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Discrete supertetrahedral T3 InQ Clusters (Q = S, S/Se, Se, Se/Te): Ionothermal Syntheses and Tunable Optical and Photodegradation Properties Nan-Nan Shen, Bing Hu, Chu-Chu Cheng, Guo-Dong Zou, Qianqian Hu, Cheng-Feng Du, Jian-Rong Li, and Xiao-Ying Huang Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01437 • Publication Date (Web): 09 Jan 2018 Downloaded from http://pubs.acs.org on January 10, 2018

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Crystal Growth & Design

Discrete supertetrahedral T3 InQ Clusters (Q = S, S/Se, Se, Se/Te): Ionothermal Syntheses and Tunable Optical and Photodegradation Properties Nan-Nan Shen,a,b Bing Hu,a Chu-Chu Cheng,c Guo-Dong Zou,a Qian-Qian Hu,a Cheng-Feng Du,a Jian-Rong Li,*a and Xiao-Ying Huang*a a

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, P. R. China. b

c

University of Chinese academy of Sciences, Beijing 100049, P. R. China.

College of Chemistry, Fuzhou University, Fuzhou, Fujian, 350116, P.R. China.

ABSTRACT: Presented are the ionothermal syntheses, characterizations and photodegradation properties

of

four

isostructural

chalcogenidometalate

compounds,

namely

[Bmmim]5[In10Q16Cl3(Bim)] (Q = S (IL-InS-1), S7.12Se8.88 (IL-InSSe-2), Se (IL-InSe-3), Se13.80Te2.20 (IL-InSeTe-4); Bmmim = 1-butyl-2,3-dimethylimidazolium, Bim = 1-butyl-2methylimidazole). According to the single-crystal X-ray diffraction analysis, the title compounds belong to the C2/c space group and feature isolated supertetrahedral T3 anionic units of [In10Q16Cl3(Bim)]5– stabilized by [Bmmim]+ cations. The ionic liquid not only provided the [Bmmim]+ as the counter ions but also acted as the reactive solvent releasing [Bim] ligands that

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Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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are covalently bonded to In atoms. Unlike the widely-reported extended frameworks that contain T3 InS/Se as building units, IL-InSe-3 represents the first example of discrete T3 InSe clusters, and InTe-based discrete T3 cluster (IL-InSeTe-4) was characterized for the first time. The optical absorption edges of the title compounds showed gradual red-shifts along with the change of chalcogens from S, S/Se, Se, to Se/Te. As a result, their photocatalytic activities were tunable with the optical response moving from ultraviolet (UV) to visible light region.

INTRODUCTION Supertetrahedral chalcogenide clusters (e.g. Tn) represent a family of unique structural units that can be used as the secondary building units (SBU) for the construction of metal chalcogenide extended frameworks.1-5 On the other hand, the discrete Tn cluster-like structures can be regarded as the smallest semiconductor quantum dots;6-12 knowledge of their well-defined size, chemical composition and exact structure may provide an access to the study of structureproperty relationship in nanoscale.13-15 Indium, a 13 group metal element, has been widely utilized as a component in the synthesis of supertetrahedral chalcogenide clusters, due to its tendency to form tetrahedral coordination geometry with chalcogens.16 Among them, the [In10Q20]10– (Q = S, Se) T3 clusters have been found to be one of the most popular SBUs for the construction of multidimensional chalcogenides. For instance, in 1998, Parise et al. firstly reported an InS T3-based three-dimensional (3D) interpenetrating diamond net of DMA-InSSB117 followed by the isolation of two isomers of DEA-InS-SB1/SB2 in 2000.18 The anionic unit of DEA-InS-SB1 was similar to that of DMA-InS-SB1, while a layered arrangement of cornerlinked [In10S20]10– clusters was found in DEA-InS-SB2. In 1999, three 3D architectures with large cavities constructed from the same T3 InS SBUs were synthesized by Yaghi et al.1 In 2002, Feng et al. reported a family of amine-directed 3D frameworks assembled by [In10Se20]


2

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clusters,19 and in 2011, they explored a family of 3D four-connected superlattices consisting of T3 InS clusters linked by imidazole derivatives.20 Since 2010, Dai et al. has developed a series of 1D and 2D polymeric InS T3 clusters integrated with transition metal coordination complex cations.9–10,

