Packing atomic metal cations with C60: Mass spectrometric observation of M+(C60)n with M = Sr and Mo and n = 0–4

The atomic cations of Sr and Mo have been observed to add sequentially up to four molecules of C60 in helium at 0.35 Torr and room temperature in the flow tube of a modified inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The available center-of-mass energy in collision-induced dissociation experiments of approximately 1.3 eV failed to remove C60 from M+(C60)4. A structure is proposed for M+(C60)4 cations in which the bonding involves η6 interaction of the metal with the C60 ligands and η2-to-η2 interactions between the C60 ligands.