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'-dimethyl-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 ClO 4 - . Multiply charged ions with the charge state from 8+ to 3+ were observed in the full- scan ES mass spectra. Different charged ions were generated by the combination of counterion loss and protonation/deprotonation of the bridging ligand B. Collision-induced dissociation (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, whereas complete fragmentation takes place for higher charge states and the fragments are based on a subunit group of [Met(II)L 2 B] 2+ . Insertion of formal O 2 - produced from ClO 4 - 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 spectrometry are demonstrated for these multinuclear compounds and the CID chemistry of the ions investigated is discussed.