21–23

Compared with the significant progress in constructing extended structures

based on T3 InS/Se clusters, however, only a limit number of isolated T3 InS clusters have been reported9–11 and their selenide/telluride analogues in discrete form have not been documented. Doping is one of the most powerful ways to regulate the optical, electronic, and catalytic properties of metal chalcogenides. For example, Wu et al. found that atomically precise doping could be achieved in T4 and T5 chalcogenide clusters, which resulted in the enhancement of their luminescent, electrochemiluminescent and catalytic properties.24–28 In contrast to metal sulfides, the selenides and tellurides tend to have smaller band gaps. Therefore, the development of Tn–based chalcogenide materials as well as their multi-chalcogen solid solutions by element doping is expected to be an effective way to tuning the band structures and physical/chemical properties.29 Ionothermal synthesis that is carried out in ionic liquids under a sealed system, has gained tremendous interest in preparing inorganic materials owing to the unique properties of ionic liquids (ILs), such as generally negligible vapour pressure, wide liquid range, good solubility, good chemical and thermal stability.30–32 In contrast to traditional molecular solvents, the ionic liquids possess unique ionic reaction environment, which may contribute to the formation of novel compounds that are inaccessible by using molecular solvents. So far, many zeolites,33–35 metal-organic frameworks,35–39 inorganic nanostructures,40–41 as well as metal chalcogenide nanoparticles,42 have been prepared in the ionic liquids. In recent years, the researches on the synthesis of crystalline chalcogenides via ionothermal approaches have increased rapidly.43–50


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Nevertheless, utilization of ionic liquids in the synthesis of metal chalcogenide Tn clusters is still in its infancy. In 2013, Dai et al. reported several extended structures assembled by T3 or T4 clusters under solvothermal conditions with the ionic liquids as auxiliary solvents. However, the ionic liquids have not been included in the final structures.23 Our group has developed new strategies for the syntheses of Tn clusters in ionic liquids, achieving a series of discrete CuMS (M = Ga, In) T5 clusters8 and some extended structures based on InSnSe T2,2 units.51 In order to explore the synthesis of discrete Tn clusters, herein the reactions of In and chalcogens were performed in the ionic liquid of 1-butyl-2,3-dimethylimidazolium chloride ([Bmmim]Cl).

Four

isostructural

chalcogenidometalate

compounds,

namely

[Bmmim]5[In10Q16Cl3(Bim)] (Q = S (IL-InS-1), S7.12Se8.88 (IL-InSSe-2), Se (IL-InSe-3), Se13.80Te2.20 (IL-InSeTe-4); Bim = 1-butyl-2-methylimidazole) were obtained. The structures feature isolated T3 anionic units of [In10Q16Cl3(Bim)]5– stabilized by [Bmmim]+ cations. ILInSe-3 represents the first example of discrete T3 InSe clusters while the InTe-based discrete T3 cluster (IL-InSeTe-4) was characterized for the first time. In the synthesis, the ionic liquid was the solvent and provided its cation [Bmmim]+ to enter the final structure as the counter ion; in addition, its decomposition released the [Bim] as a neutral terminal ligand for the corner In atom of T3 cluster. The development of multi-chalcogen solid solutions by element doping is desirable to tune the electronic and optical properties of the resulting chalcogenide compounds. EXPERIMENTAL SECTION Materials and physical measurements Indium and tellurium powder (99.99%) were purchased from Xin Long Tellurium & Technique Development Co., Ltd. (Sichuan, China); selenium powder (AR) was purchased from


