Issue 33, 2020

Slow magnetic relaxation in penta-coordinate cobalt(ii) field-induced single-ion magnets (SIMs) with easy-axis magnetic anisotropy

Abstract

Two penta-coordinate complexes of the general formula [Co(Ln)(NCS)]ClO4, where L1 = {bis[(3,5-dimethyl-1H-pyrazol-1-yl)ethyl]-[(3,4-dimethoxypyridin-2-yl)methyl]}amine and L2 = {bis[(3,5-dimethyl-1H-pyrazol-1-yl)ethyl]-[(4-methoxy-3,5-dimethylpyridin-2-yl)methyl]}amine, 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 geometry in [Co(L2)(NCS)]ClO4 (2) as revealed using the SHAPE analysis. Differences in interatomic parameters among the cobalt(II) and donor atoms in 1 and 2 have definite impact on the magnetic features of both compounds. 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, τ0 = 1.28 × 10−6 s. In the 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 Ueff = |D| × (S2 − 1/4). It has been demonstrated that the degree of substitution and the type of substituents on the pyridyl moieties of the tripodal ligands (L1 and L2) used in these penta-coordinate cobalt(II) complexes have significant impact on structural and magnetic features.

Graphical abstract: Slow magnetic relaxation in penta-coordinate cobalt(ii) field-induced single-ion magnets (SIMs) with easy-axis magnetic anisotropy

Supplementary files

Article information

Article type
Paper
Submitted
02 7月 2020
Accepted
28 7月 2020
First published
14 8月 2020

Dalton Trans., 2020,49, 11715-11726

Slow magnetic relaxation in penta-coordinate cobalt(II) field-induced single-ion magnets (SIMs) with easy-axis magnetic anisotropy

S. S. Massoud, Z. E. Perez, J. R. Courson, R. C. Fischer, F. A. Mautner, J. Vančo, M. Čajan and Z. Trávníček, Dalton Trans., 2020, 49, 11715 DOI: 10.1039/D0DT02338H

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