Effect of Substituents in Equatorial Hexaazamacrocyclic Schiff Base Ligands on the Construction and Magnetism of Pseudo <i>D</i><sub>6h</sub> Single-Ion Magnets
Xiang Zhong, Dongyang Li, Chen Cao, Tong-Kai Luo, Zhao‐Bo Hu, Yan Peng, Sui‐Jun Liu, Yan‐Zhen Zheng, He‐Rui Wen
Abstract
Three mononuclear Dy III compounds [DyL 1 (Ph 3 SiO) 2 ][BPh 4 ]·MeCN·2H 2 O ( 1 ), [DyL 2 (Ph 3 SiO) 2 ][BPh 4 ]·C 2 H 5 OH·H 2 O ( 2 ), and [DyL 3 (Ph 3 SiO)(OAc)][BPh 4 ]·CH 3 OH·3H 2 O ( 3 ) and their corresponding Y III diluted analogues [Dy 0.0967 Y 0.9033 L 1 (Ph 3 SiO) 2 ][BPh 4 ]·MeCN·2H 2 O ( 1@Y ), [Dy 0.2668 Y 0.7332 L 2 (Ph 3 SiO) 2 ][BPh 4 ]·C 2 H 5 OH·H 2 O ( 2@Y ), and [Dy 0.1260 Y 0.8740 L 3 (Ph 3 SiO)(OAc)][BPh 4 ]·CH 3 OH·3H 2 O ( 3@Y ) were synthesized with hexaazamacrocyclic Schiff base ligands as an equatorial ligand. The substituents in the equatorial hexaazamacrocyclic Schiff base ligand show a significant effect on the replacement of the axial ligands. Compounds 1, 2, and 3 are typical zero dc field single-molecule magnets with effective energy barriers ( U eff ) of 1092(6), 946.1(7), and 150.1(9) K, respectively. Although the effective energy barriers of 1 and 2 are close, the magnetic hysteresis remains open up to 20 K for 1, twice as large as that of 2 (10 K), which is different from the previously reported compounds, probably due to nonplanarity N6 in the equator. Ab initio calculations indicate that the ground states of compounds 1 and 2 exhibit high anisotropy and pure second and third excited states, while compound 3 exhibits pure ground-state anisotropy and highly mixed excited states, leading to the easy occurrence of quantum tunneling of magnetization between the ground and excited states in compound 3 . This work indicates that the substituents in equatorial hexaazamacrocyclic Schiff base ligands have a significant effect on the construction and magnetic properties of Dy III SIMs with D 6h symmetry.