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

The synthesis, structure, and magnetic properties of three Dy III complexes of different nuclearity, [Dy 2 (H 2 L) 2 (NO 3 )] [NO 3 ]·2H 2 O·CH 3 OH ( 1 ), [Dy 4 (HL) 2 (piv) 4 (OH) 2 ] ( 2 ), and [Dy 6 (H 2 L) 3 (μ 3 -OH)(μ 3 -CO 3 ) 3 (CH 3 OH) 4 (H 2 O) 8 ] 5Cl·3H 2 O ( 3 ) [(H 4 L) = 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 Dy III 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 τ 0 = 6.4(3) × 10 -9 s. Under an applied magnetic field of 0.1 T, these parameters change to U eff = 101(3) K, τ 0 = 2.5(1) × 10 -9 s. Complex 2 shows zero-field SMM behavior with U eff = 31(2) K, τ 0 = 4.2(1) × 10 -7 s or τ 01 = 2(1) × 10 -7 s, U eff1 = 37(8) K, τ 02 = 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, τ 01 = 4.6(3) × 10 -8 s, and U eff1 = 2(1) K, τ 02 = 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 Dy III 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 .