4 research outputs found
Adsorption and Subsequent Reaction of a Water Molecule on Silicate and Silica Cluster Anions
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
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
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
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)Âglycine)
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