface were bound together by the Ag···Ag interactions,45–47 and the distances were in the scope of 2.70–3.40 Å. The Ag58 shell consisted of four triangular faces, six edges, and four vertexes simplified to a tetrahedron (Figure 1c). There were nine Ag atoms on each triangular face, observed as a distorted hexagon overlapped with a homocentric trigon ( Supporting Information Figure S1). The Ag58 shell had three orthogonal C2 rotation axes and four pseudo-C3 axes passing through the vertex and the center of the opposite triangular face, approximating a Td symmetry. Figure 1 | (a) The X-ray crystal structure of SD/Ag58a. All H atoms were omitted for clarity. (b) The coordination modes of seven iPrC6H4S− ligands on a triangular face of Ag58 tetrahedron. Only S atom of iPrC6H4S− ligand was left for clarity. (c) The tetrahedral skeleton comprised 58 Ag atoms. Color labels: purple, Ag; yellow, S; gray, C; green, F; and red, O. Download figure Download PowerPoint The most interesting element in SD/Ag58a was an unanticipated supramolecular cluster of CS4H6, which was neither observed in the supramolecular chemistry nor discussed in the anion-templated silver clusters. The CS4H6 was established by the H-bonding between methanol, sulfate, and water molecules (Figure 2a). The detailed geometrical parameters of H-bonds in CS4H6 are listed in Supporting Information Table S3. CS4H6 contained four sulfates situating under the four vertexes of Ag58 supertetrahedron, and each tetrahedral sulfate was coaxial but 60° staggered with respect to the Ag58 supertetrahedron along the pseudo-C3 axis. For each sulfate, one of four O atoms (O7) exclusively triply ligated to three different Ag atoms on Ag58 shell (Figure 2b), whereas the other three O atoms of sulfate not only interact with water molecules via Owater–H···Osulfate H-bonds (O···O distances: 2.69–2.81 Å; Supporting Information Table S3) but also coordinated to three different Ag atoms on Ag58 shell, thus, giving the sulfate an overall μ6-η3:η1:η1:η1 coordination mode ( Supporting Information Figure S2; Ag–O distances: 2.27–2.53 Å). The methanol molecule, disordered in four orientations, was encapsulated into the [(SO4)4(H2O)6] supramolecular cage to form the final ternary supramolecular cluster, CS4H6 (Omethanol–H···Osulfate distance: 3.04 Å; Supporting Information Table S3), where each water molecule served as a double-donor of H-bond bridges to two sulfates to form an edge of CS4H6 supramolecular tetrahedron. Except for the formation of H-bonds, a water molecule also joins two adjacent trigonal faces of the Ag58 shell through the Ag–O bonds (μ2-Owater; 2.34–2.38 Å, Supporting Information Figure S3). In all, four-coordinated sulfates and six water molecules were arranged into a tetrahedron (Figure 2c) and an octahedron (Figure 2d), respectively, which were concentrical around a methanol molecule in the center ( Supporting Information Figure S4), acting as a ternary supramolecular template in building the SD/Ag58a. This is the first case of the generation of a novel anion-templated ternary supramolecular silver-thiolate nanocluster. Figure 2 | (a) Detailed structure of the supramolecular cluster of CS4H6 in SD/Ag58a. Intermolecular O–H···O H-bonds are shown in black dashed lines. (b) The binding modes of entrapped SO42− and H2O toward Ag atoms. SO42− is represented by a yellow polyhedron. Ag–O bonds are highlighted by bold green lines. (c) The (SO4)4 supramolecular tetrahedron. (d) The (H2O)6 supramolecular octahedron. Color labels: purple, Ag; yellow, S; gray, C; cyan, H; and red, O. Download figure Download PowerPoint The tetrahedral molecular architecture of SD/Ag58a is reminiscent of previously reported truncated tetrahedral Ag3750 and two recently reported Ag42 nanoclusters ( SD/Ag42a and SD/Ag42b),48 which contained different AgS4, Ag6S4, and Ag6Se4 tetrahedral cores, respectively, trapped by outer Ag36 shell with similar size. Due to the differences (e.g., charge states and sizes) between AgS4, Ag6S4, Ag6Se4, and CS4H6, obvious outer shell expansion of the Ag58 versus Ag36 could be observed (Figures 3a–3d). The shape, arrangement, and linking modes of the CS4H6 anion were the critical factors that dictated the expanded tetrahedral SD/Ag58a. Meanwhile, note that the symmetry of the template could transfer to the main framework of silver nanocluster through a suite of coordinate bonds. Therefore, introducing such supramolecular templates into the assembly of silver nanoclusters might provide an alternative way to build more fantastic stable, sulfate-based supramolecular structures. Figure 3 | The compared skeletal structures of SD/Ag58a (a), Ag37 (b), SD/Ag42a (c), and SD/Ag42b (d). The inner SO42−, AgS4 core and Ag6 core are shown