通讯作者地址: Zheng, NF (通讯作者), Xiamen Univ, State Key Lab Phys Chem Solid Surface, Xiamen 361005, Peoples R China  
地址: 
1. Xiamen Univ, State Key Lab Phys Chem Solid Surface, Xiamen 361005, Peoples R China 
2. Xiamen Univ, Dept Chem, Coll Chem & Chem Engn, Xiamen 361005, Peoples R China  
电子邮件地址: nfzheng@xmu.edu.cnOwing to its good affinity with Ag+, Br- is able to truncate a silver thiolate polymer and induce the formation of a high-nuclearity silver thiolate nanocluster, [Br@Ag-36(SC(6)H(4)tBu-4)(36)](-) The nanocluster has a disc-like structure with one Br- anion trapped at the center of the cluster in an octahedral coordination.National Natural Science Foundation of China 20871100,20721001,20925103  
Natural Science Foundation of Fujian 2009 J06005  
Key Scientific Project of Fujian Province  2009HZ0002-

Liu, Xiaomin

Yang, Huayan

Zheng, Lansun

Zheng, Nanfeng

刘晓敏

杨华艳

郑兰荪

郑南峰

European Journal of Inorganic Chemistry

Xiamen University Institutional Repository

SHORT COMMUNICATIONDOI: 10.1002/ejic.200900668Bromide-Induced Formation of a Highly Symmetric Silver Thiolate ClusterContaining 36 Silver Atoms from an Infinite Polymeric Silver ThiolateXiaomin Liu,[a] Huayan Yang,[a] Nanfeng Zheng,*[a] and Lansun Zheng[a]Keywords: Nanostructures / Cluster compounds / Silver / HalidesOwing to its good affinity with Ag+, Br– is able to truncate asilver thiolate polymer and induce the formation of a high-nuclearity silver thiolate nanocluster, [Br@Ag36(SC6H4tBu-IntroductionMolecular chalcogenide nanoclusters, consisting of tensand hundreds of covalently bound atoms, represent oneclass of important nanoclusters.[1–5] With a size at the lowlimit of the size spectrum of nanoparticles and usually lessthan the exciton Bohr radius of their bulk counterparts,these nanoclusters exhibit a significant quantum confine-ment effect.[1,6–9] In addition, chalcogenide nanoclusterscan be considered as truly monodispersed in size and shape.They can serve as artificial atoms for the construction ofhighly ordered and even functional materials (e.g. superlat-tices, porous materials).[6,8,10,11] The ease of crystallizationof the clusters into single crystals makes it possible to deter-mine the precise molecular structure of the clusters.Owing to their good affinity to metals, thiolates havebeen widely used as capping agents in the synthesis of dif-ferent chalcogenide nanoclusters (e.g. [Cd54S32(SPh)48-(H2O)4–],[9] [Ag352S128(St-C5H11)96],[10] [Ag490S188(S-t-C5H11)114],[10] [Ag70S16(SPh)34(PhCO2)4(triphos)4],[12][Ag123S35(StBu)50],[13] [Ag344S124(StBu)96],[13] [Ag262-S100(StBu)62(dppb)6],[14] [Ag70S20(SPh)28(dppm)10](CF3-CO2)2,[14] [Ag65S13(SC6H4NMe2)39(dppm)5][15]). Currently,there are two approaches to prepare high-nuclearity silverthiolate nanoclusters. In one approach, silver salts (i.e.Ph3CO2Ag, CF3COOAg), highly reactive thiolates [i.e.S(Ph)SiMe3], and a sulfide precursor [i.e. S(SiMe3)2] wereused as the reactants for the direct synthesis of the nanoclu-sters. The key in this approach was to prevent the facileformation of polymeric silver thiolates, which was mainlyachieved by the delicate control of the reaction conditions[a] State Key Laboratory of Physical Chemistry of Solid Surfaceand Department of Chemistry,College of Chemistry and Chemical Engineering, XiamenUniversity,Xiamen 361005, ChinaFax: +86-592-2183047E-mail: nfzheng@xmu.edu.cnSupporting information for this article is available on theWWW under http://dx.doi.org/10.1002/ejic.200900668.© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2010, 2084–208720844)36]–. The nanocluster has a disc-like structure with one Br–anion trapped at the center of the cluster in an octahedralcoordination.such as the low reaction temperature. In the other ap-proach, polymeric silver thiolates were applied as the pre-cursors to react with a reactive sulfide precursor, S(SiMe3)2,to yield silver thiolate clusters, which has become very effec-tive in the synthesis of some extra-large silver thiolate nano-clusters.[10,16,17]The possibility of using polymeric silver thiolates to pre-pare discrete nanoclusters arises mainly because of thestrong affinity of sulfide to silver, which facilitates the breakdown of the polymeric chain. Similarly to sulfide, a halideanion (e.g. Cl–, Br–) reacts easily with a silver cation. Itwould be highly useful to know whether halide anions canalso induce the formation of discrete nanoclusters from sil-ver thiolate polymers. Starting from an Ag-SC6H4tBu-4polymer, we report here the successful synthesis of [HNEt3]+-[Br@Ag36(SC6H4tBu-4)36]– (1), containing a high-nu-clearity silver thiolate nanocluster, assisted by a bromideanion.Results and DiscussionThe polymeric silver thiolate compound studied in thiswork was prepared according to the literature method andhas a composition of {[HNEt3]2[Ag10(SC6H4tBu-4)12]}n.