Extending the Distance Range in Double Electron–Electron Resonance Measurements of Transition Metal Clusters

We report ligand manipulation of high-nuclearity, paramagnetic transition metal clusters based on heterometallic {Cr₇Ni} rings to significantly prolong electron spin phase memory time constants. This enables the application of Double Electron-Electron Resonance (DEER) spectroscopy methods to measure cluster···cluster interactions to longer distances. Specifically, replacing bridging pivalates by cyclopropyl-carboxylates enables DEER up to 4.2 nm. This is applied to four new hybrid [2]- and [3]rotaxanes based on hetero- and homodimers, respectively, of {Cr₇Ni} rings about organic threads. The crystal structures of these supramolecules are reported and are in excellent agreement with the DEER results.