ELECTROSPRAY AND COLLISION-INDUCED DISSOCIATION MASS ANALYSIS OF STAR-BURST TYPE TETRANUCLEAR COMPLEXES

A number of star-burst type tetranuclear complexes denoted by [Met(II) L(2)B](3)RuX(8) (Met = Ru, Os) were examined by positive electrospray (ES) mass spectrometry, where L is bpy (2,2'-bipyridine) or btfmb (4,4 '-bis(trifluoromethyl)-2,2'-bipyridine), bridging ligand B is 1,1'-dim ethyl-2,2'-bis(2 ''-pyridyl)-6,6'-bibenzimidazole (dmbpbim), 2,2'-bis( benzimidazol-2-yl)-4,4'-bipyridine (bbbpyH(2)) or the related ligand, and X is ClO4-. Multiply charged ions with the charge state from 8+ to 3+ were observed in the fall- scan ES mass spectra. Different charged ions were generated by the combination of counterion loss and protona tion/deprotonation of the bridging ligand B. Collision-induced dissoci ation (CID) of the multiply charged ion made it clear that loss of one or more HX neutral is a major process for lower charge states, wherea s complete fragmentation takes place for higher charge states and the fragments are based on a subunit group of [Met(II)L(2)B](2+). Insertio n of formal O-2(-) produced from ClO4- counterion was observed for the complexes without active protons even if low-energy CID experiments, but not for the complexes with active protons. Advantages of ES mass s pectrometry are demonstrated for these multinuclear compounds and the CID chemistry of the ions investigated is discussed.