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Counterion influence on dynamic spin properties in a V(iv) complex.
Chun-Yi Lin1, Thacien Ngendahimana2, Gareth R Eaton2
1Department of Chemistry , Colorado State University , Fort Collins , Colorado 80523 , USA .
Chemical Science
|February 13, 2019
Summary
The counterion significantly impacts V(iv) spin properties in ionic complexes. Larger cations affect solution tumbling, while counterion methyl groups influence phase memory time (T_m) in solid-state electron paramagnetic resonance (EPR) studies.
Area of Science:
- Inorganic Chemistry
- Spin Chemistry
- Materials Science
Background:
- Transition metal ions are crucial for spin-based technologies like electron paramagnetic resonance imaging (EPRI) and quantum computation.
- Understanding how local chemical environments affect spin properties is essential for optimizing these applications.
- The influence of counterions on the spin dynamics of vanadium(IV) complexes has not been systematically investigated.
Purpose of the Study:
- To systematically investigate the effect of counterions on the spin properties of V(iv) ionic complexes.
- To elucidate the role of counterion size and nuclear spin density in influencing electron paramagnetic resonance (EPR) parameters.
- To provide insights into the design of V(iv) complexes for advanced spin-based applications.
Main Methods:
- Synthesis of four ionic V(iv) complexes with varying trialkylammonium counterions: (Et3NH)2[V(C6H4O2)3] (1), (n-Bu3NH)2[V(C6H4O2)3] (2), (n-Hex3NH)2[V(C6H4O2)3] (3), and (n-Oct3NH)2[V(C6H4O2)3] (4).
- Characterization using continuous-wave X-band electron paramagnetic resonance (CW-EPR) spectroscopy in solution at room temperature.
- Investigation of solid-state spin dynamics using variable-temperature X-band pulsed EPR spectroscopy (5-180 K) in an o-terphenyl glass matrix.
Main Results:
- Solution CW-EPR showed increasing linewidth with larger cations, attributed to counterion-controlled tumbling via ion pairing.
- Solid-state pulsed EPR revealed no significant effect of counterions on spin-lattice relaxation times (T1) between 5-180 K.
- Phase memory times (Tm) were significantly shorter for complex 1 (Et3NH+) compared to complexes 2-4 (larger alkyl chains) below 100 K, contrary to expectations based on 1H nuclear spin density.
Conclusions:
- Counterions play a critical role in modulating the spin properties of V(iv) complexes, particularly influencing solution dynamics and solid-state phase memory.
- The methyl groups on the counterion appear to be crucial for enhancing phase memory times (Tm) in the solid state.
- This study demonstrates the potential for tuning spin coherence by controlling counterion structure, offering a new strategy for spin-based molecular materials.
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