No 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

The structures of the homoleptic lanthanide and actinide tris(dithiolene) complexes [M(dddt)(3)](q-) (q = 3, M = Nd(3+) and q = 3 or 2, M = U(3+/4+)) have been investigated using relativistic Density Functional Theory (DFT) computations including spin-orbit corrections coupled with the COnductor-like Screening Model (COSMO) for a realistic solvation approach. The dithiolene ligands are known to be very efficient at stabilizing metal high oxidation states. The aim of the work is to explain the peculiar symmetric folding of the three Mdddt metallacycles in these complexes, some of them existing under a polymeric form, in relation with the Ln(III)/An(III) differentiation. In the [M(dddt)(3)(py)](q-) species, where an additional pyridine ligand is linked to the metal center, the Mdddt moieties appear to be almost planar. The study brings to light the occurrence of a M...C=C interaction explaining the Mdddt folding of the [U(dddt)(3)](q-) uranium species, the metal 5f electrons playing a driving role. No such interaction appears in the case of the Nd(III) complex, and the folding of the rather flexible dddt ligands in the polymeric structure of this species should be mainly due to steric effects. Moreover, the analysis of the normal modes of vibration shows that the U(III) complex [U(dddt)(3)](3-), which has not yet been isolated, is thermodynamically stable. It appears that the X-ray characterized U(IV) complex [U(dddt)(3)](2-) should be less stable than the calculated U(III) complex in a polar solvent.

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 nextadjacent 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.

No abstract

No abstract

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

No abstract