Investigation of the role of terminal ligands in magnetic relaxation in a series of dinuclear dysprosium complexes

Abstract

Herein, three dinuclear Dy(III) complexes of the general formula {Dy₂ (L₁)₂ (L₂)₂ (diphenyl phosphate)₂(MeOH)₂} (1); {Dy₂ (L₁)₂ (L₂)₂ (NO₃)₂} (2) and {Dy₂ (L₁)₂ (L₂)₂ (Cl)₂} (3) [where L₁ = (E)-2-(((2-hydroxyphenyl)imino)methyl)-6-methoxyphenol, L₂ = 1,10-phen] with different terminal ligands (diphenyl phosphate and methanol for 1, nitrate for 2 and chloride for 3) are reported. The magnetic studies reveal the presence of weak antiferromagnetic exchange interaction between the dysprosium centers and slow relaxation of magnetization at zero field with the U_eff of 161.9 cm⁻¹, 35.7 cm⁻¹ and 14.2 cm⁻¹ for complexes 1, 2 and 3 respectively. In complex 1, the small transverse anisotropy and negligible QTM in the ground state result in a higher energy barrier for magnetization reversal than complexes 2–3 and was further confirmed by ab initio calculations. The detailed analysis of relaxation dynamics discloses that the Orbach process is dominant for complex 1 whereas Raman and QTM (Quantum Tunneling of Magnetization) play an important role in complexes 2 and 3. Both the experimental and theoretical observations suggest that the binding mode of the terminal ligands closer to the hard axis (g_x, g_y) induces QTM which further affects the slow relaxation process in the studied complexes. BS-DFT calculations were carried out to provide more insight into the exchange interaction for all the complexes.