RESUMO
Three isostructural lanthanide series with a core of MnMnLn2 are reported. These three families have the formulae of [MnMnLn2(µ4-O)2(H2edte)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 H2edte = N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine and piv = pivalate; [MnMnLn2(µ4-O)2(H2edte)2(benz)6(NO3)2], where benz = benzoate, or [MnMnLn2(µ4-O)2(edteH2)2(benz)6(NO3)2]·2MeCN {Ln = Gd, Tb, Dy (14-16); and [MnMnLn2(µ4-O)2(edteH2)2(piv)8].solv {solv = 4MeCN, Ln = La (17); solv = 2MeCN·tol·H2O, Ln = Pr, Nd, Sm, Tb (18-20, 22); solv = 2MeCN·H2O, Ln = Gd (21). These compounds crystallize in two different systems, namely, monoclinic in the space groups P21/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 P1[combining macron] 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 MnIIIMnIII is antiferromagnetically (AF) coupled and MnIIMnIII, MnIILn and MnIIILn 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 Ueff = 21.2 K and a pre-exponential factor of τ0 = 4.0 × 10-9 s.
RESUMO
The reaction of 2,6-pyridinedimethanol (pdmH(2)), CoCl(2)·6H(2)O, Ln(NO(3))(3)·6H(2)O and pivalic acid (pivH) in the presence of triethylamine in MeCN and CH(2)Cl(2) under ambient conditions results in the tetranuclear heterobimetallic compounds [Co(II)(2)Ln(2)(pdmH)(4)(Piv)(6)]·4CH(3)CN (Ln = Y (1), Gd (2), Tb (3), Ho (4)) and [Co(II)(2)Dy(2)(pdmH)(4)(Piv)(6)]·2CH(3)CN (5). The molecular structures of 1-5 were determined by single-crystal X-ray diffraction and reveal that they are isostructural. However, compounds 1-4 crystallize in the monoclinic space group P2(1)/n, while compound 5 crystallizes in the orthorhombic space group Pnna. In all of these compounds, the four metal ions are held together by four alkoxide mu(3)-RCH(2)O(-) bridges to form novel Co(2)Ln(2)O(4)-heterocubanes. Magnetic properties of 1-5 have been investigated using dc and ac susceptibility measurements. Of these compounds, only compound 5 displays an out-of-phase signal in the ac susceptibility and exhibits slow relaxation of the magnetization, which is attributed to the presence of the anisotropic Dy(III) ions.