Xi Kang

Crystal Structure of Selenolate-Protected Au24(SeR)20 Nanocluster

We report the X-ray structure of a selenolate-capped Au24(SeR)20 nanocluster (R = C6H5). It exhibits a prolate Au8 kernel, which can be viewed as two tetrahedral Au4 units cross-joined together without sharing any Au atoms. The kernel is protected by two trimeric Au3(SeR)4 staple-like motifs as well as two pentameric Au5(SeR)6 staple motifs. Compared to the reported gold-thiolate nanocluster structures, the features of the Au8 kernel and pentameric Au5(SeR)6 staple motif are unprecedented and provide a structural basis for understanding the gold-selenolate nanoclusters.

Bimetallic Au2Cu6 Nanoclusters: Strong Luminescence Induced by the Aggregation of Copper(I) Complexes with Gold(0) Species

The concept of aggregation-induced emission (AIE) has been exploited to render non-luminescent Cu(I) SR complexes strongly luminescent. The Cu(I) SR complexes underwent controlled aggregation with Au(0) . Unlike previous AIE methods, our strategy does not require insoluble solutions or cations. X-ray crystallography validated the structure of this highly fluorescent nanocluster: Six thiolated Cu atoms are aggregated by two Au atoms (Au2 Cu6 nanoclusters). The quantum yield of this nanocluster is 11.7 %. DFT calculations imply that the fluorescence originates from ligand (aryl groups on the phosphine) to metal (Cu(I) ) charge transfer (LMCT). Furthermore, the aggregation is affected by the restriction of intramolecular rotation (RIR), and the high rigidity of the outer ligands enhances the fluorescence of the Au2 Cu6 nanoclusters. This study thus presents a novel strategy for enhancing the luminescence of metal nanoclusters (by the aggregation of active metal complexes with inert metal atoms), and also provides fundamental insights into the controllable synthesis of highly luminescent metal nanoclusters.

The Magic Au60 Nanocluster: A New Cluster‐Assembled Material with Five Au13 Building Blocks

Herein, we report the synthesis and atomic structure of the cluster-assembled [Au60Se2(Ph3P)10(SeR)15](+) material. Five icosahedral Au13 building blocks from a closed gold ring with Au-Se-Au linkages. Interestingly, two Se atoms (without the phenyl tail) locate in the center of the cluster, stabilized by the Se-(Au)5 interactions. The ring-like nanocluster is unprecedented in previous experimental and theoretical studies of gold nanocluster structures. In addition, our optical and electrochemical studies show that the electronic properties of the icosahedral Au13 units still remain unchanged in the penta-twinned Au60 nanocluster, and this new material might be a promising in optical limiting material. This work offers a basis for deep understanding on controlling the cluster-assembled materials for tailoring their functionalities.

Shape-Controlled Synthesis of Trimetallic Nanoclusters: Structure Elucidation and Properties Investigation.

The shape-controlled synthesis of metal nanoclusters (NCs) with precise atomic arrangement is crucial for tailoring the properties. In this work, we successfully control the shape of alloy NCs by altering the dopants in the alloying processes. The shape of the spherical [Pt1 Ag24 (SPhMe2 )18 ] NC is maintained when [AuI SR] is used as dopant. By contrast, the shape of Pt1 Ag24 is changed to be rodlike by alloying with [AuI (PPh3 )Br]. The structures of the trimetallic NCs were determined by X-ray crystallography and further confirmed by both DFT and far-IR measurements. The shape-preserved [Pt1 Au6.4 Ag17.6 (SPhMe2 )18 ] NC is in a tristratified arrangement-[Pt(center)@Au/Ag(shell)@Ag(exterior)]-and is indeed the first X-ray crystal structure of thiolated trimetallic NCs. On the other hand, the resulting rodlike NC ([Pt2 Au10 Ag13 (PPh3 )10 Br7 ]) exhibits a high quantum yield (QY=14.7 %), which is in striking contrast to the weakly luminescent Pt1 Ag24 (QY=0.1 %, about 150-fold enhancement). In addition, the thermal stabilities of both trimetallic products are remarkably improved. This study presents a controllable strategy for synthesis of alloy NCs with different shapes (by alloying heteroatom complexes coordinated by different ligands), and may stimulate future work for a deeper understanding of the morphology (shape)-property correlation in NCs.

Modulating photo-luminescence of Au2Cu6 nanoclusters via ligand-engineering

In this work, the luminescence of Au2Cu6 nanoclusters was controlled by tailoring the ligand to metal charge transfer via engineering the phosphine ligands with electron-donating or -withdrawing substituents. The fluorescence intensity was significantly enhanced from the Au2Cu6 nanocluster with P(Ph–F)3 ligands (quantum yield QY = 5.7%) to that with P(Ph–OMe)3 ligands (QY = 17.7%). In addition, the fluorescence of Au2Cu6 protected by P(Ph–OMe)3 slightly red-shifts compared to that of Au2Cu6 protected by P(Ph–F)3, which is similar to the trends of UV-vis spectra tendency.

