38 research outputs found
The resolution of the weak-exchange limit made rigorous, simple and general in binuclear complexes
The correct interpretation of magnetic properties in the weak-exchange regime
has remained a challenging task for several decades. In this regime, the
effective exchange interaction between local spins is quite weak, of the same
order of magnitude or smaller than the various anisotropic terms, which
\textit{in fine} generates a complex set of levels characterized by spin
intercalation if not significant spin mixing. Although the model multispin
Hamiltonian, \hms{} = \js{} + \da{} +\db{} + \dab{}, is considered good enough
to map the experimental energies at zero field and in the strong-exchange
limit, theoretical works pointed out limitations of this simple model. This
work revives the use of \hms{} from a new theoretical perspective, detailing
point-by-point a strategy to correctly map the computational energies and wave
functions onto \hms{}, thus validating it regardless of the exchange regime. We
will distinguish two cases, based on experimentally characterized dicobalt(II)
complexes from the literature. If centrosymmetry imposes alignment of the
various rank-2 tensors constitutive of \hms{} in the first case, the absence of
any symmetry element prevents such alignment in the second case. In such a
context, the strategy provided herein becomes a powerful tool to rationalize
the experimental magnetic data, since it is capable of fully and rigorously
extracting the multispin model without any assumption on the orientation of its
constitutive tensors. Finally, previous theoretical data related to a known
dinickel(II) complex is reinterpreted, clarifying initial wanderings regarding
the weak-exchange limit
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Use of 15N NMR spectroscopy to probe covalency in a thorium nitride.
Reaction of the thorium metallacycle, [Th{N(R)(SiMe2)CH2}(NR2)2] (R = SiMe3) with 1 equiv. of NaNH2 in THF, in the presence of 18-crown-6, results in formation of the bridged thorium nitride complex, [Na(18-crown-6)(Et2O)][(R2N)3Th(Ό-N)(Th(NR2)3] ([Na][1]), which can be isolated in 66% yield after work-up. Complex [Na][1] is the first isolable molecular thorium nitride complex. Mechanistic studies suggest that the first step of the reaction is deprotonation of [Th{N(R)(SiMe2)CH2}(NR2)2] by NaNH2, which results in formation of the thorium bis(metallacycle) complex, [Na(THF) x ][Th{N(R)(SiMe2CH2)}2(NR2)], and NH3. NH3 then reacts with unreacted [Th{N(R)(SiMe2)CH2}(NR2)2], forming [Th(NR2)3(NH2)] (2), which protonates [Na(THF) x ][Th{N(R)(SiMe2CH2)}2(NR2)] to give [Na][1]. Consistent with hypothesis, addition of excess NH3 to a THF solution of [Th{N(R)(SiMe2)CH2}(NR2)2] results in formation of [Th(NR2)3(NH2)] (2), which can be isolated in 51% yield after work-up. Furthermore, reaction of [K(DME)][Th{N(R)(SiMe2CH2)}2(NR2)] with 2, in THF-d 8, results in clean formation of [K][1], according to 1H NMR spectroscopy. The electronic structures of [1]- and 2 were investigated by 15N NMR spectroscopy and DFT calculations. This analysis reveals that the Th-Nnitride bond in [1]- features more covalency and a greater degree of bond multiplicity than the Th-NH2 bond in 2. Similarly, our analysis indicates a greater degree of covalency in [1]- vs. comparable thorium imido and oxo complexes
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A diuranium carbide cluster stabilized inside a C80 fullerene cage.