in a polyhedral mode. Color labels: purple and cyan, Ag; yellow, S; brown, Se; red, O; and gray, C. Download figure Download PowerPoint The solution behavior of SD/Ag58a in CH2Cl2 solution was investigated by positive-ion mode electrospray ionization mass spectrometry (ESI-MS). Two visible envelopes were observed in the m/z range of 4950–6950 ( Supporting Information Figure S5). The most abundance envelope consisted of two overlapping species at the m/z = 6725.40 ( 1b) and 6732.35 ( 1b′). By attentively comparing the experimental and simulated isotopic distributions, two doubly charged species 1b and 1b′ were assigned to [CH3[email protected](SO4)4(H2O)6@Ag57(iPrC6H4S)40(CF3COO)6(H2O)(CH3OH)]2+ (Calcd. m/z = 6725.38) and [CH3[email protected](SO4)4(H2O)6@Ag57(iPrC6H4S)40(CF3COO)6(CH3OH)2]2+ (Calcd. m/z = 6732.39), respectively. The difference between the two species rests in the outer solvent shell with some extent of exchange. The Ag58 shell could not remain intact due to the loss of one silver atom, most possibly from the vertex of the Ag58 tetrahedron. Two overlapped doubly charged species ( 1a and 1a′) made up another envelope with lower abundance attributed to [CH3[email protected](SO4)4(H2O)6@Ag41(iPrC6H4S)34(H2O)3]2+ (Exp. m/z = 5071.52; Calcd. m/z = 5071.51) and [CH3[email protected](SO4)4(H2O)6@Ag41(iPrC6H4S)34(CH3OH)(H2O)2]2+ (Exp. m/z = 5078.58; Calcd. m/z = 5078.51) and represented a more severe fragmentation of SD/Ag58a in solution or ionization process under the ESI-MS conditions. The solid-state UV–vis absorption spectrum of SD/Ag58a (Figure 4a) recorded in the diffuse reflection mode showed a dual-hump profile with two adjacent maximum peaks at 357 and 397 nm, which might be originated from the π → π* transition of iPrC6H4S− ligand, consistent with the light-colored appearance of a bulk sample. Based on the Kubelka–Munk function of (αhυ)1/2 = κ(hυ-Eg) (Eg is the bandgap (eV), h is the Planck's constant (J·s), υ is the light frequency (s−1), κ is the absorption constant, and α is the absorption coefficient),49,50 the Tauc plot estimated the bandgap of SD/Ag58a to be 2.47 eV (inset in Figure 4a). Furthermore, SD/Ag58a maintained its color and morphology for at least 6 months under ambient conditions, indicating that it was stable to light, atmospheric moisture, and oxygen, supported by comparing the initial and sixth month IR and UV–vis spectra ( Supporting Information Figure S6). Figure 4 | (a) UV–vis absorption spectrum of SD/Ag58a. Inset: Tauc plot showing the bandgap energy determined from the optical absorption spectrum. (b) Photocurrent responses of SD/Ag58a, (iPrC6H4SAg)n precursor and blank ITO electrodes in 0.2 M Na2SO4 aqueous solution cycling irradiation with 420 nm-LED light. Download figure Download PowerPoint The photocurrent response of SD/Ag58a was measured in a three-electrode system in 0.2 M Na2SO4 aqueous solution with the coated ITO glass electrode as the working electrode, platinum wire as the auxiliary electrode, and a Ag/AgCl (3 M KCl) as the reference electrode. Compared with (iPrC6H4SAg)n-modified ITO electrode, an obvious photocurrent response was detected upon on-off cycling irradiation using 420 nm-light-emitting diode (LED) light (50 W) at the interval of 10 s, indicating a better electron and hole separation efficiency of SD/Ag58a (Figure 4b). The photocurrent density reached up to 0.19 μA cm−2, and the intensity was kept nearly constant with increased test times, indicating high photophysical stability of SD/Ag58a. SD/Ag58a was emission silent at room temperature under irradiation with a hand-held UV lamp in the solid state but could luminesce red light when placed in a liquid nitrogen environment. Based on these observations, we investigated the temperature-dependent emission behavior of SD/Ag58a. The emission spectra of SD/Ag58a were measured under 365 nm excitation from 83 to 293 K with an interval of 30 K (Figure 5a). SD/Ag58a showed a broad and temperature-independent emission peak in the near-IR (NIR) region with a λem maxima constant at 775 nm in the 83–173 K range. The possible excited state of the widened emission peak was a mixture of ligand-centered (LC), metal-to-ligand charge transfer (MLCT), and cluster-centered (CC) transitions, but the MLCT might be the predominant emission origin, albeit the other two could not be completely ruled out.51–53 The apparent boost of emission could be related to the suppression of the energy-losing nonradiative decay under cryogenic temperatures. The Commission Internationale de l'Eclairage (CIE) chromaticity coordinates were x = 0.63, y = 0.37, indicating a red emission ( Supporting Information Figure S7). The correlation between the emission intensity and temperature in the range