Two Penta-Supertetrahedral Cluster-Based Chalcogenide Open

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Two Penta-Supertetrahedral Cluster-Based Chalcogenide Open Frameworks: Effect of the Cluster Spatial Connectivity on the Electron-Transport Efficiency Jing Lv,† Jiaxu Zhang,† Chaozhuang Xue,† Dandan Hu,† Xiang Wang,† Dong-Sheng Li,‡ and Tao Wu*,† †

College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, Jiangsu 215123, China College of Materials and Chemical Engineering, Hubei Provincial Collaborative Innovation Center for New Energy Microgrid, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, China Three Gorges University, Yichang, Hubei 443002, China

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‡

S Supporting Information *

Cn clusters) with different sizes and compositions through different connecting modes.13−19 Most of the chalcogenide frameworks are built from 4-connected clusters, and adjacent clusters are connected by corner-sharing mode. Only a few open frameworks were found to be constructed from low-connected clusters (n = 2, 3).10,20 Therefore, the effect of the connection pathway in metal chalcogenide frameworks on the electrontransport efficiency has never been investigated in the catalytic reactions. The main reason is that it is difficult to obtain a set of chalcogenide materials that are built from the same of clusters with the same or similar components but differing only in their connectivity mode.19,21,22 Herein, we for the first time synthesized two chalcogenide open frameworks built from penta-supertetrahedral P2 clusters with Cu−In−Sn−S components but different cluster-based connectivities. The building units of the P2-CuInSnS cluster are connected into an interrupted open chalcogenide framework (MCOF-1) through a 3-connected mode and a diamond topological framework (MCOF-2) through a 4-connected mode. According to the results of the photoelectric response and electrocatalytic oxygen reduction reaction (ORR) activity test, it can be clearly demonstrated that MCOF-2 with a higherconnected framework has faster electron-transport efficiency than MCOF-1 with a low-connected framework. Red prismatic crystals of MCOF-1 and octahedral crystals of MCOF-2 were simultaneously obtained from the solvothermal reaction of cuprous iodide, indium, stannous chloride, and sulfur in mixed solvents of 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) and (R)-(−)-2-amino-1-butanol (2-AB) at 180 °C for 10 days. The molar ratio of Cu/In/Sn in the resulting crystals was determined by inductively coupled plasma atomic emission spectroscopy results (Table S1), which were in line with the energy-dispersive spectroscopy results (Figure S1). In addition, template molecules such as protonated DBU and 2-AB residing in the crystal lattices were also confirmed by IR spectra (Figure S2). On the basis of C/H/N elemental analysis and thermogravimetric analysis (TGA; Figure S3), the formulas of MCOF-1 and MCOF-2 were determined to be [(Cu 6.2 In 10.6 Sn 9.2 S 42.5 )·9.2H + -DBU·H + -2-AB·6H 2 O] 4 and

ABSTRACT: High-degree connectivity of clusters in open-framework chalcogenide semiconductors conceptually facilitates electron mobility between clusters; however, no direct evidence was obtained to prove the prediction because of the shortage of suitable structure models among such systems. Herein, two open-framework chalcogenides built from the same types of heterometallic P2-CuInSnS clusters but with different spatial connectivities of clusters were obtained, in which 3-connected clusters are assembled into a 3D framework with SrSi2 topology (MCOF-1) and 4-connected clusters (μ4-P2) are arranged into diamond topology (MCOF-2). Compared to MCOF-1, MCOF-2 exhibits a relatively rapid photocurrent response, good reproducibility, and high electrocatalytic oxygen reduction reaction activity. This work substantially demonstrates that cluster-based chalcogenide frameworks with higher-degree cluster connectivity possess faster electron-transport efficiency between adjacent clusters relative to low-connected ones with the same building units.

