Enhancement of Tb^III–Cu^II Single‐Molecule Magnet Performance through Structural Modification

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).

Fine Tuning the Energy Barrier of Molecular Nanomagnets via Lattice Solvent Molecules

“…Exceptionally, complex 4 does not reach the maximum value until 2.0 K (44.60 cm 3 K mol −1 ). These magnetic behaviours are very similar to those of {Tb 2 Cu 3 (H 3 L) 2 X n } (X = OAc − and NO 3 − ) 35 , suggesting that all four complexes are also ferromagnetic. The small difference in dc magnetic susceptibilities of 1 – 4 means that there is a solvatomagnetic effect in this [Cu 3 Tb 2 (H 3 L) 2 (OAc) 2 (hfac) 4 ] SMM system.…”

“…In the main structure [Cu 3 Tb 2 (H 3 L) 2 (OAc) 2 (hfac) 4 ], a {Cu 3 (H 3 L) 2 } linear unit is formed through bridging two terminal {Cu(H 3 L)} − fragments using a central Cu 2+ ion, then two Tb 3+ ions link to this {Cu 3 (H 3 L) 2 } linear unit in the opposite direction, in which each Tb 3+ ion connects with the central Cu 2+ ion and one external Cu 2+ ion through sharing one μ 3 -O atom and one μ -O atom from one H 3 L 3− ligand, and one μ 3 -O atom from the other H 3 L 3− ligand (Fig. 2a ), similar to those in {Ln 2 Cu 3 (H 3 L) 2 X n } 35 . The eight-coordinate sphere of each Tb 3+ ion is finally completed by two hfac − anions and one OAc − anion.…”

“…Recently, Murrie et al . reported a series of 3d-4f complexes formulated as {Ln 2 Cu 3 (H 3 L) 2 X n } (X = OAc − , Ln = Gd, Tb or X = NO 3 − , Ln = Gd, Tb, Dy, Ho, Er) 35 ; they found that changing the auxiliary ligand OAc − through NO 3 − may lead to a remarkable improvement of the energy barrier of {Tb 2 Cu 3 (H 3 L) 2 X n } (X = OAc − and NO 3 − ) complexes, which suggests that the anion co-ligand has a great impact on the energy barrier of {Tb 2 Cu 3 (H 3 L) 2 X n } SMMs. In the recent process of pursuing new SMMs, we observed that using Ln(OAc)(hfac) 2 (H 2 O) 2 as the lanthanide (III) salt source may lead mixed co-ligands OAc − and hfac − into 3d-4f heterometallic clusters effectively 36 .…”

“…Therefore, we adopted this synthesis strategy to obtain the [Cu 3 Tb 2 (H 3 L) 2 (OAc) 2 (hfac) 4 ] SMM with different ROH lattice solvent molecules (methanol, ethanol and isopropyl alcohol), in which not only the OAc − anion but also the hfac − anion are co-ligands. Notably, our synthetic procedures were completed at room temperature rather than at 60 °C used by Murrie group 35 . Products using methanol, ethanol and isopropyl alcohol as reaction solvents were [Cu 3 Tb 2 (H 3 L) 2 (OAc) 2 (hfac) 4 ]∙2MeOH ( 1 ), [Cu 3 Tb 2 (H 3 L) 2 (OAc) 2 (hfac) 4 ]∙2EtOH ( 2 ) and [Cu 3 Tb 2 (H 3 L) 2 (OAc) 2 (hfac) 4 ]∙2iso-C 3 H 7 OH ( 3 ), respectively; while [Cu 3 Tb 2 (H 3 L) 2 (OAc) 2 (hfac) 4 ]∙2H 2 O ( 4 ) was quantitatively transformed from complex 1 by taking place of methanol molecules with water molecules.…”

A Novel Family of Triangular CoII2LnIII and CoII2YIII Clusters by the Employment of Di-2-Pyridyl Ketone

“…The study of mixed-metal 3d/4f reaction systems, as a means for the isolation of new SMMs with a high energy barrier for the magnetization reversal, has led to a large variety of such species that now include Mn/4f [16][17][18][19][20][21], Fe/4f [22][23][24][25], Ni/4f [8,26], Cu/4f [27][28][29][30] and Co/4f [8,[31][32][33] compounds [1,2]. It is noteworthy that the majority of 3d/4f SMMs are Mn/4f clusters containing some Mn III centers with an S = 2 spin state and a significant uniaxial anisotropy.…”