Chemically made, atomically precise phosphine-stabilized clusters Au₉(PPh₃)₈(NO₃)₃ were deposited on titania and silica from solutions at various concentrations and the samples heated under vacuum to remove the ligands. Metastable induced electron spectroscopy was used to determine the density of states at the surface, and X-ray photoelectron spectroscopy for analysing the composition of the surface. It was found for the Au₉ cluster deposited on titania that the ligands react with the titania substrate. Based on analysis using the singular value decomposition algorithm, the series of MIE spectra can be described as a linear combination of 3 base spectra that are assigned to the spectra of the substrate, the phosphine ligands on the substrate, and the Au clusters anchored to titania after removal of the ligands. On silica, the Au clusters show significant agglomeration after heat treatment and no interaction of the ligands with the substrate can be identified.

Quantum Chemical Topology (QCT) is used to reveal the dynamics of atom–atom interactions in a liquid. A molecular dynamics simulation was carried out on an ethanol–water liquid mixture at its azeotropic concentration (X_ethanol = 0.899), using high-rank multipolar electrostatics. A thousand (ethanol)₉ –water heterodecamers, respecting the water–ethanol ratio of the azeotropic mixture, were extracted from the simulation. Ab initio electron densities were computed at the B3LYP/6-31+G(d) level for these molecular clusters. A video shows the dynamical behavior of a pattern of bond critical points and atomic interaction lines, fluctuating over 1 ns. A bond critical point distribution revealed the fluctuating behavior of water and ethanol molecules in terms of O–H⋯O, C–H⋯O and H⋯H interactions. Interestingly, the water molecule formed one to six C–H⋯O and one to four O–H⋯O interactions as a proton acceptor. We found that the more localized a dynamical bond critical point distribution, the higher the average electron density at its bond critical points. The formation of multiple C–H⋯O interactions affected the shape of the oxygen basin of the water molecule, which is shown in three dimensions. The hydrogen atoms of water strongly preferred to form H⋯H interactions with ethanol's alkyl hydrogen atoms over its hydroxyl hydrogen.

In this work, we use density functional theory calculations with a hybrid exchange–correlation functional and effective core pseudopotentials to determine the geometry of bare and phosphine-protected Au₈ nanoclusters and characterize their electronic structure. Au₈ clusters were bonded to four and eight PH₃ ligands in order to evaluate the effect of ligand concentration on the electronic structure, while different positional configurations were also tried for four ligands attached to the cluster. We show that the neutral clusters become more nucleophilic as the ligands bind to the clusters at stable sites. The ground-state planar configuration of Au₈ is maintained depending on the concentration and position of ligands. The effect of ionizing to the +2 charge state results in disruption of planar geometry in some cases because of inoccupation of a molecular orbital with the Au–Au bonding character. Natural bond order charge analyses showed that Au atoms oxidize upon ionization, instead of phosphine. The net positive charge makes the clusters more electrophilic with a capacity to absorb electrons from nucleophiles depending on the concentration and position of ligands and on the concentration of low-coordinated gold atoms. Besides, ionization energies and electron affinities were calculated through different mechanisms, finding that both variables are much higher for charged systems and change inversely with the concentration of ligands.