Combining the Single-Atom Engineering and Ligand-Exchange Strategies: Obtaining the Single-Heteroatom-Doped Au16Ag1(S-Adm)13 Nanocluster with Atomically Precise Structure

Obtaining cognate single-heteroatom doping is highly desirable but least feasible in the research of nanoclusters (NCs). In this work, we reported a new Au16Ag1(S-Adm)13 NC, which is synthesized by the combination of single-atom engineering and ligand-exchange strategies. This new NC is so far the smallest crystallographically characterized Au-based NC protected by thiolate. The Au16Ag1(S-Adm)13 exhibited a tristratified Au3-Au2Ag1-Au1 kernel capped by staple-like motifs including one dimer and two tetramers. In stark contrast to the size-growth from Au18(S-C6H11)14 to Au21(S-Adm)15 via just the ligand-exchange method, combining single Ag doping on Au18(S-C6H11)14 resulted in the size-decrease from Au17Ag1(S-C6H11)14 to Au16Ag1(S-Adm)13. DFT calculations were performed to both homogold Au18 and single-heteroatom-doped Au17Ag1 to explain the opposite results under the same ligand-exchange reaction. Our work is expected to inspire the synthesis of new cognate single-atom-doped NCs by combining single-atom engineering and ligand-exchange strategies and also shed light on extensive understanding of the metal synergism effect in the NC range.

Ligand-induced change of the crystal structure and enhanced stability of the Au11 nanocluster

In this paper, we report a highly stable gold nanocluster co-protected by the selenophenol and 1,5-bis(diphenylphosphino)pentane (L5 for short) ligands, formulated as [Au11(L5)4(SePh)2]+. The structure of this nanocluster is determined by X-ray crystallography. The L5-ligands are in the form of “Au–PPh2(CH2)5Ph2P–Au”, similar to the “staple motif” in the Aun(SR)m nanoclusters. The purity of this nanocluster is confirmed by electrospray ionization mass spectrometry (ESI-MS) and the thermogravimetric analysis (TGA). Moreover, we have also systematically investigated the stability of the [Au11(L5)4(SePh)2]+ (Au11-Se for short). The results show that Au11-Se is significantly more stable than both Au11(PPh3)7Cl3 (Au11-7 for short) and [Au11(PPh3)8Cl2]Cl (Au11-8 for short), even in the presence of excess thiol (RSH). This work will provide a new opportunity for future wide research on gold nanoclusters.

Aggregation-Induced Emission (AIE) in Ag−Au Bimetallic Nanocluster

Herein we report the synthesis and structure determination of a non-fluorescent Au4 Ag5 (dppm)2 (SAdm)6 (BPh4 ) (dppm=bis(diphenylphosphino)methane and HSAdm=1-adamantane mercaptan) nanocluster in methanol with extremely strong AIE when aggregating to the solid state (i.e., film or crystal). This phenomenon was rarely reported in structural determined noble metal nanoclusters. The extended X-ray absorption fine structure (EXAFS) measurement ruled out the hypothesis that the luminescence originated from the structure change in different states. Besides, the crystal structure (determined by X-ray diffraction) revealed that the tightly combined left- and right-handed enantiomers induced the strong restriction of intramolecular motions (RIM), which may have an impact on aggregation-induced emission.

Thiol-Induced Synthesis of Phosphine-Protected Gold Nanoclusters with Atomic Precision and Controlling the Structure by Ligand/Metal Engineering

Efficient synthesis of atomically precise phosphine-capped gold nanocluster (with >10 metal atoms) is important to deeply understand the relationship between structure and properties. Herein, we successfully utilize the thiol-induced synthesis method and obtain three atomically precise phosphine-protected gold nanoclusters. Single-crystal X-ray structural analysis reveals that the nanoclusters are formulated as [Au13(Dppm)6](BPh4)3, [Au18(Dppm)6Br4](BPh4)2, and [Au20(Dppm)6(CN)6] (where Dppm stands for bis(diphenylphosphino)methane), which are further confirmed by electrospray ionization mass spectrometry, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Meanwhile, [Au18(Dppm)6Br4](BPh4)2 could be converted into [Au13(Dppm)6](BPh4)3 and [Au20(Dppm)6(CN)6] by engineering the surface ligands under excess PPh3 or moderate NaBH3CN, respectively. Furthermore, according to the different binding ability of silver with halogen, we successfully achieved target metal exchange on [Au18(Dppm)6Br4](BPh4)2 with Ag-SAdm (where HS-Adm stands for 1-adamantane mercaptan) complex and obtained [AgxAu18-x(Dppm)6Br4](BPh4)2 (x = 1, 2) alloy nanoclusters. Our work will contribute to more intensive understanding on synthesizing phosphine-protected nanoclusters as well as shedding light on the structure-property correlations in the nanocluster range.

Theoretical investigations on the structure–property relationships of Au13 and AuxM13−x nanoclusters

As a fundamental building block in ultrasmall, noble metal nanoclusters, icosahedral AuxM13−x structures have recently attracted extensive research interest. In this study, density functional theory (DFT) and time-dependant DFT calculations have been carried out to investigate the structure–property (optical and electronic) relationships of a series of Au13 and AuxM13−x (M = Au, Ag, Cu, and Pd) nanoclusters co-protected by phosphine and chloride ligands. It was found that the size of the peripheral ligands significantly affects the geometric structure: the larger exterior ligands (with a larger cone angle) result in relatively longer Au–M bond distances and weaker metallic interactions within the AuxM13−x core. Therefore, the optical peak (in the UV-vis spectrum) corresponding to the HOMO → LUMO transition red-shifts accordingly. When different foreign atom(s) are incorporated, the preferential doping site is different, and the electronic and optical structures alter accordingly.