The copper carbonyl complexes revisited: Why are the infrared spectra and structures of copper mono and dicarbonyl so different?

International audienceNew Infrared absorption data have been obtained using isolation in solid argon and neon on copper carbonyl molecules, CuCO and Cu(CO) 2 , two very reactive molecules. For CuCO, all three fundamentals are now observed and it presents an unusually large matrix effect, in line with former results indicating a weak metal carbon interaction and a large total dipole moment. With help of isotopic effects, new data indicates unambiguously that Cu(CO) 2 is linear and presents a notably stronger metal-carbon interaction than CuCO. Quantum chemical calculation have been carried out at the CCSD(T) level for determining energies and structural properties, as well as spectroscopic observables. The results enable an assessment of the high stability of the Cu(CO) 2 molecule (first bond dissociation energy of 66 kJ/mole) which suggest that observation at room temperature is possible and give a first evidence of Renner effect on a penta-atomic molecule

Asynchronous character of concerted mechanisms: decomposition into primitive processes

International audienceSome concerted mechanisms result from the combination of several simple processes in a very asynchronous manner. Some years ago, we proposed that such elementary reactions were characterized by peculiarities in their reaction profiles (e.g. shoulder in the potential energy profile, maximum in the hardness profile shifted with respect to the transition state, more than 2 extrema in the reaction force profile ; see Figure). [1] On the other hand, several theoretical studies have shown that the use of an external electric field could affect the reaction rate but also the selectivity of a given reaction by modifying its mechanism. [2,3] Here we propose to apply an external electric field to control the asynchronous character of simple concerted mechanisms and decompose them into primitive processes. The objective is to study to what extent these primitive processes follow reactivity principles such as the Maximum Hardness Principle [4] more than their parent concerted mechanisms

Chemins réactionnels conduisant à la formation des oxydes des métaux de transition 3dn (n>5) (structure électronique des composés antiferromagnétiques M2O2 (M=Cr, Mn, Fe, Co, Ni, Cu))

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

International audienceAgostic bonding is of paramount importance in C–H bond activation processes. The reactivity of the σ C–H bond thus activated will depend on the nature of the metallic center, the nature of the ligand involved in the interaction and co-ligands, as well as on geometric parameters. Because of their importance in organometallic chemistry, a qualitative classification of agostic bonding could be very much helpful. Herein we propose descriptors of the agostic character of bonding based on the electron localization function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) topological analysis. A set of 31 metallic complexes taken, or derived, from the literature was chosen to illustrate our methodology. First, some criteria should prove that an interaction between a metallic center and a σ X–H bond can indeed be described as “agostic” bonding. Then, the contribution of the metallic center in the protonated agostic basin, in the ELF topological description, may be used to evaluate the agostic character of bonding. A σ X–H bond is in agostic interaction with a metal center when the protonated X–H basin is a trisynaptic basin with a metal contribution strictly larger than the numerical uncertainty, i.e. 0.01 e. In addition, it was shown that the weakening of the electron density at the X–Hagostic bond critical point with respect to that of X–Hfree well correlates with the lengthening of the agostic X–H bond distance as well as with the shift of the vibrational frequency associated with the νX–H stretching mode. Furthermore, the use of a normalized parameter that takes into account the total population of the protonated basin, allows the comparison of the agostic character of bonding involved in different complexes

Dehydrocoupling of dimethylamine borane by titanocene: Elucidation of ten years of inconsistency between theoretical and experimental descriptions

International audienceMore than ten years ago, Manners and coworkers published the first experimental study on the efficiency of titanocene to catalyze the dehydrocoupling of dimethylamine borane (DMAB, JACS 2006, 128, 9582). Several experimental investigations have shown that a two-step mechanism leads to the formation of a cyclic diborazane (Me 2 N-BH 2) 2 via the linear diborazane (HNMe 2-BH 2-NMe 2-BH 3). This finding stood in contradiction with following theoretical investigations of the reaction pathway. Herein, using dispersion-corrected density functional theory (DFT-D), we propose an energetically favored reaction mechanism in perfect agreement with the experimental findings. It is shown that van der Waals interactions play a prominent role in the reaction pathway. The formation of 3-center 2-electron interactions, classical dihydrogen bonds, as well as non-classical dihydrogen bonds, was identified with the help of topological and localized orbital approaches

