Investigation of metal complex coordination structure using collision-induced dissociation and ion-molecule reactions in a quadrupole ion trap mass spectrometer

A technique described previously using ion-molecule (I-M) reactions to dete rmine metal complex coordination number has been combined with collision-in duced dissociation (CID) in a quadrupole ion trap mass spectrometer. Nitrog en-containing tripodal ligands complexed with some first-row transition met als [i.e. Mn(LI), Co(II), Fe(II), and Ni(II)I are generated by electrospray ionization, and the coordination number of these metal complex ions are de termined in the gas phase using I-M reactions. Information about the coordi nation sphere structure (i.e. metal-ligand connectivity) is then gathered b y dissociating the metal complexes, reacting their product ions, and compar ing the coordination number of these product ions with their parent ions. R esults suggest that a change in the coordination number upon dissociation a llows identification of the functionality involved in coordination to the m etal. Conversely, no change in the coordination number indicates either the lost functional group is not involved in the coordination or the ligand re arranges to fill a coordination site vacated by the dissociated group. Dist inguishing between the two processes (i.e, when coordination number does no t change) was very difficult in these studies, but results suggest that, in some cases, ligand rearrangement does not occur. Also, some product ions d id not provide any useful coordination information upon reaction. In these cases the product ions either did not contain the metal or contained the me tal in a reduced oxidation state. The preliminary results presented here ar e promising and suggest that with further investigation of the dynamics of metal complex I-M reactions, a combination of CID and I-M reaction may allo w metal-complex coordination structure to be determined using mass spectrom etry. (C) 2001 Elsevier Science B,V.