Effect of Charge and Phosphine Ligands on the Electronic Structure of the Au₈ Cluster

Abstract

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 Au 8 nanoclusters and characterize their electronic structure. Au 8 clusters were bonded to four and eight PH 3 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 Au 8 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.

Au101–rGO nanocomposite: immobilization of phosphine-protected gold nanoclusters on reduced graphene oxide without aggregation

“…In addition, the electronic structure and reactivity of the clusters could be improved due to electronic and steric factors imposed by the phosphine ligands. 11 As a result, phosphine-protected gold clusters formulated as Au n (PPh 3 ) m , such as Au 9 (PPh 3 ) 8 (NO 3 ) 3 and Au 101 (PPh 3 ) 21 Cl 5 , have been shown to exhibit catalytic activity in a wide range of reactions, such as hydrogenation of terminal alkynes into alkenes, 12 CO oxidation, 13,14 styrene oxidation to benzaldehyde 15 and styrene epoxide, 16 and benzyl alcohol oxidation. 17,18 However, the size-specific catalytic activity of AuNCs has often been difficult to determine experimentally as clusters are prone to aggregation either during deposition or activation on the support, 19,20 or deactivation of the catalyst following initial reaction.…”

Density-functional tight-binding for phosphine-stabilized nanoscale gold clusters

“…Density functional theory (DFT) methods are most oen employed in theoretical investigations, as they are capable to accurately describe electronic, geometrical, and vibrational structure of gold clusters and nanoparticles. [16][17][18][19][20][21][22][23][24][25][26][27][28][29] In particular, the DFT-based simulation of IR, Raman, and UV-vis spectra has been achieved for a range of gold clusters, thus providing useful theoretical ngerprints to distinguish between bonding arrangements and orientations between gold atoms and ligands, and ligandligand interactions within clusters. 23,[30][31][32][33][34] Unfortunately, DFT calculations can become prohibitively expensive with system size, 35 and routine theoretical investigations are limited to moderate system sizes.…”

“…triphenylphosphine (PPh 3 ) is replaced by phosphine (PH 3 ) or trimethylphosphine (PMe 3 ). 17,18,22,25,26,28,29,36 This, as with the complete ligand removal approach, has the additional benet that conformational searching is simplied, as the torsions of the three phenyl groups per ligand give rise to a large number of local minima with similar energies. Nevertheless, it is well known that the electronic effects of the larger ligands are different from those of the smaller ones, for instance inductive effects, [36][37][38][39] and a computational truncation of the ligands will inuence the chemistry and therefore description of the catalytic properties in calculations.…”

Caracterización computacional de ligandos orgánicos derivados de ácido fumárico para la adsorción selectiva de mercurio inorgánico

“…Al tener los valores de reactividad calculados por dos aproximaciones se evita la incertidumbre que se genera con el Teorema de Koopmans que desde su fundamento teórico aplica para HF y no para DFT (Vargas et al, 2005). Sin embargo, se reportan estudios con valores de reactividad con DFT en acuerdo con valores calculados incluso con la aproximación adiabática, es decir, optimizando la estructura de los sistemas cargados (Burgos et al, 2019). Adicionalmente, véase en López et al, (2013) una breve descripción de los fundamentos teóricos de DFT y a partir de ésta la obtención del potencial de ionización, dureza química, electronegatividad, así como sus expresiones análogas empleando el teorema de Koopmans.…”