Experimental and theoretical studies of tetramethoxy-p-benzoquinone: infrared spectra, structural and lithium insertion properties

International audienceIn the search for low-polluting electrode materials for batteries, the use of redox-active organic compounds represents a promising alternative to conventional metal-based systems. In this article we report a combined experimental and theoretical study of tetramethoxy-p-benzoquinone (TMQ). In carbonate-based electrolytes, electrochemical behaviour of this compound is characterized by a reversible insertion process located at approximately 2.85 V vs. Li+/Li0. This relatively high potential reactivity, coupled with our effort to develop computational methodologies in the field of organic electrode materials, prompted us to complement these experimental data with theoretical studies performed using density functional theory (DFT). Single crystals of TMQ were synthesized and thoroughly characterized showing that this quinonic species crystallised in the P21/n space group. The experimental crystal structure of TMQ was then used to assess various DFT methods. The structural features and vibrational spectra were thus predicted by using as a whole five common density functionals (PBE, LDA, revPBE, PBEsol, B3PW91) with and without a semi-empirical correction to account for the van der Waals interactions using either Grimme's (DFT-D2) or Tkatchenko-Scheffler (TS) scheme. The most reliable combination of the DFT functional and the explicit dispersion correction was chosen to study the Li-intercalated molecular crystal (LiTMQ) with the view of indentifying Li insertion sites. A very close agreement with the experiment was found for the average voltage by using the most stable relaxed hypothetical LiTMQ structure. Additionally, a comparison of vibrational spectra gained either for TMQ molecule and its dimer in gas phase or through periodic calculation was undertaken with respect to the experimentally measured infrared spectra. The topological features of the bonds were also investigated in conjunction with estimates of net atomic charges to gain insight into the effect of chemical bonding and intermolecular interaction on Li intercalation. Finally, π-electron delocalization of both quinone and alkali salts of p-semiquinone were determined using the Harmonic Oscillator model of Aromaticity (HOMA) or aromatic fluctuation index (FLU) calculations

Exotic Topochemical Alteration of the Cationic Sublattices in Oxides

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Modification topotactiques de composés du fer

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Exotic Topochemical Alteration of the Cationic Sublattices in Oxides: The complex crystallography behind

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New structural topologies of bismuth oxides and salts (crystallochemistry, modular approach and properties)

Un des enjeux majeurs en chimie du solide concerne la découverte de matériaux inorganiques à propriétés ciblées. En l absence d un protocole unique permettant d y arriver, la situation des laboratoires français de chimie du solide en termes de prospection de nouveaux composés reste critique. A l UCCS, notre groupe a une grande expérience et un savoir-faire reconnu liés à l élaboration et la caractérisation de nouveaux matériaux à base de bismuth. Récemment, une stratégie de Design de composés innovants a été mise en place et développée pour cette série de composés. Il a ainsi été possible de décrire la majeure partie de nos composés en termes de briques élémentaires structurales permettant, à postériori de prédire, préparer et caractériser de nouveaux membres. Dans les systèmes ternaires Bi2O3 MO P2O5 (M= métal de transition) à l origine de ce travail, ces prédictions ont été rendues possibles parce que chacune de ces unités structurales peut être utilisée, modifiée et assemblée de différentes façons. Le point commun à ces briques élémentaires repose sur la description mettant en œuvre des tétraèdres centrés sur les anions (ici O) et entourés par des atomes de bismuth. Ainsi, dans le cadre de l ANR jeune chercheur Multi-D InMaDe, nous avons exploré les systèmes Bi/M/X/O avec M= Cu, Co, Mn et X= P, V, As, Mo, Se et Cl. De nouveaux composés présentant des topologies innovantes ont été obtenus et leurs propriétés mesurées dans certains cas.One of the primary challenges concerns the discovery of novel inorganic compounds using a rational design in order to predict crystal structures and possible structure/properties relationships. In the absence of unified protocol for such a task, it remains a hot topic in the solid state chemistry community. At the UCCS, our group has a long experience and a strong savoir-faire related to the elaboration and characterization on new bismuth based compounds. Recently, a strategy to Design novel innovative compounds and/or establish bases for related mega-series of related compounds have been developed for these broad series compounds by our group. Results are such as a large family of compounds with related crystal structures have been understood in terms of building principles leading to the post prediction, preparation and characterization of novel members. In the chemical Bi2O3 MO - P2O5 (M = various divalent metals) systems, at the origin of this work, these predictions have been feasible because versatile building units (BU) can be handled, modified and assembled in various manners. The key-description used for BUs rely on the anion-centered polyhedra theory related to the bismuth atom. Thus, in the framework of ANR Multi-D InMaDe we have explored the Bi/M/X/O system, where M = Cu, Co, Mn etc. and X = P, V, As, Mo, Se and Cl. Several new compounds with new topologies have been obtained and their corresponding properties have been measured.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Design of New Structural Types from oxocentered Tetrahedra : Continous Polycationic Series from 1D Chains to 2D Planes in New Bismuth Compounds.

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Bi3+/M2+ Oxyphosphate: A Continuous Series of Polycationic Species from the 1-D, single chain to the 2-D Planes : Part. 1: from HREM images to crystal structure deduction.

