A hierarchically assembled 88-nuclei silver-thiacalixarene nanocluster.
ABSTRACT: Thiacalixarenes as a family of promising ligands have been widely used to construct polynuclear metal clusters, but scarcely employed in silver nanoclusters. Herein, an anion-templated Ag88 nanocluster (SD/Ag88a) built from p-tert-butylthiacalixarene (H4TC4A) is reported. Single-crystal X-ray diffraction reveals that C4-symmetric SD/Ag88a resembles a metal-organic super calix comprised of eight TC4A4- as walls and 88 silver atoms as base, which can be deconstructed to eight [CrO4@Ag11(TC4A)(EtS)4(OAc)] secondary building units arranged in an annulus encircling a CrO42- in the center. Local and global anion template effects from chromates are individually manifested in SD/Ag88a. The solution stability and hierarchical assembly mechanism of SD/Ag88a are studied by using electrospray mass spectrometry. The Ag88 nanocluster represents the highest nuclearity metal cluster capped by TC4A4-. This work not only exemplify the specific macrocyclic effects of TC4A4- in the construction of silver nanocluster but also realize the shape heredity of TC4A4- to overall silver super calix.
Project description:Surface organic ligands are critical for the formation and properties of atomically precise metal nanoclusters. In contrast to the conventionally used protective ligands such as thiolates and phosphines, thiacalixarene has been used in the synthesis of a silver nanocluster, [Ag35(H2L)2(L)(C?CBu(t))16](SbF6)3, (H4L, p-tert-butylthiacalix-arene). This is the first structurally determined calixarene-protected metal nanocluster. The chelating and macrocyclic effects make the thiacalixarene a rigid shell that protects the silver core. Upon addition or removal of one silver atom, the Ag35 cluster can be transformed to Ag36 or Ag34 species, and the optical properties are changed accordingly. The successful use of thiacalixarene in the synthesis of well-defined silver nanoclusters suggests a bright future for metal nanoclusters protected by macrocyclic ligands.
Project description:We report the synthesis and structures of two 34-atom metal nanoclusters, namely [Ag34(BTCA)3(C[triple bond, length as m-dash]CBu t )9(tfa)4(CH3OH)3]SbF6 and [AuAg33(BTCA)3(C[triple bond, length as m-dash]CBu t )9(tfa)4(CH3OH)3]SbF6, where H4BTCA is p-tert-butylthiacalixarene and tfa is trifluoroacetate. Their compositions and structures have been determined by single-crystal X-ray structural analysis and ESI-MS. The cationic cluster consists of a centered icosahedron M@Ag12 (M = Ag or Au) core that is surrounded by 21 peripheral silver atoms. Surrounding protection is provided by four kinds of ligands, including three BTCA, nine t BuC[triple bond, length as m-dash]C, four tfa, and three methanol solvent ligands. It was found that the Ag5@BTCA ?5-coordination motif of thiacalixarene is critical for high stability of the title clusters, and extra stability enhancement can be achieved by doping a gold atom at the center of the silver cluster. This work suggests that coordination saturation should be taken into account in addition to electronic and geometric factors for analyzing metal nanocluster stabilities.
Project description:Isomerization is highly important in all aspects of science, yet it is rarely observed in nanoscience. Here, we synthesized a unique triple core-shell Ag84 nanocluster displaying isomerism, which is controlled by different carboxylic acids and a one-way transformation (SD/Ag84a → SD/Ag84b). The innermost core is a rare Ag10 nanocluster which comprises an Ag6 octahedral unit as seen in face-centred cubic (fcc) silver metal and four capped Ag atoms. It templates two crescent-shaped polyoxometalate (W7O26)10- shells which are then enclosed in a shell of silver shaped as rugby balls. The organic ligands (iPrS-, n PrCOO- and PhCOO-) finally shield the metallic clusters. Due to slight differences in structure at two poles and the steric hindrance of n PrCOO- and PhCOO-, SD/Ag84a and SD/Ag84b adopt the shapes of flat-headed and cuspidal prolate spheres, respectively. Interestingly, PhCOOH is dominant over n PrCOOH whereby crystals of SD/Ag84b were isolated if PhCOOH is added during the synthesis of SD/Ag84a. This demonstrates that PhCOOH not only alters the organic coats but also induces metal shell re-organization. This work reveals carboxylate-controlled skeletal isomerism in silver nanoclusters for the first time, thus deepening the understanding of silver nanocluster assembly, flexibility and reactivity.
Project description:Noble metal nanoclusters are ultrasmall nanomaterials with tunable properties and huge application potential; however, retaining their enhanced functionality is difficult as they readily lose their properties without stabilization. Here, we demonstrate a facile synthesis of highly photostable silver nanoclusters in a polymer thin film using visible light photoreduction. Furthermore, the different stages of the nanocluster formation are investigated in detail using absorption and fluorescence spectroscopy, fluorescence microscopy, and atomic force microscopy. A cost-effective fabrication of photostable micron-sized fluorescent silver nanocluster barcode is demonstrated in silver-impregnated polymer films using a low-power continuous-wave laser diode. It is shown that a laser power of as low as 0.75?mW is enough to write fluorescent structures, corresponding to the specifications of a commercially available laser pointer. The as-formed nanocluster-containing microstructures can be useful in direct labeling applications such as authenticity marking and fluorescent labeling.