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lectron-transport efficiency within the catalysts is thought to be one of the important factors in controlling the performance of photocatalysis, electrocatalysis, and photoelectrocatalysis.1−7 In general, three-dimensional dense-phase semiconducting materials have more complex connectivity, which endows them with relatively higher conductivity and electron-transport efficiency than those of low-dimensional materials with the same components.8,9 However, it is difficult to intuitively establish the accurate structure−activity relationship between the charge-transfer pathway and transfer efficiency at the microscopic scale because of their complex connection modes. As the hollowed-out counterparts of dense-phase II−VI semiconductors, cluster-based open-framework metal chalcogenide materials could be ideal models for exploring the structure−activity relationship between the pathway characteristics and charge-transfer efficiency because of their well-defined structure and cluster-based connectivity.10−12 During the past 20 years, a series of metal chalcogenide open frameworks have been built from supertetrahedral clusters (including Tn, Pn, and © XXXX American Chemical Society

Received: December 17, 2018

A

DOI: 10.1021/acs.inorgchem.8b03503 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry [(Cu6In12.5Sn7.5S42)·1.4DBU·10.5H+-2-AB·6H2O]2, respectively. The phase purity of the as-synthesized compounds was confirmed by powder X-ray diffraction (PXRD) measurements (Figure S4). Single-crystal X-ray diffraction (SCXRD) analysis reveals that MCOF-1 and MCOF-2 consist of the same types of P2CuInSnS clusters but crystallize in different space groups of P43212 and Pbca, respectively. A typical isolated P2 cluster with a formula of [M26S44] (M = Cu, In, and Sn here) is usually regarded as an assembly from four T2 clusters at the edge and one anti-T2 at the center, as shown in Figure 1a. According to

respectively (Figure 2). In the srs chiral framework, P2 clusters are interconnected via corner S sites to form right- and left-

Figure 2. 3D open frameworks of MCOF-1 with chiral srs topology (a) and MCOF-2 with double-interpenetrated dia topology (b).

handed helices, which are parallel to the c axis (Figure S5). One full turn of the right- and left-handed helices contains four and eight clusters, respectively. Each right-handed helix connects to four left-handed helices. In cluster-based chalcogenide open frameworks, the chiral nets were only observed in Cd−S−SPh systems, which were built by the C1 or P1 cluster.26 Although MCOF-1 and MCOF-2 have different framework topologies, their framework densities (defined as the number of P2 clusters per 1000 Å3) are similar: 6.27 for MCOF-1 and 6.65 MCOF-2. The void spaces of MCOF-1 and MCOF-2 were calculated as 62.1% and 59.8%, respectively, according to the program PLATON.27 Unfortunately, MCOF-1 and MCOF-2 cannot keep their original structures after Cs+-exchange experiments (Figure S6). By analyzing the frameworks and components of the above two chalcogenide semiconductors, we observed that the main difference between them is the spatial connectivity of the clusters. Thus, they can be used as good models for exploring the effect of the cluster connectivity on the charge-transfer efficiency. First, optical absorption measurements reveal that the band gaps of MCOF-1 and MCOF-2 are 1.83 and 1.85 eV (Figure 3a), respectively. Their similar band structure indicates that the spatial connectivity of P2 clusters has no obvious influence on their optical absorption capability. Then, using a three-electrode photoelectrochemical cell equipped with an on−off mode of illumination, the photoelectric response performances of MCOF-1 and MCOF-2 were also investigated. Figure 3b shows the rapid response and good reproducibility of MCOF-2 under pulsed illumination at 0.4 V bias potential. This result suggests that MCOF-2 with higher-connected P2 clusters has a better electron-transport efficiency than MCOF-1. In

Figure 1. (a) Penta-supertetrahedral P2-CuInSnS cluster constructed from four supertetrahedron T2 clusters and one anti-T2 cluster. (b) 3connected P2 (μ3-P2) cluster in MCOF-1. (c) 4-connected P2 (μ4-P2) cluster in MCOF-2.

Pauling’s electrostatic bond valence rule and SCXRD and elemental analysis, six metal sites at the anti-T2 cluster are rationally recognized to be occupied by Cu+ ions. The bond length Cu−S and bond angle S−Cu−S are in the ranges of 2.256(4)−2.432(3) Å and 98.2(15)−116.3(7)°, respectively. The angle Sn−S−Sn for the bridging S sites is in the ranges of 108.435(31)−114.107(24)° in MCOF-1 and 105.686(19)− 117.913(25)° in MCOF-2, which all both in agreement with the previously reported values.23−25 However, because of similar scattering factors between the In and Sn atoms, the absolute sites of In and Sn at four T2 clusters cannot be differentiated through SCXRD analysis, and they are randomly distributed on four T2 clusters. The most remarkable structural feature of open framework MCOF-1 is the interrupted connectivity, in which each P2 cluster connects with three adjacent P2 clusters via a cornersharing mode, and the remaining one is dangling, which results in an interrupted open framework (Figure 1b). Actually, such cluster-based chalcogenide open frameworks with interrupted sites are very rare, which were only observed in CSZ-510 and SCU-3620 built from T2 and T3 clusters, respectively. Different from MCOF-1, each P2 cluster in MCOF-2 is connected to four P2 clusters through a corner-sharing mode (Figure 1c). When each P2 cluster is treated as a node, MCOF-1 and MCOF-2 can be simplified into chiral srs and double-diamond topologies, B

