Facile synthesis and optical properties of magic-number Au13 clusters

Abstract

Synthesis of molecular gold clusters through a post-synthetic scheme involving HCl-promoted nuclearity convergence was examined with various phosphine ligands. Systematic studies with a series of bis(diphenylphosphino) ligands (Ph₂P-(CH₂)_m-PPh₂) using electrospray ionization mass spectrometry (ESI-MS) and electronic absorption spectroscopy demonstrated that the use of dppp (m = 3), dppb (m = 4) and dpppe (m = 5) as the ligands resulted in the formation of [Au₁₃P₈Cl₄]⁺ type clusters, whereas the [Au₁₃P₁₀Cl₂]³⁺ type cluster was formed with dppe (m = 2). The cluster species did not survive the HCl treatment step when monophosphines PPh₃, PMe₂Ph, and POct₃ were employed, but [Au₁₃(POct₃)₈Cl₄]⁺ was isolated as a minor product in the NaBH₄ reduction of Au(POct₃)Cl in aqueous THF. Electronic absorption and photoluminescence studies of a series of Au₁₃ clusters revealed that their optical properties are highly dependent on the phosphine/chloride composition ratio, but are far less so on the phosphine structure.