All-selenolate-protected eight-electron platinum/silver nanoclusters

The first atomically and structurally precise platinum/silver superatoms protected by Se-donor ligands were synthesized in high yield by adopting ligand replacements on [PtAg₂₀{S₂P(OⁿPr)₂}₁₂] (3) with 12 equiv. of di-alkyl diselenophosph(in)ates. Structures of [PtAg₂₀{Se₂P(OR)₂}₁₂] (R = ⁿPr (1a), ⁱPr (1b)) and [PtAg₂₀{Se₂P(CH₂CH₂Ph)₂}₁₂] (2) were accurately determined by single-crystal X-ray diffraction to reveal an eight-electron [Pt@Ag₁₂]⁴⁺ icosahedral core embedded within a cube of eight silver(i) atoms and wrapped into a shell of 12 diselenophosph(in)ates. While the lowest energy absorption band of the Se derivatives is red-shifted to longer wavelengths in comparison with the S analogue, it is blue-shifted in the emission spectra. Density functional theory (DFT) and TD-DFT calculations rationalize the electronic structures as those of eight-electron superatoms, with their HOMO and LUMO being the 1P and 1D levels, respectively. The two UV-visible lowest bands are associated with 1P → 1D metal to metal charge transfer (MMCT) transitions. The blue shift observed for the S analogue results from a larger HOMO-LUMO gap in the case of dithiolate ligands.