Superatomic Ligand-Field Splitting in Ligated Gold Nanoclusters

Abstract

Gold nanoclusters are attractive because of their electronic and optical properties. Many theoretical models have been proposed to explain their electronic structures through an electron-counting approach. However, subtle features may not be well explained by electron-counting rules. In this work, we have discovered a unique example of ligand-controlled skeletal bonding in two recently reported gold nanoclusters with very similar compositions and geometries. We have shown that the superatomic orbitals of the common kernel of the two clusters undergo different ligand-field splitting because of the different ligand-field strengths in the two clusters. Such a difference is clearly revealed by constructing the Jellium orbitals via an orbital alignment process, and a subsequent localization of the Jellium orbitals allows us to obtain localized bonding models. Finally, on the basis of localized bonding models, we predict the existence of a ligated gold cluster with a [Au 32 ] 4+ kernel.

Elucidating Pathfinding Elements from the Kubi Gold Mine in Ghana

“…The agreement with the calculated peak positions in the valence band is improved when experimental lattice parameters (a = 4.078 Å) are used, while the theoretical (relaxed) lattice parameter of 4.156 Å is larger and results in peak positions that have extremely low BE. The valence band spectra in Figure 8 show the coordination complex Au (transition metal) with an octahedral geometry where the d orbitals split into a t2g set (lower energy) and an eg set (higher energy) [82,83]. From the spectra, the eg set moves towards higher BE due to the high involvement of the d orbitals in the eg set in a metal-ligand sigma (σ) interaction.…”

“…This means that the t2g orbitals are completely metal based and contribute to metallic bonding. From the valence band spectra, the pronounced The valence band spectra in Figure 8 show the coordination complex Au (transition metal) with an octahedral geometry where the d orbitals split into a t 2g set (lower energy) and an e g set (higher energy) [82,83]. From the spectra, the e g set moves towards higher BE due to the high involvement of the d orbitals in the e g set in a metal-ligand sigma (σ) interaction.…”

“…From the spectra, the e g set moves towards higher BE due to the high involvement of the d orbitals in the e g set in a metal-ligand sigma (σ) interaction. These orbitals in the e g are directed towards the axis where they are opposed by strong repulsive forces from ligands; hence, they acquire higher energy than the t 2g , thus favoring covalent bonding in e g towards higher energy [83]. The shift in BE along the e g set for the powder sample (coarse-grained) is an indication of the covalent bonding of Au with the oxides (ligands) in the powder samples and these extend beyond the e g to higher BE.…”

“…The lower energy t 2g orbitals do not favor sigma interactions with ligands. The t 2g symmetry favors the participation of π interactions with ligands due to their weaker interactions in metal complexes [83]. This means that the t 2g orbitals are completely metal based and contribute to metallic bonding.…”

“…For the Au (film, bulk, fine, and coarse-grained) samples, the valence band width and the binding energies of the two Au 5d and 4f 7/2 peaks depend solely on the mean coordination number [44,83,84]. The 4f photoemission from Au split into two distinct peaks, namely Au 4f 7/2 and Au 4f 5/2 with different BE as a result of spin-orbit coupling effects corresponding to final states, with angular momentum of j+ = + 1/2 = 7/2 and j− = + 1/2 = 5/2, respectively [88,89].…”