Unsupported non-bridged uranium-carbon double bonds have long been sought after in actinide chemistry as fundamental synthetic targets in the study of actinide-ligand multiple bonding. Here we report that, utilizing Ih(7)-C80 fullerenes as nanocontainers, a diuranium carbide cluster, U=C=U, has been encapsulated and stabilized in the form of UCU@Ih(7)-C80. This endohedral fullerene was prepared utilizing the KrĂ€tschmer-Huffman arc discharge method, and was then co-crystallized with nickel(II) octaethylporphyrin (NiII-OEP) to produce UCU@Ih(7)-C80·[NiII-OEP] as single crystals. X-ray diffraction analysis reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unexpectedly short uranium-carbon distances (2.03âĂ
) indicative of covalent U=C double-bond character. The quantum-chemical results suggest that both U atoms in the UCU unit have formal oxidation state of +5. The structural features of UCU@Ih(7)-C80 and the covalent nature of the U(f1)=C double bonds were further affirmed through various spectroscopic and theoretical analyses
The OpenMolcas Web: A Community-Driven Approach to Advancing Computational Chemistry
The developments of the open-source OpenMolcas chemistry software environment since spring 2020 are described, with a focus on novel functionalities accessible in the stable branch of the package or via interfaces with other packages. These developments span a wide range of topics in computational chemistry and are presented in thematic sections: electronic structure theory, electronic spectroscopy simulations, analytic gradients and molecular structure optimizations, ab initio molecular dynamics, and other new features. This report offers an overview of the chemical phenomena and processes OpenMolcas can address, while showing that OpenMolcas is an attractive platform for state-of-the-art atomistic computer simulations
GĂ©omĂ©tries, structures Ă©lectroniques et propriĂ©tĂ©s physico-chimiques dâespĂšces de lâastate : une application de la mĂ©canique quantique relativiste
Les tentatives menĂ©es pour dĂ©truire des cellules cancĂ©reuses avec les agents radiothĂ©rapeutiques Ă base de 211 At qui ont Ă©tĂ© synthĂ©tisĂ©s jusquâĂ prĂ©sent ne sont pas encore pleinement satisfaisantes car elles sont entachĂ©es par une deastatination in vivo. Ătant donnĂ© que ce problĂšme est liĂ© aux connaissances actuelles qui sont limitĂ©es concernant la chimie de base de lâastate et de ses espĂšces, des recherches fondamentales combinant des expĂ©riences Ă lâĂ©chelle des ultra-traces et des Ă©tudes thĂ©oriques ont Ă©tĂ© lancĂ©es. Dans cette thĂšse, une Ă©tude thĂ©orique de plusieurs espĂšces de lâastate est rĂ©alisĂ©e au moyen de mĂ©thodes relativistes basĂ©es sur la thĂ©orie de la fonctionnelle de la densitĂ© ou des mĂ©thodes Ă basĂ©es sur la fonction dâonde. Tout d'abord, les mĂ©thodes qui peuvent ĂȘtre utilisĂ©es pour faire des prĂ©dictions pertinentes sont Ă©tablies. A lâaide de ces approches, nous rationaliserons les structures Ă©lectroniques, gĂ©omĂ©tries et propriĂ©tĂ©s physicochimiques des diffĂ©rents systĂšmes d'intĂ©rĂȘt thĂ©orique ou expĂ©rimental, en particulier les espĂšces AtF3 et AtO+. Finalement, nous identifierons formellement une nouvelle espĂšce de lâastate Ă lâaide de rĂ©sultats expĂ©rimentaux et de calculs, ce qui non seulement complĂšte le diagramme de Pourbaix de lâastate en milieu aqueux non complexant, mais aussi donne des informations cruciales pour identifier des conditions expĂ©rimentales pour rendre le plus « rĂ©actif » possible le prĂ©curseur Atâ, qui est de nos jours impliquĂ© dans la synthĂšse dâagents radiothĂ©rapeutiques innovants.Trials to destroy cancer cells with currently synthesized 211 At-based radiotherapeutic agents are not yet fully satisfactorily since they resume to in vivo deastatination. Since this issue is related to the limited knowledge of the basic chemistry of At and its species, fundamental researches combining ultra-trace experiments and computational studies have been initiated. In this thesis, a computational study of several At species is performed, by means of relativistic density functional theory and wave-function-based calculations. First, the quantum mechanical approaches that can