5 years ago

Quantitative Estimation of Ising-Type Magnetic Anisotropy in a Family of C3-Symmetric CoII Complexes

Quantitative Estimation of Ising-Type Magnetic Anisotropy in a Family of C3-Symmetric CoII Complexes
Jesús Jover, Amit Kumar Mondal, Sanjit Konar, Eliseo Ruiz
In this paper, the influence of the structural and chemical effects on the Ising-type magnetic anisotropy of pentacoordinate CoII complexes has been investigated by using a combined experimental and theoretical approach. For this, a deliberate design and synthesis of four pentacoordinate CoII complexes [Co(tpa)Cl]⋅ClO4 (1), [Co(tpa)Br]⋅ClO4 (2), [Co(tbta)Cl]⋅(ClO4)⋅(MeCN)2⋅(H2O) (3) and [Co(tbta)Br]⋅ClO4 (4) by using the tripodal ligands tris(2-methylpyridyl)amine (tpa) and tris[(1-benzyl-1 H-1,2,3-triazole-4-yl)methyl]amine) (tbta) have been carried out. Detailed dc and ac measurements show the existence of field-induced slow magnetic relaxation behavior of CoII centers with Ising-type magnetic anisotropy. A quantitative estimation of the zero-field splitting (ZFS) parameters has been effectively achieved by using detailed ab initio theory calculations. Computational studies reveal that the wavefunction of all the studied complexes has a very strong multiconfigurational character that stabilizes the largest ms=±3/2 components of the quartet state and hence produce a large negative contribution to the ZFS parameters. The difference in the magnitudes of the Ising-type anisotropy can be explained through ligand field theory considerations, that is, D is larger and negative in the case of weak equatorial σ-donating and strong apical π-donating ligands. To elucidate the role of intermolecular interactions in the magnetic relaxation behavior between adjacent CoII centers, a diamagnetic isostructural ZnII analog (5) was synthesized and the magnetic dilution experiment was performed. Magnetic anisotropy in Co complexes: A quantitative estimation of magnetic anisotropy has been done for C3-symmetric CoII complexes with Ising-type magnetic anisotropy by using a combined experimental and theoretical approach (see figure).

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201702108

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