[17]This polymer is insoluble in acetonitrile. Upon addition ofan aqueous solution of (C4H9)4N+Br–, the acetonitrile dis-persion of the polymer microcrystals quickly became a clearsolution. This observation indicates that the original silverthiolate polymer is broken down by the introduction of Br–ions. Upon heating at 60 °C, the resulting clear solutionyielded 1. As illustrated in Figure 1, single crystal structureanalysis of 1 reveals the formation of [Br@Ag36(SC6H4tBu-4)36]– nanoclusters from the polymeric silver thiolate pre-cursor. The [Br@Ag36(SC6H4tBu-4)36]– clusters crystallizewith [HNEt3]+ as the counterions to form 1. The presenceof bromine in the compound was confirmed by energy dis-persive X-ray analysis (see Supporting Information). The[Br@Ag36(SC6H4tBu-4)36]– cluster is highly symmetric withBromide-Induced Formation of a Symmetric Silver Thiolate Clustera threefold rotational axis that passes through its center.The asymmetric unit of the cluster contains only one Br–ion, six Ag+ ions and six thiolate anions. The cluster has acore-shell structure with a flattened-cage-like core[Br@Ag18S12]– and a crown-like shell [Ag12S12-(AgS2)6].The flattened structure is common among many reportedsilver thiolate clusters.Figure 1. The structure of the [Br@Ag36(SC6H4tBu4)36]– cluster:grey globe spheres, Ag; multishaded spheres, S; black sphere, Br;grey sticks, C–C and S–C bonds.In the core of the cluster (Figure 2), the Br– ion sits inthe center and is sandwiched by two Ag3S3 units with anAg–Br distance of 3.0024(6) Å. This bond length is consis-tent with the Ag–Br lengths observed in previously reportedcompounds containing a Br– anion with a similar coordina-tion environment.[18] The Ag···Ag contacts in the centralBr(Ag3S3)2 sandwich unit are 3.2391(10) Å. The centers ofthe Ag3S3 units and the Br– ion define the threefold rota-tional axis of the cluster. The Br(Ag3S3)2 sandwich unit isthen enclosed by a cyclic Ag12S6 to form the flattened-cage-like core. As a result, the Br– anion is fully encapsulated.In contrast to the cluster core, the shell of the clusterhas a crown-like structure (Figure 3). Twelve Ag+ ions andtwelve thiolate anions are alternatively linked together toform a cyclic structure. The Ag12S12 ring is then trans-formed by six additional AgS2 units into an arrangementconsisting of six S-bridged Ag3S3 units, [S(Ag3S3)]6. The sil-ver atom in the AgS2 units is two coordinate. A linear two-coordination arrangement is a common coordination geom-etry for AgI, but has rarely been revealed in silver thiolateclusters. It should be noted that MS2 units have recentlybeen reported as important surface structure components inmany thiolate-capped metallic gold compounds.[19–21] Thepresence of AgS2 staple motifs in [Br@Ag36(SC6H4tBu-4)36]– is of the utmost significance since it implies such unitsmight be present in thiolate-protected silver clusters. Thetwelve thiolate anions on the crown-like shell, [Ag18S24], areEur. J. Inorg. Chem. 2010, 2084–2087 © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org 2085Figure 2. The structure of the core cage of the[Br@Ag36(SC6H4tBu4)36]– cluster: (a) the Br(Ag3S3)2 sandwich unitat the center of the cluster. (b) top and (c) side view of the flattenedcage in the core of the [Br@Ag36(SC6H4tBu4)36]– cluster.connected to the twelve outer Ag+ ions in the core unit[Br@Ag18S12]– to form the overall structure of the Ag36cluster.Figure 3. The structure of the crown-like shell of the[Br@Ag36(SC6H4tBu4)36]– cluster. All carbon atoms are omitted forclarity.The use of Br– anions is important for the transforma-tion of silver thiolate polymers into discrete [Br@Ag36-(SC6H4tBu-4)36]– clusters. In the polymeric precursor, halfof the Ag+ sites are fourfold coordinated to the thiolateanions. Each thiolate is shared by either two or three Ag+ions, which means that the bond valence contributed to Ag+X. Liu, H. Yang, N. Zheng, L. ZhengSHORT COMMUNICATIONby each thiolate anion is either 1/2 or 1/3. According toPauling’s electrostatic valence rule, the four-coordinate sil-ver sites in the polymeric precursor are not structurallystable. Indeed, with the introduction of Br– ions, all of thesefour-coordinate Ag+ ions, the structurally least-stable sites,break down, which results in the formation of high-nu-clearity clusters in which all silver cations are either two- orthreefold coordinated to the thiolate groups.Experimentally, when Br– was replaced by Cl– or I–, wefailed to obtain the Ag36 cluster. We did not obtain a clearsolution from the polymeric silver thiolate