Au<sub><i>n</i></sub> (<i>n</i> = 1,11) Clusters Interacting With Lone-Pair Ligands

2016-05-17T00:00:00Z (GMT) by Tomáš Rajský Miroslav Urban
We analyze the pattern of binding energies (BEs) of small Au<sub><i>n</i></sub> clusters (<i>n</i> = 1–7, 11) with lone-pair ligands (L = H<sub>2</sub>O, SH<sub>2</sub>, NH<sub>3</sub>, PH<sub>3</sub>, PF<sub>3</sub>, PCl<sub>3</sub>, and PMe<sub>3</sub>) employing the density functional theory. We use PBE0 functional with the dispersion correction and scalar relativistic effective core potential. This approach provides correct BEs when compared with benchmark CCSD­(T) calculations for Au–L and Au<sub>2</sub>–L complexes. The pattern of BEs of Au<sub><i>n</i></sub>–L complexes is irregular with BE for Au<sub>3</sub> ≈ Au<sub>4</sub> > Au<sub>2</sub> > Au<sub>7</sub> > Au<sub>5</sub> > Au<sub>11</sub> > Au<sub>6</sub> > Au<sub>1</sub>. Electron affinities (EAs) of Au<sub><i>n</i></sub> clusters exhibit oscillatory pattern with the cluster size. Binding energies of Au<sub><i>n</i></sub>–L complexes are oscillatory as well following EAs of Au<sub><i>n</i></sub> clusters. BEs of odd and even Au<sub><i>n</i></sub>–L complexes were analyzed separately. The bonding mechanism in odd Au<sub><i>n</i></sub>–L complexes is dominated by the lone pair → metal electron donation to the singly occupied valence Au<sub><i>n</i></sub> orbital accompanied by the back–donation. Even Au<sub><i>n</i></sub> clusters create covalent Au<sub><i>n</i></sub>–L bonds with BEs higher than those in odd Au<sub><i>n</i></sub>–L complexes. The BEs pattern and optimized geometries of Au<sub><i>n</i></sub>–L complexes correspond to the picture of creating the gold–ligand bond through the lone pair of a ligand interacting with the singly occupied molecular orbital in odd clusters or lowest unoccupied molecular orbital in even clusters of Au<sub><i>n</i></sub>. Ligands in both odd and even Au<sub><i>n</i></sub>–L complexes form three groups with binding energies that correlate with their ionization energies. The lowest BE is calculated for H<sub>2</sub>O as a ligand, followed by SH<sub>2</sub> and NH<sub>3</sub>. PX<sub>3</sub> ligands exhibit highest BEs.