safely be used to make adequate predictions are established. Using these approaches, we attempt to rationalize the electronic structures, geometries, and physico-chemical properties of various systems of theoretical and/or experimental interest, in particular the AtF3 and AtO+ ones. By the end, we firmly identify a new At species by combining outcomes of experiments and calculations. This new species not only completes the Pourbaix diagram of At in aqueous and non-complexing media, but also gives clues of identifying experimental conditions to make best reactive the Atâ precursor, which is currently involved in the synthesis of promising radiotherapeutic agents
GeÌomeÌtries, structures eÌlectroniques et proprieÌteÌs physico-chimiques dâespeÌces de lâastate : une application de la meÌcanique quantique relativiste
Trials to destroy cancer cells with currently synthesized 211At-based radiotherapeutic agents are not yet fully satisfactorily since they resume to in vivo deastatination. Since this issue is related to the limited knowledge of the basic chemistry of At and its species, fundamental researches combining ultra-trace experiments and computational studies have been initiated. In this thesis, a computational study of several At species is performed, by means of relativistic density functional theory and wave-function-based calculations. First, the quantum mechanical approaches that can safely be used to make adequate predictions are established. Using these approaches, we attempt to rationalize the electronic structures, geometries, and physico-chemical properties of various systems of theoretical and/or experimental interest, in particular the AtF3 and AtO+ ones. By the end, we firmly identify a new At species by combining outcomes of experiments and calculations. This new species not only completes the Pourbaix diagram of At in aqueous and non-complexing media, but also gives clues of identifying experimental conditions to make best reactive the Atâ precursor, which is currently involved in the synthesis of promising radiotherapeutic agents.Les tentatives meneÌes pour deÌtruire des cellules canceÌreuses avec les agents radiotheÌrapeutiques aÌ base de 211At qui ont eÌteÌ syntheÌtiseÌs jusquâaÌ preÌsent ne sont pas encore pleinement satisfaisantes car elles sont entacheÌes par une deastatination in vivo. EÌtant donneÌ que ce probleÌme est lieÌ aux connaissances actuelles qui sont limiteÌes concernant la chimie de base de lâastate et de ses espeÌces, des recherches fondamentales combinant des expeÌriences aÌ lâeÌchelle des ultra-traces et des eÌtudes theÌoriques ont eÌteÌ lanceÌes. Dans cette theÌse, une eÌtude theÌorique de plusieurs espeÌces de lâastate est reÌaliseÌe au moyen de meÌthodes relativistes baseÌes sur la theÌorie de la fonctionnelle de la densiteÌ ou des meÌthodes aÌ baseÌes sur la fonction dâonde. Tout d'abord, les meÌthodes qui peuvent eÌtre utiliseÌes pour faire des preÌdictions pertinentes sont eÌtablies. A lâaide de ces approches, nous rationaliserons les structures eÌlectroniques, geÌomeÌtries et proprieÌteÌs physico-chimiques des diffeÌrents systeÌmes d'inteÌreÌt theÌorique ou expeÌrimental, en particulier les espeÌces AtF3 et AtO+. Finalement, nous identifierons formellement une nouvelle espeÌce de lâastate aÌ lâaide de reÌsultats expeÌrimentaux et de calculs, ce qui non seulement compleÌte le diagramme de Pourbaix de lâastate en milieu aqueux non complexant, mais aussi donne des informations cruciales pour identifier des conditions expeÌrimentales pour rendre le plus « reÌactif » possible le preÌcurseur Atâ, qui est de nos jours impliqueÌ dans la syntheÌse dâagents radiotheÌrapeutiques innovants
Pseudo Jahn-Teller effect, spin-orbit coupling, and electron correlation in the XF<sub>3</sub> (X=Cl, Br, I, At) series
International audienc
Ground-state reversal induced by solvation: Electronic structure of AtO<sup>+</sup> in water
International audienc
Investigating AtO<sup>+</sup>-(OH<sup>â</sup>)<sub>n</sub> complexes at the molecular scale using quantum mechanical methods
National audienc
Investigation of the AtO(OH)<sub>2</sub><sup>-</sup> hydrolysed species: Relativistic calculations
International audienc