Formation and characterization of polymetallic {Cr_xM_y} rings in vacuo

Understanding the (dis)assembly mechanisms of large metallosupramolecules is critical in their design, stability and application. The inherent complexity of these structures leads to many potential pathways for combining (or separating) the constituent building blocks, which makes this task difficult. Here we use collision-induced dissociation mass spectrometry to study the disassembly of heterometallic complexes. Collisional activation leads to the formation of a series of previously unknown smaller ring products and we characterize their geometry using ion mobility. The disassembly of both {CrxCu2} hourglass structures (x = 10, 12) and of a {Cr12Gd4} cluster shows the formation of rare closed, heptametallic species {Cr6Cu}, {Cr5Cu2} and {Cr5Gd2} as dominant products, as well as other closed ions such as {Cr5Cu}, {Cr10Cu}, {Cr12Cu}, {Cr-10}, {Cr-12} 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. As these rings are non-trivial to synthesize individually in solution, we propose the presented workflow to identify and characterize feasible molecules for bulk phase synthesis.