Electronic Structure and Magneto-Structural Correlations Study of Cu 2 UL Trinuclear Schiff Base Complexes: A 3d-5f-3d Case.

The magnetic properties of trinuclear Schiff base complexes M 2 AnL i (M II = Zn, Cu; An IV = Th, U; L i = Schiff base; i = 1-4, 6, 7, 9), exhibiting the [M(μ-O) 2 ] 2 U core structure with adjacent M1···U and M2···U and next-adjacent M1···M2 interactions, featuring 3d-5f-3d subsystems, have been investigated theoretically using relativistic ZORA/B3LYP computations combined with the broken symmetry (BS) approach. Bond order and natural population analyses reveal that the covalent contribution to the bonding within the Cu-O-U coordination is important thus favoring superexchange coupling between the transition metal and the uranium magnetic centers. The calculated coupling constants J CuU between the Cu and U atoms, agree with the observed shift from the antiferromagnetic (AF) character of the L 1,2,3,4 complexes to the ferromagnetic (ferro) of the L 6,7,9 ones. The structural parameters, i.e., the Cu···U distances and the Cu-O-U angles, as well as the electronic factors driving the magnetic couplings are discussed. The analyses are supported by the study of the mixed ZnCuUL i and Cu 2 ThL i systems, where in the first complex the Cu II (3d 9 ) ion is replaced by the diamagnetic Zn II (3d 10 ) one, whereas in the second complex the U IV (5f 2 ) paramagnetic center is replaced by the diamagnetic Th IV (5f 0 ) one.