Synthesis, Structural Features and Physical Properties of a Family of Triply Bridged Dinuclear 3d-4f Complexes

Itziar Oyarzabal,Antonio Rodríguez-Diéguez,Eider San Sebastián,José Manuel Seco,Estitxu Echenique-Errandonea,Enrique Colacio

doi:10.3390/magnetochemistry7020022

Itziar Oyarzabal, Antonio Rodríguez-Diéguez + Show 4 more

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https://doi.org/10.3390/magnetochemistry7020022

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Abstract

New dinuclear MII-LnIII complexes of general formulas [Cu(µ-L)(µ-OAc)Ln(NO3)2]·CH3CN·H2O (LnIII = Gd (1), Tb (2), Dy (3) and Er (4)), [Ni(CH3CN)(µ-L)(µ-OAc)Ln(NO3)2]·CH3CN (LnIII = Nd (5), Gd (6), Tb (7), Dy (8), Er (9) and Y (10)) and [Co(CH3CN)(µ-L)(µ-OAc)Ln(NO3)2]·CH3CN (LnIII = Gd (11), Tb (12), Dy (13), Er (14) and Y (15)) were prepared from the compartmental ligand N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromo-benzyl)ethylenediamine (H2L). In all these complexes, the transition metal ions occupy the internal N2O2 coordination site of the ligand, whereas the LnIII ions lie in the O4 external site. Both metallic ions are connected by an acetate bridge, giving rise to triple mixed diphenoxido/acetate bridged MIILnIII compounds. Direct current (dc) magnetic measurements allow the study of the magnetic exchange interactions between the 3d and 4f metal ions, which is supported by density functional theory (DFT) theoretical calculations for the GdIII-based counterparts. Due to the weak ferromagnetic exchange coupling constants obtained both experimentally and theoretically, the magneto-thermal properties of the less anisotropic systems (compounds 1 and 6) are also studied. Alternating current (ac)magnetic measurements reveal the occurrence of slight frequency dependency of the out-of-phase signal for complexes 8, 9 and 13, while complex 15 displays well-defined maximums below ~6 K.

Highlights

The design and synthesis of molecular complexes that display slow relaxation of the magnetization, i.e., single-molecule magnet behaviour (SMMs), has gained increasing attention in the past few decades [1,2,3,4,5,6]
We have demonstrated that the Mannich-type ligand H2 L (N,N 0 -dimethyl-N,N 0 -bis(2hydroxy-3-formyl-5-bromo-benzyl)ethylenediamine), with high backbone flexibility and inner N2 O2 and outer O4 coordination sites, allows the preparation of a series of dinuclear
The coordination environment of the LnIII ions is similar in all complexes, the NiII and CoII ions are coordinated to an additional acetonitrile molecule compared to the CuII -based analogues, which leads into a more twisted disposition of the ligand around the metal ions and an increase in the hinge angle for the former. dc magnetic measurements have been carried out in order to study the magnetic exchange interactions between MII

Summary

Introduction

The design and synthesis of molecular complexes that display slow relaxation of the magnetization, i.e., single-molecule magnet behaviour (SMMs), has gained increasing attention in the past few decades [1,2,3,4,5,6]. Research efforts in the field of SMMs have shown that the use of heavy lanthanide ions (e.g., DyIII and TbIII ) is a good strategy to obtain compounds with these unique properties, as lanthanides have large angular momentum in the ground multiplet state and, large anisotropy [9,10]. Such complexes often display additional relaxation pathways, such as quantum tunnelling of the magnetization (QTM) or spinphonon couplings, which lead to narrow hysteresis loops and/or the absence of slow relaxation of the magnetization without the application of an external field.

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