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

Area of Science:

• Inorganic Chemistry
• Chemical Physics
• Materials Science

Background:

• Magnetic resonance techniques are crucial for noninvasive temperature mapping in medical applications.
• Developing sensitive molecular thermometers is essential for accurate disease diagnosis and treatment monitoring.

Purpose of the Study:

• To introduce a novel design strategy for molecular thermometers based on chemical control of vibrational partition functions.
• To investigate the temperature sensitivity of four air-stable cobalt(iii) complexes using 59Co NMR.

Main Methods:

• Variable-temperature 59Co Nuclear Magnetic Resonance (NMR) spectroscopy was employed.
• Four cobalt(iii) complexes, Co(accp)3, Co(bzac)3, Co(tBu2-acac)3, and Co(acac)3, were synthesized and analyzed.
• Temperature sensitivity (Δδ/ΔT) was measured at a 100 mM concentration.

Main Results:

• The study identified 59Co chemical shift temperature sensitivity values for the complexes.
• Complexes 1 (Co(accp)3) and 2 (Co(bzac)3) exhibited record sensitivities of 3.50(2) and 3.39(3) ppm °C⁻¹, respectively.
• Higher sensitivities in complexes 1 and 2 were attributed to ligand asymmetry influencing Raman-active vibrational modes.

Conclusions:

• The demonstrated design strategy offers a new approach for creating advanced molecular thermometers.
• The findings highlight the potential of specific cobalt(iii) complexes for sensitive, noninvasive temperature measurements.
• Ligand design plays a critical role in tuning the performance of magnetic resonance-based thermometers.