Prévoir l’évolution spontanée d’un système chimique : diagnostic, pistes et recommandations

Hi ha moltes idees alternatives que tenen els estudiants sobre la predicció de l’evolució espontània d’un sistema químic i sobre l’estat d’equilibri químic. Aquestes idees alternatives són insistents i perjudiquen els estudiants fins i tot a un nivell avançat dels estudis superiors. És important conèixer-les per tal d’adaptar el seu ensenyament, evitar crear-les i/o reforçar-les. Apareixen dos problemes principals: una deficient representació del comportament de la matèria en un sistema en evolució i una fossilització de l’equilibri químic (Rota, 2021a, 2021b).There are many misconceptions students have about predicting the spontaneous evolution of a chemical system and about the state of chemical equilibrium. These misconceptions are tenacious and handicap students up to an advanced level of higher education. It is important to know them in order to adapt its teaching to avoid creating and/or feeding them. Two main problems appear: a misrepresentation of the behaviour of matter in an evolving system and a “fossilization” of the chemical equilibrium (Rota, 2021a, 2021b).Les conceptions erronées des élèves sur la prévision de l’évolution spontanée d’un système chimique et sur l’état d’équilibre chimique sont nombreuses. Ces fausses conceptions sont tenaces et handicapent les élèves jusqu’à un niveau avancé des études supérieures. Il est important de les connaître de manière à adapter son enseignement pour éviter de les créer et/ou de les alimenter. Deux problèmes principaux apparaissent : une mauvaise représentation du comportement de la matière dans un système en évolution et une « fossilisation » de l’équilibre chimique (Rota, 2021a, 2021b)

Microscopic origins of the ferromagnetic exchange coupling in oxoverdazyl-based Cu(II) complex

The exchange channels governing the experimentally reported coupling constant Jexpt=6 cm−1 value in the verdazyl-ligand based Cu II complex Cu hfac 2 imvdz are inspected using wave function-based difference dedicated configuration interaction calculations. The interaction between the two spin 1/2 holders is summed up in a unique coupling constant J. Nevertheless, by gradually increasing the level of calculation, different mechanisms of interaction are turned on step by step. In the present system, the calculated exchange interaction then appears alternatively ferromagnetic/ antiferromagnetic/ferromagnetic. Our analysis demonstrates the tremendously importance of some specific exchange mechanisms. It is actually shown that both parts of the imvdz ligand simultaneously influence the ferromagnetic behavior which ultimately reaches Jcalc=6.3 cm−1, in very good agreement with the experimental value. In accordance with the alternation of J, it is shown that the nature of the magnetic behavior results from competing channels. First, an antiferromagnetic contribution can be essentially attributed to single excitations involving the network localized on the verdazyl part. In contrast, the ligand-to-metal charge transfer LMCT involving the imidazole moiety affords a ferromagnetic contribution. The distinct nature / of the mechanisms is responsible for the net ferromagnetic behavior. The intuitively innocent part of the verdazyl-based ligands is deeply reconsidered and opens new routes into the rational design of magnetic object

Zero field splitting of the chalcogen diatomics using relativistic correlated wave-function methods.

International audienceThe spectrum arising from the (π*)(2) configuration of the chalcogen dimers, namely, the X(2)1, a2, and b0(+) states, is calculated using wave-function theory based methods. Two-component (2c) and four-component (4c) multireference configuration interaction (MRCI) and Fock-space coupled cluster (FSCC) methods are used as well as two-step methods spin-orbit complete active space perturbation theory at 2nd order (SO-CASPT2) and spin-orbit difference dedicated configuration interaction (SO-DDCI). The energy of the X(2)1 state corresponds to the zero-field splitting of the ground state spin triplet. It is described with high accuracy by the 2- and 4-component methods in comparison with experiment, whereas the two-step methods give about 80% of the experimental values. The b0(+) state is well described by 4c-MRCI, SO-CASPT2, and SO-DDCI, but FSCC fails to describe this state and an intermediate Hamiltonian FSCC ansatz is required. The results are readily rationalized by a two-parameter model; Δε, the π* spinor splitting by spin-orbit coupling and K, the exchange integral between the π(1)* and the π(-1)* spinors with, respectively, angular momenta 1 and -1. This model holds for all systems under study with the exception of Po(2)

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

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Description ab initio de propriétés magnétiques d'édifices d'architectures variées à base de radicaux verdazyles

