Publication in Dalton Transactions

Two penta-coordinate cobalt(II) complexes have been synthesized and thoroughly characterized. Each of the cobalt(II) atoms is penta-coordinated in the {CoN5} donor set with a distorted square-pyramidal geometry in [Co(L1)(NCS)]ClO4·MeOH (1), while the vicinity of the central atom can be described as a distorted trigonal-bipyramidal in [Co(L2)(NCS)]ClO4 (2). The complexes show an easy-axis magnetic anisotropy (D = -38.5 cm-1 for 1 and D = -8.5 for 2), and both complexes reveal a large rhombicity with E/D = 0.21 for 1 and E/D = 0.29 for 2. The ZFS parameters (g, D and E) were also calculated using CASSCF/NEVPT2 methods and they are in good agreement with those determined from experimental data. A frequency dependent out-of-phase susceptibility has been observed in external magnetic field (Bdc = 0.1 T) revealing the following parameters of slow relaxation of magnetization for 1: energy of the spin reversal barrier, Ueff = 16.0 cm-1 (Ueff/kB = 23.0 K) and the relaxation time, t0 = 1.28×10-6 s. In case of complex 2, no maxima of frequency dependent out-of-phase susceptibility have been observed and thus, the value of Ueff = 17 cm-1 has been estimated using the expression of Ueff = |D| ´ (S2-1/4).

Massoud, S. S; Perez, Z. E.; Courson, J. R.; Fischer, R. C.; Mautner, F. A.;  Vančo, J.; Čajan, M.; and Trávníček, Z.; Dalton Transactions 2020, 49,11715-11726.!divAbstract