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The Largest Supertetrahedral Oxychalcogenide Nanocluster and Its Unique Assembly Huajun Yang, Jiaxu Zhang, Min Luo, Wei Wang, Haiping Lin, Youyong Li, Dongsheng Li, Pingyun Feng, and Tao Wu J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.8b07349 • Publication Date (Web): 08 Aug 2018 Downloaded from http://pubs.acs.org on August 8, 2018
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Journal of the American Chemical Society
The Largest Supertetrahedral Oxychalcogenide Nanocluster and Its Unique Assembly Huajun Yang,a,† Jiaxu Zhang,a,† Min Luo,a Wei Wang,a Haiping Lin,b Youyong Li,b Dongsheng Li,c Pingyun Feng,d and Tao Wu*,a a
College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, Jiangsu 215123, China Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory for Carbon-Based Functional Materials &Devices, Soochow University, Suzhou, Jiangsu 215123, China c 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 d Department of Chemistry, University of California, Riverside, California 92521, United States b
Supporting Information Placeholder ABSTRACT: Supertetrahedral oxychalcogenide Tn nanoclusters (NCs, n denotes the number of metal-chalcogen layers) integrate chemically distinct but ordered oxygen and chalcogen sites in zinc-blend-type “quantum dots". They therefore offer a new level of control over various properties of semiconducting materials. So far, few such structures are known, and the cluster size is also limited to only T4 with 20 metal sites. Herein, we report an unusual oxysulfide T5 nanocluster with 35 metal sites. It has unprecedented In-O@In-S “core-shell” nanostructure and is also the largest supertetrahedral oxychalcogenide NC. Through cocrystallization, we further demonstrate that such oxychalcogenide NCs can be assembled to form multi-dimensional structures. In addition to N-donor imidazolates that help to form a 3-D structure with chiral quartz net, the O-donor benzenetricarboxylate (BTC) has also been found to successfully organize such T5 NCs. It is worth noting that no carboxylate ligands have been shown earlier for assembling chalcogenide clusters, despite their prevalence in MOFs. Given the wide availability of O-donor ligands, this work introduces a versatile platform with promise for a new generation of semiconducting inorganic-organic hybrid materials.
Nanoscale inorganic semiconducting materials, examplified by colloidal quantum dots, have aroused great interest in recent decades due to their diverse applications resulting from the quantum confinement effect.1 Understanding their structureproperty relationship is very important to design the synthetic strategy for specific applications.2 Supertetrahedral metal chalcogenide NCs (Tn, n indicates the number of metal sites along the edge of the tetrahedron), being the ultrasmall semiconductor nanocrystal, could serve as model system for such study due to their precisely defined structure and composition.3 Doping is generally recognized as an effective tool to modulate the properties of nanoscale materials.4 Realization of various doping in nanosized Tn clusters is particularly intriguing since their structure can be characterized by single-crystal X-ray diffraction and thus facilitate the precise probing of dopant positions. Thus far, a lot of works have proved that the metal ion doping in Tn clusters can introduce profound change in the properties of the resulting NCs and even change the size of the
clusters.5 However, few efforts were focused on the doping behavior on chalcogen sites (S or Se). In fact, doping non-metal elements (such as O or P) into chalcogenide NCs is very interesting since they could effectively tailor band gap and even enhance the stability.6 Notwithstanding, O-doped chalcogenide (also called oxychalcogenide) NCs are much less explored, compared with metal ion doping, because it is difficult to combine the hard Lewis base of O and soft Lewis base of S/Se. So far, only Tn (n=2, 3, 4) oxychalcogenide NCs have been obtained (Figure 1),7 despite the fact that the regular Tn clusters have been extended to T6 recently.8 There has always been a strong interest in integration of organic components with chalcogenide clusters, which offers opportunities not only to create porous frameworks, but also to generate synergistic properties resulting from both the inorganic and organic components.9 The first developed covalent organization of supertetrahedral chalcogenide clusters are based on neutral N-donor pyridines, which has led to one-dimensional chains, two-dimensional layers, and three-dimensional photoluminescent superlattices.10 Recently, further progresses have also been made in assembly of the supertetrahedral sulfide clusters by N-donor imidazolates.9, 11 However, hybrid chalcogenide frameworks in which the clusters are linked by Odonor ligand have not been found to date. As mentioned above, the big mismatch between M-S and M-O arising from the hardness difference of S and O could be responsible for this again. Herein, we made a major breakthrough in extending oxychalcogenide Tn NC. The obtained unusual indium oxysulfide NC (T5-InSO) represents the largest metal oxychalcogenide supertetrahedral NC, in which a high-valent In3+ is for the first time observed to locate at the core site of T5 NC. The coassembly between such NC and N-donor imidazole formed a three-dimensional chiral qtz net (denoted as IOS-2). What is more interesting, these NCs can also be assembled into a semiconducting 2D superlattice through an unexpected O-donor carboxylate ligand (denoted as IOS-1). The crystallization of IOS-2 is from mixed solvents of organic amines and acetonitrile. Differently, IOS-1 was experimentally realized by solvothermal reaction in the mixed solvents of DMF and DBU (BTC = 1, 3, 5-benzenetricarboxylate, DMF = dimethyl formamide, DBU = 1, 8-diazabicyclo [5. 4. 0] undec-7-ene). The
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Table 1. Summary of crystal data and refinement results. Name IOS-1 IOS-2(P) IOS-2(M) IOS-3 FIS-1 IS-1
Framework Formula [(In35S48O8)(BTC)(H2O)]10[(In35S48O8)(Im)2]9[(In35S48O8)(Im)2]9[(In10S16)(H2O)2(H·BTC)] [(Fe4In16S31) ·(H2O)3 (BTC)1/3]7[In34S54]6-
Space Group P63/mmc P3212 P3112 P21/c P63/m I41/acd
synthetic media are quite similar to that for metal-organic frameworks (MOFs) rather than that for the chalcogenide clusterbased open frameworks in term of solvent and O-donor ligand. Contrast experiments demonstrated that each raw reagent is necessary for the formation of IOS-1. In addition, replacing indium nitrate and thiourea with indium element and sulfur powder only resulted in a clear solution.
