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

Abstract

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/quantuminformation 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) 2 ) 3 ) 2 Co](SbCl 6 ) where Cp = cyclopentadienyl and R = Me (1), Et (2), i-Pr (3), and t-Bu (4). Nuclear magnetic resonance analyses of the 59 Co nuclear spins reveal 59 Co chemical-shift temperature sensitivity (Δδ/ΔT) values that span from 101(1) ppm/°C in 1 to 149(1) ppm/°C in 2 and 150(2) ppm/°C in 4, where the latter two are record temperature sensitivities for any nuclear spin. Additionally, complexes 2 and 4 have T 2 * 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.

Asymmetry-enhanced 59Co NMR thermometry in Co(iii) complexes

“…Among 59 Co NMR thermometers, these are the highest resolutions, eclipsing the recent spin-crossover 59 Co results. 20 They are also notably higher than the record temperature sensitivities for 1 H and 31 P. The sole measurement that eclipses our results in this manuscript is the original measurement of Co(acac) 3 . Again, we stress the difference in the measurement technique as an essential part of the comparison, specifically the field of measurement which is likely affecting linewidth (11.7 T vs. ca.…”

“…38.eCollected in CH 2 Cl 2 at 400 mM, 500 MHz magnet, see ref. 20.fFor 1 H NMR signal, from ref. 21.gFor 31 P NMR signal, from ref.…”

Modulation of triplet quantum coherence by guest-induced structural changes in a flexible metal-organic framework

“…In the second quantum revolution, quantum information science (QIS) comprises the application of quantum mechanics to fields such as quantum computing 1,2 , quantum communication 3,4 , and quantum sensing [5][6][7][8][9][10] . Quantum bits (qubits) are its building blocks, and manipulating these superposition states creates new properties that cannot be achieved by classical bits 11,12 .…”

Quantum chemical sensing using molecular triplet qubits in a flexible metal–organic framework

“…In the second quantum revolution, quantum information science (QIS) comprises the application of quantum mechanics to fields such as quantum computing 1,2 , quantum communication 3,4 , and quantum sensing [5][6][7][8][9][10] . Quantum bits (qubits) are its building blocks, and manipulating these superposition states creates new properties that cannot be achieved by classical bits 11,12 .…”

“…Quantum bits (qubits) are its building blocks, and manipulating these superposition states creates new properties that cannot be achieved by classical bits 11,12 . Among the quantum technologies, quantum sensing will have an impact on a wide range of fields, including chemistry 9 and biology 10 . Quantum sensing is defined as satisfying one or, in a narrower sense, all of the following three conditions 5 : (i) the use of qubits (two levels), qutrits (three levels), or qunuts (n levels) to measure physical quantities; (ii) the use of quantum coherence to measure physical quantities; and (iii) the use of quantum entanglement to improve the sensitivity and accuracy of measurements.…”