Ligand dissociation and core fission from diphosphine-protected gold clusters

Highly monodisperse samples of diphosphine ligand (1,3-bis(diphenylphosphino)propane- or 1,5-bis(diphenylphosphino)pentane)-protected gold nanoparticles form rapidly in a mixed methanol/chloroform solvent environment. Methanol soluble octagold, decagold, and undecagold monolayer protected clusters yield very stable ion currents when introduced into a mass spectrometer via electrospray ionization. In addition to neutral ligand loss pathways, collision-induced dissociation generates [AuL](+) and [Au3L](+) (L = diphosphine ligand) as particularly stable product ions from all clusters considered. Furthermore, deca- and undecagold clusters are found to be more resistant to collision induced dissociation, and more susceptible to partial ligand losses than octagold clusters. This suggests that for the deca- and undecagold species, Au-P and P-Ph (Ph = phenyl) bonds within the ligand-protected clusters are of comparable strength.