Adduct Ions as Diagnostic Probes of Metallosupramolecular Complexes using Ion Mobility Mass Spectrometry

Following electrospray ionization (ESI), it is common for analytes to enter the gas phase accompanied by an additional small ion or molecule. Although these may not be influential in solution, they often determine the charge of the entire complex and can markedly tune their properties in the gas phase. Therefore, measuring their relative influence can be used to assist our understanding of the structure and stability of the target molecule. Because these adducts are usually distinguishable by their mass, differences in the behaviour of the analyte resulting from these added species can be extracted readily. Here, we use ion mobility mass spectrometry (IM-MS), supported by density functional theory (DFT), to investigate how different charge carriers (H+, Na+, K+, Cs+) as well as water influence the disassembly, stability, and conformational landscape of the homometallic ring [Cr8F8(O2CtBu)16] and different heterometallic rotaxanes [NH2RR’][Cr7MF8(O2CtBu)16], where M = Mn, Fe, Co, Ni, Cu, Zn, and Cd. The results yield new insights on their disassembly mechanisms and support previously reported trends in cavity size and transition metal properties, demonstrating the potential of adduct ion studies for characterising metallosupramolecular complexes in general.