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Gold Nanoclusters with Atomic Precision: Optical Properties
Published in Yan Zhu, Rongchao Jin, Atomically Precise Nanoclusters, 2021
The study of the transition of nanoparticles from nonmetallic to metallic states has experienced difficulties. Fortunately, in 2017, Dass et al. obtained the largest thiol ligand-protected gold cluster to date by using a three-step synthesis method [87] [Step 1: crude synthesis, Step 2: thermochemical treatment (etching), and Step 3: isolation of molecularly pure Au279 nanocrystals and crystallization]. The heavy atom molecular formula, Au279S84, was established by a low-temperature X-ray diffraction study. This composition was independently verified by ESI (electrospray ionization) mass spectrometry (vide infra), and its molecular formula was established as Au279(SPh-tBu)84 (denoted as Au279). Dass et al. conducted an in-depth analysis of the structure of the giant cluster, including the structure of the metal core and the ligand layer [88]. Spectroscopic analysis indicated that Au279 exhibited a SPR peak at 510 nm. The following year, Jin et al. also reported the crystal structure of Au279 and discussed its optical properties in depth [89]. As an example, femtosecond transient absorption spectroscopic analysis was performed by pumping at 360 nm and probing in the 430–820 nm range to probe the excited-state dynamics of Au279. As shown in Fig. 7.6a,b, they found that the sharpening of the ground-state bleaching (GSB) peak with time evolution corresponds to the phonon induction after photoexcitation, similar to larger sized plasmonic nanoparticles [90, 91]. To obtain a deeper understanding of the nature of Au279, TA measurements were performed under different pump fluencies (Fig. 7.6c). In contrast to laser power-independent dynamics in Au246 and smaller Au nanoclusters, all the relaxation dynamics in Au279 are dependent on the laser fluence (Fig. 7.6d). This result further supports that Au279 has a plasma-like electronic structure. However, unlike typical plasma nanoparticles, when Au279 is excited at 360 nm, a broad ESA up to 1600 nm can be observed. In addition, the long-lived τph–ph (~300 ps) in Au279 also implies that the heavy gold cluster is in a primary plasmonic state [89].
Hierarchical clusters of lanthanide cluster plus gold cluster
Published in Inorganic and Nano-Metal Chemistry, 2021
Kai Zheng, Zhipeng Zhao, Haoran Li, Zeng Chenghui
Development of ligand protected gold cluster is the subject of an increasing number of studies in the last decade,[1] the research is mainly driven by the challenges of synthesis, structural determination, and excellent properties.[2] To date, a number of gold clusters have been identified,[3] and a few of them have been structurally characterized.[4] They show highly promising applications in catalysis,[5] optics,[6] sensing,[7] medical therapy,[8] bioimaging,[9] oxidation,[10] and so on.[11,12] Nevertheless, the application study of Au cluster is still in its infancy.
New Y-shaped structures of tetra-gold cation clusters stabilised by absorption of oxygen molecules
Published in Molecular Physics, 2021
Chao-Yong Mang, Cai-Ping Liu, Ke-Chen Wu
In 2014, Woodham and Fielicke [10] obtained a series of naked gold cluster cations Aum+ by the laser ablation of a solid target, and subsequently prepared cationic gold cluster complexes with multiple oxygen molecule ligands Aum(O2)n+ by the introduction of a pulse of oxygen. The infrared (IR) absorption spectra were measured by the mass-resolved IR multiple photon dissociation spectroscopy. For these complexes, the most remarkable spectral feature was found to be the O–O stretching mode of superoxo moiety (O2-). This vibrational absorption occurred at 1065 cm−1 for Au10(O2)n+ (n = 2∼6) and Au22O2+ as well as at 1063 cm−1 for Au21(O2)3+ and Au12(O2)n+ (n = 2∼5). In addition, the vibrational absorption of a physisorbed dioxygen ligand was observed. This absorption appeared at 1523 cm−1 for Au10(O2)n+ (n = 1∼6).
Metal–ligand bond directionality in the M2–NH3 complexes (M = Cu, Ag and Au)
Published in Molecular Physics, 2018
The nature of interactions between coinage metal atoms (M) and different ligand molecules has been widely studied [4,6,14–22]. Using energy decomposition analyses (EDA), Frenking and co-workers showed that in the coinage metal cyanides (M–CN) and isocyanides (M–NC), the covalent interactions are the driving force for the formation of metal–ligand bonds; however, these bonds are better described in terms of electrostatic pictures [16]. Sadlej and co-workers studied the interactions between coinage metal atoms and small lone-pair donating ligand (L) molecules (e.g. H2O, H2S and NH3) [4,6,18]. They showed that the charge transfer from the lone-pair of the ligand to the metal atom is the driving force for M–L interactions. Urban and Rajský investigated the interactions between small gold clusters, Aun, and different lone-pair donating ligands [22]. They suggested that charge transfer from the ligand lone-pair to the gold cluster is mainly responsible for the formation of Au–L bonds. Caramori etal. studied cyclic trinuclear complexes of Au(I), Ag(I) and Cu(I) by natural bond orbital (NBO) and EDA combine with natural orbitals for chemical valence (EDA-NOCV) approaches [14]. Their results revealed that M–L interactions are mainly electrostatic in nature; however, the covalent character is also significant. From the quantum theory of atoms in molecules (QTAIM) point of view, Pakiari and Jamshidi showed that the interactions between coinage metal clusters and chalcogens are partially electrostatic and partially covalent [21]. Using the molecular electrostatic potential (ESP) maps, Zhao studied the interactions between Aun clusters (n = 2, 3 and 4) and some halogen-containing molecules [23]. He showed that the interactions between positive and negative potentials on the surfaces of the Au and halogens are responsible for the formation of different types of Au–halogen interactions.