Formation and Characterisation of Polymetallic {CrxMy} Rings in vacuo

Understanding the (dis)assembly mechanisms of large metallosupramolecules is critical in their design, stability and diverse applications. Yet this task is difficult because of the inherent complexity of the structures, with many potential pathways of combining (or separating) the constituent building blocks. Here, we use collision-induced dissociation mass spectrometry to study the disassembly of heterometallic complexes, which have attracted interest due to their potential properties as new materials. Collisional activation leads to the formation of a series of previously unknown smaller ring products and we characterise their geometry using ion mobility. Specifically, the disassembly of both {CrxCu2} hourglass structures (x = 10, 12) and of a {Cr12Gd4} cluster shows the formation of rare closed, heptametallic species namely {Cr6Cu}, {Cr5Cu2} and {Cr5Gd2} as dominant products, as well as other closed ions like {Cr5Cu}, {Cr10Cu}, {Cr12Cu}, {Cr10}, {Cr12}, and {Cr6Gd2}. The collision cross section of cyclic products and precursors has a linear correlation with ion mass, a relationship that does not hold for acyclic systems. Thus, ion mobility mass spectrometry can determine whether a candidate polymetallic complex exists as a closed or open structure. As these rings are non-trivial to synthesize individually in solution, we propose the presented workflow as a means to identify and characterise feasible target molecules.