of 83–173 K was in accordance with a linear equation: Imax = 4.45 × 105–2454.64T (R2 = 0.954, Figure 5b). When the temperature changed from 83 to 293 K, the emission intensity showed an overall attenuation of 92.92%. The emission decay time of SD/Ag58a at 83 K is shown in Figure 5b top right inset, and the average emission lifetime (70.47 μs) at microsecond level was of triplet phosphorescence nature.51 Figure 5 | (a) The emission spectra of SD/Ag58a under 365 nm excitation from 83 to 293 K. (b) The correlation between emission intensity and temperature (red line: the linear fitting in the range of 83–173 K). Insets in the bottom: the photographs of SD/Ag58a under the irradiation with hand-held ultraviolet (UV) lamp at 298 and 77 K. Inset in the top right corner: The emission decay curve of SD/Ag58a recorded at 83 K. Download figure Download PowerPoint Conclusion A ternary supramolecular cluster ( CS4H6) was initially trapped as a template in a 58-nuclei silver nanocluster. The supratetrahedral silver cage was interiorly supported via the Ag–O interactions involving the water molecules and sulfates in CS4H6 and further exteriorly protected by iPrC6H4S−, CF3COO−, and aqua ligands. Four SO42− anions and six water molecules were arranged into tetrahedron and octahedron, respectively, which were concentrical around a methanol molecule in the center and acted as a ternary supramolecular template to build the SD/Ag58a. This work not only extends the types of supramolecular cluster templates in the assembly of silver nanocluster but also offers a possible way for understanding the nucleation mechanism of solvated anions. We anticipate that such a synthetic strategy would engender a wider variety of silver nanoclusters and sulfate-based supramolecular clusters. Supporting Information Supporting information is available and includes the experimental section, X-ray crystallography, IR spectra, UV–vis spectra, EDS, ESI-MS, PXRD, and crystallographic information. Conflicts of Interest The authors declare no competing financial interest. Funding Information This work was supported financially by the National Natural Science Foundation of China (grant nos. 91961105, 21822107, 21571115, and 21827801), the Fok Ying Tong Education Foundation (grant no. 171009), the Natural Science Foundation of Shandong Province (grant nos. ZR2020ZD35, ZR2019ZD45, JQ201803, and ZR2017MB061), the Taishan Scholar Project of Shandong Province of China (grant nos. tsqn201812003 and ts20190908), the Qilu Youth Scholar Funding of Shandong University, and Project for Scientific Research Innovation Team of Young Scholar in Colleges and Universities of Shandong Province (grant no. 2019KJC028). Acknowledgments The authors acknowledge the assistance of Shandong University Structural Constituent and Physical Property Research Facilities. References 1. Negishi Y.; Nobusada K.; the and Scholar at Scholar C. O. The Silver Scholar Liu Y.; K.; of the Scholar Wang Y.; Y.; Li and of the with a Scholar Y.; and of Silver Scholar and and Scholar K.; Xue Y.; in Scholar Gao Wang of Supramolecular Scholar Liu Li K.; C. with Scholar Gao C. of an Anion in a Scholar C. A Novel of Supramolecular Scholar Y.; K.; K. of Structural in and Scholar Wang Y.; Zheng by and and Crystal Scholar Wang with an and an Scholar Wang Y.; Zheng and with Scholar K.; Silver Scholar Li Lei Wang Scholar Wang Su Liu Wang Wang Tung Sun Zheng of Silver into a Scholar Wang Y.; Li Wang Zheng Silver with Scholar C. and Crystal of the and Scholar Wang Liu of with the and of Silver Scholar Scholar of Scholar Wang Sun by in Situ from Scholar Li Wang Su Feng Tung Sun Zheng Silver by and Scholar Wang Li Liu Feng Tung Sun Supramolecular from Silver and Scholar Liu Y.; Li Gao Structural of a a Silver Scholar Shi K.; Wang Silver with Scholar Scholar Liu C. Wang Based on a = Scholar C. Silver with and Scholar C. with Scholar Gao C. of by in a Scholar Su Wang Wang Tung Sun in Scholar Wang Sun Liu Wang Tung Sun Silver in a Scholar Liu Su Wang Li Wang Tung Sun Zheng Silver Cluster by Scholar Liu Wang Anion A Silver Cluster a Scholar Liu Feng Su Wang Wang Tung Sun Zheng of and Scholar Wang Su Tung Sun Zheng an Ag6 in a Scholar Wang Su Tung Sun Zheng from to Scholar Liu Wang Wang Tung Sun of Silver Scholar Wang Su Tung Sun Zheng in Silver Scholar Li Su K.; Wang Sun Zheng Solid Ag37 Scholar Scholar in Scholar in of the Scholar Wang Liu Su Wang Tung Sun Zheng = S or and Scholar to the of Scholar K.; in Scholar Based on and Scholar C. of a Scholar C. K.; of and Scholar Information Chemical supramolecular authors acknowledge the assistance of Shandong University Structural Constituent and Physical Property Research Facilities.

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