This work deals with the crystal-structure deduction of new structural types of Bi3+-M2+ oxyphosphates (M is a transition element) from HREM images. Previous studies showed the unequivocal attribution of particular HREM contrasts to the corresponding Bi/M/O-based polycationic species in similar materials. On this basis, the examination of isolated crystallites of polyphased samples led to new HREM contrasts assigned to new polycationic species in three new structural types. This helped us to solve one crystal structure, and the two other forms have been deduced through HREM image decoding. It helped to model the investigated materials from the structural point of view as well as the chemical one. The three assumed crystal structures are formed by polycationic ribbons, n tetrahedra wide, surrounded by PO4 groups, as already encountered in these series of oxyphosphates. However, here we deal with the original n= 4-6 cases, whereas, up to this work, only the n= 1-3 ribbons have been reported. The greater size of ribbons is associated with particular structural modifications responsible for complex HREM contrasts. The validity of the proposed models is verified in Part 2 of this work

Les oxydes type-pérovskite La1-xMxMn1-yM'yO3+ (M : Pr ; Eu ou M' : Al, (0<=x,y<=1) ) (synthèse par combustion et études des propriétés physico-chimiques et catalytiques)

La synthèse par combustion est un procédé simple et économique qui se base sur une réaction d oxydoréduction entre un combustible (glycine) et un comburant (nitrates). La synthèse d une série d oxydes LaMnO3+ purs a été optimisée en faisant varier le rapport glycine/nitrate=r de 0,43 à 0,8.Les surfaces spécifiques obtenues varient de 18 à 37 m /g. Différentes espèces O2 désorbent des solides LMr : celles faiblement liées à la surface (a1-O2) et celles associées au réseau a2-O2 et b-O2 dont la désorption s accompagne respectivement de la réduction de Mn4+ en Mn3+ et de Mn3+ en Mn2+. Les mélanges riches en glycine (r>0,53) améliorent la surface spécifique et la mobilité des espèces a2-O2 ce qui favorise une activité catalytique importante dans l oxydation totale de CH4. Le solide obtenu avec un rapport stœchiométrique (r=0,53) est le plus stable thermiquement. La synthèse par combustion s est avérée aussi efficace pour l obtention des oxydes LaMn1-yAlyO3+ (0<=y<= 1). La substitution progressive de Mn par Al dans le sous réseau B de la structure type-pérovskite améliore la mobilité d espèces a2-O2 dans le réseau. Le catalyseur le plus actif est obtenu pour y=0,1 en raison de sa surface spécifique et sa concentration superficielle en Mn les plus élevées. Le procédé par combustion a été aussi mis à profit pour préparer des solides type-pérovskite La1-xLnxMnO3+ (Ln : Pr ;Eu, 0<=x<=1) substitués dans le sous réseau A. La mobilité de l oxygène a2-O2 est améliorée par cette substitution particulièrement avec l europium comme substituant. Un taux de substitution de 20% s est avéré optimum pour l activité catalytique dans l oxydation du méthane.Combustion synthesis is a simple and safe-time process. It is based on redox reaction between fuel ( glycine) and oxidant agent (nitrates). A series of nanocristalline powders LaMnO3+ were successfully obtained by varying glycine/nitrate ratio (r) from 0.43 to 0.8. The obtained specific areas range in 18-37 m /g. Different desorbed oxygen species from these solids were identified: those weakly adsorbed to the surface (a1-O2) and those diffusing from the bulk (a2-O2 and b-O2 ). The desorption of a2-O2 and b-O2 causes respectively the reduction of Mn4+ to Mn3+ and Mn3+ to Mn2+. The use of fuel rich precursor enhances the specific surface area, the reducibility of manganese and the mobility of desorbed oxygen. This criterion allows interesting catalytic properties in CH4 deep oxidation. The LM0,53 catalyst obtained in stoichiometric conditions exhibits the best thermal stability.The combustion synthesis is also useful to obtain LaMn1-yAlyO3+ oxides in a large range of Al content (0<=y<= 1). The Al-substitution for Mn improves a2-O2 mobility. The best catalyst is obtained for the optimal fraction y=0.1 of Al due to their higher surface areas and superficial Mn concentration. A series of substituted lanthanum manganite in the A sublattice of the perovskite-type structure La1-xLnxMnO3+ (Ln : Pr ;Eu, 0<=x<=1) were obtained by combustion synthesis. The a2-O2 mobility was improved by this substitution. A fraction of 20% was found to be optimum for catalytic activity in deep oxidation of methane.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Bi3+/M2+ Oxyphosphate: A Continuous Series of Polycationic Species from the 1D Single Chain to the 2D Planes. Part 2: Crystal Structure of Three Original Structural Types Showing a Combination of New Ribbonlike Polycations.

With the assistance of structural models deduced from the high-resoln. electron microscope (HREM) investigation presented in Part 1 of this work, three new structural types were pointed out in Bi2O3-MO-P2O5 ternary systems. Their crystal structures are built on the arrangement of 2D polycationic ribbons formed of edge-sharing O(Bi,M)4 tetrahedra and isolated by PO4 groups. Prior to this study, materials with ribbons up to n = 3 tetrahedra wide have been discovered. The original structures presented here display longer n = 4-6 cases, which suggests a possible continuous series of polycationic entities that range from the single chain (one tetrahedron wide) to the infinite [Bi2O2]2+ Aurivillius layer. The ribbons with n > 3 show strong structural modifications that are able to bring a good ribbon-phosphate cohesion. In addn. to these fascinating structural results, this work fully confirms the validity of the decoding established from HREM images of a single crystallite in inhomogeneous mixts