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Yingda Rare Chemical Regents Factory (Tianjin, China); 1-butyl-2,3-dimethylimidazolium chloride ([Bmmim]Cl) was purchased from Lanzhou Yulu Fine Chemical Co., LTD. (Lanzhou, China); methylamine (25–30% aqueous solution) and sulfur powder (CP) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All the chemicals were used without further purification. Elemental analyses of C, H, and N were performed using a German Elementary Vario EL III instrument. Energy–dispersive spectroscopy (EDS) and the elemental distribution maps were recorded on a JEOL JSM–6700F scanning electron microscope (SEM). Powder X–ray diffraction (PXRD) patterns were measured in the angular range of 2θ = 3–65° on a Rigaku Miniflex II diffractometer by using CuKα radiation. The solid state optical diffuse reflectance spectra were performed at room temperature using a Shimadzu UV–2600 spectrometer (for ILInS-1, IL-InSSe-2 and IL-InSeTe-4) and PE Lambda 900 UV/Vis spectrometer (for IL-InSe-3) in the range of 200–800 nm with a BaSO4 plate as a standard (100% reflectance). The absorption data were calculated from reflectance spectra by using the Kubelka–Munk function α/S = (1 – R)2/2R, where α is the absorption coefficient, S is the scattering coefficient which is practically independent of wavelength when the particle size is larger than 5 µm, and R is the reflectance. Thermogravimetric analysis (TGA) was carried out on a NETZSCH STA 449F3 unit at a heating rate of 5 K min–1 under a N2 atmosphere from 25 to 700 °C. Fourier-transform infrared (FTIR) spectroscopy was performed on a Bruker Vertex 70 FTIR spectrometer photometer as a KBr pellet within the range of 4000–400 cm–1. Syntheses


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[Bmmim]5[In10S16Cl3(Bim)] (IL-InS-1). A mixture of In powder (0.115 g; 1.00 mmol), S (0.058 g; 1.81 mmol) and [Bmmim]Cl (0.50 g; 2.65 mmol) was loaded into a 10 mL Teflon-lined stainless steel autoclave. 0.20 mL methylamine (25–30% aqueous solution) was added to the autoclave as an auxiliary solvent. The container was closed, heated at 160 °C for 5 days, and then cooled to room temperature at a cooling rate of 0.1 K min–1. The product was washed with ethanol for several times to remove the residual liquids, then dried in air at room temperature. Colorless block-like crystals were isolated by manually selection (Yield: 0.121 g; 45.3% based on In). Elemental analysis, calcd. (%) for C53H99N12Cl3In10S16: C 23.82, H 3.73, N 6.29; found: C 24.16, H 3.87, N 6.19. [Bmmim]5[In10S7.12Se8.88Cl3(Bim)] (IL-InSSe-2). In powder (0.115 g; 1 mmol), S powder (0.028 g; 0.87 mmol), Se powder (0.071 g; 0.90 mmol), [Bmmim]Cl (0.50 g; 2.65 mmol), 0.20 mL methylamine (25–30% aqueous solution) were sealed in a 10 mL Teflon-lined stainless steel autoclave. After heating for 5 days at 160 °C, the autoclave was cooled at an average rate of 0.1 K min–1 to room temperature. The product was washed with ethanol for several times to remove the residual liquids, then dried in air at room temperature. Light-yellow block-like crystals of ILInSSe-2 were isolated by manually selection (Yield: 0.167 g; 53.9% based on In). Elemental analysis, calcd. (%) for C53H99N12Cl3In10S7.15Se8.85: C 20.61, H 3.23, N 5.44; found: C 20.93, H 3.07, N 5.50. [Bmmim]5[In10Se16Cl3(Bim)] (IL-InSe-3). A similar method used in the syntheses of IL-InS-1 was applied, except that S powder was replaced by Se powder (0.142 g; 1.80 mmol). The product was washed with ethanol to remove the residual liquids and then dried in air at room temperature, giving rise to a single phase of yellow block–like crystals (Yield 0.252 g; 73.6% based on In).


