New paper published in Appl. Magn. Res.

Our article, Monitoring S = 0 ↔ S = 2 Spin-State Switching in Fe(II) Complex Using FT EPR and Trityl Radical as Local Magnetic Field Sensor” was published online today, 02-10-2025, in Applied Magnetic Resonance. Check it out.
The use of EPR spectroscopy for studying spin crossover (SCO) is often limited due to the fact that a large number of complexes do not have an EPR signal in X- and Q-bands. At the same time, EPR spectroscopy, being insensitive to diamagnetic impurities and having excellent sensitivity to paramagnetic centers, provides unique advantages compared to direct current magnetometry. In this paper, we propose a method for detecting the thermal spin transition in a spin crossover Fe(II)-based complex by pulsed EPR in the direct dimension with a specially designed spin-probe. The spin probe is non-contact and reusable, consisting of an ampoule of 1 mm diameter filled with a Finland triarylmethyl radical. To detect the SCO transition, the probe is surrounded by a powder of the SCO complex under investigation. In such a design, the transition can be observed through the shift of the line in the EPR spectrum of the spin probe. The latter occurs due to an addition to the external magnetic field of the spectrometer caused by the transition of the spin crossover complex to a high-spin state, in which it demonstrates paramagnetic properties. The experimental results showed that the proposed method allows one to register a transition in [FeL₂][BF₄]₂ complex, where L is 2,6-di(pyrazol-1-yl)pyridine, in the temperature range of 260–262 K with a 2 K wide hysteresis. The change in the local magnetic field at the location of the spin probe of about 0.004 mT was registered, which is in agreement with the numerical calculations performed.