11 research outputs found
Electron and Hydride Addition to Gold (I) Thiolate Oligomers: Implications for Gold–Thiolate Nanoparticle Growth Mechanisms
Electron and hydride addition to Au(I):SR oligomers is investigated using density functional theory. Cyclic and chain-like clusters are examined in this work. Dissociation to Au– ions and Aun(SR)n+1– chains is observed after 2–4 electrons are added to these systems. The free thiolate (SR–) is rarely produced in this work; dissociation of Au– is preferred over dissociation of SR–. Electron affinities calculated in gas phase, toluene, and water suggest that the electron addition process is unlikely, although it may be possible in polar solvents. In contrast, hydride addition to Au(I):SR oligomers yields free thiols and complexes containing Au–Au bonds, which are plausible intermediates for gold nanoparticle growth. The resulting compounds can react to form larger nanoparticles or undergo further reduction by hydride to yield additional Au–Au bonds
Incremental Binding Energies of Gold (I) and Silver (I) Thiolate Clusters
Density functional theory is used to find incremental fragmentation energy, overall dissociation energy, and average monomer fragmentation energy of cyclic gold(I) thiolate clusters and anionic chain structures of gold(I) and silver(I) thiolate clusters as a measure of the relative stability of these systems. Two different functionals, BP86 and PBE, and two different basis sets, TZP and QZ4P, are employed. Anionic chains are examined with various residue groups including hydrogen, methyl, and phenyl. Hydrogen and methyl are shown to have approximately the same binding energy, which is higher than phenyl. Gold–thiolate clusters are bound more strongly than corresponding silver clusters. Lastly, binding energies are also calculated for pure Au25(SR)18–, Ag25(SR)18–, and mixed Au13(Ag2(SH)3)6– and Ag13(Au2(SH)3)6– nanoparticles
The Golden Pathway to Thiolate-Stabilized Nanoparticles: Following the Formation of Gold (I) Thiolate from Gold (III) Chloride
Pathways for the formation of gold thiolate complexes from gold(III) chloride precursors AuCl4– and AuCl3 are examined. This work demonstrates that two distinct reaction pathways are possible; which pathway is accessible in a given reaction may depend on factors such as the residue group R on the incoming thiol. Density functional theory calculations using the BP86 functional and a polarized triple-ζ basis set show that the pathway resulting in gold(III) reduction is favored for R = methyl. A two-to-one ratio of thiol or thiolate to gold can reduce Au(III) to Au(I), and a three-to-one ratio can lead to polymeric Au(SR) species, which was first suggested by Schaaff et al. J. Phys. Chem. B, 1997, 101, 7885 and later confirmed by Goulet and Lennox J. Am. Chem. Soc., 2010, 132, 9582. Most transition states in the pathways examined here have reasonable barrier heights around 0.3 eV; we find two barrier heights that differ substantially from this which suggest the potential for kinetic control in the first step of thiolate-protected gold nanoparticle growth
Oxidation of Gold Clusters by Thiols
The formation of gold–thiolate nanoparticles via oxidation of gold clusters by thiols is examined in this work. Using the BP86 density functional with a triple ζ basis set, the adsorption of methylthiol onto various gold clusters AunZ (n = 1–8, 12, 13, 20; Z = 0, −1, +1) and Au384+ is investigated. The rate-limiting step for the reaction of one thiol with the gold cluster is the dissociation of the thiol proton; the resulting hydrogen atom can move around the gold cluster relatively freely. The addition of a second thiol can lead to H2 formation and the generation of a gold–thiolate staple motif
Theoretical Examination of Solvent and R Group Dependence in Gold Thiolate Nanoparticle Synthesis
