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Magneto-structural diversity of Co(ii) compounds with 1-benzylimidazole induced by linear pseudohalide coligands

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We report the preparation, spectroscopic characterisation, crystal structure determination and cryomagnetic investigation of three cobalt(II) complexes of formula trans-[Co(bim)4(NCS)2] (1), [Co(bim)2(NCO)2] (2) and [Co(bim)2(N3)2]n (3) (bim = 1-benzylimidazole). The structure of 1 is made up of neutral [Co(bim)4(NCS)2] mononuclear units, where the cobalt(II) ion is six-coordinate with four monodentate bim ligands in equatorial positions and two N-thiocyanato groups in the axial sites building a slightly compressed octahedron. In contrast to 1, each cobalt(II) ion in 2 is four-coordinate with two imidazole-nitrogen atoms from two bim molecules and two N-cyanato ligands describing a slightly distorted tetrahedral geometry, the value of Okuniewski's structural parameter being 0.925. The structure of 3 consists of uniform chains of cobalt(II) ions connected by double end-to-end azido bridges in equatorial positions with two trans-coordinated bim molecules occupying the axial sites. The Co–Nbim bond lengths in 3 are ca. 0.06 Å shorter than the Co–Nazido distances, the value of the tetragonality parameter being 1.03. The intrachain cobalt–cobalt separation is 5.361(1) Å, a value which is much shorter than the shortest interchain one (ca. 12.4 Å). Detailed solid state ac and dc magnetic studies show that 1 and 2 are field-induced single-ion magnets with D = +88.6 (1) and −6.8 cm−1 (2). Q-band EPR spectrometry measurements for polycrystalline samples of 1 and 2 confirm the signs of D and reveal the occurrence of a strong (1)/low (2) low asymmetry in the g-tensors. Theoretical calculations by CASSCF/NEVPT2 support the results from magnetometry and EPR for 1 and 2. The values of the spin reversal barrier which were obtained from the corresponding Arrhenius plots cover the ranges 48.0–50.2 cm−1 (1) and 25.9–27.2 and 11.5–13.1 cm−1 for the high- and low-temperature relaxation processes (2). Compound 3 exhibits an overall antiferromagnetic behaviour with a maximum of the magnetic susceptibility at ca. 70 K, the intrachain antiferromagnetic coupling being J = −26.5 cm−1 (the spin Hamiltonian being defined as Image ID:d0qi00752h-t1.gif). This value is of the same nature and its size compares well with those reported for the scarce examples of this type of cobalt(II) chain.

Graphical abstract: Magneto-structural diversity of Co(ii) compounds with 1-benzylimidazole induced by linear pseudohalide coligands

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Article information

24 Jun 2020
25 Sep 2020
First published
28 Sep 2020

Inorg. Chem. Front., 2020, Advance Article
Article type
Research Article

Magneto-structural diversity of Co(II) compounds with 1-benzylimidazole induced by linear pseudohalide coligands

A. Świtlicka, B. Machura, R. Kruszynski, N. Moliner, J. M. Carbonell, J. Cano, F. Lloret and M. Julve, Inorg. Chem. Front., 2020, Advance Article , DOI: 10.1039/D0QI00752H

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