Redox properties of biscyclopentadienyl uranium(V) imido-halide complexes: a relativistic DFT study

International audienceCalculations of ionization energies (IE) and electron affinities (EA) of a series of biscyclopentadienyl imido-halide uranium(V) complexes Cp*2U(=N-2,6-(i)Pr2-C6H3)(X) with X = F, Cl, Br, and I, related to the U(IV)/U(V) and U(V)/U(VI) redox systems, were carried out, for the first time, using density functional theory (DFT) in the framework of the relativistic zeroth order regular approximation (ZORA) coupled with the conductor-like screening model (COSMO) solvation approach. A very good linear correlation (R(2) = 0.993) was obtained, between calculated ionization energies at the ZORA/BP86/TZP level, and the experimental half-wave oxidation potentials E1/2. A similar linear correlation between the computed electron affinities and the electrochemical reduction U(IV)/U(III) potentials (R(2) = 0.996) is obtained. The importance of solvent effects and of spin-orbit coupling is definitively confirmed. The molecular orbital analysis underlines the crucial role played by the 5f orbitals of the central metal whereas the Nalewajski-Mrozek (N-M) bond indices explain well the bond distances variations following the redox processes. The IE variation of the complexes, i.e., IE(F) < IE(Cl) < IE(Br) < IE(I) is also well rationalized considering the frontier MO diagrams of these species. Finally, this work confirms the relevance of the Hirshfeld charges analysis which bring to light an excellent linear correlation (R(2) = 0.999) between the variations of the uranium charges and E1/2 in the reduction process of the U(V) species

A DFT and experimental investigation of the electron affinity of the triscyclopentadienyl uranium complexes Cp3UX

International audienceRelativistic Density Functional Theory (DFT) based methods coupled with the Conductor-like Screening Model (COSMO) for a realistic solvation approach are used to investigate the electron affinity (EA) of a series of triscyclopentadienyl uranium complexes Cp3UX (X = Cl, BH4, SPh, SiPr and OiPr) related to the U(IV)/U(III) redox system. E1/2 half-wave potentials have been measured in solution (THF) under the same rigorous conditions for all the species under consideration. A good correlation (r2 = 0.99) is found between the computed EA values, either in the gas phase or in solution, and the experimental half-wave potentials; the study brings to light the importance of spin-orbit coupling effects which must be taken into account in order to achieve the observed agreement between theory and experiment. The influence of the electron donating character of the X ligand on the orbital involved in the reduction process, namely the lowest unoccupied molecular orbital (LUMO) of the neutral U(IV) complexes, and on the EAs is discussed

DFT investigation of methane metathesis with L2AnCH3 actinide complexes catalysts (L = Cl, Cp, Cp*; An = Ac, Th, Pa, U, Np, Pu)

In order to understand the catalytic activity of the actinide complexes L2AnCH3 (An = Ac, Th, Pa, U, Np and Pu; L = Cl, Cp and Cp∗) towards the activation of the CH bond of methane, relativistic ZORA/DFT investigations have been carried out. The results obtained from Linear Transit (LT) and Intrinsic Reaction Coordinate (IRC) calculations show that the mechanism involved in these reactions starts with a proton transfer from methane to the methyl group of the complex leading to the formation of a four center transition state characteristic of a bond metathesis process. The U(III) and Np(III) complexes exhibit a high ability to activate the methane CH bond, the activation energies being respectively equal to 10.5, 17.1 and 21.0 kcal/mol for Cl2NpCH3, Cp2NpCH3 and Cp∗2UCH3 respectively whereas the Th(III) complexes exhibit the highest activation energy, 34.9 kcal/mol for Cp∗2ThCH3. Since the initial step of the reaction is viewed as a proton transfer, the analysis of the charges evolution and frontier molecular orbitals of the complexes and the transition states, shows that a facile polarization of the bonds involved in the reaction has the effect of reducing the activation energy. The role of the metallic 5f orbitals in the reactivity of the L2AnCH3 compounds towards CH4 is analyzed and discussed. More important the 5f actinide orbital contribution, less important is the activation energy

Density Functional Theory Investigation of the Redox Properties of Tricyclopentadienyl- and Phospholyluranium(IV) Chloride Complexes

