Effect of ligand substitution on the SMM properties of three isostructural families of double-cubane Mn(4)Ln(2) coordination clusters

摘要

Three isostructural lanthanide series with a core of Mn(2)(III)Mn(2)(II)Ln(2) are reported. These three families have the formulae of [Mn(2)(III)Mn(2)(II)Ln(2)(mu(4)-O)(2)(H(2)edte)(2)(piv)(6)(NO3)(2)] {no crystallization solvent, Ln = La, Ce, Pr, Nd, Eu (1-4, 6); solv = 3MeCN, Ln = Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Y (5, 7-13)}, where H(2)edte = N, N, N', N'-tetrakis(2-hydroxyethyl) ethylenediamine and piv = pivalate; [Mn(2)(III)Mn(2)(II)Ln(2)(mu(4)-O)(2)(H(2)edte)(2)(benz)(6)(NO3)(2)], where benz = benzoate, or [Mn(2)(III)Mn(2)(II)Ln(2)(mu(4)-O)(2)(edteH(2))(2)(benz)(6)(NO3)(2)]center dot 2MeCN {Ln = Gd, Tb, Dy (14-16); and [Mn(2)(III)Mn(2)(II)Ln(2)(mu(4)-O)(2)(edteH(2))(2)(piv)(8)]center dot solv {solv = 4MeCN, Ln = La (17); solv = 2MeCN center dot tol center dot H2O, Ln = Pr, Nd, Sm, Tb (18-20, 22); solv = 2MeCN center dot H2O, Ln = Gd (21). These compounds crystallize in two different systems, namely, monoclinic in the space groups P2(1)/n for 1-4, 6, and 14-16 and C2/c for 5, 7-13, 18-20, and 22 and triclinic in the space group P (1) over bar for 17 and 21. The crystal structures of these compounds display a face-fused dicubane structure connected by different types of bridged oxygen atoms. Solid-state dc magnetic susceptibility characterization was carried out for 1-22, and fitting showed that Mn-III. . .Mn-III is antiferromagnetically (AF) coupled and Mn-II. . . Mn-III, Mn-II. . .Ln and Mn-III. . .Ln are weakly ferromagnetically coupled. In addition, ac measurements were carried out and showed that only 7, 15, and 22 for Tb, 8 and 16 for Dy, and 20 for Sm exhibited slow magnetization relaxation. In the case of 15, it was possible to determine the energy barrier of the slow-relaxation behavior by fitting peak temperatures to the Arrhenius law, which gave a value of U-eff = 21.2 K and a pre-exponential factor of tau(0) = 4.0 x 10(-9) s.