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Elemental analysis, calcd. (%) for C53H99N12Cl3In10Se16: C 18.60, H 2.92, N 4.91; found: C 18.92, H 3.08, N 5.02. [Bmmim]5[In10Se13.80Te2.20Cl3(Bim)] (IL-InSeTe-4). In powder (0.115 g; 1 mmol), Se powder (0.071 g; 0.90 mmol), Te powder (0.115 g; 0.90 mmol), [Bmmim]Cl (0.50 g; 2.65 mmol), 0.20 mL methylamine (25–30% aqueous solution) were sealed in a 10 mL Teflon-lined stainless steel autoclave. After heating for 5 days at 180 °C, the autoclave was cooled at an average rate of 0.1 K min–1 to room temperature. After washing with ethanol several times to remove the residual liquids, brown block–like crystals were obtained by manually selection (Yield 0.132 g; 37.0% based on In). Elemental analyses, calcd. (%) for C53H99N12Cl3In10Se13.80Te2.20: C 18.04, H 2.83, N 4.76; found: C 18.03, H 2.82, N 4.69. Single Crystal X-ray Diffraction Suitable single crystals of the four title compounds were carefully selected under optical microscope and mounted with epoxy on a glass fiber. Data of compounds IL-InS-1 and ILInSe-3 were collected on Shanghai Synchrotron Radiation Facility (SSRF) (λ = 0.65251 Å) at 100 K. Data of compounds IL-InSSe-2 and IL-InSeTe-4 were collected on a Rigaku MM007 CCD diffractometer using graphite-monochromated MoKα radiation (λ = 0.71073 Å) at 298 K. The structures were solved by directed methods and refined by full-matrix least-squares on F2 using the SHELX-2016 program package.52 The asymmetric unit contains four and two-half [Bmmim]+ cations in addition to the anionic T3 unit. The organic cations and the [Bim] ligands in the anion unit are highly disordered. Some of the C, H and N atoms on three of the four unique [Bmmim]+ cations, the Bim ligands and one of two half-[Bmmim]+ are split into two positions with equal S.O.Fs., while the remaining half-[Bmmim]+ is also disordered with half SOF. Thus


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several restraints (ISOR, DELU, DFIX, FLAT, SIMU, SADI) was included in the structural refinements to obtain reasonable chemical models. Non-hydrogen atoms were refined anisotropically, and the hydrogen atoms bonded to C atoms were positioned with idealized geometries. As for IL-InSSe-2 and IL-InSeTe-4, initial refinements confirmed that all the sixteen crystallographically independent chalcogen sites might contain both Se and S (or Se and Te), thus the S.O.Fs, and positions of the Se/S (or Se/Te) sites were refined while EADP was applied for each Se/S (or Se/Te) site. As a result, the resultant formulae from structural refinements with refined S: Se (or Se:Te) ratios match with that deduced from the EA results. The empirical formulae were also verified by EDS and TGA. The crystallographic data and details of structural-refinement parameters for the title compounds are given in Table 1. Selected bond lengths and angles are listed in Table S1 in the ESI. Detailed process of photo-degradation of methyl orange (MO) The photocatalytic reactions were performed in a quartz reaction vessel with a flat section of 18 cm2 by mixing the as-prepared samples (30 mg) with the MO aqueous solution (100 mL, 10–5 M). Before the photocatalytic experiments, sufficient grinding was necessary for all the as-prepared catalysts. Before irradiation, the mixture was magnetic stirred in the dark environment for 60 min to achieve adsorption/desorption equilibrium between the sample and solution. Under the UV light irradiation, a 300 W Xe lamp (Perfect Light, PLS– SXE300C) with an appropriate long pass cut-off filter was used as the radiation source. In the visible light irradiation process, another 300 W Xe lamp (Perfect Light, PLS– SXE300UV) with a 420 nm cut off filter was used. Every 20 min, 5 mL of the suspension was sampled from the reaction system and centrifuged at the speed of 9000 rpm min–1 for 2

min.

The

supernatant

was

monitored

on

a

Shimadzu

UV–2600

UV–Vis


8

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spectrophotometer to evaluate the capability of degradation of MO. After exposed to light irradiation for several hours, the photocatalysts were separated from the suspension by centrifugation and then analysed by PXRD to verify its components. Meanwhile, blank experiments in the absence of as-prepared samples were carried out via the similar method. RESULTS AND DISCUSSION Synthesis The title compounds were prepared by similar redox reactions among Indium and chalcogens under ionothermal conditions. The optimized molar ratio of indium and chalcogen is 1: 1.8. The effects of temperature, IL, and assisted solvent on the syntheses of title compounds have been explored. Taking IL-InSe-3 as an example, detailed information of various reactions for its preparation is listed in Table S2 in the ESI. IL-InSe-3 could be obtained at 160–180 ˚C in [Bmmim]Cl mixed with methylamine (25–30% aqueous solution), and programmed cooling process was necessary for obtaining the pure phase. The molar ratio of ionic liquid and indium element could be varied between 2.6: 1 and 3.2: 1, while the ratio beyond this range might be disadvantageous for the acquirement of IL-InSe-3. Auxiliary solvent was indispensable to decrease the viscosity of ionic liquid in this reaction system. Several kinds of amines were selected, because they have not only been widely demonstrated as good solvents and template agents, but also offer alkaline environments for the crystallization of metal chalcogenides. Yellow block-like crystals were obtained only in the presence of methylamine (25–30% aqueous solution) with the appropriate volume of 0.20 mL, while some unknown phases or crystals of IL-


