Ligand and Solvent Effects on the Structural and Optical Properties of Au13L83+ Clusters: a Density Functional Theory Study

Density functional theory (DFT) calculations have been performed to develop a systematic structural analysis of Au13L83+, where L = SCH3, SeCH3, SCH2OCH3 and S(CH2)2NH2, in order to examine the influence of different ligands. Binding energy calculations indicate that the gold core is more stabilized by the ligand in the following sequence S(CH2)2NH2 > SCH2OCH3 > SeCH3 > SCH3. Natural bond orbital (NBO) analysis describes the interaction between the gold and the ligands, showing that the strongest electron donation occurs from a lone pair orbital on the sulfur and selenium atoms to the antibonding acceptor σ* (Au-S) and σ* (Au-Se) orbitals, respectively. The NBO analysis allowed to understand the origin of enhanced stability of the [Au13(S(CH2)2NH2)8]3+. Time-dependent DFT (TDDFT) calculations have been performed to simulate the optical absorption spectra of Au13L83+ in gas phase and under the effect of solvents with different polarities. The absorption spectrum of [Au13(S(CH2)2NH2)8]3+ shows a spectral profile that differs considerably from the others in gas phase and which is strongly affected by the solvent.