A relativistic DFT study of magnetic exchange coupling in ketimide bimetallic uranium(IV) complexes

Abstract

International audienceMagnetic exchange couplings in bis(ketimide) binuclear UIV/UIV complexes [Cp′2UCl]2(μ-ketimide) diuranium(IV) and [(C5H5)2(Cl)An]2(μ-ketimide) (Cp′ = C5Me4Et; ketimide = N=CMe-(C6H4)-MeC=N) have been investigated computationally using relativistic density functional theory (DFT) combined with the broken symmetry (BS) approach. Using the B3LYP hybrid functional, the BS ground state of these UIV/UIV 5f 2-5f 2 complexes has been found of lower energy than the high spin (HS) quintet state, indicating an antiferromagnetic character (estimated coupling constant |J| < 5 cm−1) which has not yet been evidenced unambiguously experimentally. On the contrary, the BP86 GGA functional overestimates greatly the antiferromagnetic character of the complexes (|J| > 100 cm−1). As recently reported for para-bis(imido) [(C5H5)3U]2(μ-imido) uranium(V) complex, spin polarization is mainly responsible for the antiferromagnetic coupling through the π-network orbital pathway within the bis(ketimide) bridge. Furthermore, spin polarization is exalted by the combined roles of the 5f metal orbitals and of the π-conjugated ketimide bridging ligand which permit electronic communication between the two uranium atoms albeit separated by a distance of the order of 10 Å. The MO analysis clarifies which MOs contribute to the antiferromagnetic coupling in the binuclear complexes under consideration and brings to light the 5f orbitals driving contribution

DFT Investigations of the Magnetic Properties of Actinide Complexes

“…The DFT/BS approach for computing and modeling the exchange coupling interactions faces situations in actinide systems which are different from the lanthanide ones because of their potential for more covalent metal-ligand interactions especially for uranium [8,21,[71][72][73]75]. Even so, numerous DFT/BS studies aiming at rationalizing the sign and strength of the exchange coupling for various bridged diuranium by drawing magneto-structural correlations have been carried out [105][106][107][108][109][110][145][146][147].…”

“…However, the magnetic character of the coupling between the metal centers could not be shown unambiguously. Computationally, the exchange coupling constant has be estimated considering the simplified [(C 5 H 5 ) 2 (Cl)An] 2 (µ-ketimide) model (An/An = U IV /U IV and U IV /Th IV ), where C 5 Me 4 Et is replaced by the Cp = C 5 H 5 ring ( Figure 14) [147]. Using ZORA/B3LYP computations, the BS ground state of these U IV /U IV 5f 2 -5f 2 complexes has been found of lower energy than the quintet HS state, indicating a weak AF character (estimated coupling constant |J| < 5 cm −1 ) which has not yet been confirmed experimentally to our knowledge.…”

“…Structures of the bis(ketimide) diuranium(IV) complexes (reprinted with permission from[147], Springer-Verlag, 2012).…”

“…ZORA/B3LYP spin-density (difference of alpha and beta electron densities) distribution plots for the HS (a) triplet and BS states (b) of U 2 bis(ketimide) (blue color: positive spin density and red color: negative spin density). (Reprinted with permission from[147], Springer-Verlag, 2012).…”

Electronic structure and magnetic properties of naphthalene- and stilbene-diimide-bridged diuranium(V) complexes: a theoretical study

“…50 Nevertheless, they could introduce spurious contributions when computed for the fictitious BS state. The procedure we adopted in this study is in line with previous DFT calculations of magnetic exchange coupling for diuranium(IV) and (V) species, 19,20,[30][31][32][33] which did not include spin-orbit corrections either. The magnetic interaction between two atomic spins is usually described by the Heisenberg-Dirac-Van Vleck (HDvV) Hamiltonian, given by Ĥ = − 2 J Ŝ A •Ŝ B , where J is the coupling constant between the A and B magnetic sites with total spin operators Ŝ A and Ŝ B .…”