Theoretical Investigation of the Electronic Structure and Heisenberg‐Like Exchange Couplings of Single‐Atom Bridged Diuranium U─X─U (U III/IV ; X = N 3− , O 2− , S 2 − ) Complexes

Electronic structure and Heisenberg‐like exchange couplings of single‐atom bridged aryl diuranium [(U(OAr) 3 ) 2 (μ‐X)] q (U III/IV/V ; X = N 3− , O 2− , S 2− ; q = −3, −2, −1, 0; ArO − = 2,6‐di‐ tert ‐butylphenoxide) complexes, exhibiting a linear U─X─U magnetic core, have been investigated computationally using scalar relativistic density functional theory (DFT). These complexes include nitride U─N─U [(U(OAr) 3 ) 2 (μ‐N)] q species, oxide U─O─U [(U(OAr) 3 ) 2 (μ‐O)] q , and their sulfide U─S─U [(U(OAr) 3 ) 2 (μ‐S)] q congeners, exhibiting trivalent U III /U III state, tetravalent U IV /U IV , and mixed‐valence U III /U IV derivatives. The calculated coupling constants J U─U , using the Broken Symmetry (BS) approach, agree with the antiferromagnetic (AF) character observed in the case of the U IV /U IV [(U(OAr) 3 ) 2 (μ−N)] − and the U III /U III [(U(OAr) 3 ) 2 (μ‐O)] 2− complexes. Coupling constant values, not yet measured experimentally, have been estimated for several complexes. These values are experimentally relevant since they can be compared to the values obtained by the so‐called subtraction method, in which the local orbital momenta are in the end subtracted to derive the spin couplings. The Mayer and Nalewajski/Mrozek (NM) bond orders and the magnetic molecular orbital analyses reveal that the U(5f)─X(2p/3p)─U(5f) covalent contribution to the bonding within the U─X─U coordination is more important for the nitride U─N─U species complexes than for the oxide U─O─U and sulfide U─S─U congeners, thus strengthening the AF superexchange coupling between the two uranium magnetic centers in the nitride species. The special case of mixed‐valence complexes exhibiting double exchange is discussed. In this case, we show that the same approach cannot be used to extract coupling constants, even if the high‐spin character of the ground state is no doubt.