On the accurate estimation of intermolecular interactions and charge transfer: the case of TTF-CA

International audienceHigh-resolution X-ray diffraction experiments and state-of-the-art density functional theory calculations have been performed. The validity of the atoms-in-molecules approach is tested for the neutral-ionic transition of TTF-CA which involves a transfer of less than one electron between the donor and acceptor molecules. Foremost, crystallographical data have been reassessed along the temperature-induced neutral-ionic phase transition undergone by this charge transfer complex. Based on accurate X-ray structures at 105 and 15 K, topological analysis of both DFT and the experimental multipolar electron densities allowed detailed characterization of intra- and interstack intermolecular interactions. Direct quanti. cation of the intermolecular charge transfer and the dipole moment are discussed

Numerical computation of critical properties and atomic basins from three-dimensional grid electron densities

Claudine Katan ‘s present address : CNRS UMR6082 FOTON, INSA de Rennes, 20 avenue des Buttes de Coësmes, CS 70839, 35708 RENNES cedex 7, FranceInternational audienceInteGriTy is a software package that performs topological analysis following the AIM (atoms in molecules) approach on electron densities given on three-dimensional grids. Tricubic interpolation is used to obtain the density, its gradient and the Hessian matrix at any required position. Critical points and integrated atomic properties have been derived from theoretical densities calculated for the compounds NaCl and TTF-(2,5)Cl(2)BQ (tetrathiafulvalene-2,5-dichlorobenzoquinone), thus covering the different kinds of chemical bonds: ionic, covalent, hydrogen bonds and other intermolecular contacts

Densite d'electrons dans les composes peptidiques par methode X-X et calcul theorique : la (N) acetyl-L-tryptophane-methylamide et la (N)-acetyl-#alpha#-#beta#-dehydrophenylalanine-methylamide, influence de la #alpha#-#beta#-dehydrogenation et etude critiq..

SIGLECNRS T 64246 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Modélisation expériementale des matériaux magnétiques moléculaires (études combinées par diffraction X, neutrons et neutrons polarisés)

Nous avons développé un modèle et un programme d'affinement joint des densités de charge et spin. Lors des premiers tests plusieurs difficultés sont apparues et ont été étudiées puis résolues notamment par la mise en place de contraintes. Après la mise en place d'un programme stable d'affinement joint nous avons testé celui-ci sur le complexe MnCu(pba)...(H2O)3...2H2O, ou pba représente le 1,3-propylenbis(oxamato) en réutilisant les données provenant d'une expérience de diffraction de neutrons polarisés et en effectuant une nouvelle expérience de diffraction des rayons X à 10K, température à laquelle l'expérience de diffraction des neutrons polarisés a été conduite. Cette étude a permis de tester trois schémas de pondération, ainsi que les contraintes. Ces tests ont montré que l'affinement joint permet de retrouver les résultats des différents affinements séparés mais aussi d'aller plus loin en autorisant un affinement de la densité de spin avec plus de paramètres pertinents. Suite à ces premiers tests nous nous sommes intéressés à un complexe azido cuivre (Cu2L2(N3)2 avec L=1,1,1-trifluoro-7-(dimethylamino)-4-méthyle-5-aza-3-heptène-2-onato). L'affinement joint a permis d'avoir accès, pour la première fois, à la densité de valence expérimentale résolue en spin et d'affiner également des paramètres de contraction/dilatation différents pour la valence avec un spin up ou un spin down. Dans le dernier chapitre nous avons étudié un complexe de cobalt qui présentait des propriétés magnétiques intéressantes. Cependant la particularité magnétique du composé venant d'une forte anisotropie magnétique a rendu l'étude par affinement joint délicate dans un premier temps, c'est pourquoi nous avons étudié ce composé uniquement d'un point de vue de la densité de charge. Cette étude a tout de même permis de mettre en évidence expérimentalement à 100K un angle de torsion de 39 entre les axes principaux des atomes de cobalt, prédit par la théorieWe developed a model and a refinement program for charge and spin densities. During the first tests several difficulties have arisen and have been investigated and solved by implementation of constraints. After the establishment of stable joint refinement program, we tested it on the MnCu(pba)...(H2O)3...2H2O, with pba = 1,3-propylenbis(oxamato) complex reusing data from an experiment of polarized neutron diffraction and making a new experience of X-ray diffraction at 10K. This study tested three weighting schemes and constraints. These tests showed that the joint refinement give access to the same results as the separated refinements but also allow us to go further by refining the spin density with more pertinent parameters. Following these initial tests, we were interested in a copper azido complex (Cu2L2(N3)2 with L=1,1,1-trifluoro-7-(dimethylamino)-4-methyl-5-aza-3-hepten-2-onato). The joint refinement give us access for the first time to the experimental spin-resolved valence density and also to refine the parameters of contraction / expansion for spin up or spin down separately. In the last chapter we studied a cobalt complex which shows interesting magnetic properties. However, the magnetic properties of the compound come from a high magnetic anisotropy which complicates a study by joint refinement. That is why we studied only the charge density of this compound. This study still allowed to show experimentally a torsion angle of 39 between the principal axes of the cobalt atoms, which was predicted by a previous theoretical studyMETZ-SCD (574632105) / SudocNANCY1-Bib. numérique (543959902) / SudocNANCY2-Bibliotheque electronique (543959901) / SudocNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Étude structurale par diffraction, absorption des rayons X et simulations Monte-Carlo de matériaux zéolithiques

