Field-induced slow relaxation of magnetization in a pentacoordinate Co(ii) compound [Co(phen)(DMSO)Cl2]

Abstract

The static and dynamic magnetic properties of a pentacoordinate [Co(phen)(DMSO)Cl₂] compound (phen = 1,10′-phenanthroline, DMSO = dimethyl sulfoxide) were thoroughly studied by experimental (SQUID magnetometry and HF-EPR spectroscopy) and theoretical methods (DFT and CASSCF calculations). It has been found from temperature/field-dependent magnetization measurements that the studied compound possesses a large and negative magnetic anisotropy (D = −17(1) cm⁻¹) with large rhombicity (E/D = 0.24(5)), and these experimental results are in agreement with ab initio calculations (D = −17.7 cm⁻¹, E/D = 0.31). Interdoublet resonances were not observed in the HF-EPR measurements, but the large rhombicity was confirmed (D_EPR = −17.7 cm⁻¹ (fixed from CASSCF calculations), E/D_EPR = 0.33). A frequency dependent out-of-phase susceptibility signal was observed only in a non-zero static magnetic field (B = 0.1 T) and the following parameters of slow-relaxation of magnetisation were derived from the experimental data: either the energy of spin reversal barrier, U_eff = 10.4 K, and the relaxation time, τ₀ = 5.69 × 10⁻⁹ s using the Debye model, or U_eff = 21.4–40.3 K and τ₀ = 0.248–58.3 × 10⁻⁹ based on a simplified model.