Project description:Explicit solvent interactions can significantly alter the physical and chemical properties of noble metal (e.g., gold and silver) nanoclusters. In order to compute these solvent interactions at a reasonable computational cost, a quantum mechanical (QM)/molecular mechanics (MM) approach, where the metal nanocluster is treated with full QM and the water molecules are treated with a MM force field, can be used. However, classical MM force fields were typically parameterized using molecules containing main group elements as the reference. The accuracy of noble metal-solvent interactions obtained with these force fields therefore remains unpredictable. The effective fragment potential (EFP) force field, designed to model explicitly solvated systems, represents an attractive method to simulate solvated noble metal nanoclusters because it is derived from first principles and contains few or no fitted parameters, depending on implementation. At the density functional theory-optimized geometries, good correlation is obtained between the nanocluster-water interaction energies computed with EFP and those computed with the reference coupled cluster singles, doubles, and perturbative triples method. It is shown that the EFP method gives qualitatively accurate interaction energies at medium-large intermolecular distances for various molecular configurations. In order to achieve higher quantitative accuracy, the first solvation shell should be treated with full QM, if possible. EFP is therefore a promising method for the QM modeling of explicitly solvated silver and gold nanoclusters.
Project description:Organic ligand-protected metal nanoclusters have attracted extensively attention owing to their atomically precise composition, determined atom-packing structure and the fascinating properties and promising applications. To date, most research has been focused on thiol-stabilized gold and silver nanoclusters and their single crystal structures. Here the single crystal copper nanocluster species (Cu6(SC7H4NO)6) determined by X-ray crystallography and mass spectrometry is presented. The hexanuclear copper core is a distorted octahedron surrounded by six mercaptobenzoxazole ligands as protecting units through a simple bridging bonding motif. Density functional theory (DFT) calculations provide insight into the electronic structure and show the cluster can be viewed as an open-shell nanocluster. The UV-vis spectra are analyzed using time-dependent DFT and illustrates high-intensity transitions involving primarily ligand states. Furthermore, the as-synthesized copper clusters can serve as promising nonenzymatic sensing materials for high sensitive and selective detection of H2O2.
Project description:The synthesis of atomically precise thiolate-stabilized silver (Ag) nanoclusters is the subject of intense research interest, yet the formation mechanism of such nanoclusters remains obscure. Here, electrospray ionization mass spectrometry is successfully applied to monitor the reaction intermediates formed during the sodium-borohydride-reduction of silver 4-tert-butylbenzenethiolate (AgSPh-tBu). We demonstrate a unique evolution route to thiolate-stabilized Ag nanoclusters mediated by Ag-thiolate clusters. The Ag-thiolate clusters form in the initial stage of reduction contain tens of Ag atoms and similar number of ligands, and they are transformed into Ag17(SPh-tBu)123- and Ag44(SPh-tBu)304- nanoclusters in the later reduction process. The number of Ag atoms in the Ag-thiolate clusters determines the reaction path to each final nanocluster product. A similar mechanism is found when silver 2,4-dimethylbenzenethiolate (AgSPhMe2) is used as precursor. This mechanism differs markedly from the long-established bottom-up evolution process, providing valuable new insights into the synthesis of metal nanoclusters.
Project description:Silver-based products are becoming popular as antimicrobial agents because of the failure of antibiotics available for tackling the drug-resistant microbial strains. As silver is well tolerated by normal human cells, silver complexes have emerged as important antineoplastic agents. Further, if silver ions are encapsulated within an organic molecule—an azacorand—it may serve as a better substitute for cisplatin or other metal complexes. The calix-salen-type corates were synthesized using silver ions as the template. 5,5?-methylene-bis-salicylaldehyde was reacted with ethylene diamine in methanol at room temperature in the presence of silver nitrate. The resultant corand trapped the silver template in their cavity. The electron-withdrawing and electron-releasing groups like ?NO2, ?Br, ?C(CH3)3, and ?OCH3 were substituted on the bis-aldehyde to study their effects on the antimicrobial and anticancer activities of silver corates. The silver corates were found to have better antimicrobial activity than some of the standard drugs. Bromo-substituted corate-3, nitro-substituted corate-4, and tert-butyl-substituted corate-5 were found to be potent antibacterial agents among all. The bromo-substituted corate-3 was found to be the most potent fungicidal agent among all silver corates. The result of antineoplastic activity suggests that unsubstituted corate-1 and bromo-substituted corate-3 are potential candidates to be used as therapeutic molecules for cancer treatment, which requires further validation.
Project description:The synthesis of an alloy nanocluster that is atomically precise is the key to understanding the metal synergy effect at the atomic level. Using the Ag?Au25(SR)18 nanocluster as a model, we reported a third approach for the metal exchange reaction, that is, intramolecular metal exchange. The surface adsorbed metal ions (i.e., Ag) can be exchanged with the kernel metal atoms (i.e., Au) that are promoted by thiol ligands. The exchanged gold atoms can be further stripped by the thiol ligands, and produce the AgxAu25-x(SR)18- nanocluster.
Project description:Methylene-bridged calixarenes have emerged as extremely versatile ligand supports in the formation of new polymetallic clusters possessing fascinating magnetic properties. Metal ion binding rules established for this building block allow one to partially rationalise the complex assembly process. The ability to covalently link calixarenes at the methylene bridge provides significantly improved control over the introduction of different metal centres to resulting cluster motifs. Clusters assembled from bis-calixarenes and transition metal ions or 3d-4f combinations display characteristic features of the analogous calixarene supported clusters, thereby demonstrating an enhanced and rational approach towards the targeted synthesis of complex and challenging structures.