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 U^IV ion adopts the same dodecahedral configuration in all of these compounds, while the Cu^II 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 Cu^II ions, while for the largest Cu···U distances (i = 6−9), the Cu−U coupling is ferromagnetic and no interaction is observed between the Cu^II ions. The magnetic behavior of the [{CuLⁱ}₂Th] 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.