precursor whenBr– was substituted by I–. Upon addition of Cl–, we ob-served the formation of a clear solution from the polymer.Single crystals with a space group of P21/n were successfullygrown from the solution. Although the precise structure de-termination of the single crystals was hampered by the lackof quality, the preliminary structural analysis reveals thatthe yielded cluster contains chloride anions and its struc-ture is significantly different from that of the Ag36 clusterdiscussed above (see Supporting Information).In 1, the highly symmetric [Br@Ag36(SC6H4tBu-4)36]–clusters crystallize in the R-3 space group, and pack in ahexagonal pattern in the ab plane with a intercluster dis-tance of 26.151(4) Å (center to center). Along the c axis,the hexagonal layers of the clusters have an ABC arrange-ment with a layer-to-layer distance of 17.913(4) Å. The in-tercluster space is occupied by charge balancing cations, tri-ethylammonium. The shortest distance between the protonon the triethylammonium cation and the sulfur on the Ag36clusters is 6.2105(20) Å, which indicates no strong interac-tion between the clusters and cations.Figure 4. (a) Thermal gravimetric analysis (TGA) curve and (b)UV/Vis absorption spectrum of 1.www.eurjic.org © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Eur. J. Inorg. Chem. 2010, 2084–20872086To investigate the thermal stability of the as-preparedAg36 clusters, thermal gravimetric analysis of vacuum-dried1 was carried out under nitrogen. As shown in Figure 4a,the analysis reveals a weight loss of 2.1% between 110 and220 °C, which corresponds to the removal of the counterionand Br– (calcd.: 1.8%). The major weight loss of about57.0 % occurs between 220 and 400 °C. At this stage,Ag36(SC6H4tBu-4)36 decomposes into Ag with the loss of(SC6H4tBu-4)36 (calcd.: 57.2%). The final product was alsoconfirmed by X-ray powder diffraction measurement. Op-tical absorption data derived from the reflectance showsthat 1 absorbs light with an onset at 487 nm (Figure 4b),which corresponds to an optical band gap of 2.5 eV.Experimental SectionGeneral: The polymeric anionic silver thiolate, [HNEt3]n[Ag10(SC6H4tBu-4)12]n, was first prepared according to the literaturemethod.[17]1: In a glass vial, the polymeric silver thiolate (60 mg) was dispersedin acetonitrile (3 mL). A solution containing (C4H9)4NBr (10 mg)in water (0.1 mL) was then added into the polymer dispersion. Af-ter being stirred for 30 min at room temperature, the mixture be-came clear. The clear solution was sealed and heated at 60 °C for1 d. 1 (18 mg) was obtained in the form of pale-yellow crystals witha yield of 35%. IR: ν̃ = 2958 (s), 2915 (m), 2869 (m), 2784 (vw),2698 (w), 1614 (s), 1384 (vs), 1268 (m), 1190 (w), 1159 (w), 1118(s), 1080 (w), 1010 (m), 821 (s), 732 (w), 588 (w), 546 (m), 478 (w)cm–1.Structure Determination: Intensities were collected at 173 K withan Oxford Gemini S ultra diffractometer. The structures weresolved by direct methods and refined by using SHELXL-97, allnon-hydrogen atoms were refined anisotropically. Selected refine-ment results are summarized in Table 1. CCDC-684173 containsthe supplementary crystallographic data for the structure. Thesedata can be obtained free of charge from The Cambridge Crystallo-graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.Table 1. Selected details of the data collection and structure refine-ment of 1.HN(C2H5)3[Br@Ag36-(SC6H4tBu-4)36]–·Color pale yellowCrystal size [mm] 0.250.200.20Crystal system rhombohedralSpace group R-3a [Å] 26.151(4)c [Å] 53.740(11)V [Å3] 31829 (9)Z 3ρcalcd. [gcm–3] 1.583F(000) 15147µ [mm–1] 1.955θ range [°] 3.04–25.00Reflections collected 12432Data/restraints/parameters 5810/2/672Rint 0.1034Goodness-of-fit on F2 1.014Final R indices [I2σ(I)] R1 = 0.0772, wR2 = 0.2210Largest difference peak and hole [eÅ–3] 1.773, –1.306Bromide-Induced Formation of a Symmetric Silver Thiolate ClusterThermal Gravimetric Analysis: Thermoanalytical measurementswere performed with a DTA-TG device SDT Q600 from TA. Allmeasurements were performed under a nitrogen atmosphere (flowrate: 100 mLmin–1) with Al2O3 crucibles. 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Soc. 2008, 130, 5883.Received: July 16, 2009Accepted: August 4, 2009Revision: March 12, 2010Published Online: April 13, 2010

Bromide-Induced Formation of a Highly Symmetric Silver Thiolate Cluster Containing 36 Silver Atoms from an Infinite Polymeric Silver Thiolate

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Bromide-Induced Formation of a Highly Symmetric Silver Thiolate Cluster Containing 36 Silver Atoms from an Infinite Polymeric Silver Thiolate

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