Synthesis, Structure, and Magnetic Behavior of a Series of Trinuclear Schiff Base Complexes of 5f (U^IV, Th^IV) and 3d (Cu^II, Zn^II) Ions

The reaction of [M(H2Li)] (M = Cu, Zn) and U(acac)4 in refluxing pyridine produced the trinuclear complexes [{MLi(py)x}2U] [Li = 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 UIV ion adopts the same dodecahedral configuration in all of these compounds, while the CuII ion coordination geometry and the Cu···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 Cu···U distances (i = 1−5), the Cu−U coupling is antiferromagnetic and weak antiferromagnetic interactions are present between the CuII ions, while for the largest Cu···U distances (i = 6−9), the Cu−U coupling is ferromagnetic and no interaction is observed between the CuII ions. The magnetic behavior of the [{CuLi}2Th] compounds (i = 1, 2), in which the ThIV ion is diamagnetic, confirms the presence of weak intramolecular antiferromagnetic coupling between the CuII ions.