Complexes of dibromo(ethylenediamine)-palladium(II) observed from aqueous solutions by electrospray mass spectrometry

Aqueous solutions of dichloro(ethylenediamine)palladium(II) were investigated using electrospray mass spectrometry (ESMS). The most abundant peak (m/z 436.8) was attributed to the dimeric Pd(en)Cl2.Pd(en)Cl+ ion. We conjecture that the structures of the observed ions arise from the clustering of the hydrolysis products of the parent compound. This hypothesis was tested experimentally by carrying out a series of collision-induced dissociation (CID) experiments and deuterium exchange reactions. It was also assessed by performing density functional theory (DFT) calculations, from which optimized structures and reaction energetics were obtained. These results were compared with our earlier ESMS study of an aqueous Pd(en)Br2 solution. Calculations were also carried out on the Pd(en)Br2 system to facilitate the comparisons. Conclusions are drawn regarding the species present in the two aqueous solutions.