Electrospray ionization ion trap mass spectrometry of a tetrahedral supramolecular Ti4L4 cluster

The analysis of self-assembled supramolecular clusters held together by metal–ligand interactions is a relatively new area in mass spectrometry. These complexes may have molecular weights exceeding several kDa, are often highly charged and their composition is most sensitive to their chemical environment. Electrospray ionization appears to be the ionization technique of choice for their mass spectral characterization. The analysis (positive and negative ion detection mode) of the prototype compound [Ti₄L₄]⁸⁻ (L = a catechol-based tris-bidentate ligand; MW of cluster = 2293 u) using a Paul trap mass analyzer is reported. The combination of electrospray ionization and high resolution ion trap technology is a powerful tool which provides the unambiguous solution state characterization of this supramolecular cluster. The results are correlated with the known solid state structure of the cluster and reactions previously reported for mononuclear Ti(IV) catecholates.