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InSe-3 with vast impurities were obtained in the reactions with other auxiliary solvents. Similar reaction conditions were employed in the preparation of IL-InS-1, IL-InSSe-2 and IL-InSeTe-4. It has been demonstrated that supertetrahedral chalcogenide clusters tend to self-assemble generating extended structures under solvothermal approaches.20 However, it seems to be different when the reactions occur in the unique ionothermal conditions with the formation of discrete Tn clusters.8 In this study, it is anticipated that the [Bmmim]+ cations serve as an aromatic environment to stabilize isolated T3 clusters and hinder the formation of higher condensed phases (as described in more detail in crystal structural descriptions section). Furthermore, the terminal sites of T3 cluster were occupied by monodentate Cl– and [Bim] groups, rather than bridging Q2– ions. Moreover, the neutral [Bim] ligand covalently bonded to corner In atoms also decreases the electronegativity of T3 cluster, which might also contribute to the generation of InQ T3 clusters in discrete form. Noticeably, both the [Bim] and Cl– moieties originated from [Bmmim]Cl, and [Bim] ligand was generated by the in situ decomposition of [Bmmim]Cl; similar phenomena have been reported before.8 Crystal structure descriptions Single crystal structural analyses confirm that the four title compounds are isostructural, belonging to the space group of C2/c. The asymmetric unit contains one discrete T3 anion [In10Q16Cl3(Bim)]5– (Q = S, S7.12Se8.88, Se, or Se13.80Te2.20) with the size of about 1.2 nm, four and two half-[Bmmim]+ cations. As shown in Figure 1, in the [In10Q16Cl3(Bim)]5– anion cluster, all the In atoms adopt tetrahedral coordination geometry and the chalcogenide atoms exhibit biand tri-bridging modes, while the corner chalcogenide atoms for regular T3 cluster were substituted by three Cl– ions and one [Bim] moiety generated by in situ decomposition of [Bmmim]+ cations. Obviously, the bond lengths of the bi-bridging In–Q modes are shorter than


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those of tri-bridging types, which are in accordance with the results in previously reported T3 clusters19 (for more details, see Table S1 in the ESI). Since they are isostructural to each other, only the packing structure of IL-InSe-3 is described in detail. As shown in Fig. 1b, the anion units in IL-InSe-3 are alternatingly arranged along the b axis with one of the tetrahedral faces of T3 cluster parallel to those of two adjacent clusters, forming a zipper-like structure and the [Bim] ligands point outwards. Three kinds of [Bmmim]+ cations are located in the spaces between neighboring tetrahedral faces. Such zipper-like structures are parallel to each other, stacking along the a and c axis (Figure 1c), respectively. The remaining three kinds of cations surround the zippers, with their imidazole rings parallel to the tetrahedral faces of T3 clusters; the shortest distances between imidazole rings and Se atoms on the tetrahedral faces is 3.2845(5) Å, indicating the presence of anion-π interactions (Table S3 and Figure S1 in the ESI). These weak supramolecular interactions may help stabilize the isolated clusters. Energy dispersive X-ray spectroscopy (EDS) analyses on IL-InSSe-2 and IL-InSeTe-4 confirm the coexistence of two types of chalcogens. (Figure S2 in the ESI) and the elemental distribution maps of IL-InSSe-2 and IL-InSeTe-4 are shown in Figure 2. In company with the results from crystal structure refinements and element analyses, the final formulae of IL-InSSe-2 and

IL-InSeTe-4

were

determined

as

[Bmmim]5[In10S7.12Se8.88Cl3(Bim)]

and

[Bmmim]5[In10Se13.80Te2.20Cl3(Bim)], respectively. Although isolated T3 InS clusters have been reported,9–11 this is the first time for the successful synthesis of discrete T3 InSe cluster. Moreover, as indicated by the previous researches, the InTe-containing supertetrahedral clusters are quite rare and only a limited number of extended frameworks based on T2-InTe53–56 and T3MInTe (M = other metal ions than In, e.g. Cd2+)55-56 clusters have been reported. While the


