In the fields of nanotechnology and catalysis, atomically precise gold-copper heterodimer systems have drawn interest due to their unique properties and improved performance over their monometallic versions. In this work, we will be investigating the optical characteristics of the Au₁₃Cu₅(5-chloropyridine-2-thiolate)₉(BINAP)₃cluster and its electronic structure to further elucidate the experimental findings. To fully ascertain the stoichiometry of the system, which can be challenging for copper-containing nanoclusters, our initial investigations involved first investigating the charge of the system, and secondly, examining the possibility of having a hydride in the cluster. We conducted calculations with z = -1, 0, and +1 charge states for the [Au₁₃Cu₅(5-chloropyridine-2-thiolate)₉(BINAP)₃]^z cluster. Many experimental copper clusters have hydrides but these are difficult to see in an X-ray crystal structure, so we also considered adding a hydride to the nanocluster in various positions. Theoretical investigations were initiated with density functional theory (DFT) computations on the [Au₁₃Cu₅(5-chloropyridine-2-thiolate)₉(BINAP)₃]^z cluster by optimizing the geometry of the system. This was conducted via the BP86-D3/DZ level of theory using the crystal structure as the initial coordinates for the cluster. To determine the optical absorption properties, simplified time-dependent density functional theory (sTDDFT) calculations were conducted on the optimized geometries. In this computation, the B3LYP/DZ level of theory was applied. The resulting theoretical absorption spectra indicate that the z = +1 charged system significantly matches the major absorption peaks from the experimental spectrum, so we further analyzed the +1 charged system. Both experimental and theoretical spectra indicate that there are three major peaks within the visible region. Our investigations showed that these peaks are not a result of a single excitation, but a conjunction of multiple excitations within the same region. Overall, the individual electronic transitions involved in these excitations are evaluated as a mixture of molecular orbital contributions.

Sulalith Samarasinghe

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