Regulating the magnetic properties of seven-coordinated Dy() single-ion magnets through the effect of positional isomers on axial crystal-field

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 5; no. 46; pp. 17328 - 17337
• Main Authors: Dong, Yubao, Zhu, Li, Yin, Bing, Zhu, Xinrui, Li, Dongfeng
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 30.11.2021
• Subjects: Crystal structure; Dysprosium; Ethylenediamine; Halides; Hysteresis loops; Isomers; Ligands; Magnetic measurement; Magnetic properties; Magnetism; Magnets; Mathematical analysis; Steric effects
• ISSN: 1477-9226; 1477-9234; 1477-9234
• DOI: 10.1039/d1dt02925h

Six Dy( iii ) single-ion magnets (SIMs) [Dy( n -OMe-bbpen)X] were synthesized by a solvothermal reaction with three positional isomers ( ortho , meta , and para ) of ligands n -OMe-H 2 bbpen and dysprosium halides DyX 3 , ( n -OMe-H 2 bbpen = N , N ′-bis(2-hydroxy- n -methoxybenzyl)- N , N ′-bis(2-methylpyridyl)ethylenediamine; n = 3, X = Cl, 1 ; n = 3, X = Br, 2 ; n = 4, X = Cl, 3 ; n = 4, X = Br, 4 ; n = 5, X = Cl, 5 ; n = 5, X = Br, 6 ). Dynamic magnetic measurements revealed that the six complexes possess notably different effective barriers of magnetic reversal: 872.0 K ( 1 ), 1210.1 K ( 2 ), 137.9 K ( 3 ), 602.6 K ( 4 ), 907.0 K ( 5 ) and 1216.7 K ( 6 ). 6 showed the best performance as SIMs among the six Dy( iii ) complexes. Moreover, the magnetic hysteresis loops of 6 remained open at 21 K. The crystal structures indicate the switching of local symmetry around Dy( iii ) ion, aroused by the variation in intermolecular interactions and steric effects. This switch is primarily correlated with the distinction of magnetic properties. In addition, ab initio calculations confirmed that the different electrostatic potential around Dy( iii ) ion stemming from the electronic effect of the OMe-substituted group is another factor leading to the distinction in magnetic properties. This work warns us that when designing ligands for Dy-SIMs, the effect of positional isomerism on magnetic performance must be considered, which is one of the factors that can easily be overlooked. Six Dy( iii ) SIMs based on positional isomerism strategy were synthesized. Their SMM properties are noteworthily modulated by positional isomerism of methoxyl group, which changed both local symmetry and electrostatic potential around the Dy( iii ) ion.