What is the hydrophobic interaction contribution to the stabilisation of micro-hydrated complexes of trimethylamine oxide (TMAO)? A joint DFT-D, QTAIM and MESP study

International audienceMicro-hydrated trimethylamine oxide (TMAO) has been investigated using a range-separated-hybrid functional including empirical dispersion correction. Electrophilic and nucleophilic sites on TMAO and water clusters have been identified using the molecular electrostatic potential (MESP). The nature of the chemical bonding in the different isomers of the micro-hydrated complexes has been investigated with the topological analysis of the electron density (QTAIM) method. For complexes containing one to four water molecules, the strongest intermolecular interactions consist in hydrogen bonding between the oxygen atom of the TMAO and hydrogen atoms of water molecules. From five water molecules, interactions between water molecules become the main source of stabilization of the most stable isomer. From four stationary points corresponding to the 1:1 (TMAO:H 2 O) complex, we determined the minimum distances between water molecules and central TMAO allowing the latter molecule to be encapsulated within a water clathrate-type cage. Optimization of TMAO encapsulated within two water cages (5 12 and 5 12 6 2) suggests that only in the case of the 5 12 6 2 water cage the insertion of TMAO, the preservation of the hydrogen bonding between water molecules is energetically favorable. The interaction energy between one inserted TMAO and the 5 12 6 2 water cage was calculated to be around 150 kJ/mol with respect to the ground state of two partners. This result suggest that a thorough investigation of mono-hydrated complexes may be particularly relevant to identify the most suitable water cage for encapsulating a given solute

Spectra and structures of the Pdm-CO complexes: An infrared matrix isolation and density functional study

International audienceThe Pd + CO reaction has been reinvestigated using deposition of ground state reagents in solid argon and neon and the formation of Pdm-CO (m = 2–4) and Pd2-(CO)2 molecules is evidenced by many absorption in the range of 2015–1700 cm−1. These bands are also accompanied by other signals in far-infrared. In argon, selective irradiation in visible leads to conversion between two Pd2-CO isomers distinguished by the stretching frequency of the diatomic CO: bridged T-shaped (νCO = 1856 cm−1) and end on (νCO = 2015 cm−1). The experimental data, with the help of isotopic effects, are fully supported by theoretical calculations with density functional theory. The nature of chemical bonding has been also discussed within the topological approach. It has been shown that the CO complex adapts his valence basins to the geometrical symmetry of Pdm-CO when interacting with Pdm clusters

Infrared Spectroscopic and Density Functional Theory Investigations of PdTi Heterodimer Reactivity with Carbon Monoxide Isolated in Solid Argon

International audienceThe reactivity of diatomic palladium-titanium toward carbon monoxide has been studied in solid argon by infrared spectroscopy (FTIR) in the carbonyl stretching frequency region. Our technique of sublimation of Ti and Pd atoms from two filaments heated separately allowed the identification of five new molecules. Small polynuclear carbonyl clusters, PdTi(CO) n (n=1-3) have been characterized on the basis of isotopic substitutions, metal atoms and CO concentration variations and irradiation effects. Selective irradiation in visible leads to conversion between two isomers distinguished by the stretching frequency of the diatomic CO: PdTiCO Ti-eo (ν CO =1908.4 cm-1) and PdTiCO Pd-eo (ν CO =2009.3 cm-1). The Density Functional Theory (DFT) calculations have been carried out to elucidate the geometrical and electronic structures and support the spectral assignments. The nature of the metal-carbon bonding has been discussed using the topology of the Laplacian of the electron density