Le magnétisme moléculaire est un domaine à l'interface entre science fondamentale et appliquée. Les objets créés au laboratoire trouvent des applications concrètes comme le stockage de l'information ou la miniaturisation de systèmes déjà existants. Cette science profondément expérimentale a un grand besoin de rationalisation afin d'optimiser les propriétés des objets créés, et d'innovation dans la conception de matériaux aux propriétés toujours plus surprenantes. Récemment l'approche métal radical a ouvert des possibilités en brisant le dogme qui place le métal au centre des préoccupations. Des matériaux utilisant le radical verdazyle associé à un métal d'une terre rare ou encore des objets purement organiques ont été synthétisés par les expérimentateurs. Peu d'études théoriques ont été menées sur ces objets et il est apparu essentiel de porter sur eux un regard analytique afin de décrypter les mécanismes qui sous-tendent leurs propriétés magnétiques. Grâce à des méthodes de chimie quantique ab initio utilisant la fonction d'onde, ce travail de thèse propose, en collaboration avec des expérimentateurs, une étude théorique sur trois importantes familles de composés magnétiques utilisant le radial verdazyle. Les résultats montrent que le radical verdazyle est un composé très efficace pour bâtir des objets magnétiques à propriétés contrôlées. En effet, sa structure électronique permet la mise en place de mécanismes magnétiques sensibles à l'effet des substituants pouvant ainsi jouer le rôle de modulateur magnétique . Enfin il semblerait que le radical verdazyle soit également un bon candidat pour la synthèse de matériaux purement organiques à transition de spin.Molecular magnetism lies at the frontier of theory and experiments. Synthetised magnetic objects find applications in information storage and miniaturization of existing systems. This domain calls for rationalisation to optimise the properties of the designed objects and to prepare systems with ever more amazing behaviour. Recently, the metal radical approach has opened a new route breaking the metal-centered vision of molecular magnetism. Different materials have been considered, considering a pure organic structure or an association of the radical with a d or f metal. However, few theoretical studies have been performed on these objects. Thus, we felt that futher inspection should be carried out. Using wavefunction theory, this PhD work focuses on three original families of magnetic compounds. Results show that the verdazyl radical is very efficient to build magnetic compounds holding controlled properties. The versatile electronic structure gives birth to intriguing magnetic mechanisms which are affected to the substituant structures. The verdazyl substituant can be seen as a magnetic modulateur . Finally, we show that the verdazyl radical could be used for the synthesis of organic spin-crossover compounds.LYON-ENS Sciences (693872304) / SudocSudocFranceF

Etat nutritionnel des patients d'un centre de lutte contre le cancer et protocoles de prise en charge

REIMS-BU Santé (514542104) / SudocSudocFranceF

Magnetic and conduction properties in 1D organic radical materials: an ab initio inspection for a challenging quest.

International audienceThe chemical control of magnetic and conduction properties for organic radicals is mainly based on t, the resonance integral, and U, the on-site repulsion, used in the Hubbard model. A qualitative analysis based on the competition between the kinetic and the Coulomb contribution, and the expression of the magnetic exchange coupling suggests that U should be roughly 800 cm(-1) while the resonance integral |t| should be 200 cm(-1) to reach bifunctionality. Ab initio wavefunction-based calculations allowed us to quantitatively measure those quantities for several organic materials considered as 1D systems starting from their reported crystal structures. The extraction of t and U parameters from the exchange coupling constants between neighbouring radicals allowed us to anticipate a possible metallic behaviour. Finally, the impact of chemical changes in the constitutive units is measured to rationalize the macroscopic behaviour modifications. It is shown that the intriguing regime characterized by simultaneous itinerant and localized electrons might be achieved by molecular engineering

Inspection of the duality of a verdazyl-based radical in transition metal complexes: A pi* donor ligand and a magnetic partner

International audienceThe behavior of a verclazyl-based radical bound to open-shell transition metal ions in the structurally and magnetically characterized [M(hfac)(2)imvd(o)] (M = Mn, Ni; hfac = (1,1,1,5,5,5)hexafluoro-acetylacetonate; imvd(o) = 3-(2'-imidazolyl)-1,5-dimethyl-6-oxoverdazyl) complexes is rationalized using ab initio wave-function-based calculations analysis. The calculated exchange coupling constants J (H = -JS(M).Simvd(o); J(Mn)(calcd) = -63 cm(-1), J(Ni)(calcd), = 205 cm-1) are in excellent agreement with the experimental ones (J(Mn)(exP) = -63 cm(-1), J(Ni)(exp) = 193 cm(-1)). Even though both rings are involved through the binding mode of the imvd(o) radical, the spin density remains essentially localized on the nitrogen-rich ring. The singularity stems from its bidentate coordinating character. The analysis of the correlated wave function suggests that the verdazyl-based radical acts as a pi* donor ligand which allows ligand-to-metal charge transfer and excludes metal-to-ligand charge transfer. This reflects the weak covalent character of the M-imvd(o) pi coordination bond. From a magnetic point of view, the through-space exchange governs the ferromagnetic character in the Ni derivative up to 153 cm(-1) as expected from a description limited to the magnetic orbitals. Nevertheless, the Cl expansion displays the participation of excited doublet and quartet states (spin polarization) on the verdazyl moiety which leads to a significant additional ferromagnetic contribution (52 cm(-1)). In the [Mn(hfac)(2)imvd(o)] analogue, the antiferromagnetic contribution arising from kinetic exchange is only one-third of the observed exchange coupling constant. It is necessary to introduce dynamical correlation effects to quantitatively recover the exchange interaction in this compound. Since the pi* donor and spin-polarized characters of the verdazyl moiety dominate over the negligible polarizability of the imidazole part, it is concluded that the noninnocent nature of the imvd(o) radical is held by the verdazyl ring part