Synthesis, Structure, and Zero-Field SMM Behavior of Homometallic Dy2, Dy4, and Dy6 Complexes

Abstract

The synthesis, structure, and magnetic properties of three DyIII complexes of different nuclearity, [Dy2(H2L)2(NO3)] [NO3]·2H2O·CH3OH (1), [Dy4(HL)2(piv)4(OH)2] (2), and [Dy6(H2L)3(μ3–OH)­(μ3–CO3)3(CH3OH)4(H2O)8] 5Cl·3H2O (3) [(H4L) = 6-((bis­(2-hydroxyethyl)­amino)-N′-(2-hydroxybenzylidene)­picolinohydrazide)], are described. This variety of complexes with the same ligand could be obtained by playing with the metal-to-ligand molar ratio, the type of DyIII salt, the kind of base, and the presence/absence of coligand. 1 is a dinuclear complex, while 2 is a tetranuclear assembly with a butterfly-shaped topology. 3 is a homometallic hexanuclear complex that exhibits a propeller-shaped topology. Interestingly, in this complex 3, three atmospheric carbon dioxide molecules are trapped in the form of carbonate ions, which assist in holding the hexanuclear complex together. All of the complexes reveal a slow relaxation of magnetization even in zero applied field. Complex 1 is a zero-field SMM with an effective energy barrier (U eff) of magnetization reversal equal to 87(1) K and a relaxation time of τ0 = 6.4(3) × 10–9 s. Under an applied magnetic field of 0.1 T, these parameters change to U eff = 101(3) K, τ0 = 2.5(1) × 10–9 s. Complex 2 shows zero-field SMM behavior with U eff = 31(2) K, τ0 = 4.2(1) × 10–7 s or τ01 = 2(1) × 10–7 s, U eff1 = 37(8) K, τ02 = 5(6) × 10–5 s, and U eff2 = 8(4) by considering two Orbach relaxation processes, while 3, also a zero-field SMM, shows a double relaxation of magnetization [U eff1 = 62.4(3) K, τ01 = 4.6(3) × 10–8 s, and U eff1 = 2(1) K, τ02 = 4.6(2) × 10–5 s]. The ab initio calculations indicated that in these complexes, the Kramer’s ground doublet is characterized by an axial g-tensor with the prevalence of the m J = ±15/2 component, as well as that due to the weak magnetic coupling between the metal centers, the magnetic relaxation, which is dominated by the single DyIII centers rather than by the exchange-coupled states, takes place via Raman/Orbach or TA-QTM. Moreover, theoretical calculations support a toroidal magnetic state for complex 2.

A single-ion magnet building block strategy toward Dy2single-molecule magnets with enhanced magnetic performance

“…Although both the ferromagnetic and antiferromagnetic interactions between the Dy 3+ ions have been observed in many Dy 2 complexes, rare examples have been reported on switching the magnetic couplings in a system with the same first coordination environment (O 5 N 3 ). 14–18 The present system provides a good chance to closely detect the comprehensive effect of structural parameters on magnetic interactions. Interestingly, dramatic switching of magnetic couplings was achieved based on a SIM complex platform by a synthetic approach.…”

“…13 Toward this end, dilanthanide complexes as the simplest exchange-coupled polynuclear systems are quite attractive for both experimental and theoretical studies, and provide great model compounds for the understanding of lanthanide–lanthanide magnetic interactions and single-ion anisotropy at the same time. 14–18 In fact, except for the Ln 3+ SIM, dilanthanide SMMs dominate the Ln SMM families and provide a significant contribution to the development of SMMs. For example, the strongest magnetic coupling for Gd 3+ ions and the hardest molecular magnet (before 2011) was achieved in N 2 3− -radical-bridged binuclear Gd 3+ and Tb 3+ complexes, respectively.…”

“…4 c,d Although dinuclear Ln-SMMs are highly interesting and crucial for the design of SMMs with improved properties, most of the reported complexes were synthesized serendipitously using bridging ligands such as O donors, S donors, halogen donors, phthalocyanines, and so on, which hinders a systematic preparation of Ln 2 SMMs in a designed way with desired structures. 14–18…”

Synthesis, structures and magnetic properties of four dysprosium-based complexes with a multidentate ligand with steric constraint

“…The bond lengths of Dy(III)-O/N are in the range of 2.245-2.536 Å and the bond angles of O-Dy(III)-O/N range from 65.33 to 151.34°, matching the reported values in the literature. [54][55][56][57][58] Dy 4 . Single crystal X-ray diffraction analysis shows that Dy 4 crystallizes in the triclinic P1 ¯space group.…”

Enhancing magnetic relaxation through subcomponent self-assembly from a Dy2to Dy4grid

“…The quantitative contribution of these charge analyses can be addressed via further ab initio calculations. 68,69…”