Les composites organiques-inorganiques avec la zéolithe comme matrice hôte sont de plus en plus étudiés dans le but de concevoir des matériaux multifonctionnels conjuguant les propriétés de la molécule organique et celle de la zéolithe (ex. : élaboration de commutateurs magnétiques/optiques, doubleurs de fréquence). Les propriétés macroscopiques recherchées (SHG, transition de spin) dépendent des interactions entre les espèces organiques invitées et la zéolithe (charpente, cations compensateurs de charge), qui sont encore mal connue, en particulier en raison de l'absence de structures cristallographiques précises. Cette thèse s'est intéressée à deux types de composites principalement : (Co2+(bpy)3-zéolithe X) réputé présenter une transition de spin en température et dmpNA-MORdénite), à propriété potentielle de génération de second harmonique. Dans l étude du composite magnétique, nous nous sommes particulièrement penché sur l'évolution de la structure de la zéolithe précurseur Na,Co-X dans différents état d hydratation. Des études complémentaires par diffraction des rayons X sur monocristal, EXAFS et simulations Monte-Carlo ont mis en évidence la forte interaction entre cations cobalt et charpente aluminosilicatée ainsi que la migration des cations Co2+ accompagnant l'hydratation progressive de la zéolithe Na,Co-X. L étude structurale du composite dmpNA-mordénite par diffraction des rayons X sur poudre (synchrotron SPring-8, Japon) a montré que les canaux droits de la mordénite sont presque totalement occupés par les molécules de dmpNA, qui adoptent un empilement quasi linéaire favorable à la Génération de Seconde Harmonique.The organic-inorganic composites with zeolite as host matrix are mostly studied to produce performing materials for non-linear optics, optoelectronics, optical/magnetic memories. The performances of these new materials are driven by the coupling between the guest and host properties, in particular, by the molecularframework, molecular-cation interactions. Actually, only few accurate crystallographic structures of such composite are available in literature, so the guest-host interactions are still little known. In this work, I m interested in the crystallographic structures of two composites: temperature induced spin crossover Co2+(bpy)3-zeolite X and dmpNA-mordenite that have to produce the Second Harmonic Generation signal. In the case of magnetic composite, I have particularly studied the composite precursor, zeolite Na,Co-X, in the different hydration states in order to follow an insight on structural modifications induced by water molecules desorption. Because of desorder, the structural studies are difficult. Nevertheless, the complementarities of the experimental (X-ray Diffraction and Absorption) and simulations (Monte-Carlo) approaches were fruitful to obtain the accurate partially/completely hydrated and dehydrated structures. These structures clearly show the cell volume contraction and cation migrations over dehydration that where caused by the strong cobalt framework interactions. The crystal structure of dmpNA-mordenite has been determined from high resolution synchrotron powder diffraction and showed that zeolite straight channels are completely loaded with dmpNA molecules with a moderate tilt angle relative to the channel axe which is favourable to frequency doubling signal.NANCY1-Bib. numérique (543959902) / SudocSudocFranceF