The growth of gold thiolate nanoparticles can be affected by the solvent and the R group on the ligand. In this work, the difference between methanol and benzene solvents as well as the effect of alkyl (methyl) and aromatic (phenyl) thiols on the reaction energies and barrier heights is investigated theoretically. Density functional theory (DFT) calculations using the BP86 functional and a triple ζ polarized basis set show that the overall reaction favors methylthiol over phenylthiol with reaction energies of −0.54 and −0.39 eV in methanol, respectively. At the same level of theory, the methanol solvent is favored over the benzene solvent for reactions forming ions; in benzene, the overall reaction energies for methylthiol and phenylthiol reacting with AuCl4− to form Au(HSR)2+ are 0.37 eV and 0.44 eV, respectively. Methylthiol in methanol also has the lowest barrier heights at about 0.3 eV, whereas phenylthiol has barrier heights around 0.4 eV. Barrier heights in benzene are significantly larger than those in methanol
Prediction of Nonradical Au (0)-Containing Precursors in Nanoparticle Growth Processes
This density functional theory (DFT) investigation examines the formation of nonradical Au(0) species from the reduction of Au(I) species. The Au(I) complexes of interest are AuCl2–, AuBr2–, AuI2–, AuClPH3, and AuCl(H)SCH3(−), which are precursors for gold nanoparticle and cluster formation. Reaction of two of the Au(I) species with a hydride results in ejection of two of the ligands and formation of Au2 with two ligands still attached. AuX2– (where X = Cl, Br, or I) reactions eject two halides and form Au2X22–. AuClL(−) (where L = PH3, HSCH3, or SCH3–) reactions can eject either chloride, HCl, PH3, HSCH3, or SCH3– and form Au(0)L2q– or Au(0)ClLq– (q = 0, 1, 2). The Au2Cl22– complex can further react with AuCl2–, which forms Au3Cl32– and a chloride anion. The new Au3Cl32– species can then react with AuCl2– or Au2Cl22– or with another Au3Cl32–. Larger clusters can be formed from these precursors. In this work, reactions in both methanol and benzene solvents are considered as models for one-phase and two-phase gold nanoparticle growth processes. Overall, this investigation shows how Au(0)-containing species can be formed without assuming the formation of Au(0) atoms (radical species)
The Golden Pathway to Thiolate-Stabilized Nanoparticles: Following the Formation of Gold(I) Thiolate from Gold(III) Chloride
Pathways for the formation of gold thiolate complexes from goldÂ(III)
chloride precursors AuCl<sub>4</sub><sup>–</sup> and AuCl<sub>3</sub> are examined. This work demonstrates that two distinct reaction
pathways are possible; which pathway is accessible in a given reaction
may depend on factors such as the residue group R on the incoming
thiol. Density functional theory calculations using the BP86 functional
and a polarized triple-ζ basis set show that the pathway resulting
in goldÂ(III) reduction is favored for R = methyl. A two-to-one ratio
of thiol or thiolate to gold can reduce AuÂ(III) to AuÂ(I), and a three-to-one
ratio can lead to polymeric AuÂ(SR) species, which was first suggested
by Schaaff et al. <i>J. Phys. Chem. B</i>, <b>1997</b>, <i>101</i>, 7885 and later confirmed by Goulet and Lennox <i>J. Am. Chem. Soc.</i>, <b>2010</b>, <i>132</i>, 9582. Most transition states in the pathways examined here have
reasonable barrier heights around 0.3 eV; we find two barrier heights
that differ substantially from this which suggest the potential for
kinetic control in the first step of thiolate-protected gold nanoparticle
growth
Electron and Hydride Addition to Gold(I) Thiolate Oligomers: Implications for Gold–Thiolate Nanoparticle Growth Mechanisms
Electron and hydride addition to Au(I):SR oligomers is investigated using density functional theory. Cyclic and chain-like clusters are examined in this work. Dissociation to Au<sup>–</sup> ions and Au<sub><i>n</i></sub>(SR)<sub><i>n</i>+1</sub><sup>–</sup> chains is observed after 2–4 electrons are added to these systems. The free thiolate (SR<sup>–</sup>) is rarely produced in this work; dissociation of Au<sup>–</sup> is preferred over dissociation of SR<sup>–</sup>. Electron affinities calculated in gas phase, toluene, and water suggest that the electron addition process is unlikely, although it may be possible in polar solvents. In contrast, hydride addition to Au(I):SR oligomers yields free thiols and complexes containing Au–Au bonds, which are plausible intermediates for gold nanoparticle growth. The resulting compounds can react to form larger nanoparticles or undergo further reduction by hydride to yield additional Au–Au bonds