Enhancement of Tb(III) -Cu(II) Single-Molecule Magnet Performance through Structural Modification.

María José Heras Ojea,Wolfgang Wernsdorfer,Mark Murrie,Gopalan Rajaraman,Simon J Coles,Claire Wilson,Lynne H Thomas,Victoria A Milway,Gunasekaran Velmurugan

doi:10.1002/chem.201601971

Abstract

We report a series of 3d–4f complexes {Ln2Cu3(H3L)2Xn} (X=OAc−, Ln=Gd, Tb or X=NO3 −, Ln=Gd, Tb, Dy, Ho, Er) using the 2,2′‐(propane‐1,3‐diyldiimino)bis[2‐(hydroxylmethyl)propane‐1,3‐diol] (H6L) pro‐ligand. All complexes, except that in which Ln=Gd, show slow magnetic relaxation in zero applied dc field. A remarkable improvement of the energy barrier to reorientation of the magnetisation in the {Tb2Cu3(H3L)2Xn} complexes is seen by changing the auxiliary ligands (X=OAc− for NO3 −). This leads to the largest reported relaxation barrier in zero applied dc field for a Tb/Cu‐based single‐molecule magnet. Ab initio CASSCF calculations performed on mononuclear TbIII models are employed to understand the increase in energy barrier and the calculations suggest that the difference stems from a change in the TbIII coordination environment (C 4v versus Cs).

Highlights

Since the discovery of the first single-molecule magnet (SMM) the synthesis of new coordination complexes that display slow relaxation of the magnetisation and magnetic hysteresis of a purely molecular origin has been one of the main challenges in molecular magnetism.[1,2,3] The great interest in SMMs is due to their potential use in technological applications, such as data storage media, quantum computing (Qubits), and spintronic devices.[4,5,6] Early studies showed that the origin of the SMM behaviour arises from two main factors, the large spin ground state of the molecule (S) and a preferential direction [c] Dr L
The ability displayed by bis–tris propane (H6L) to direct the synthesis of Cu/3d heterometallic complexes presented in previous work (3d = Mn(II/III), Zn(II))[20,21] makes it a very attractive candidate for exploring the reactivity of the {Cu(H6L)} units with magnetically more interesting metal ions, such as rare earth elements
Several experiments involving different copper and lanthanide salts have been performed in order to study the reactivity of H6L in the presence of LnIII ions

Summary

Introduction

Since the discovery of the first single-molecule magnet (SMM) the synthesis of new coordination complexes that display slow relaxation of the magnetisation and magnetic hysteresis of a purely molecular origin has been one of the main challenges in molecular magnetism.[1,2,3] The great interest in SMMs is due to their potential use in technological applications, such as data storage media, quantum computing (Qubits), and spintronic devices.[4,5,6] Early studies showed that the origin of the SMM behaviour arises from two main factors, the large spin ground state of the molecule (S) and a preferential direction [c] Dr L. (NMe4)2[Ln2Cu3(H3L)2(NO3)7(CH3OH)2](NO3)(4, Ln = Tb3+) contains a {Cu3(H3L)2} linear unit linked to two TbIII ions as seen in 2, but this time the H3L3À ligands are coordinated to external CuII centres which have two different geometries.

Results

Conclusion