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Single-Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain.

ABSTRACT: The cobalt(II) in [Co(NCS)₂ (4-methoxypyridine)₂ ]_n are linked by pairs of thiocyanate anions into linear chains. In contrast to a previous structure determination, two crystallographically independent cobalt(II) centers have been found to be present. In the antiferromagnetic state, below the critical temperature (T_c =3.94 K) and critical field (H_c =290 Oe), slow relaxations of the ferromagnetic chains are observed. They originate mainly from defects in the magnetic structure, which has been elucidated by micromagnetic Monte Carlo simulations and ac measurements using pristine and defect samples. The energy barriers of the relaxations are Δ_τ1 =44.9(5) K and Δ_τ2 =26.0(7) K for long and short spin chains, respectively. The spin excitation energy, measured by using frequency-domain EPR spectroscopy, is 19.1 cm^-1 and shifts 0.1 cm^-1 due to the magnetic ordering. Ab initio calculations revealed easy-axis anisotropy for both Co^II centers, and also an exchange anisotropy J_xx /J_zz of 0.21. The XXZ anisotropic Heisenberg model (solved by using the density renormalization matrix group technique) was used to reconcile the specific heat, susceptibility, and EPR data.

SUBMITTER: Rams M

PROVIDER: S-EPMC7078958 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Single-Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain.

Rams Michał M Jochim Aleksej A Böhme Michael M Lohmiller Thomas T Ceglarska Magdalena M Rams Marek M MM Schnegg Alexander A Plass Winfried W Näther Christian C

Chemistry (Weinheim an der Bergstrasse, Germany) 20200109 13

The cobalt(II) in [Co(NCS)2 (4-methoxypyridine)2 ]n are linked by pairs of thiocyanate anions into linear chains. In contrast to a previous structure determination, two crystallographically independent cobalt(II) centers have been found to be present. In the antiferromagnetic state, below the critical temperature (Tc =3.94 K) and critical field (Hc =290 Oe), slow relaxations of the ferromagnetic chains are observed. They originate mainly fro ...[more]

PMID: 31702081

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Project description:In this study, we synthesized a new Co(II) complex, [NMe4]2[Co(bpyO2)2] (1), using deprotonated 2,2'-bipyridine-6,6'-diol ligands (bpyO2 2-). This compound exhibits a significant zero-field splitting (D) value. The far-infrared magneto spectroscopy and high-frequency and field electron paramagnetic resonance (HFEPR) measurements indicated that compound 1 possesses D = -54.8 cm-1 and E ∼ 0 cm-1. These findings were subsequently confirmed by other experimental data, including DC magnetic susceptibilities and variable temperature and variable magnetic field reduced magnetizations. Additionally, we conducted a series of AC magnetic susceptibility measurements to investigate the kinetics of magnetization relaxation. Below 6.6 K and under zero external magnetic field, fast quantum tunneling of magnetization (QTM) dominates (∼570 Hz), and temperature-independent out-of-phase signals are observed. Above 8.1 K, temperature-dependent behavior is observed. Furthermore, we examined the AC magnetic susceptibility behavior under external magnetic fields ranging from 300 to 4000 G. The effect of QTM is significantly reduced in the presence of an external magnetic field. Temperature-dependent behavior is primarily governed by Raman relaxation. Through structural analysis of compound 1 and a series of pure nitrogen-coordinated single-ion magnets (SIMs), we propose that the oxo substituents from the double-deprotonated form of the 2,2'-bipyridine-6,6'-diol ligands donate their negative charge to the pyridine ring, forming amido anion sites. This triggers a more pronounced out-of-phase signal than that observed in pure pyridine-coordinated compounds. Moreover, we observed intermolecular interactions, including intermolecular hydrogen bonding, which, to some extent, influenced the slow relaxation of molecules. Therefore, we speculate that the slow relaxation phenomenon of compound 1 may be attributed to the combination of oxo back-donating effects and intermolecular interactions.

Dataset Information

Single-Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain.

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Single-Chain Magnet Based on Cobalt(II) Thiocyanate as XXZ Spin Chain.

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