‘Kick-in the head’: high-performance and air-stable mononuclear DyIII single-molecule magnets with pseudo-D6h symmetry from a [1 + 1] Schiff-base macrocycle approach†
Alexandros S. Armenis, Arpan Mondal, Sean R. Giblin, Dimitris I. Alexandropoulos, Jinkui Tang, Richard A. Layfield and Theocharis C. Stamatatos
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引用次数: 0
Abstract
Using the [1 + 1] condensation approach for the preparation of new macrocyclic scaffolds (LN6phen and LN4O2phen) with the rigid phenanthroline-based ‘head’ unit produces the air-stable mononuclear compounds [Dy(LN6phen)(Ph3SiO)2](PF6) (1-LN6phen) and [Dy(LN4O2phen)(Ph3SiO)2](PF6) (1-LN4O2phen) through a stepwise metal-ion templated synthesis. Both compounds exhibit pseudo-D6h symmetry with different degrees of distortion from the ideal hexagonal bipyramidal geometry, depending on the planarity of the equatorial macrocycles and the intramolecular π–π stacking interactions between the phenyl groups of the apical siloxide ligand and the equatorial macrocycle. Both compounds are single-molecule magnets (SMMs) with large energy barriers for the magnetization reversal, exhibiting out-of-phase AC susceptibility signals up to 75 K or 90 K. The closer-to-ideal D6h complex 1-LN4O2phen possesses a Ueff of 1360 K, which is the highest reported barrier among all mononuclear DyIII SMMs synthesized using the [1 + 1] Schiff-base macrocycle approach. The experimental results are supported by ab initio calculations, which indicate relaxation of the magnetization via the first- or second-excited state for 1-LN6phen and 1-LN4O2phen, respectively. The results demonstrate the ability of Schiff-base macrocycles to facilitate the synthesis of high-performance and air-stable SMMs through a chemical modulation of the individual carbonyl ‘head’ and amine subunits, deciphering the factors which affect the magnetic dynamics of SMMs.