Resistance of a PdAu(8e) Core to Growth in Collision-Induced Sequential Reductive Elimination of (C≡CR) from [PdAu(C≡CR)].

Previous studies have reported that [PdAu(PA)] (PA = 3,5-(CF)CHC≡C) with an icosahedral superatomic PdAu(8e) core underwent collision-induced sequential reductive elimination (CISRE) of 1,3-diyne (PA) ( 2020, 124, 19119). The most likely scenario after the CISRE of (PA) is the growth of the PdAu(8e) core via the fusion of the Au(0) atoms produced from the Au(PA) units on the core surface. Contrary to expectation, anion photoelectron spectroscopy and theoretical calculations regarding the CISRE products [PdAu(PA)] ( = 1-6) revealed that the electronically closed PdAu(8e) core does not grow to a single superatom with (8 + 2)e but assembles with Au(2e) units.

Revisiting the structure of [PdAu9(PPh3)8(CN)]2+ produced by atmospheric pressure plasma irradiation of [PdAu8(PPh3)8]2+ in methanol.

Some of the authors of the present research group have previously reported mass spectrometric detection of [PdAu9(PPh3)8(CN)]2+ (PdAu9CN) by atmospheric pressure plasma (APP) irradiation of [MAu8(PPh3)8]2+ (PdAu8) in methanol and proposed based on density functional theory (DFT) calculations that PdAu9CN is constructed by inserting a CNAu or NCAu unit into the Au-PPh3 bond of PdAu8 [Emori et al., J. Chem.

Gas-Phase Anion Photoelectron Spectroscopy of Alkanethiolate-Protected PtAu Superatoms: Charging Energy in Vacuum vs Solution.

The charging behavior of molecular Au clusters protected by alkanethiolate (SCH=SCn) is, under electrochemical conditions, significantly affected by the penetration of solvents and electrolytes into the SCn layer. In this study, we estimated the charging energy E(n) associated with [PtAu(SCn)]+e→[PtAu(SCn)] (n=4, 8, 12, and 16) in vacuum using mass-selected gas-phase anion photoelectron spectroscopy of [PtAu(SCn)] (z=-1 and -2). The E(n) values of PtAu(SCn) in vacuum are significantly larger than those in solution and decrease with n in contrast to the behavior reported for Au(SCn) in solution.

Gas-Phase Structures of [Au(SR)] and [Au(SR)] with Eight Electrons: Can They Support an Icosahedral Au Core?

A prototypical thiolate (RS)-protected gold cluster [Au(SR)] has high stability due to specific geometric and electronic structures: an icosahedral () Au core with a closed electronic shell containing eight electrons is completely protected by six units of Au(SR). Nevertheless, collisional excitation of [Au(SR)] in a vacuum induces the sequential release of Au(SR) to form [Au(SR)] and [Au(SR)] both containing eight electrons. To answer a naive question of whether these fragments bear an Au(8e) core, the geometrical structures of [Au(SCH)] and [Au(SCH)] in the gas phase were examined by the combination of anion photoelectron spectroscopy and density functional theory (DFT) calculation of simplified models of [Au(SCH)] and [Au(SCH)].

Non-terminal conjugation of small interfering RNAs with spermine improves duplex binding and serum stability with position-specific incorporation.

The conjugation of small interfering RNAs (siRNAs) has been studied using lipid and ligand conjugates for efficient delivery. However, most conjugates have been inserted at the terminal position; very few have been inserted at non-terminal positions. Herein, we synthesized a 4'--propyllevulinate-2'--methyluridine analog for non-terminal conjugation of spermine into the passenger strand of siRNA.

Effect of total charge on the electronic structure of thiolate-protected X@Ag superatoms (X = Ag, Au).

Electronic structures of chemically synthesized silver-based clusters [XAg(TBBT)] (X = Ag or Au; TBBT = 4--butylbenzenethiolate) having an icosahedral X@Ag superatomic core were studied by gas-phase photoelectron spectroscopy and density functional theory calculations. The electron binding energy of the highest occupied molecular orbital (HOMO) with a 1P superatomic nature was determined to be 0.23 and 0.

