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

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

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

Electronic Structure and Magnetic Properties of Y2Ti(μ-X)2TiY2 (X, YH, F, Cl, Br) Isomers

The electronic structure and magnetic properties of homodinuclear titanium(III) molecules with halide and hydride ligands have been studied using single- and multireference methods. Natural orbital occupation numbers suggest that the singlet states are essentially diradical in character. Dynamic electron correlation is required for calculating quantitatively accurate energy gaps between the singlet and triplet states. Isotropic interaction parameters are calculated, and three of the compounds studied are predicted to be ferromagnetic at the MRMP2/TZV(p) level of theory. Zero-field splitting parameters are determined using CASSCF and MCQDPT spin−orbit coupling with three different electron operator methods. Timings for these methods are compared. Calculated dimerization energies suggest that all dimers studied are lower in energy than the corresponding monomers. Monomer structures and vibrational frequencies are reported

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

Research Update: Density functional theory investigation of the interactions of silver nanoclusters with guanine

Citation: Dale, B. B., Senanayake, R. D., & Aikens, C. M. (2017). Research Update: Density functional theory investigation of the interactions of silver nanoclusters with guanine. APL Materials, 5(5). doi:10.1063/1.4977795Bare and guanine-complexed silver clusters Agnz (n = 2-6; z = 0-2) are examined using density functional theory to elucidate the geometries and binding motifs that are present experimentally. Whereas the neutral systems remain planar in this size range, a 2D-3D transition occurs at Ag5+ for the cationic system and at Ag42+ for the dicationic system. Neutral silver clusters can bind with nitrogen 3 or with the pi system of the base. However, positively charged clusters interact with nitrogen 7 and the neighboring carbonyl group. Thus, the cationic silver-DNA clusters present experimentally may preferentially interact at these sites. © 2017 Author(s)

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