Fig. 1: Crystal structures of the studied {Cr_xM_y} complexes and applied CID–IM–MS workflow.

a–c, Single crystal X-ray structure of {Cr₁₀Cu₂} (a), {Cr₁₂Cu₂} (ref. ²⁷) (b) and {Cr₁₂Gd₄} (c); Cr: dark green, Cu: brown, Gd: purple, F: yellow, O: red, N: blue, C: grey. Solvent molecules and hydrogen atoms have been removed for clarity. d, CID–IM–MS workflow following nano-electrospray of the precursor {Cr_xM_y} from solution and m/z-selection of an appropriate precursor ion. Upon collisional activation, several fragment ions are observed with different masses, and their CCS_N2 distribution can be extracted as shown for an ion of the type {Cr_x-aM_y-b}. Different structures of {Cr_x-aM_y-b} are possible, such as closed (low CCS_N2, narrow CCS_N2 distribution) or open forms (high CCS_N2, wide CCS_N2 distribution), of which only a closed {Cr_x-aM_y-b} species was found in this illustrative example.