Electron Affinities of Ligated Icosahedral M Superatoms Revisited by Gas-Phase Anion Photoelectron Spectroscopy.

The electron binding energies of the ligand-protected gold/silver-based cluster anions, [Au(SR)], [XAg(SR')] (X = Ag, Au, Pd, or Pt), and [PdAu(C≡CR″)] having icosahedral M superatomic cores, were reexamined by gas-phase photoelectron spectroscopy (PES) on a significantly intensified mass-selected ion beam. Laser fluence-dependent PE spectra and pump-probe PES revealed that the previous PE spectra were contaminated by PE signals due to the two-photon electron detachment via long-lived photoexcited states. Although the adiabatic electron affinities (AEAs) of the corresponding oxidized forms were found to be 1-2 eV larger than those previously reported, the effects of doping and ligation were not qualitatively affected.

Controlled Synthesis of Diphosphine-Protected Gold Cluster Cations Using Magnetron Sputtering Method.

We demonstrated, for the first time, atomically precise synthesis of gold cluster cations by magnetron sputtering of a gold target onto a polyethylene glycol (PEG) solution of 1,3-bis(diphenylphosphino)propane (PhPCHCHCHPPh, dppp). UV-vis absorption spectroscopy and electrospray ionization mass spectrometry revealed the formation of cationic species, such as [Au(dppp)] ( = 1, 2), [Au(dppp)] ( = 3, 4), [Au(dppp)] ( = 3, 4), and [Au(dppp)]. The formation of [Au(dppp)] was ascribed to ionization of Au(dppp) by the reaction with PEG, based on its low ionization energy, theoretically predicted, mass spectrometric detection of deprotonated anions of PEG.

Critical Role of CF Groups in the Electronic Stabilization of [PdAu(C≡CCH(CF))] as Revealed by Gas-Phase Anion Photoelectron Spectroscopy.

The role of alkynyl ligands with electron-withdrawing nature in the stability of metal clusters was investigated by gas-phase anion photoelectron spectroscopy (PES) on heteroleptic cluster anions [PdAu(C≡CAr)(C≡CPh)] (Ar = 3,5-(CF)CH). Gas-phase PES on the cluster anions with specific (= 0-6) revealed that electron binding energies decreased linearly with , indicating that the electron-withdrawing CF substituents on the alkynyl ligand played a critical role in the electronic stabilization of [PdAu(C≡CAr)]. Density functional theory calculations reproduced the decrease of electron binding energies and rationally explained the ligand effect by a mechanism similar to the modulation of the work function of gold films by organic monolayers.

Chemical transformations of [MAu(PPh)] (M = Pt, Pd) and [Au(PPh)] in methanol induced by irradiation of atmospheric pressure plasma.

The reaction processes of ligand-protected metal clusters induced by irradiating atmospheric pressure plasma (APP) were investigated using optical spectroscopy, mass spectrometry, and density functional theory (DFT) calculations. The target clusters were phosphine-protected gold-based clusters [MAu(PPh)] (M = Pt, Pd) and [Au(PPh)], which have a crown-shaped M@Au (M = Pt, Pd, Au) core with an unligated M site at the central position. The APP irradiation of [MAu(PPh)] (M = Pt, Pd) in methanol resulted in the selective formation of [PtAu(PPh)CO] and [PdAu(PPh)CN] via the addition of a CO molecule and AuCN unit, respectively, generated in situ by the APP irradiation.

Ligand-protected gold/silver superatoms: current status and emerging trends.

Monolayer-protected gold/silver clusters have attracted much interest as nano-scale building units for novel functional materials owing to their nonbulk-like structures and size-specific properties. They can be viewed as ligand-protected superatoms because their magic stabilities and fundamental properties are well explained in the framework of the jellium model. In the last decade, the number of ligand-protected superatoms with atomically-defined structures has been increasing rapidly thanks to the well-established synthesis and structural determination by X-ray crystallography.

Gas-phase studies of chemically synthesized Au and Ag clusters.

