Katsuyuki Nobusada

Isolation, structure, and stability of a dodecanethiolate-protected Pd1Au24 cluster

A dodecanethiolate-protected Pd(1)Au(24)(SC(12)H(25))(18) cluster, which is a mono-Pd-doped cluster of the well understood magic gold cluster Au(25)(SR)(18), was isolated in high purity using solvent fractionation and high-performance liquid chromatography (HPLC) after the preparation of dodecanethiolate-protected palladium-gold bimetal clusters. The cluster thus isolated was identified as the neutral [Pd(1)Au(24)(SC(12)H(25))(18)](0) from the retention time in reverse phase columns and by elemental analyses. The LDI mass spectrum of [Pd(1)Au(24)(SC(12)H(25))(18)](0) indicates that [Pd(1)Au(24)(SC(12)H(25))(18)](0) adopts a similar framework structure to Au(25)(SR)(18), in which an icosahedral Au(13) core is protected by six [-S-Au-S-Au-S-] oligomers. The optical absorption spectrum of [Pd(1)Au(24)(SC(12)H(25))(18)](0) exhibits peaks at approximately 690 and approximately 620 nm, which is consistent with calculated results on [Pd(1)@Au(24)(SC(1)H(3))(18)](0) in which the central gold atom of Au(25)(SC(1)H(3))(18) is replaced with Pd. These results strongly indicate that the isolated [Pd(1)Au(24)(SC(12)H(25))(18)](0) has a core-shell [Pd(1)@Au(24)(SC(12)H(25))(18)](0) structure in which the central Pd atom is surrounded by a frame of Au(24)(SC(12)H(25))(18). Experiments on the stability of the cluster showed that Pd(1)@Au(24)(SC(12)H(25))(18) is more stable against degradation in solution and laser dissociation than Au(25)(SC(12)H(25))(18). These results indicate that the doping of a central atom is a powerful method to increase the stability beyond the Au(25)(SR)(18) cluster.

Nonsuperatomic [Au23(SC6H11)16]− Nanocluster Featuring Bipyramidal Au15 Kernel and Trimeric Au3(SR)4 Motif

We report the X-ray structure of a cyclohexanethiolate-capped [Au23(SR)16](-) nanocluster (counterion: tetraoctylammonium, TOA(+)). The structure comprises a cuboctahedron-based bipyramidal Au15 kernel, which is protected by two staple-like trimeric Au3(SR)4 motifs, two monomeric Au(SR)2 and four plain bridging SR ligands. Electronic structure analysis reveals nonsuperatomic feature of [Au23(SR)16](-) and confirms the Au15 kernel and surface motifs. The Au15 kernel and trimeric staple motif are unprecedented and offer new insight in understanding the structure evolution of gold nanoclusters.

Effect of Copper Doping on Electronic Structure, Geometric Structure, and Stability of Thiolate-Protected Au25 Nanoclusters

Several recent studies have attempted to impart [Au25(SR)18](-) with new properties by doping with foreign atoms. In this study, we studied the effect of copper doping on the electronic structure, geometric structure, and stability of [Au25(SR)18](-) with the aim of investigating the effect of foreign atom doping of [Au25(SR)18](-). CunAu25-n(SC2H4Ph)18 was synthesized by reducing complexes formed by the reaction between metal salts (copper and gold salts) and PhC2H4SH with NaBH4. Mass analysis revealed that the products contained CunAu25-n(SC2H4Ph)18 (n = 1-5) in high purity. Experimental and theoretical analysis of the synthesized clusters revealed that copper doping alters the optical properties and redox potentials of the cluster, greatly distorts its geometric structure, and reduces the cluster stability in solution. These findings are expected to be useful for developing design guidelines for functionalizing [Au25(SR)18](-) through doping with foreign atoms.

Total structure and optical properties of a phosphine/thiolate-protected Au24 nanocluster.

We report the synthesis and total structure determination of a Au(24) nanocluster protected by mixed ligands of phosphine and thiolate. Single crystal X-ray crystallography and electrospray ionization mass spectrometry (ESI-MS) unequivocally determined the cluster formula to be [Au(24)(PPh(3))(10)(SC(2)H(4)Ph)(5)X(2)](+), where X = Cl and/or Br. The structure consists of two incomplete (i.e., one vertex missing) icosahedral Au(12) units joined by five thiolate linkages. This structure shows interesting differences from the previously reported vertex-sharing biicosahedral [Au(25)(PPh(3))(10)(SC(2)H(4)Ph)(5)X(2)](2+) nanocluster protected by the same type and number of phosphine and thiolate ligands. The optical absorption spectrum of Au(24) nanocluster was theoretically reproduced and interpreted.

Structure Determination of [Au18(SR)14]

Unravelling the atomic structures of small gold clusters is the key to understanding the origin of metallic bonds and the nucleation of clusters from organometallic precursors. Herein we report the X-ray crystal structure of a charge-neutral [Au18(SC6H11)14] cluster. This structure exhibits an unprecedented bi-octahedral (or hexagonal close packing) Au9 kernel protected by staple-like motifs including one tetramer, one dimer, and three monomers. Until the present, the [Au18(SC6H11)14] cluster is the smallest crystallographically characterized gold cluster protected by thiolates and provides important insight into the structural evolution with size. Theoretical calculations indicate charge transfer from surface to kernel for the HOMO-LUMO transition.

