Nutation Spectroscopy of a Weakly Interacting Heterobimetallic Spin System

The use of V^IV and Cu^II spins to design weakly coupled and dissymmetric spin systems has been examined. Such systems were synthesized using porphyrin-based complexes, with external coordination sites allowing for the formation of dimers via a Pd^II linker ion. Continuous-wave (CW) Electron Paramagnetic Resonance (EPR) spectroscopy allowed the unequivocal magnetic characterization of the mononuclear precursors VO and Cu. The porphyrin dimer (VO)PdCu presented a broad and overlapped spectrum that was more pronounced than for the previously reported (VO)Pd(VO), hinting at the effect of weak interspin interactions between dissimilar spins. Pulsed EPR experiments on VO, (VO)Pd(VO) and (VO)PdCu samples diluted in a diamagnetic matrix confirmed that this complication is also present in the Field-Swept Echo-Detected (FSED) spectra of the heterometallic (VO)PdCu system. Despite the strongly overlapped field-swept spectra, spin nutation experiments revealed two distinct oscillations in the case of (VO)PdCu, which are assigned to transitions with different spin characters. Remarkably, coherence is retained above liquid nitrogen temperatures for all complexes, in particular up to 295 K for VO and (VO)Pd(VO) and 150 K for (VO)PdCu.