Experimental determination of electrostatic properties of Na-X zeolite from high resolution X-ray diffraction

International audienceHigh-resolution single crystal X-ray diffraction is used for the first time to obtain the charge density distribution in dehydrated Na-X zeolite. The electron density is extracted according to the Hansen & Coppens multipolar-model, from which P-val-kappa-type atomic charges are derived. In order to compare the experimental electron density with theoretical calculations on zeolites and other minerals, a topological analysis is performed to derive AIM charges and electron density properties at bond critical points. The results are compared with that described in the literature. Finally, the electrostatic potential is evaluated in a periodic, mean field approach (disordered cation distribution in the Fd(3) over bar space group) and for a given distribution of the cations (space group P1). The electrostatic energy is, then, derived in the neighbourhood of cation sites where the molecules are usually physisorbed

Out of equilibrium charge density studies of light induced metastable states

The experimental electron density analysis is becoming a very mature field of research with outstanding applications in many areas of solid state physics and chemistry. This approach has allowed gaining new insights on bonding interactions in ground state systems often from joined experimental and theoretical methods. The extension of this technique to out of equilibrium systems is very promising and might surely lead to a better fundamental understanding of dynamic processes in solids such as phase transition or chemical reactivity [1]. Steady-state and time resolved x-ray diffraction techniques under external perturbation, like electric field [2], pressure or optical excitation [3], are more and more developed, mainly for structural purposes. We have shown that under appropriate and well controlled experimental conditions, accurate electron density distribution of metastable states can be derived [4]. State of the art in light-induced high resolution x-ray diffraction experiments and charge density analysis of molecular metastable states will be presented. Applications will cover light-induced phase transitions in Fe(II) spin-crossover complexes and solid state chemical reactivity

Kinetics of light-induced first-order phase transformation in molecular solids: Fe(btr)2(NCS)2∙H2O

International audienceThe mechanism and kinetics of the thermally and light-induced spin transition of the highly cooperative spin crossover material Fe(btr)2(NCS)2∙H2O (btr=4,4'–bis–1,2,4–triazole) have been investigated by single crystal x-ray diffraction techniques. The key role of like-spin domains is quantitatively analyzed through a nucleation, growing, and coarsening mechanism whose kinetics follow the Kolmogorov-Johnson-Mehl-Avrami model with low dimensional characteristics

Joint Refinement of Charge and Spin Densities

International audienceA new charge and spin density model and the corresponding refinement software were recently developed to combine X- ray and polarized neutron diffraction experiments [1]. This joint refinement procedure allows getting access to both charge and spin densitiy distributions by refining both spin up and down parameters for magnetic atoms. The paper is focused on the refinement procedure and its application to the case of an end-to-end azido double bridged copper(II) complex. The results of this joint refinement of X-ray and polarized neutron diffraction data are presented

Crystal structure of 3,5-bis(4-chlorophenyl)-1-propyl-1,3,5-triazacyclohexane

International audienceIn the title mol­ecule, C18H21Cl2N3, the tri­aza­cyclo­hexane ring adopts a chair conformation with both 4-chloro­phenyl substituents in axial positions and the propyl group in an equatorial site. The dihedral angle between the planes of the benzene rings is 49.5 (1)°. In the crystal, mol­ecules are arranged in a head-to-tail fashion, forming columns along [010], and pairs of weak C—H⋯π inter­actions form inversion dimers between columns