Generation of Supraclusters and Nanoclusters Using Laser Desorption/Ionisation Mass Spectrometry

Laser desorption/ionisation of discrete molecular clusters combined with time-of-flight (TOF) or Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry affords spectra in which extensive higher mass clusters are observed. The size of the largest cluster aggregates (or supraclusters) is of the same order of magnitude as nanoclusters. The spectra obtained using TOF mass spectrometry sometimes exhibit post-source decay fragmentation, depending upon the operational conditions employed during data acquisition, which, although providing useful data on the ligand dissociation dynamics, complicate spectral interpretation. Complementary FTICR mass spectra are free of such features. The identities of the supra/nanoclusters generated from the molecular cluster precursors have not been conclusively established but are mostly coordinatively unsaturated. Density functional molecular orbital calculations have identified the possible structures of the comparatively simple electronically unsaturated system, [Ru₃(CO)₆]^–, that provides a clue to the aggregation mechanism.