183W INADEQUATE 2D NMR Spectroscopy of Hetero Arsenato–Phosphato–Tungstate PV/AsV Substitution in Dawson-Type α-[AsxP2–xW18O62]6– (x = 0–2) and α-[H4AsyP1–yW18O62]7– (y = 0, 1)

International audienceThe Dawson-type arsenato-phosphato-tungstate alpha-[AsPW18O62](6-) has been prepared and unambiguously identified for the first time. A comparative study. including the four other already known compounds, the symmetric alpha-[X2W18O62](6-) and unsymmetric alpha-[H4XW18O62](7-) for X = P-V, As-V, has been performed by spectroscopic W-183 and P-31 NMR. 2-D W-183 INADEQUATE experiments were systematically employed to unequivocally verify structures, assign all resonances, and determine precisely (2)J(W-O-W) scalar couplings. The effects of P/As substitutions, generating unsymmetric structures, on the NMR observables delta(W-183), delta(P-31), (2)J(W-O-W), and (2)J(W-O-P) are discussed in relation to their bond length and bond angle alteration. General trends with respect to NMR parameter variations have been found when filling central cavities with P or As atoms, with less pronounced effects for As than for P. In addition, NMR characterization of three other isomers, i.e., beta-[X2W18O62](6-) and [As2W18O62](6-), were also provided for comparison. The present NMR results could serve as representative reference data for understanding the relationship between structure and NMR observables in polyoxotungstates

Encyclopédie des historiographies : Afriques, Amériques, Asies

Quels rapports les sociétés humaines entretiennent-elles avec leur passé et quels récits font-elles du temps révolu ? Pour ce premier volume de l’Encyclopédie des historiographies. Afriques, Amériques, Asies, 157 spécialistes représentant 88 institutions académiques en France et dans le monde explorent l’univers des productions humaines qui constituent des sources pour l’historien et déchiffrent les nombreuses modalités (« scientifiques », littéraires, artistiques, monumentales…) de l’écriture du passé. Évoquant tour à tour l’Afrique, l’Amérique latine, l’Asie, l’Océanie, les 216 notices de l’ouvrage présentent des matériaux historiques de toute nature, issus de toutes les époques, souvent méconnus, ainsi que l’histoire de leurs usages. L’entreprise collective qu’est l’Encyclopédie se veut novatrice : il s’agit de susciter une réflexion historiographique résolument non-occidentalo-centrée qui complète utilement les démarches épistémologiques traditionnelles. Nouvel outil de connaissance historique forgé à l’heure de la mondialisation, l’Encyclopédie des historiographies est aussi une véritable invitation au voyage.What are the different types of relations that non-Western societies upkeep with their past and how are narratives about the past produced by them? In this first volume of the Encyclopaedia of Historiography: Africa, America, Asia, 157 specialists from 88 international academic institutions explore the wealth of evidence that constitutes source material for historians. They also examine the immensely diverse modes or genres of narrated history: “scientific”, literary, artistic, architectural, etc. 216 entries dealing with Africa, Latin America, Oceania, and Asia, cover a large variety of sources, including many which are unfamiliar to the Western or non-Western reader, along with the history of how they have been exploited. By bringing together for the first time such an abundance of material the reader is offered the possibility of exploring continents and building meaningful connections across space and time. In addition to being a new tool for historical enquiry in an era of globalization, this encyclopaedia is also an invitation to travel the world