Fourier transform ion cyclotron resonance studies of lanthanide(III) porphyrin-phthalocyanine heteroleptic sandwich complexes by using electrospray ionization

A number of neutral Ianthanide(III) porphyrin-phthalocyanine heteroleptic sandwich complexes have been studied by using positive-ion electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry. The investigated compounds are represented as Ln^III(TPP)(Pc), Ln ₂ ^III (TPP)(Pc)₂, and Ln ₂ ^III (TPP)₂(Pc), where Ln = Sm, Eu, or Gd, TPP is 5,10,15,20-tetraphenylporphyrinate, and Pc is phthalocyaninate. In all cases, intense signals corresponding to the singly charged molecular radical cations are observed. The formation of these molecular radical cations in electrospray ionization is attributed to electrochemical oxidation at the electrospray needle. Multiply charged molecular ions up to +5 are also observed. They are tentatively assigned to be formed from successive oxidation of the ligand(s). Apart from the molecular weight information, tandem mass spectrometry offers additional structural information on these complexes. From the fragmentation pattern of the europium complexes under collision-induced dissociation conditions, the configurations of the triple-decker complexes are assigned mass spectrometrically to be (TPP)Eu(Pc)Eu(Pc) and (TPP)Eu(Pc)Eu(TPP). In comparison with the previous spectroscopic findings that the positive “hole” is localized in the ligands of the complexes, there is evidence to suggest that intramolecular charge transfer or hole delocalization does occur within the macrocycles or between the metal centers and the macrocycles before fragmentation. The occurrence of this charge-transfer process is tentatively attributed to the result of collisional activation.