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(H2L)(2)(NO3)] [NO3]center dot 2H(2)O center dot CH3OH (1), [Dy-4(HL)(2)(piv)(4)(OH)(2)] (2), and [Dy-6(H2L)(3)(mu(3)-OH)(mu(3)- CO3)(3)(CH3OH)(4)(H2O)(8)]5Cl center dot 3H(2)O (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 tau(0) = 6.4(3) X 10(-9) s. Under an applied magnetic field of 0.1 T, these parameters change to U-eff = 101(3) K, tau(0) = 2.5(1) X 10(-9) s. Complex 2 shows zero-field SMM behavior with U-eff = 31(2) K, tau(0) = 4.2(1) X 10(-7) s or tau(01) = 2(1) X 10(-7) s, U-eff1 = 37(8) K, tau(02) = 5(6) X 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, tau(01) = 4.6(3) X 10(-8) s, and U-eff1 = 2(1) K, tau(02) = 4.6(2) X 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.