Exchange Couplings and Magneto‐Structural Correlations of Trinuclear MII‐UIV‐MII (MII = Co, Ni, and Cu) Complexes.

The magnetic properties of the trinuclear Schiff base complexes M 2 UL 7 (M II =Co, Ni, Cu; L 7 = N,N’ ‐bis(3‐hydroxysalicylidene)‐2,2‐dimethyl‐1,3‐propanediamine), exhibiting the [M(μ‐O) 2 ] 2 U core structure (3d‐5 f‐3d subsystem), have been investigated theoretically using scalar relativistic ZORA/DFT computations combined with the broken symmetry (BS) approach. The calculated coupling constants J MU between the adjacent M1−U and M2−U agree with the observed ferromagnetic (Ferro) character observed in the case of the Cu 2 UL 7 complex, the antiferromagnetic (AF) character of the Ni 2 UL 7 one is consistent with the experimentally observed AF behaviour for Co 2 UL 7 . The structural parameters, in particular the M−U distances and the M−O b −U angles, as well as the electronic factors driving the superexchange couplings are discussed. The bond orders and the magnetic molecular orbital analyses reveal that the U(5 f) covalent contribution to the bonding within the M−O−U coordination is more important in the Co 2 UL 7 and Ni 2 UL 7 complexes than in the Cu 2 UL 7 congener, thus favouring AF coupling between the transition metal and the uranium magnetic centers, in the first complexes. The analyses are supported by the study of the mixed ZnMUL 7 and M 2 ThL 7 systems, where the Co II (3d 7 ) and Ni II (3d 8 ) paramagnetic ions are 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. The Natural Populations Analyses confirm the crucial role of spin delocalization that is at work in favour of the AF vs. Ferro magnetic character of the M−U−M (M=Ni, Co) and Cu−U−Cu coordination, respectively.