International audienceThe redox behavior of tricyclopentadienyl- and phospholyluranium(IV) chloride complexes L3UCl with L = C5H5 (Cp), C5H4Me (MeCp), C5H4SiMe3 (TMSCp), C5H4tBu (tBuCp), C5Me5 (Cp*), and C4Me4P (tmp), has been investigated using relativistic density functional theory calculations, with the solvent being taken into account using the conductor-like screening model. A very good linear correlation (r2 = 0.99) has been obtained between the computed electron affinities of the L3UCl complexes and the experimental half-wave reduction potentials E1/2 related to the UIV/UIII redox systems. From a computational point of view, our study confirms the crucial importance of spin-orbit coupling and solvent corrections and the use of an extended basis set in order to achieve the best experiment-theory agreement. Considering oxidation of the uranium(IV) complexes, the instability of the uranium(V) derivatives [L3UCl]+ is revealed, in agreement with experimental electrochemical findings. The driving roles of both the electron-donating ability of the L ligand and the U 5f orbitals on the redox properties of the complexes are brought to light. Interestingly, we found and explained the excellent correlation between variations of the uranium Hirschfeld charges following UIV/UIII electron capture and E1/2. In addition, this work allowed one to estimate theoretically the half-wave reduction potential of [Cp*3UCl]

C F bond breaking by bare actinide monocations in the gas phase: a relativistic DFT study

International audienceInvestigations of the CF bond activation by actinide monocation An+ (An = Ac, Th, Pa, U, Np, Pu and Am) are carried out using relativistic density functional theory (DFT) computations. Originally, the aim of the study is to compare the ability of different actinide ions to break strong bonds particularly in the context of accidental radioactive dissemination. The An+ reaction with the fluorinated hydrocarbon CH3F was selected as a representative system in this context. Unexpectedly, the considered An+ were found to react differently. Via linear transit (LT) and intrinsic reaction coordinate (IRC) calculations, three reaction mechanisms for the CF bond activation, leading to the An–F+ formation, were revealed; the first one, i.e. ‘harpoon’ mechanism which was observed in the case of Pu+, Am+, while the second called ‘insertion-elimination’ mechanism concerned the case of Th+, Pa+, U+ and Np+. DFT computations highlight the particular case of the Ac+ system which presents two different mechanisms according to its spin state: a mechanism qualified as ‘harpoon-like’ for the triplet state and an ‘insertion-elimination’ mechanism for the singlet state. The activation barrier for the fluorine elimination from CH3F is weak for all the studied systems, from 0.9 kcal/mol for Th+ to 8.2 kcal/mol for Am+. Th+ is found as the most effective ion to activate the CF bond and a considerable exergonic character (−81.5 kcal/mol) for this reaction is expected. The performed orbital, population and charge analyses permitted to reveal the role of the actinide 7s, 6d and 5f orbitals and of electron transfers during the reaction

Theoretical investigation of the reactivity of bispentamethylcyclopentadienyl uranium(IV) bisthiolate complexes with the heteroallene molecules CS2 and CO2

International audienceThe insertion reactions of the bispentamethylcyclopentadienyl bisthiolate uranium(IV) complexes [U(Cp*)(2)(SR)(2)] (Cp* = eta-C5Me5; R = Me (1), Bu-t (2), Pr-i (3), Ph (4)) with CO2 or CS2 were investigated using Density Functional Theory (DFT), solvent effects being taken into account using the SMD continuum solvation model. The optimized geometries of the bisthiolate compounds computed at the DFT/B3PW91 level are in good agreement with available X-ray experimental data. The energy profiles of their reactions with CO2 and CS2 were determined. The formation of the products can be explained by a unique reaction mechanism involving an uranium(IV)-bridged heteroallene transition state. The CO2 insertion reactions exhibit lower activation barriers than those of CS2 insertion in accordance with the experiments showing that the CO2 insertion reactions are faster. As expected, compound 2 (R = Bu-t) was found to be the most difficult to undergo the insertion reaction because of steric hindrance. The geometrical parameters of the CS2 insertion derivative [U(Cp*)(2)(StBu)((S2CSBu)-Bu-t)] (5) and the mixed insertion complex [U(Cp*)(2)((O2CSBu)-Bu-t)((S2CSBu)-Bu-t)] (6) obtained after treatment of 5 with CO2 are consistent with those determined by X-ray diffraction. The performed orbital analysis reveal the respective role of the actinide 7s, 6d and 5f orbitals, whereas the Wiberg Bond Indices (WBI) afford a good explanation of the structural variations during the insertion reactions. Finally, the Natural Population Analyses account for the different charge transfers occurring during the insertion processes. (C) 2019 Elsevier B.V. All rights reserved

Two-photon absorption of dipolar and quadrupolar oligothiophene-cored chromophore derivatives containing terminal dimesitylboryl moieties: a theoretical (DFT) structure-property investigation