Atomically precise Au and Ag clusters protected by monolayers of organic ligands have attracted growing interests as promising building units of functional materials and ideal platforms to study size-dependent evolution of structures and physicochemical properties. The use of gas-phase methods including mass spectrometry, ion mobility mass spectrometry, collision-induced dissociation mass spectrometry, photoelectron spectroscopy, and photodissociation spectroscopy will reveal novel and complementary information on their intrinsic geometric and electronic structures that cannot be obtained by conventional characterization methods. This Perspective surveys the recent progress and outlook of gas-phase studies on chemically synthesized Au/Ag clusters.

AuSi and AuSi: Electronically Equivalent but Different Polarity Superatoms.

A series of AuSi cluster anions ( = 1-4) were generated most abundantly by laser ablation of a AuSi alloy target. Photoelectron spectroscopy and density functional theory (DFT) calculation of AuSi ( = 1-4) revealed that AuSi can be viewed as an electronically closed superatom and is composed of a Si unit whose three adjacent edges of a single facet are bridged by three Au atoms. Such phase-segregated structure is facilitated by aurophilic interaction between the three Au atoms and results in a large permanent dipole moment (4.

Sequential growth of iridium cluster anions based on simple cubic packing.

Geometric structures of free iridium cluster anions, Irn-, were examined by means of ion mobility mass spectrometry and density functional theory calculation for n = 3-15 with the additional help of photoelectron spectroscopy for n = 4-10. It has been revealed that Irn- clusters with n ≥ 5 favor a square facet and take a cubic motif in contrast to the face-centered cubic structures in the corresponding nanoparticles and bulk. A growth sequence of Irn- for n = 5-15 is proposed: single Ir atoms are sequentially attached to one side of the square plane of Ir4- to form a cubic Ir8-, and are then continuously attached on one of the square facets of Ir8- for n = 9-12 and Ir12- for n = 13-15.

Ultrafast Creation of Overlapping Rydberg Electrons in an Atomic BEC and Mott-Insulator Lattice.

We study an array of ultracold atoms in an optical lattice (Mott insulator) excited with a coherent ultrashort laser pulse to a state where single-electron wave functions spatially overlap. Beyond a threshold principal quantum number where Rydberg orbitals of neighboring lattice sites overlap with each other, the atoms efficiently undergo spontaneous Penning ionization resulting in a drastic change of ion-counting statistics, sharp increase of avalanche ionization, and the formation of an ultracold plasma. These observations signal the actual creation of electronic states with overlapping wave functions, which is further confirmed by a significant difference in ionization dynamics between a Bose-Einstein condensate and a Mott insulator.

Electron Binding in a Superatom with a Repulsive Coulomb Barrier: The Case of [Ag(SCHF)] in the Gas Phase.

The electron binding mechanism in [Ag(SCHF)] (SCHF = 3,4-difluorobenzenethiolate) tetra-anion was studied by photoelectron spectroscopy (PES), collision-induced dissociation mass spectrometry (CID-MS), and density functional theory (DFT) computations. PES showed that [Ag(SCHF)] is energetically metastable with respect to electron autodetachment {[Ag(SCHF)] + e} and features a repulsive Coulomb barrier (RCB) with a height of 2.7 eV.

Abstraction of the I Atom from CHI by Gas-Phase Au ( = 1-4) via Reductive Activation of the C-I Bond.

Gas-phase reactions of atomic gold anions and small gold cluster anions, Au ( = 1-4), with CHI were investigated to clarify the effect of the cluster size on C-I bond activation and to elucidate the key properties of Au clusters that govern the reactivity. Au I identified by mass spectrometry was observed as a common reaction product. Photoelectron spectroscopy and density functional theory calculations revealed that AuI has a linear structure in which the I atom is bonded to Au, and AuI and AuI take a two-dimensional structure in which the I atom is bonded to triangular Au moieties.

Photoelectron Spectroscopy of Molecular Anion of Alq: An Estimation of Reorganization Energy for Electron Transport in the Bulk.

A molecular anion of tris(8-hydroxyquinolinato)aluminum (Alq) was generated by a pulsed discharge to the solid sample under supersonic expansion and its photoelectron spectrum was recorded after mass selection. The vertical detachment energy of Alq and the adiabatic electron affinity of Alq were determined to be 1.24 ± 0.

