Triphenylphosphine (PPh3) is commonly used during syntheses of stable closed-shell monolayer protected clusters (MPCs). Models of transition metal (TM) cluster and nanoparticle syntheses commonly assign PPh3 a passive role as a chemical placeholder, electron balancing species, or surfactant. This study provides the first direct evidence that PPh3 is a proactive etching agent that promotes the formation of specific closed-shell cluster sizes. To observe this effect, we developed a colorimetric tool that simultaneously monitors size distribution and population of PPh3- protected clusters. The distribution of the clusters forming could be assigned to different bin sizes by chemical conversion with L3: i) total conversion of PPh3-protected Au8 and Au9 clusters into [Au6L34]2+ and ii) ligand exchange with [Aux(PPh3)y]z+ (x > 10) clusters to form L3-protected Au10 and Au11 clusters (L3 = 1,3-bis(diphenylphosphino)propane). This study reveals a dual role for PPh3 as a stabilizing and etching agent in the formation of MPCs, highlighting the need for incorporating bidirectional processing into TM kinetic models phosphine ligands. The cyclic processing of growth and etching reactions with reaction rate information around the most stable species is necessary to accurately describe size-selective MPC formation. The incorporation of bidirectional pathways will be needed to accurately model the synthetic pathways for other ligands that promote size-focusing TM formation through reduction.
Citation: ACS Nano
Pub Type: Journals
ligand, gold nanoparticle, ligand exchange, mass spectrum, nanocluster, nanoparticle synthesis, nanoparticle, optical spectrum, phosphine ligand, synthesis