11


discrete InTe clusters are generally in non-supertetrahedral forms, such as [In3Te7]5–

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57

,

[In18Te30(L)6]6– 58-59 and [In8Te12(L)4]60 (L = organic amine). Hence, IL-InSeTe-4 represents the first realization of the incorporation of Te into discrete InTe-T3 cluster. PXRD and thermal stability The characterizations were conducted on the pure phases that were prepared by carefully picking out the crystals by hand from the as-prepared samples. As shown in Figure 3, although the experimental PXRD patterns for the title compounds somehow exhibit preferred orientation, they yield considerable agreement with the simulated ones from single-crystal X-ray structure analyses. The comparative PXRD patterns of the title compounds are further depicted in Figure S3 in the ESI; obviously, the diffraction patterns are similar to each other while the peaks in the PXRD patterns shift a little from high angles in IL-InS-1 to lower angles in IL-InSeTe-4 owing to the incorporation of larger chalcogen atoms, further indicating they are isostructural to each other. Thermogravimetric analyses under the N2 atmosphere showed that all compounds were stable up to 180 °C and the decomposition processes were similar, with multiple steps of weight reduction during the temperature range of 180-450 °C. As shown in Figure S4 in the ESI, the total weight loss of 40.15%, 35.72%, 34.26%, 32.82% for the four title compounds are attributed to the removal of organic components, HCl, and H2Q (Q = S, Se, Te) molecules, close to the theoretical value of 40.3%(for IL-InS-1), 33.78% (for IL-InSSe-2), 31.84% (for IL-InSe-3), 31.88% (for IL-InSeTe-4), respectively. The main post-TGA residues were identified as the phase of In2S3 for IL-InS-1, the mixture of In2S3 and In2Se3 for IL-InSSe-2, In2Se3 for IL-InSe3 and IL-InSeTe-4 by PXRD (Figure S5 in the ESI), respectively. Optical properties


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The solid state optical absorption spectra of title compounds, measured by diffuse reflectance technique, are shown in Figure 4. The band gaps, estimated from the absorption edges, are 3.31 eV for IL-InS-1, 3.00 eV for IL-InSSe-2, 2.89 eV for IL-InSe-3, 2.65 eV for IL-InSeTe-4, respectively, which are in agreement with their crystal colours. Compared with the bulk In2S3 (2.3 eV),61 In2Se3 (1.36 eV),62 In2Te3 (~1.0 eV),60 all the three compounds show a blue-shift of the absorption edges with respect to their counterparts. In addition, the absorption edge of ILInS-1 is comparable with that of polymeric and discrete InS-T3 clusters (e.g. SCIF-3 (3.35 eV),20 SCIF-7 (3.43 eV),20 Mp-InS (3.20 eV),9 Mb-InS (3.30 eV).1 It deserves to note that the absorption edges of the title compounds monotonically red-shift from UV to visible region along with the components changing from S, S/Se, Se, to Se/Te, and the difference is as large as 0.66 eV. Photodegradation Properties Indium-based chalcogenide nanomaterials have been widely used as the photocatalysts for hydrogen generation from water.63-66 By contrast, the studies on the photocatalytic performance of crystalline indium-based chalcogenidometalates were rare.29,

51, 54, 67-68

Comparative

experiments were performed to evaluate the photocatalysis capabilities of the title compounds in the photodegradation of organic pollutant under ultraviolet (UV) and visible light irradiation, by using MO as a model dye contaminant. The degradation efficiencies are defined as C/C0, where C and C0 represent the remnant and initial concentration of MO, respectively. The values of C0 and C of the selected samples were monitored by examining the intensities in the maximal absorption (464 nm for MO) in UV-Vis spectra. Blank experiments in the absence of the catalysts under UV and visible light demonstrated that it was insignificant for the selfphotodegradation of MO.


