Effects of strong coordination bonds at the axial or equatorial positions on magnetic relaxation for pentagonal bipyramidal dysprosium(III) single-ion magnets

Min Li; Jiayi Han; Haipeng Wu; Yi-En Du; Yufang Liu; Yongqiang Chen; Sanping Chen

doi:10.1039/d2dt02402k

Effects of strong coordination bonds at the axial or equatorial positions on magnetic relaxation for pentagonal bipyramidal dysprosium(III) single-ion magnets

Dalton Trans. 2022 Nov 15;51(44):16964-16972. doi: 10.1039/d2dt02402k.

Authors

Min Li¹, Jiayi Han¹, Haipeng Wu¹, Yi-En Du¹, Yufang Liu¹, Yongqiang Chen¹, Sanping Chen²

Affiliations

¹ Department of Chemistry and Chemical Engineering, Jinzhong University, Jinzhong, 030619, China. wuhp@jzxy.edu.cn.
² Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, College of Chemistry and Materials Science, Northwest University, Xi'an, 710127, China. sanpingchen@126.com.

PMID: 36300420
DOI: 10.1039/d2dt02402k

Abstract

Three pentagonal bipyramidal mononuclear Dy(III) complexes based on amino-substituted nitrophenol and tetradentate amide ligands of formulas [Dy(Hbpen)(OPhNO₂NH₂Cl)Cl₂] (1), [Dy(Hbpen)(OPhNO₂NH₂)Cl₂] (2) and [Dy(Hbpen)(OPhNO₂NH₂Cl)₃] (3) (Hbpen = N,N'-bis(2-pyridylmethyl)-ethylenediamine, OPhNO₂NH₂Cl = 2-amino-6-chloro-4-nitrophenol, and OPhNO₂NH₂ = 2-amino-4-nitrophenol) were isolated. X-ray diffraction studies illustrate that complexes 1 and 2 with one strongly coordinating phenol ligand at their equatorial positions have a similar structure except for a slight difference in the chloride substituent of the phenol ligand. Complex 3 possesses the same equatorial coordination as 1 but its apical positions are occupied by two other phenol ligands. Magnetic studies show that 1 and 2 are zero-field single-ion magnets (SIMs), and 3 exhibits field-induced SIM behavior. Upon removing the chloride substituent groups from the phenol ligand, the effective energy barrier enhances from 233.7 K (1) to 362.7 K (2) under external dc fields. The stronger quantum tunneling of magnetization observed for 3 in comparison with 1 shows the destructive influence of a strong phenoxyl oxygen ligand field contributing to the transverse component on the magnetic properties. A comparison of complex 2 and the reported Dy(III) analogue [Dy(Hbpen)Cl(OPhBr₂NO₂)₂] with two phenol ligands (2,6-dibromo-4-nitrophenol) in the axial direction leads to the conclusion that the magnetic anisotropy is strongly dependent on the Dy-O_phenoxyl bond lengths. The results provide direct information vital to understanding how the strong coordination environment at the axial or equatorial positions influences the SIM behavior.