Fig. 4: Tandem mass spectra of [{Cr₁₂Gd₄} – Piv]⁺ at different collision energies and CCS_N2 distributions of [{Cr₁₂Gd₄} – Piv]⁺ and fragment ions.

a, MS² spectra of [{Cr₁₂Gd₄} – Piv]⁺ at collision energies of 0 eV, 210 eV and 250 eV. Occurring fragmentation pathways are labelled: (i) – [NH₂^n/iPr₂]⁺, – Piv⁻; (iii) – [NH₂^n/iPr₂]⁺, – F⁻ and (v) – Cr^III, – 3 Piv⁻. Satellite peaks (labelled with ‘s’) correspond to the labelled main peak via the exchange of one anionic ligand for another one (Piv⁻ for F⁻ or F⁻ for Piv⁻; mass difference 82 Da). The spectrum at 210 eV shows two regions, one at lower m/z and one at higher m/z. Minor contaminant features were observed that were m/z-selected in the quadrupole along with [{Cr₁₂Gd₄} – Piv]⁺, and hence produce different fragments (labelled with ‘c’). b, CCS_N2 distributions of [{Cr₁₂Gd₄} – Piv]⁺ (m/z = 4,688) and the fragment ions {Cr₆Gd₂} (m/z = 2,499) and {Cr₅Gd₂} (m/z = 1,940). Data were recorded at collision energies of 0 eV (precursor), 130 eV for {Cr₆Gd₂} and 190 eV for {Cr₅Gd₂}, respectively. Insets: schematics of {Cr₁₂Gd₄} and the two products {Cr_xGd₂} (x = 5, 6; Cr, green; Gd, purple). Fragment ions that are assigned as closed, due to the ion mobility data, are presented schematically; as the IM–MS experiment informs on the stoichiometry but not on the exact connectivity between the metal centres.

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