Disassembly Mechanisms and Energetics of Polymetallic Rings and Rotaxanes with Ion Mobility Mass Spectrometry

Abstract

Understanding the fundamental reactivity of polymetallic complexes is challenging due to the complexity of their structures with many possible bond breaking and forming processes. Here we apply ion mobility mass spectrometry (IM-MS) coupled with density functional theory (DFT) to investigate the disassembly mechanisms and energetics of a family of heterometallic rings and rotaxanes with the general formula [NH2RR’][Cr7MF8(O2CtBu)16] with M = MnII, FeII, CoII, NiII, CuII, ZnII, CdII. Our results show that their stability can be tuned both by altering the d-metal composition in the macrocycle and by the end groups of the secondary ammonium cation [NH2RR’]+. Ion mobility probes the conformational landscape of the disassembly process from intact complex to structurally distinct isobaric fragments, providing unique insights to how a given divalent metal tunes the structural dynamics.

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

“…11 These were found to be ≈ 9% larger than experiment, which we previously observed for the similar heterometallic rings [RingM]and discussed there in detail. 12 In agreement with the experimental values, only minor differences in the calculated CCSN2 values were found for different A + .…”

“…The variation in the CCSN2 data of [AmM + H] + can be rationalized with the binding site of H + and the covalent radii of M. As shown in our previous work, 12 the protonated species [AmM + H] + and [PhM + H] + dissociate via the loss of pivalic acid (HPiv), indicating that the proton is located at the ring and likely close to M II because of the lower charge density there compared to the Cr III sites. For the complexes with the largest d-metals, Cd II and Mn II , protons presumably are located between the anionic pivalate ligands, coordinated to the -O or possibly -F atoms.…”

“…Here, we extend this work by enumerating the E50 values of the potassium and caesium adducts, [AmM + A] + and [PhM + A] + (A + = K + , Cs + ), and compare them to the data of the sodiated forms (Table 2, Figure 2b including dissociation reactions). 12 In addition to the influence of the divalent metal, the data show notable differences with respect to the alkali metal. show the Na + adducts to be most stable, followed by the respective K + and Cs + species; the minor exception is for M = Mn II (Figure 2b left).…”

“…13,14 Previously, we have extensively studied the disassembly of [RingM] -, [AmM + A] + , and [PhM + A] + (A + = H + , Na + ), using IM-MS, and demonstrated that the d-metal present and the thread strongly influence the E50 value and disassembly mechanism of these cations. 12 Major differences were also observed between protonated and sodiated forms, showing that the charge-carrying species is an important factor when considering the disassembly of these complexes (Table 2, Figure S10). Here, we extend this work by enumerating the E50 values of the potassium and caesium adducts, [AmM + A] + and [PhM + A] + (A + = K + , Cs + ), and compare them to the data of the sodiated forms (Table 2, Figure 2b including dissociation reactions).…”

“…Error bars are shown but, in all cases, are smaller than the symbol size. Data for the series [PhM + Na] + were obtained from our previous work 12.…”