Two Series of Homodinuclear Lanthanide Complexes: Greatly Enhancing Energy Barriers through Tuning Terminal Solvent Ligands in Dy2 Single-Molecule Magnets

Yaru Qin; Haifeng Zhang; Hao Sun; Yangdan Pan; Yu Ge; Yahong Li; Yi-Quan Zhang

doi:10.1002/asia.201701065

Two Series of Homodinuclear Lanthanide Complexes: Greatly Enhancing Energy Barriers through Tuning Terminal Solvent Ligands in Dy₂ Single-Molecule Magnets

Chem Asian J. 2017 Nov 2;12(21):2834-2844. doi: 10.1002/asia.201701065. Epub 2017 Oct 9.

Authors

Yaru Qin¹, Haifeng Zhang², Hao Sun¹, Yangdan Pan¹, Yu Ge¹, Yahong Li¹, Yi-Quan Zhang³

Affiliations

¹ College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou, 215123, P.R. China.
² Department of Chemistry and Chemical Engineering, Jining University, Qufu, 273155, P.R. China.
³ Jiangsu Key Laboratory for NSLSCS, School of Physical Science and Technology, Nanjing Normal University, Nanjing, 210023, P.R. China.

PMID: 28840651
DOI: 10.1002/asia.201701065

Abstract

The utilization of 2-ethoxy-6-{[(2-hydroxy-3-methoxybenzyl)imino]methyl}phenol (H₂ L) as a chelating ligand, in combination with the employment of alcohols (EtOH and MeOH) as auxiliary ligands, in 4 f-metal chemistry afforded two series of dinuclear lanthanide complexes of compositions [Ln₂ L₂ (NO₃ )₂ (EtOH)₂ ] (Ln=Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7)) and [Ln₂ L₂ (NO₃ )₂ (MeOH)₂ ] (Ln=Sm (8), Eu (9), Gd (10), Tb (11), Dy (12), Ho (13), Er (14)). The structures of 1-14 were determined by single-crystal X-ray crystallography. Complexes 1-7 are isomorphous. The two lanthanide(III) ions in 1-7 are doubly bridged by two deprotonated aminophenoxide oxygen atoms of two μ₂ :η⁰ :η¹ :η² :η¹ :η¹ :η⁰ -L^2- ligands. One nitrogen atom, two oxygen atoms of the NO₃^- anion, two methoxide oxygen atoms of two ligand sets, and one oxygen atom of the terminally coordinated EtOH molecule complete the distorted dodecahedron geometry of each lanthanide(III) ion. Compounds 8-14 are isomorphous and their structures are similar to those of 1-7. The slight difference between 1-7 and 8-14 stems from purposefully replacing the EtOH ligands in 1-7 with MeOH in 8-14. Direct-current magnetic susceptibility studies in the 2-300 K range reveal weak antiferromagnetic interactions for 3, 4, 7, 10, 11, and 14, and ferromagnetic interactions at low temperature for 5, 6, 12, and 13. Complexes 5 and 12 exhibit single-molecule magnet (SMM) behavior with energy barriers of 131.3 K for 5 and 198.8 K for 12. The energy barrier is significantly enhanced by dexterously regulating the terminal ligands. To rationalize the observed difference in the magnetic behavior, complete-active-space self-consistent field (CASSCF) calculations were performed on two Dy₂ complexes. Subtle variation in the angle between the magnetic axes and the vector connecting two dysprosium(III) ions results in a weaker influence on the tunneling gap of individual dysprosium(III) ions by the dipolar field in 12. This work proposes an efficient strategy for synthesizing Dy₂ SMMs with high energy barriers.

Keywords: energy barriers; lanthanides; magnetic properties; solvent effects; structure elucidation.