Figure 1. Four oxychalcogenide Tn (n = 2, 3, 4 and 5) NCs and the In13O8 core in IOS-1. Single-crystal XRD analysis revealed that IOS-1 crystallizes in a highly-symmetric hexagonal system with space group P63/mmc and IOS-2 crystallizes in a chiral space group of P3212 (Table 1). The framework composition can be unambiguously determined to be [(In35S48O8)(BTC)(H2O)]10- and [(In35S48O8)(Im)2]9- for IOS-1 and IOS-2, respectively, whereas the charge-balancing protonated amine molecules are fully disordered (Figure S1). The composition and structure of IOS-1 and IOS-2 were further confirmed through energy dispersive spectra (EDS), infrared (IR) spectra and powder X-ray diffraction (PXRD) experiments (Figure S2-S12). The secondary building unit of IOS-1 and IOS-2 is unusual, which represents the largest supertetrahedral oxysulfide NC among Tn series. The corner of this cluster is either occupied by oxygen from BTC in IOS-1 or nitrogen from imidazolate in IOS-2. Excluding the corners, this oxysulfide T5InSO NC can be considered as an ideal T5-InS NC ([In35S52]) doped with eight oxygen atoms in the core (Figure 1), which can be divided into two types depending on their corresponding location in an ideal T5-InS NC: tetrahedrally coordinated interstitial oxygen (Oi) and triangularly coordinated substitutional
a (Å) 24.8037(8) 21.5880(13) 21.5809(19) 25.029(2) 37.421(3) 29.569(2)
b (Å) 24.8037(8) 21.5880(13) 21.5809(19) 30.399(3) 37.421(3) 29.569(2)
c (Å) 44.986(3) 41.146(3) 41.108(4) 17.1175(17) 20.6962(17) 54.901(8)
β, γ (°) 90, 120 90, 120 90, 120 109.996(6), 90 90, 120 90, 90
R(F) 0.0878 0.0317 0.0314 0.1341 0.0792 0.1061
oxygen (Os). As suggested by the name, the Oi atom is embedded in the adamantane cage. In contrast, Os atom occupies the chalcogenide site in a regulate T5 NC along with its location shifting towards the corner of NC. It should be noted that the oxygen dopants in all other reported Tn oxysulfide NC belong to Oi mode,7a,7b and the Os mode found in IOS-1 and IOS-2 is unprecedented (Table S1). The most prominent structural feature of the unusual T5-InSO NC is the In-O@In-S “core-shell” nanostructure with the core stuffed by a high-valent In3+ ion. According to Pauling’s electrostatic valence rule, an ideal T5-InS NC ([In35S56]) with trivalent metal cation locating at the core is usually extremely unstable. As a result, the stable T5-InS NC can be realized through placing low-valent (+1 or +2) metal ions at its core site. Alternatively, the stable T5-InS NC can be also formed with the metal core missing, which can avoid the excessive positive charge accumulating at central core area, as indicated in IS-1 (Figure S13 for further structural details) and UCR-15.12 Surprisingly, the unusual T5-InSO NC in IOS-1 and IOS-2 is formed with the indium core surrounded by eight O2- ions. According to Brown’s bond valence rule,13 the bond valence sum of indium ion at the core is calculated to be 2.91, in consistent with the positive charge of trivalent indium ion (Table S2). In other words, the high-valent metal ion is successfully secured at the core site of T5-InSO NC through introducing eight oxygen ions. It should be noted that, to prevent excessive negative charge created at the core site, the location of Os ion slightly shifts away from indium core. Thus, the contribution to the bond valence sum of core indium ion from Os ions is smaller due to the longer bond length (~ 2.7 Å) (Figure 1). In addition, the introduction of oxygen ions also results in variable coordination environments of indium ions, covering four InS3O at the corner, eighteen InS4 at edge, twelve InS3O2 at face, and one InO8 at core. Assembly of T5-InSO NCs with N-donor imidazolate ligands in IOS-2 forms a chiral quartz net, which has been confirmed to be racemic conglomerate (Figure 2b and Table S1). The assembly between chalcogenide clusters and N-donor ligands in IOS-2 has been observed perviously.9 More importantly, co-assembly between BTC ligands and T5-InSO NCs observed in IOS-1 represents a significant advance in assembling metal chalcogenide Tn NCs with O-donor ligand. Each T5-InSO NC is planarly connected with three BTC ligands, and vice versa to form a 2D layered superlattice (Figure 2a and Figure S14). Two single layers are nested with each other head to head to form a super-layer, and the resulting super-layers are stacked with a staggered configuration along c direction (Figure S15). The framework of IOS-1 adopts a honeycomb-like topology by treating T5 NC and BTC as 3-connected nodes. The integration of O-donor ligands into purely inorganic metal chalcogenide frameworks is much more exotic due to the large metal affinity gap between oxygen and sulfur. The connection mode between T5 NC and BTC may be partially ascribed to the suitable crystallization environment created by the mixed templated amines and DMF. In fact, by adjusting the ratio of indium source and thiourea or adding the Fe2(SO4)3 in the mixed solvents, we can obtain two other hybrid