Characterization of chemically modified gold and silver clusters in gas phase.

Atomically precise Au and Ag clusters protected by organic ligands can be viewed as chemically modified Au/Ag superatoms and have attracted interest as promising building units of functional materials and ideal platforms for studying the size-dependent evolution of structures and properties. Their structures, stability, and physicochemical properties have been characterized in solution and solid (or crystalline) phases by various methods conventionally used in materials science. However, novel and complementary information on their intrinsic stability and structures can be obtained by applying a variety of gas-phase methods, including mass spectrometry, ion mobility mass spectrometry, collision- or surface-induced dissociation mass spectrometry, photoelectron spectroscopy, and photodissociation mass spectrometry, to the chemically modified Au/Ag superatoms isolated in the gas phase.

Elucidating the Doping Effect on the Electronic Structure of Thiolate-Protected Silver Superatoms by Photoelectron Spectroscopy.

Gas-phase photoelectron spectroscopy (PES) was conducted on [XAg (SPhMe ) ] (X=Ag, Au) and [YAg (SPhMe ) ] (Y=Pd, Pt), which have a formal superatomic core (X@Ag ) or (Y@Ag ) with icosahedral symmetry. PES results show that superatomic orbitals in the (Au@Ag ) core remain unshifted with respect to those in the (Ag@Ag ) core, whereas the orbitals in the (Y@Ag ) (Y = Pd, Pt) core shift up in energy by about 1.4 eV.

The stability of binary AlX nanoclusters (X = Sc and Ti): superatom or Wade's polyhedron.

Binary nanoclusters (NCs) exhibit strong potential as building blocks for tailor-made scientific materials based on the precise tuning of their electron countings and spin states along with the synergistic effects that originate from the constituent elements. Herein, we studied the electronic and geometric structures of transition metal (TM) doped aluminum (Al) AlX NCs (X  =  Sc and Ti), which are binary systems that extend from representative superatom [Formula: see text] anions. On the basis of the photoelectron spectroscopy (PES) and density functional theory (DFT) calculations, AlX anion and neutral structures are characterized as vertex-replaced icosahedron.

Collision-Induced Dissociation of Undecagold Clusters Protected by Mixed Ligands [Au(PPh)X] (X = Cl, C≡CPh).

We herein investigated collision-induced dissociation (CID) processes of undecagold clusters protected by mixed ligands [Au(PPh)X] (X = Cl, C≡CPh) using mass spectrometry and density functional theory calculations. The results showed that the CID produced fragment ions [Au (PPh) X ] with a formal electron count of eight via sequential loss of PPh ligands and AuX(PPh) units in a competitive manner, indicating that the CID channels are governed by the electronic stability of the fragments. Interestingly, the branching fraction of the loss of the AuX(PPh) units was significantly smaller for X = C≡CPh than that for X = Cl.

Gold Ultrathin Nanorods with Controlled Aspect Ratios and Surface Modifications: Formation Mechanism and Localized Surface Plasmon Resonance.

We synthesized gold ultrathin nanorods (AuUNRs) by slow reductions of gold(I) in the presence of oleylamine (OA) as a surfactant. Transmission electron microscopy revealed that the lengths of AuUNRs were tuned in the range of 5-20 nm while keeping the diameter constant (∼2 nm) by changing the relative concentration of OA and Au(I). It is proposed on the basis of time-resolved optical spectroscopy that AuUNRs are formed via the formation of small (<2 nm) Au spherical clusters followed by their one-dimensional attachment in OA micelles.

Structure Determination of a Water-Soluble 144-Gold Atom Particle at Atomic Resolution by Aberration-Corrected Electron Microscopy.

Structure determination by transmission electron microscopy has revealed the long sought 144-gold atom particle. The structure exhibits deviations from face-centered cubic packing of the gold atoms, similar to the solution structure of another gold nanoparticle, and in contrast to a previous X-ray crystal structure. Evidence from analytical methods points to a low number of 3-mercaptobenzoic acid ligands covering the surface of the particle.