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Figures 5a and 5b show the degradation rates of MO over as-synthesized samples under UV and visible light illumination, respectively. Obviously, the photocatalytic activity of title T3 InS cluster was higher than that of S/Se, Se or Se/Te-containing clusters under UV light irradiation. The degradation ratio of MO over IL-InS-1 reached nearly 95.4% after 80 min under UV light irradiation, while it needed 120 min for IL-InSSe-2 and IL-InSe-3 to reach about 95.7%. For IL-InSeTe-4, the degradation ratio of MO only reached about 69.4% after 120 min illumination (Figure 5a). Nevertheless, the results under visible light illumination were totally different. As shown in the Figure 5b, after 3-hour illumination, the degradation ratios of MO were 94.1% for IL-InSeTe-4, 86.4% for IL-InSe-3, 7.72% for IL-InSSe-2 and 4.36% for IL-InS-1, respectively. The different orders of degradation abilities for MO of the four title compounds under UV and visible light irradiation were attributed to their different band structures.29 Along with the variation of chalcogens from S, S/Se, Se, to Se/Te, the absorption edges of as-prepared samples exhibit a red shift, thus promoting the transformation of optical absorption response from UV to visible light region in photocatalytic processes. The PXRD patterns of title compounds after selected photodegradation processes demonstrated that the phase variations did not occur, while the crystallinity of as-prepared samples decreased, Figure S7 in the ESI. CONCLUSIONS In summary, by means of one-pot ionothermal methods, four isolated InQ T3 clusters were obtained. The ionic liquid acted as not only solvent and counter ion, but also reactive agent releasing [Bim] ligand covalently bonded to In atom. It is the first time for the successful synthesis of discrete T3 InSe cluster (IL-InSe-3) and realization of the incorporation of Te into discrete T3 clusters (IL-InSeTe-4). Variations of the chalcogen content from S, Se to Se/Te led to a red shift of absorption edges and consequently tuneable photocatalytic activities with a


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transformation of optical response from UV to visible light region. Introducing imidazolium cations of ionic liquids into the structures may hinder the aggregation of Tn cluster, preventing them from forming polymeric framework structures. Hence, we envisage that more discrete Tn supertetrahedral compounds can be prepared by such ionothermal approaches.


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FIGURES

Figure 1. (a) Crystallograhpically asymmetric unit of IL-InSe-3. (b) A zipper-like structure formed by isolated clusters stacking along the b axis with the [Bmmim]+ cations located in the spaces of neighbouring tetrahedral faces. (c) View of IL-InSe-3 along the b axis showing the arrangement of zipper-like structures (one of which is circled) and the remaining [Bmmim]+ cations; the [Bmmim]+ cations within the zipper-like structures are omitted for clarity. All the hydrogen atoms are omitted for clarity. (d)-(f) show the T3 anionic clusters in IL-InS-1, ILInSSe-2, and IL-InSeTe-4, respectively.

Figure 2. SEM images and elemental distribution maps of IL-InSSe-2 and IL-InSeTe-4.


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Figure 3. PXRD patterns of the four title compounds compared to the simulated ones from the single-crystal X-ray data, respectively.

Figure 4. Solid-state optical absorption spectra of the four title compounds. Inset: crystal photos of the four title compounds.


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Figure 5. Photodegradation of MO monitored as the normalized change in concentration as a function of irradiation time under (a) UV light and (b) visible light.


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Table 1. Crystallographic data for IL-InSe-3. IL-InS-1 Empirical formula CCDC Formula Mass Crystal system Space group a/Å b/Å c/Å β/° V/Å3 Z T/K λ/Å F(000) ρcalcd/g cm–3 µ/mm–1 Measured refls. Independent refls. No. of parameters Rint

IL-InSSe-2

IL-InSe-3

IL-InSeTe-4

C53H99N12Cl3In10S1C53H99Cl3N12In10S7 C53H99N12Cl3In10S C53H99Cl3In10N12S e16 e13.80Te2.20 6 .12Se8.88 1579742 2671.95 monoclinic C2/c 39.879(8) 16.750(3) 29.064(6) 110.22(3) 18218(7) 8 100(2) 0.65251 10384 1.948 2.325 345700 23967 1306 0.056

1579743 3088.18 monoclinic C2/c 41.360(15) 17.025(6) 29.322(11) 108.563(7) 19573(12) 8 298(2) 0.71073 11662 2.096 5.881 75042 21753 1370 0.0616

