Generation and dissociation of oxygen‐ and chloride‐bridged iron(III) and manganese(III) tetraphenylporphyrin dimer ions in the gas phase

Electrospray ionization mass spectrometry (ESI/MS) has allowed the discovery of novel dimer ions emerging from solutions of metalloporphyrin salts and their investigation by collision‐induced dissociation (CID) with N₂ molecules. ESI mass spectra have been recorded for the formation of the oxygen or chloride‐bridged dimer ions (FeTPP)₂OH]⁺, (MnTPP)₂OH]⁺, (FeTPP)₂Cl]⁺ and (MnTPP)₂Cl]⁺ derived from various solutions of FeTPPCl and MnTPPCl salts. The CID of (FeTPP)₂OH]⁺ proceeds mainly by neutral loss of (FeTPP)OH to form FeTPP]⁺ and, to a minor extent, to form the charge‐reversed products. The CID of (MnTPP)₂OH]⁺ exhibits exclusively the product ion MnTPP]⁺ by loss of neutral (MnTPP)OH. (FeTPP)₂Cl]⁺ and (MnTPP)₂Cl]⁺ dissociate by loss of (Fe/MnTPP)Cl to give rise to Fe/MnTPP]⁺. (FeTPP)₂O]⁺ and (FeTPP)₂OH]⁺ were generated from a solution of the dimer, (FeTPP)₂O. Dissociation of (FeTPP)₂O]⁺ yields two product ions, FeTPP]⁺ and (FeTPP)O]⁺, with higher onsets compared to the equivalent fragments formed from (FeTPP)₂OH]⁺. Copyright © 2009 John Wiley & Sons, Ltd.