Ligand-directed assembly of trinuclear and one-dimensional heterotrimetallic Cu(II)Ln(III)Fe(III) complexes: unusual antiferromagnetic (CuFeIII)-Fe-II coupling via cyano bridges

New heterotrimetallic complexes [Cu(valpn)(H2O)Ln(H2O)(3)Fe(CN)(6)]center dot xH(2)O (Ln = Gd, x = 3 for complex 1; Ln = Tb, x = 3 for complex 2; Ln = Dy, x = 1.75 for complex 3; H(2)valpn = N,N'-bis(3-methoxysalicylidene)-1,3-diaminopropane), {[Cu(Me(2)valpn)](2)Ln(H2O)Fe(CN)(6)center dot xH(2)O center dot yCH(3)CN}(n) (Ln = Gd, x = 5, y = 2.5 for complex 4; Ln = Tb, x = 4.5, y = 1.5 for complex 5; Ln = Dy, x = 5.5, y = 2.5 for complex 6; Ln = Y, x = 6, y = 4 for complex 7; H(2)Me(2)valpn = N,N'-bis(3-methoxysalicylidene)-2,2-dimethyl-1,3-diaminopropane) have been synthesised by a reaction of Cu(valpn) (or Cu(Me(2)valpn)), Ln(3+) and [Fe(CN)(6)](3-) in a molar ratio of 2 : 1 : 1. Complexes 1-3 have a CuLnFe trinuclear structure, consisting of phenoxo-bridged Cu-Ln and cyano-bridged Ln-Fe moieties. Complexes 4-7 contain phenoxo-bridged Cu(2)Ln units that are connected by [Fe(CN)(6)](3-) to form a one-dimensional (1D) zig-zag structure. In the trinuclear complexes 1-3, the [Fe(CN)(6)](3-) anion coordinates to Ln(3+), whereas it coordinates to Cu2+ in complexes 4-7. Magnetic studies demonstrate that there exists a ferromagnetic interaction between Cu(II) and Gd(III) ions via the phenoxo bridges, while the cyano-bridges transit antiferromagnetic coupling between low-spin Fe(III) and Cu(II) or Gd(III). The fitting to the magnetic susceptibilities of complexes 1 and 4 gave the parameters of J(CuGd) = 2.392 and 2.945 cm(-1), and J(FeGd) = -0.341 cm(-1) and J(FeCu) = -0.378 cm(-1). The ac magnetic measurements reveal that complex 6 shows slow magnetization relaxation with an energy barrier of 12.3 K and a relaxation time of tau(0) = 1.65 x 10(-6) s, which is typical of a single-chain magnet.