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Journal of the American Chemical Society compounds (denoted as IOS-3 and FIS-1). In IOS-3, T3-InSO NCs ([In10S16O2]) are bridged by BTC ligands to form 1D chain, whereas in FIS-1, three T4 ([Fe4In16S31(H2O)3]) clusters are joined by one BTC ligand to form a discrete complex (Figure S19-20).
energy of the conductivity was calculated to be 0.34 eV. All of the values fall into the scope of typical semiconductor materials, which are also comparable to other hybrid inorganic–organic semiconductors.14
Figure 3. Arrhenius plot of IOS-1 (the inset: the photograph of the single crystal of IOS-1 for electrical measurement and temperature-dependent I–V curve).
Figure 2. a) Layered superlattice with T5-InSO NCs bridged by BTC linkers in IOS-1. b) Three-dimensional quartz lattice with T5-InSO NCs bridged by imidazolate linkers in IOS-2 (only one set is shown for clarity). Solid-state sample of IOS-1 exhibits the characteristic semiconducting property. Its optical band gap was determined to be 2.19 eV by solid-state UV-Vis diffuse reflectance spectrum (Figure S21). In comparison with IOS-3 (band gap 3.42 eV) built on small T3-InSO NCs, a large red shift of 1.23 eV was observed for IOS-1. Such large red shift trend was not observed in other pure inorganic Tn-InS based frameworks. For example, IS-1, built on T5-InS NC ([In34S56]), exhibits a wide band gap of 2.89 eV and a relatively small red shift compared with UCR-7 (band gap 3.39 eV) built on T3-InS NC ([In10S20]) (Figure S22-23). This may be explained that the BTC linkers in IOS-1 and IOS-3 effectively separate supertetrahedral NCs, and make them behave more like the discrete “QDs”. Quantum confinement effects should be thereby responsible for the size-dependent optical band gap, which is further supported by DFT calculations (Figure S24). Direct current two-terminal method was applied to measure the electric transport properties. As shown in the inset of Figure 3, the conductivity of the single-crystal sample of IOS-1 at 30 ℃ was determined to be 3×10-9 S cm-1. The electric conductivity was also found to be positively correlated with temperature, which is a characteristic feature of semiconductor materials. The activation
Structurally speaking, the compounds reported here represent significant advances in several aspects. Firstly, the indium oxysulfide T5-InSO NC in IOS-1 and IOS-2 represents the largest oxysulfide NC in Tn series. Specially, there exists a type of substitutional oxygen in the oxysulfide NC, which was never found in other oxysulfide Tn NCs. It proved that stabilizing a high valent indium ion at the core site of T5-InS NC is possible through introducing more oxygen dopants around the core indium ion. Secondly, IOS-1 with O-donor bridging ligand also represents an important step forward in the integrative chemistry between MOFs and inorganic metal chalcogenide frameworks. The synthetic strategy and reaction media reported here for coassembly between carboxylate ligands and metal chalcogenide NCs could lead to a new generation of inorganic-organic hybrid materials due to the wide availability of carboxylate ligands.
ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Experimental Procedures and compound characterization data (PDF) Crystallographic data for IOS-1, IOS-2, IOS-3, FIS-1, and IS-1 (CIF)
AUTHOR INFORMATION Corresponding Author E-mail:
[email protected] Author Contributions † These authors contributed equally.
Notes The authors declare no competing financial interests.
ACKNOWLEDGMENT
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We acknowledge National Natural Science Foundation of China (21671142), Jiangsu Province Natural Science Fund for Distinguished Young Scholars (BK20160006), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). T. W. would thank Dr. Zhenyi Zhang for structure refinement and Dr. Guane Wang for the measurement of the electric transport property.
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