Synthesis, structure, and magnetic behavior of a series of trinuclear Schiff base complexes of 5f (UIV, ThIV) and 3d (CuII, ZnII) ions

The reaction of [M(H2L')] (M = Cu, Zn) and U(acac)(4) in refluxing pyridine produced the trinuclear complexes [{MLi(py)(x)}(2)U] [L-i = N,N'-bis(3-hydroxysalicylidene)-R, R = 1,2-ethanediamine (i = 1), 2-methyl-1,2-propanediamine (i = 2), 1,2-cyclohexanediamine (i = 3), 1,2-phenylenediamine (i = 4), 4,5-dimethyl-1,2-phenylenediamine (i = 5), 1,3-propanediamine (i = 6), 2,2-dimethyl-1,3-propanediamine (i = 7), 2-amino-benzylamine (i = 8), or 1,4-butanediamine (i = 9); x = 0 or 1]. The crystal structures show that the central U-IV ion adopts the same dodecahedral configuration in all of these compounds, while the Cu-II ion coordination geometry and the (CuU)-U-... distance vary with the length of the diimino chain of the Schiff base ligand Li. These geometrical parameters have a major influence on the magnetic properties of the complexes. For the smallest (CuU)-U-... distances (i = 1-5), the Cu-U coupling is antiferromagnetic and weak antiferromagnetic interactions are present between the Cull ions, while for the largest (CuU)-U-... distances (i = 6-9), the Cu-U coupling is ferromagnetic and no interaction is observed between the Cull ions. The magnetic behavior of the [{CuLi}(2)Th] compounds (i = 1, 2), in which the Th-IV ion is diamagnetic, confirms the presence of weak intramolecular antiferromagnetic coupling between the Cu-II ions.