Record Chemical-Shift Temperature Sensitivity in a Series of Trinuclear Cobalt Complexes.

Designing spins that exhibit long-lived coherence and strong temperature sensitivity is central to designing effective molecular thermometers and a fundamental challenge in the chemistry/quantum-information space. Herein, we provide a new pathway to both properties in the same molecule by designing a nuclear spin, which possesses a robust spin coherence, to mimic the strong temperature sensitivity of an electronic spin. This design strategy is demonstrated in the group of trinuclear Co(III) spin-crossover compounds (CpCo(OP(OR)))Co where Cp = cyclopentadienyl and R = Me (), Et (), -Pr (), and -Bu (). Nuclear magnetic resonance analyses of the Co nuclear spins reveal Co chemical-shift temperature sensitivity (Δδ/Δ) values that span from 101(1) ppm/°C in to 149(1) ppm/°C in and 150(2) ppm/°C in , where the latter two are record temperature sensitivities for any nuclear spin. Additionally, complexes and have values of 74 and 78 μs in solution at ambient temperatures surpassing those from electron-spin-based complexes, which typically display long coherence times only at extremely low temperatures. Our results suggest that spin-crossover phenomena can enable electron-spin-like temperature sensitivities in nuclear spins while retaining robust coherence times at room temperature.