1503814 3422.35 monoclinic C2/c 41.314(8) 16.952(3) 28.921(6) 107.76(3) 19289(7) 8 100(2) 0.65251 12688 2.329 8.401 186599 25500 1306 0.057

1579744 3529.48 monoclinic C2/c 42.578(17) 17.262(6) 29.765(13) 108.609(9) 20733(14) 8 298(2) 0.71073 13005 2.261 7.745 78499 23051 1370 0.0742

R indices [I> 0.0785, 0.1756 2σ(I)]; R1, wR2

0.0681, 0.1529

0.0567, 0.1668

0.0984, 0.1719

R indices (all data) R1, wR2

0.0977, 0.1713

0.0626, 0.1733

0.1519, 0.1976

a

GOF

0.0865, 0.1808

1.035 1.067 1.059 2 [a] R1 = ∑║Fo│–│Fc║/∑│Fo│, wR2 = [∑w(Fo -Fc2)2/∑w(Fo2)2]1/2

1.098

ASSOCIATED CONTENT Supporting Information. More structural details and figures, tables for selected bond lengths and angles, Figures for TGA, EDS, comparative PXRD patterns and PXRD patterns of residues


19


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after TGA, IR spectra and more results for photocatalysis. This material is available free of charge via the internet at http://pubs.acs.org. Accession Codes CCDC

numbers

1579742,

1579743,

1503814, 1579744

contain

the supplementary

crystallographic data for the title compounds. The 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. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected], [email protected]; Fax: (+86)591-63173145. Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (No. 21521061 and 21371001), the 973 program (No. 2014CB845603) and the NSF of Fujian Province (Grant 2016J01083). REFERENCES 1. Li, H. L.; Laine, A.; O'Keeffe, M.; Yaghi, O. M. Science 1999, 283, 1145-1147. 2. Zheng, N. F.; Bu, X. H.; Wang, B.; Feng, P. Y. Science 2002, 298, 2366-2369. 3. Zheng, N. F.; Bu, X. H.; Feng, P. Y. Nature 2003, 426, 428-432. 4. Feng, P. Y.; Bu, X. H.; Zheng, N. F. Acc. Chem. Res. 2005, 38, 293-303.


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For Table of Contents Use Only Discrete supertetrahedral T3 InQ Clusters (Q = S, S/Se, Se, Se/Te): Ionothermal Syntheses and Tunable Optical and Photodegradation Properties Nan-Nan Shen, Bing Hu, Chu-Chu Cheng, Guo-Dong Zou, Qian-Qian Hu, Cheng-Feng Du, Jian-Rong Li,* and Xiao-Ying Huang*

Four InQ-based compounds [Bmmim]5[In10Q16Cl3(Bim)] (Q = S, S/Se, Se, Se/Te) featuring a discrete T3 cluster were prepared ionothermally and exhibited composition-dependent band gaps and photocatalytic properties.


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Figure 1. (a) Crystallograhpically asymmetric unit of IL-InSe-3. (b) A zipper-like structure formed by isolated clusters stacking along the b axis with the [Bmmim]+ cations located in the spaces of neighbouring tetrahedral faces. (c) View of IL-InSe-3 along the b axis showing the arrangement of zipper-like structures (one of which is circled) and the remaining [Bmmim]+ cations; the [Bmmim]+ cations within the zipper-like structures are omitted for clarity. All the hydrogen atoms are omitted for clarity. (d)-(f) show the T3 anionic clusters in IL-InS-1, IL-InSSe-2, and IL-InSeTe-4, respectively. 79x38mm (300 x 300 DPI)



Figure 2. SEM images and elemental distribution maps of IL-InSSe-2 and IL-InSeTe-4.


Page 28 of 32

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Figure 3. PXRD patterns of the four title compounds compared to the simulated ones from the single-crystal X-ray data, respectively. 74x66mm (300 x 300 DPI)



Figure 4. Solid-state optical absorption spectra of the four title compounds. Inset: crystal photos of the four title compounds.


Page 30 of 32

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Figure 5. Photodegradation of MO monitored as the normalized change in concentration as a function of irradiation time under (a) UV light and (b) visible light. 122x181mm (300 x 300 DPI)



Table of contents 34x16mm (300 x 300 DPI)


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Te

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