Evaluation of ultrasmall coinage metal M13(dppe)6 M = Cu, Ag, and Au clusters. Bonding, structural and optical properties from relativistic DFT calculations

Abstract

Ultrasmall ligand-protected clusters are prototypical species for evaluating the variation at the bottom of the nanoscale range. Here we explored the ultrasmall gold–phosphine M₁₃(dppe)₆ cluster, as a prototypical framework to gain insights into the fundamental similarities and differences between Au, Ag, and Cu, in the 1–3 nm size range, via relativistic DFT calculations. Different charge states involving 8- and 10-cluster electron (ce) species with a 1S²1P⁶ and 1S²1P⁶1D² configuration, leading to structural modification in the Au species between Au₁₃(dppm)₆⁵⁺ and Au₁₃(dppm)₆³⁺, respectively. Furthermore, this structural distortion of the M₁₃ core is found to occur to a lower degree for the calculated Ag and Cu counterparts. Interestingly, optical properties exhibit similar main patterns along with the series, inducing a blue-shift for silver and copper, in comparison to the gold parent cluster. For 10-ce species, the main features of 8-ce are retained with the appearance of several weak transitions in the range. The ligand–core interaction is enhanced for gold counterparts and decreased for lighter counterparts resulting in the Au > Cu > Ag trend for the interaction stabilization. Hence, the Ag and Cu counterparts of the Au₁₃(dppm)₆ cluster appear as useful alternatives, which can be further explored towards different cluster alternatives for building blocks for nanostructured materials.