Ligand-Induced Stability of Gold Nanoclusters: Thiolate versus Selenolate

Thiolate-protected gold nanoclusters have attracted considerable attention as building blocks for new functional materials and have been extensively researched. Some studies have reported that changing the ligand of these gold nanoclusters from thiolate to selenolate increases cluster stability. To confirm this, in this study, we compare the stabilities of precisely synthesized [Au25(SC8H17)18](-) and [Au25(SeC8H17)18](-) against degradation in solution, thermal dissolution, and laser fragmentation. The results demonstrate that changing the ligand from thiolate to selenolate increases cluster stability in reactions involving dissociation of the gold-ligand bond but reduces cluster stability in reactions involving intramolecular dissociation of the ligand. These results reveal that using selenolate ligands makes it possible to produce gold clusters that are more stable against degradation in solution than thiolate-protected gold nanoclusters.

Doping and alloying in atomically precise gold nanoparticles

AbstractThe recent success in the synthesis and total structure determination of atomically precise gold nanoparticles has provided exciting opportunities for fundamental studies as well as the development of new applications. These unique nanoparticles are of molecular purity and possess well defined formulas (i.e., specific numbers of metal atoms and ligands), resembling organic compounds. Crystallization of such molecularly pure nanoparticles into macroscopic single crystals allows for the determination of total structures of nanoparticles (i.e., the arrangement of metal core atoms and surface ligands) by X-ray crystallography. In this perspective article, we summarize recent efforts in doping and alloying gold nanoparticles with other metals, including Pd, Pt, Ag and Cu. With atomically precise gold nanoparticles, a specific number of foreign atoms (e.g., Pd, Pt) can be incorporated into the gold core, whereas a range of Ag and Cu substitutions is observed but, interestingly, the total number of metal atoms in the homogold nanoparticle is preserved. The heteroatom substitution of gold nanoparticles allows one to probe the optical, structural, and electronic properties truly at the single-atom level, and thus provides a wealth of information for understanding the intriguing properties of this new class of nanomaterials.

Gold tetrahedra coil up: Kekulé-like and double helical superstructures.

Structures of gold clusters resemble the benzene and DNA molecules and reveal a “supermolecule” origin of the magic-sized clusters. Magic-sized clusters, as the intermediate state between molecules and nanoparticles, exhibit critical transitions of structures and material properties. We report two unique structures of gold clusters solved by x-ray crystallography, including Au40 and Au52 protected by thiolates. The Au40 and Au52 clusters exhibit a high level of complexity, with the gold atoms in the cluster first segregated into four-atom tetrahedral units—which then coil up into a Kekulé-like ring in the Au40 cluster and a DNA-like double helix in Au52. The solved structures imply a new “supermolecule” origin for revealing the stability of certain magic-sized gold clusters. The formation of supermolecular structures originates in the surface ligand bonding–induced stress and its propagation through the face-centered cubic (FCC) lattice. Moreover, the two structures reveal anisotropic growth of the FCC lattice in the cluster regime, which provides implications for the important roles of ligands at the atomic level. The rich structural information encoded in the Au40 and Au52 clusters provides atomic-scale insight into some important issues in cluster, nanoscale, and surface sciences.

Observation of Body-Centered Cubic Gold Nanocluster.

The structure of nanoparticles plays a critical role in dictating their material properties. Gold is well known to adopt face-centered cubic (fcc) structure. Herein we report the first observation of a body-centered cubic (bcc) gold nanocluster composed of 38 gold atoms protected by 20 adamantanethiolate ligands and two sulfido atoms ([Au38S2(SR)20], where R=C10H15) as revealed by single-crystal X-ray crystallography. This bcc structure is in striking contrast with the fcc structure of bulk gold and conventional Au nanoparticles, as well as the bi-icosahedral structure of [Au38(SCH2CH2Ph)24]. The bcc nanocluster has a distinct HOMO-LUMO gap of ca. 1.5 eV, much larger than the gap (0.9 eV) of the bi-icosahedral [Au38(SCH2CH2Ph)24]. The unique structure of the bcc gold nanocluster may be promising in catalytic applications.

New implementation of the trajectory surface hopping method with use of the Zhu–Nakamura theory

A new implementation of the trajectory surface hopping (TSH) method is proposed to treat multidimensional nonadiabatic dynamics by incorporating the analytical Zhu–Nakamura semiclassical theory of nonadiabatic transition. The problem of classically forbidden hops in the TSH method can now be solved and dealt with just as easily as the classically allowed hops by introducing nonvertical hopping techniques. This is made possible, because the theory can treat both classically allowed and forbidden hops accurately in a unified way. The Zhu–Nakamura theory also enables us to predetermine important regions of potential energy surface before carrying out any dynamics calculations, and thus to save a lot of computational efforts. The charge transfer processes in the collinear H3+ system are studied numerically to test the new TSH method. Comparing the new and old versions of TSH with exact quantum calculations, the new method shows much better agreement with the exact calculations. It also works well when all tra...