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

The static and dynamic magnetic properties of a pentacoordinate [Co(phen)(DMSO)Cl-2] 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, tau(0) = 5.69 x 10(-9) s using the Debye model, or U-eff = 21.4-40.3 K and tau(0) = 0.248-58.3 x 10(-9) based on a simplified model.