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Ligand Control of 59Co Nuclear Spin Relaxation Thermometry
Tyler M Ozvat1, Spencer H Johnson1, Anthony K Rappé1
1Department of Chemistry, Colorado State University, 1301 Center Ave., Fort Collins, CO 80523-1872, USA.
Magnetochemistry (Basel, Switzerland)
|June 7, 2021
Summary
This study explores how molecular structure affects nuclear spin dynamics in cobalt complexes, revealing that ligand encapsulation enhances temperature sensitivity for spin-based probes. Findings suggest tunable quadrupolar coupling interactions are key for improved thermometric applications.
Area of Science:
- Coordination Chemistry
- Physical Chemistry
- Materials Science
Background:
- Understanding the relationship between molecular structure and temperature-dependent nuclear spin dynamics is crucial for developing advanced thermometric nuclear magnetic resonance (NMR) spin-based probes.
- Cobalt(III) complexes offer a versatile platform for investigating these structure-property relationships due to their diverse coordination environments.
Purpose of the Study:
- To investigate the impact of progressively encapsulating ligands on the temperature-dependent spin-lattice (T1) and spin-spin (T2) relaxation times of 59Co nuclei in a series of Co(III) complexes.
- To correlate changes in molecular structure and ligand encapsulation with variations in temperature sensitivity of NMR relaxation parameters.
- To explore the potential of tunable quadrupolar coupling interactions for designing enhanced temperature-sensitive nuclear spin probes.
Main Methods:
- Synthesis and characterization of a series of Co(III) complexes with varying degrees of ligand encapsulation, including K3[Co(CN)6], [Co(NH3)6]Cl3, [Co(en)3]Cl3, [Co(tn)3]Cl3, [Co(tame)2]Cl3, and [Co(dinosar)]Cl3.
- Temperature-dependent measurements of 59Co spin-lattice (T1) and spin-spin (T2) relaxation times over a temperature range of 10-60 °C.
- Analysis of temperature-dependent dephasing times (T2*) and calculations of the temperature-dependent quadrupolar coupling parameter (Δe²qQ/ΔT).
Main Results:
- All studied 59Co complexes exhibited an increase in T1 and T2 relaxation times with increasing temperature (10-60 °C).
- Complexes with greater ligand encapsulation, specifically [Co(tn)3]Cl3 (4) and [Co(en)3]Cl3 (3), showed the highest temperature sensitivities for T1 and T2, respectively.
- Temperature-dependent T2* analyses revealed the highest sensitivities in the most encapsulated structures, with [Co(dinosar)]Cl3 (6) showing up to 4.64% T2*/°C. Calculations of the temperature-dependent quadrupolar coupling parameter provided insights into these observed trends.
Conclusions:
- Ligand encapsulation significantly influences the temperature dependence of 59Co nuclear spin relaxation times in Co(III) complexes.
- The observed trends in temperature sensitivity are linked to the degree of molecular encapsulation and can be further understood through quadrupolar coupling interactions.
- Tunable quadrupolar coupling interactions represent a promising design strategy for developing novel, highly sensitive nuclear spin-based thermometric probes.
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