Chelating Guanidinates for Dysprosium(III) Single‐Molecule Magnets^†

Abstract

Guanidinate ligand | Magnetic properties | Lanthanides | Single-molecule magnets | Ab initio calculations Two chelating guanidinate-based dysprosium(III) complexes, namely the monomeric {(Me 3 Si) 2 NC(N i Pr) 2 } 2 Dy(μ-Cl) 2 Li(THF) 2 1 and the dimeric [{(Me 3 Si) 2 NC(N iPr) 2 } 2 Dy(μ-Cl)] 2 2, have been confirmed to be single-molecule magnets. Moreover, the alteration from 1 to 2 leads to an obvious mitigated quantum tunnelling of magnetization at zero field of the hysteresis loop and much enhanced magnetic relaxation barrier (up to 312 K). 5% dilution with the yttrium(III) analogue for 2 shows no clear change for the hysteresis, indicating the single-ion nature of the magnetic behavior.

Guanidinate Rare-Earth Tetraphenylborate Complexes and Their Prospects in Single-Molecule Magnetism

“…The guanidinate ligands coordinate asymmetrically to the metal center, with RE−N guan distances (where N guan represents the chelating nitrogen atoms) spanning from 2.290(1) to 2.412(2) Å and from 2.276(2) to 2.415(2) Å for 1 and 2, respectively. The range of these values is slightly larger than for the respective "ate" salts (2.338(5)−2.389(5) Å for Dy), 8,33 due to the torsion experienced by the ligand. The coordination mode of the BPh 4…”

“…33,46 We followed the first synthetic route and produced Li[(Me 3 Si) 2 NC(N i Pr) 2 ] in a large quantity prior to complexation with RECl 3 (RE = Y, Dy) in THF via salt metathesis to yield the monometallic "salt-like" compounds {(Me 3 Si) 2 NC(N i Pr) 2 } 2 RE(μ-Cl) 2 Li(THF) 2 . 8,33 Treatment of an n-hexane solution of {(Me 3 Si) 2 NC(N i Pr) 2 } 2 RE(μ-Cl) 2 Li-(THF) 2 with 0.16 M t BuLi yielded a light green solution, which after evaporation to dryness afforded a tacky solid, indicative of the targeted alkyl complex with the general formula {(Me 3 Si) 2 NC(N i Pr) 2 } 2 RE( t Bu). The high reactivity of the latter demanded in situ generation prior to further reaction.…”

“…54 The observed and expected high magnetic anisotropy for the Kramers Dy III ion may engender single-molecule magnet behavior, especially when paired with ligands such as guanidinates that are known to impose an axial ligand field. 8 This effect could be augmented by weakly coordinating moieties such as BPh 4 − , 55 which are positioned equatorially and as such ideally minimize transverse anisotropy which introduces fast relaxation pathways. To probe the occurrence of SMM behavior, the dynamic magnetic properties of 2 were explored.…”

“…4 The nature of the functional group inherent to the N-chelate ligand that is bound to a metal ion evokes distinct chemical and physical properties of a given complex encompassing reactivity, 5 catalysis, 6 and singlemolecule magnetism (SMM). 7,8 In general, for certain applications, the construction of large molecular and extended systems is desired, which necessitates soluble building blocks in aprotic solvents. To this end, ligands that readily dissociate from the metal ion are compelling to employ, as those partake more readily in double-displacement reactions such as salt metathesis.…”

“…{(Me 3 Si) 2 NC(N i Pr) 2 } 2 RE(μ-Cl) 2 Li(THF) 2 (RE = Y, Dy) were prepared by salt metathesis reactions between the ligand, Li[(Me 3 Si) 2 NC(N i Pr) 2 ], and RECl 3 , as described in the literature. 8,33 {(Me 3 Si) 2 NC(N i Pr) 2 } 2 RE( t Bu) is produced in situ here but was isolated previously. 34 Synthesis of [{(Me 3 Si) 2 NC(NiPr) 2 } 2 Y][(μ-η 6 -Ph)(BPh 3 )] (1).…”