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

Magnetic exchange couplings in bis(ketimide) binuclear U^IV/U^IV 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 U^IV/U^IV 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 ?. 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.     

Electronic structure and energy decomposition of binuclear transition metal complexes containing β-diketiminate and imido ligands: spin state and metal’s nature effects

DFT calculations with full geometry optimization using BP86-D and OPBE functionals have been performed on series of [(BDI)M(NH)]₂(Bz) and [(BDI)M(NH)]₂(Tol) (M = Ti, V, Nb, Cr, Mn, Fe, Co, and Ni; BDI = β-diketiminate; NH = imido group; Bz = benzene; and Tol = toluene) of various spin states (singlet S = 0, triplet S = 1, quintet S = 2, and singlet S = 0 of broken symmetry method). Depending on the metal nature and its electron count and the spin state, the six-membered ring in [(BDI)M(NH)]₂(Bz) and [(BDI)M(NH)]₂(Tol) adopts various hapticities that involve full or partial coordination, giving rise to a flat or a distorted ring, respectively. The NH^2? imido group is linear or bent with respect to its sp or sp² hybridization acting as a six- or a four-electron donor, respectively. The (BDI)^? anion is a bidentate ligand as a six-electron donor. The optimized geometries do not show direct metal-metal bonding and correspond to long separations. The optimized structures for Nb metal are comparable to the available experimental ones. The Ziegler-Rauk energy decomposition analysis scheme was employed to characterize the geometry distortion, the steric interaction (electrostatic and Pauli), and the orbital interaction terms in the total bonding energy. The results showed that the interaction terms in all the studied complexes are governed by one third covalent and two thirds ionic characters, which are in agreement with the ΔE_elstat (electrostatic) and ΔE_orb (orbital) contributions, respectively, into the total attractive interaction (ΔE_elstat + ΔE_orb).     

Remarks on the two-dimensional Benjamin equation

We generalize some recent results proved for the KP equation to the generalized Benjamin equation. First, we establish that the Cauchy problem cannot be solved by an iteration method. As a consequence, the flow map fails to be smooth. The second goal is to prove that the zero-mass constraint is satisfied at any non-zero time even it is not satisfied at the initial time.     

Chemical composition and antioxidant activity of a polar extract of Thymelaea microphylla Coss. et Dur.

Thymelaea microphylla Coss. et Dur. (Thymelaeaceae) is a rare medicinal plant endemic to Algeria. In order to continue our studies on this species, herein we report the isolation and characterisation of 20 compounds from a hydroalcoholic extract (EtOH–H₂O 7:3) of the aerial parts. They include monoterpene glucosides (1–3), phenolic acid derivatives (4, 8 and 9), phenylpropanoid glucosides (5 and 6), flavonoids (7, 10 and 11), a benzyl alcohol glucoside (12), ionol glucosides (13–16), lignans (17–19) and a bis-coumarin (20). All the structures were elucidated by spectroscopic methods including 1D and 2D NMR experiments, as well as ESI-MS analysis. Moreover, the extract of T. microphylla showed a significant and concentration-dependent free radical-scavenging activity in vitro, correlated to the presence of phenolic and chlorogenic acid derivatives (8, 9 and 4).