Unravelling of a [High Spin – Low Spin] ↔ [Low Spin – High Spin] Equilibrium in Spin-Crossover Iron(II) Dinuclear Helicates Using Paramagnetic NMR Spectroscopy

Spin-crossover between high-spin (HS) and low-spin (LS) states of selected transition metal ions in polynuclear and polymeric compounds is behind their use as multistep switchable materials in breakthrough electronic and spintronic devices. Here we report the first successful attempt to observe the dynamics of the rarely found broken-symmetry spin state in binuclear complexes, which mixes the states [HS-LS] and [LS-HS] on a millisecond timescale. The slow exchange between these two states identified by paramagnetic NMR spectroscopy in solutions of two spin-crossover iron(II) binuclear helicates, which are amenable to molecular design, opens the way for them to emerge as double quantum dot cellular automata for information storage and processing.