Today, organometallic pincer complexes constitute important tools in homogeneous catalysis in order to synthesize chemical building blocks apart from traditional harsh conditions in organic chemistry. During classical chemical synthesis of pincer complexes it was of interest to structurally characterize the pure ligands without the metal coordination center as well as the metal complexes. Unfortunately, due to the paramagnetic properties of such complexes, it turned out to be very difficult to obtain detailed structural information by nuclear magnetic resonance spectroscopy. As a powerful alternative for structural elucidation of those compounds either matrix-assisted laser desorption ionization mass spectrometry or electrospray ionization (ESI) mass spectrometry in combination with tandem mass spectrometry and accurate mass determination are meanwhile well-established techniques. Initially, the fragmentation behavior of several mono- and bidentate pincer ligands was investigated by ESI low-energy CID in combination with tandem mass spectrometry and accurate mass determinations exhibiting fragmentation mainly either between the P-isopropyl or the N-P bond [1]. As an extension of our work several pincer complexes with nickel (II) and cobalt (II) chloride were measured by the same strategy. Both types of complexes readily ionize by loss of one chloride yielding abundant singly charged ions, which were selected for tandem mass spectrometric experiments. At first glance nickel and cobalt complexes containing the same pincer ligand exhibit an unexpected different fragmentation pattern making detailed interpretations rather difficult. Even accurate mass determinations did not help further. A careful look at the electron configuration of nickel and cobalt finally turned out that only cobalt (II) contains an odd number of electrons thus yielding as precursor ions for ⁵⁸Ni (II) [M−Cl]+ and for ⁵⁹Co (II) [M−Cl]+ •. Therefore, the corresponding product ion spectra are starting either with a pure cation (Ni) or a radical cation (Co) thus strongly influencing the subsequent fragmentation pattern, which will be discussed in detail.