Conspectus The past decades have witnessed great advances in the synthesis, structure determination, and properties investigation of coinage metal nanoclusters. These monodisperse clusters have well-defined molecular structures, which is advantageous in correlating structures and properties. Metal nanoclusters are large molecules consisting of many components, so it is a big challenge to prepare them in a rational way. Strenuous efforts have been made to control their geometric and electronic structures, in order to optimize their various properties. A metal nanocluster normally contains a metal core and a peripheral ligand shell. The ligands do not only function as simple stabilizing agents. It has been revealed that these ligands are able to influence the formation processes of the nanoclusters, and they may also dictate the sizes, shapes, and properties of nanoclusters. There are mainly three types of ligands that are widely used as surface anchors on coinage metal nanoclusters: thiolates, phosphines, and halides. Recent ligand engineering has extended the scope to alkynyl ligands. As alkynyl ligands are versatile in interacting with metal atoms, interesting alkynyl–metal interfacial structures including linear, L-shaped, and V-shaped staple motifs can be generated, as well as a series of novel coinage metal nanoclusters that exhibit intriguing molecular geometries. The staple motifs do not simply resemble the surface structures of thiolate-protected nanoclusters, because the incorporation of alkynyl ligands may significantly alter diverse properties of nanoclusters. Compared with thiolate-protected gold nanoclusters, alkynyl-protected ones with identical metal cores exhibit distinctly different absorption profiles and show much improved catalytic activities for semihydrogenation of alkynes. In addition, the participation of alkynyl ligands could profoundly affect the luminescent properties of nanoclusters. These “ligand effects” are mainly attributed to the different nature of alkynyl ligands, as electronic perturbation through π-conjugated units may largely modulate the electronic structure of the whole cluster. In this Account, we describe the development of coinage metal nanoclusters protected with alkynyl ligands. We will first briefly bring up the emergence of alkynyl ligands as anchoring groups on the surfaces of nanoclusters. Then we present the direct reduction method for the synthesis of the following four categories of nanoclusters: (a) gold nanoclusters with mixed-ligand shells, (b) all alkynyl-protected gold nanoclusters, (c) heterobimetallic gold nanoclusters, and (d) silver nanoclusters. Their molecular structures are described, and their various alkynyl–metal interfacial structures are compared with thiolate–metal staples. Finally, ligand effects on the properties of the clusters, including optical absorption, luminescence, and catalysis, are discussed. The alkynyl ligands play an important role in terms of both structural and property aspects. We believe this Account will attract increasing at...
For the first time total structure determination of homoleptic alkynyl-protected gold nanoclusters is reported. The nanoclusters are synthesized by direct reduction of PhC≡CAu, to give Au (PhC≡C) and Au (PhC≡C) . The Au and Au nanoclusters have fcc-type Au and Au kernels, respectively, as well as surrounding PhC≡C-Au-C (Ph)Au-C≡CPh dimeric "staples" and simple PhC≡C bridges. The structures of Au (PhC≡C) and Au (PhC≡C) are similar to Au (SR) and Au (SR) , but the UV/Vis spectra are different. The protecting ligands influence the electronic structures of nanoclusters significantly. The synthesis of these two alkynyl-protected gold nanoclusters indicates that a series of gold nanoclusters in the general formula Au (RC≡C) as counterparts to Au (SR) can be expected.
We report the controlled synthesis and structures of two isomeric gold nanoclusters, whose compositions are determined to be Au 23 (CCBu t ) 15 (denoted as Au 23 -1 and Au 23 -2) by single-crystal X-ray diffraction and matrixassisted laser desorption ionization time-of-flight mass spectrometry. This is the first time isomerism is discovered in alkynyl-protected gold nanoclusters. The metal-toligand ratios in these two clusters are different from known Au n (SR) m systems and have not been observed in the Au x (CCPh) y family. This pair of isomers exhibits different optical properties, although they have similar structures and identical components. For both Au 23 clusters, time-dependent density functional theory calculations revealed the frontier orbitals highest occupied molecular orbital (HOMO)−1, HOMO, and lowest unoccupied molecular orbital (LUMO) are mainly constructed from the Au 15 kernel and V-shaped alkynyl−gold motifs. The HOMO → LUMO transition of Au 23 -1 is optically forbidden, whereas it is allowed in Au 23 -2. It is also found that Au 23 -2 cluster can be transformed to Au 23 -1 spontaneously under ambient conditions. This work offers further insight into the synthesis and isomerism of all-alkynyl-protected gold nanoclusters and will stimulate more investigation of isomeric metal nanoclusters.
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