International audienceA series of dipolar and quadrupolar dimesitylboryl (BMes(2)) derivatives containing different thiophene oligomers as the central conjugated bridge to which BMes(2) substituents are appended at both ends have been investigated theoretically via density functional theory (DFT) and time-dependent (TD) DFT calculations. The results indicate that for all quadrupolar compounds studied the excited state reached by the two-photon absorption (2PA) is the S-2 state which is one-photon forbidden and which corresponds to the HOMO to LUMO+1 electronic transition. When the terminal alkene (double) bonds in the nV species, containing n thiophene rings in the conjugated bridge, are replaced by alkyne (triple) bonds, giving the nT compounds, an increase of the 2PA cross-sections is always stated. Modification of the conjugated linker and addition of trimethylammonium (NMe3+) substituents to the phenyl rings of the terminal BMes(2) moieties show two 2PA peaks at different wavelengths with the low energy one corresponding to the population of the S-2 excited state and the second one corresponding to the population of a higher excited state. Substitution of the NMe3+ groups by neutral electron-attracting cyano (CN) groups shows lower 2PA cross-sections

Comprehensive approach to simulate vibrationally resolved phosphorescence spectra of gold(III) complexes using DFT including temperature effects

International audienceThe present paper reports on a full quantum investigation of the optical properties of six Au(III) luminescent complexes. Among others, the most striking result concerns the reproduction of the luminescent spectra of two key complexes. These simulations are in very good agreement with the measured data when temperature effects are included in the computations. Vibrational modes involved in the emission signature are assigned for one complex. In this comprehensive approach, the model used is very complete and takes into account solvent effects and vibrational contributions to the electronic transitions among others

Electron affinities of biscyclopentadienyl and phospholyl uranium(IV) borohydride complexes: Experimental and DFT studies

International audienceElectron affinities (EAs) of a series of biscyclopentadienyl and phospholyl uranium(IV) complexes L2U(BH4)2 [L2 = Cp2, (tmp)2, (tBuCp)2, (Cp*)(tmp) and Cp*2] related to the U(III)/U(IV) redox system were calculated using relativistic Density Functional Theory (DFT) based methods coupled with the Conductor-like Screening Model for Real Solvents (COSMO-RS) approach. Electrochemical measurements of half-wave potentials in solution (tetrahydrofuran THF) were carried out for all these compounds under the same rigorous conditions. A good correlation (r2 = 0.99) is obtained between the calculated EA values, at the ZORA/BP86/TZ2P level, and the half-wave reduction potentials measured by electrochemistry. The investigations bring to light the importance of spin-orbit coupling and solvent effect and the use of a large basis set in order to achieve such a good agreement between theory and experiment. The study confirms the instability of the Cp2U(BH4)2 complex during the reduction process. The influence of the substituted aromatic ligand L2, namely their electron donating ability, on EA was studied. The role of involved orbitals (singled occupied molecular orbital -SOMO- of anionic species or lowest unoccupied molecular orbital -LUMO- of neutral species) in the redox process was revealed

New insights into the reactivity of the triscyclopentadienyl monothiolate uranium(IV) complexes: CS2 and CO2 insertion and redox properties. A DFT theoretical approach

International audienceThe structural properties of a series of triscyclopentadienyl monothiolate uranium(IV) complexes [U(Cp)3(SR)] (Cp = η5–C5H5; R = Me (1), iPr (2), Ph (3), tBu (4)) as well as their reactions with CO2 or CS2 leading to their insertion into the Usingle bondS bond, have been investigated using relativistic Density Functional Theory (DFT) calculations. The computed activation barriers of these reactions show that insertion of CO2 into the Usingle bondS bond of the thiolate complexes is easier and faster than that of CS2, in agreement with the experimental observation. The study brings to light the electrostatic interactions and steric hindrance effects that play an important role in these processes. The redox behavior of the thiolate [U(Cp)3(SR)] complexes has also been investigated, permitting to find a very nice linear correlation (R2 = 0.99) between the computed electron affinities and the experimental reduction half–wave potentials E1/2. This correlation allowed to estimate the reduction potentials of [U(Cp)3(SMe)] (1) and [U(Cp)3(StBu)] (4) for which the electrochemical measurement failed. Several population analyses were carried out, among them Nalewajski–Mrozek Bond Orders (NMBO) and Hirshfeld charges Analysis (HA) allowing to rationalize the insertion reactions and redox processes and to highlight the driving role of the uranium 5f orbitals