4 research outputs found

    Adsorption and Subsequent Reaction of a Water Molecule on Silicate and Silica Cluster Anions

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    We present reactions of size-selected free silicate, Mg<sub><i>l</i></sub>SiO<sub><i>m</i></sub><sup>–</sup>, and silica, Si<sub><i>n</i></sub>O<sub><i>m</i></sub><sup>–</sup>, cluster anions with a H<sub>2</sub>O molecule focusing on H<sub>2</sub>O adsorption. It was found that H<sub>2</sub>O adsorption to Mg<sub><i>l</i></sub>SiO<sub><i>m</i></sub><sup>–</sup> with <i>l</i> = 2 and 3 (<i>m</i> = 4–6) is always followed by molecular oxygen release, whereas reactivity of the clusters with <i>l</i> = 1 (<i>m</i> = 3–5) was found to be much lower. On the contrary, in the reaction of Si<sub><i>n</i></sub>O<sub><i>m</i></sub><sup>–</sup> (<i>n</i> = 3–8, 2<i>n</i> – 1 ≤ <i>m</i> ≤ 2<i>n</i> + 2), a H<sub>2</sub>O adduct is observed as a major reaction product. Larger and oxygen-rich clusters tend to exhibit higher reactivity; the rate constants of the adsorption reaction are 2 orders of magnitude larger than those of CO adsorption previously reported. DFT calculations revealed that H<sub>2</sub>O is dissociatively adsorbed on Si<sub><i>n</i></sub>O<sub><i>m</i></sub><sup>–</sup> to form two SiO<sub>3</sub>(OH) tetrahedra. The site selectivity of H<sub>2</sub>O adsorption is governed by the location of the singly occupied molecular orbital (SOMO) on Si<sub><i>n</i></sub>O<sub><i>m</i></sub><sup>–</sup>. The present findings give molecular-level insights into H<sub>2</sub>O adsorption on silica and silicate species in the interstellar environment

    Collision-Induced Fission of Oblate Gold Superatom in [Au<sub>9</sub>(PPh<sub>3</sub>)<sub>8</sub>]<sup>3+</sup>: Deformation-Mediated Mechanism

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    Collision-induced dissociation (CID) patterns of the phosphine-protected Au-based clusters [PdAu8(PPh3)8]2+ (PdAu8) and [Au9(PPh3)8]3+ (Au9), featuring crown-shaped M@Au8 (M = Pd, Au) cores, were investigated. For PdAu8, ordinary sequential PPh3 losses (PdAu8 → [PdAu8(PPh3)m]2+ + (8 – m)PPh3 (m = 7, 6, 5)) were observed. In contrast, Au9 underwent cluster-core fission (Au9 → [Au6(PPh3)6]2+ (Au6) + [Au3(PPh3)2]+ (Au3)) upon sufficiently high energy collision, associated with splitting the number of valence electrons in the superatomic orbitals from 6e (Au9) into 4e (Au6) and 2e (Au3). Density functional theory calculations revealed oblate and prolate cores of Au9 and Au6 with semiclosed superatomic electron configurations of (1S)2(1Px)2(1Py)2 and (1S)2(1Pz)2, respectively. This result indicated a significant deformation of the cluster-core motif during the CID process. We attribute the clear difference between PdAu8 and Au9 to the softer Au–Au bond in Au9 and propose that the collision-induced structural deformation plays a critical role in the fission

    Collision-Induced Fission of Oblate Gold Superatom in [Au<sub>9</sub>(PPh<sub>3</sub>)<sub>8</sub>]<sup>3+</sup>: Deformation-Mediated Mechanism

    No full text
    Collision-induced dissociation (CID) patterns of the phosphine-protected Au-based clusters [PdAu8(PPh3)8]2+ (PdAu8) and [Au9(PPh3)8]3+ (Au9), featuring crown-shaped M@Au8 (M = Pd, Au) cores, were investigated. For PdAu8, ordinary sequential PPh3 losses (PdAu8 → [PdAu8(PPh3)m]2+ + (8 – m)PPh3 (m = 7, 6, 5)) were observed. In contrast, Au9 underwent cluster-core fission (Au9 → [Au6(PPh3)6]2+ (Au6) + [Au3(PPh3)2]+ (Au3)) upon sufficiently high energy collision, associated with splitting the number of valence electrons in the superatomic orbitals from 6e (Au9) into 4e (Au6) and 2e (Au3). Density functional theory calculations revealed oblate and prolate cores of Au9 and Au6 with semiclosed superatomic electron configurations of (1S)2(1Px)2(1Py)2 and (1S)2(1Pz)2, respectively. This result indicated a significant deformation of the cluster-core motif during the CID process. We attribute the clear difference between PdAu8 and Au9 to the softer Au–Au bond in Au9 and propose that the collision-induced structural deformation plays a critical role in the fission

    An Au<sub>25</sub>(SR)<sub>18</sub> Cluster with a Face-Centered Cubic Core

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    A representative thiolate (RS)-protected gold cluster, Au<sub>25</sub>(SR)<sub>18</sub>, shows a fingerprint-like characteristic spectral profile regardless of the R-groups, reflecting the common motif of the structural backbone made of Au and S: an icosahedral Au<sub>13</sub> core fully protected by six staple units of Au<sub>2</sub>(SR)<sub>3</sub>. On the other hand, we reported in 2006 that an Au<sub>25</sub>(SPG)<sub>18</sub> cluster (PGSH = <i>N</i>-(2-mercaptopropionyl)­glycine) exhibited an optical absorption spectrum significantly different from that of the conventional Au<sub>25</sub>(SR)<sub>18</sub>, suggesting the formation of a nonicosahedral Au core. Here, we investigated the structure of Au<sub>25</sub>(SPG)<sub>18</sub> by UV–vis spectroscopy, extended X-ray absorption fine structure analysis and density functional theory calculations. Spectroscopic results indicated that Au<sub>25</sub>(SPG)<sub>18</sub> has a face-centered cubic (FCC) Au core. We proposed a model structure formulated as Au<sub>15</sub>(SPG)<sub>4</sub>[Au<sub>2</sub>(SPG)<sub>3</sub>]<sub>2</sub>[Au<sub>3</sub>(SPG)<sub>4</sub>]<sub>2</sub> in which an Au<sub>15</sub>(SPG)<sub>4</sub> core with an FCC motif is protected by two types of staples with different lengths, Au<sub>2</sub>(SPG)<sub>3</sub> and Au<sub>3</sub>(SPG)<sub>4</sub>. The formation of an FCC-based Au core is attributed to bulkiness around the α-carbon of the PGS ligand
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