DOI: 10.1021/acs.inorgchem.8b03503 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

Figure 4. (a) RRDE voltammograms for MCOF-1/CB and 2/CB at a rotation speed of 1600 rpm in an O2-saturated 0.1 M KOH solution. (b) Peroxide yield (%) and electron-transfer number (n) at various potentials for MCOF-1/CB and MCOF-2/CB derived from RRDE measurement.

with different spatial connectivities were obtained for the first time, in which μ3-P2 clusters are assembled into a 3D framework with srs-type topology (MCOF-1) and μ4-P2 clusters are arranged into a higher-connected diamond topology (MCOF2). Because of more electron-transport pathways, MCOF-2 with higher connectivity obviously exhibited faster electron-transfer efficiency than MCOF-1 with low connectivity, according to the results of the photoelectric response and ORR property. This study experimentally emphasizes the influence of the spatial connectivity in open frameworks on the electron-transport efficiency.

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Figure 3. (a) Tauc plots of MCOF-1 and MCOF-2 derived from UV− vis diffuse-reflectance spectra. (b) Photocurrent response curves of MCOF-1 and MCOF-2.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b03503. Experimental characterizations, additional structural presentations, SEM, EDS, FT-IR, TGA, PXRD patterns, and SCXRD data (PDF)

addition, the resistivity of MCOF-1 (8.97 kΩ·cm) is higher than that of MCOF-2 (6.88 kΩ·cm), which further demonstrates that higher connectivity facilitates fast electron-transport efficiency. Given that efficient oxygen reduction electrocatalysis is inextricably linked to the electron-transport efficiency within the catalysts, we investigated the activity on oxygen reduction catalytic reactions of two cluster-based open frameworks to further demonstrate the connectivity-dependent electron-transport efficiency between them. As shown in Figure S7, the cyclic voltammetry curves of MCOF-1/CB and MCOF-2/CB display an obviously enhanced cathodic peak at 0.80 V in O2-saturated 0.1 M KOH. However, at the same potential when the electrolyte was saturated with Ar, a much smaller reduction peak was obtained, which suggested that both MCOF-1 and MCOF-2 show potential electrocatalytic activity for ORR. In addition, rotating-ring-disk-electrode (RRDE) voltammetry was used to further explore the reaction kinetics and pathways. As shown in Figure 4a, the ring current is significantly smaller than the disk current, and MCOF-2/CB has a smaller initial potential, indicating that it has better catalytic activity. At a potential range of 0.35−0.55 V, the average n of MCOF-2/CB is 3.51, and the corresponding hydrogen peroxide yield is 25%, which are better than those of MCOF-1/CB (n, 3.36; yield, 31%; Figure 4b). Furthermore, alternating-current impedance spectrometry was used to prove the charge-transport efficiency. It is obvious that MCOF-2/CB has a lower electrical resistance than MCOF-1/CB and exhibits higher electrical conductivity (Figure S8). In summary, two open-framework chalcogenides constructed from the same types of heterometallic P2-CuInSnS clusters but

Accession Codes

CCDC 1864627 and 1885358 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

Xiang Wang: 0000-0001-7354-6491 Dong-Sheng Li: 0000-0003-1283-6334 Tao Wu: 0000-0003-4443-1227 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the National Natural Science Foundation of China (Grants 21671142 and 21875150), Jiangsu Province Natural Science Fund for Distinguished Young Scholars (Grant BK20160006), and the Priority Academic Program Development of Jiangsu Higher Education Institutions. C

DOI: 10.1021/acs.inorgchem.8b03503 Inorg. Chem. XXXX, XXX, XXX−XXX

Communication

Inorganic Chemistry

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DOI: 10.1021/acs.inorgchem.8b03503 Inorg. Chem. XXXX, XXX, XXX−XXX