Series of Benzoquinone-Bridged Dicobalt(II) Single-Molecule Magnets

• Published in: Inorganic chemistry Vol. 61; no. 39; pp. 15392 - 15397
• Main Authors: Yao, Binling, Zhang, Yi-Quan, Deng, Yi-Fei, Li, Tianran, Zhang, Yuan-Zhu
• Format: Journal Article
• Language: English
• Published: American Chemical Society 03.10.2022
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.2c01851

Mononuclear complexes within a particular coordination geometry have been well recognized for high-performance single-molecule magnets (SMMs), while the incorporation of such well-defined geometric ions into multinuclear complexes remains less explored. Using the rigid 2-(di­(1H-pyrazol-1-yl)­methyl)-6-(1H-pyrazol-1-yl)­pyridine (PyPz3) ligand, here, we prepared a series of benzoquinone-bridged dicobalt­(II) SMMs [{(PyPz3)­Co}2(L)]­[PF6]2, (1, L = 2,5-dioxo-1,4-benzoquinone (dhbq2–); 2, L = chloranilate (CA2–); and 3, L = bromanilate (BA2–)), in which each Co­(II) center adopts a distorted trigonal prismatic (TPR) geometry and the distortion increases with the sizes of 3,6-substituent groups (H (1) < Cl (2) < Br (3)). Accordingly, the magnetic study revealed that the axial anisotropy parameter (D) of the Co ions decreased from −78.5 to −56.5 cm–1 in 1–3, while the rhombic one (E) increased significantly. As a result, 1 exhibited slow relaxation of magnetization under a zero dc field, while both 2 and 3 showed only the field-induced SMM behaviors, likely due to the increased rhombic anisotropy that leads to the serious quantum tunneling of the magnetization. Our study demonstrated that the relaxation dynamics and performances of a multinuclear complex are strongly dependent on the coordination geometry of the local metal ions, which may be engineered by modifying the substituent groups.