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

The synthesis, structure, and magnetic properties of three Dy complexes of different nuclearity, [Dy(HL)(NO)] [NO]·2HO·CHOH (), [Dy(HL)(piv)(OH)] (), and [Dy(HL)(μ-OH)(μ-CO)(CHOH)(HO)] 5Cl·3HO () [(HL) = 6-((bis(2-hydroxyethyl)amino)-'-(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 Dy salt, the kind of base, and the presence/absence of coligand. is a dinuclear complex, while is a tetranuclear assembly with a butterfly-shaped topology. is a homometallic hexanuclear complex that exhibits a propeller-shaped topology. Interestingly, in this complex , 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 is a zero-field SMM with an effective energy barrier () of magnetization reversal equal to 87(1) K and a relaxation time of τ = 6.4(3) × 10 s. Under an applied magnetic field of 0.1 T, these parameters change to = 101(3) K, τ = 2.5(1) × 10 s. Complex shows zero-field SMM behavior with = 31(2) K, τ = 4.2(1) × 10 s or τ = 2(1) × 10 s, = 37(8) K, τ = 5(6) × 10 s, and = 8(4) by considering two Orbach relaxation processes, while , also a zero-field SMM, shows a double relaxation of magnetization [ = 62.4(3) K, τ = 4.6(3) × 10 s, and = 2(1) K, τ = 4.6(2) × 10 s]. The calculations indicated that in these complexes, the Kramer's ground doublet is characterized by an axial g-tensor with the prevalence of the = ±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 Dy 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 .