Cytosine-Cytosinium Dimer Behavior in a Cocrystal with a Decavanadate Anion as a Function of the Temperature

International audienceWe have performed X-ray diffraction measurements on single crystals of Na-3[V10O28](C4N3OH5)(3)-(C4N3OH6)(3)center dot 10H(2)O as a function of the temperature. When the sample is cooled, from room temperature to 100 K, we have observed additional peaks well indexed in PI, while the phase at room temperature crystallizes in P (1) over bar. The molecular structure at 210 K indicates that the center of inversion is located between two cytosinium molecules, formally described with a charge of +0.5. When this crystal is heated to room temperature and the structure in P (1) over bar reindexed, some peaks remained unindexed. A protonation-deprotonation process gives rise to additional diffraction peaks at temperatures lower than 210 K. The triply bridged hydrogen bonded cytosine-cylosinum dimer is discussed according to the results of the charge density analysis and topological analysis at 210 K. The structure at 100 K has been completely solved based on a comparative study with other compounds containing cytosine-cytosinium dimer. This description could be considered as a reference for such dimer. It could help for discrimination between cytosine and cytosinium molecules, for any new structure containing a cytosine-cytosinium pair, and for which the quality does not allow a precise determination of the hydrogen localization

Cation ordering and order-disorder phase transition in co-substituted Li4Ti5O12 spinels

International audienceIn this paper we present the results of the synthesis, crystal structure investigations and in situ X-ray diffraction studies of the order - disorder phase transition in cobalt substituted lithium titanate oxide spinels, Li 1.33x Co 2-2x Ti 1+0.67x O 4 (0 ≤ x ≤ 1). Depending on the chemical composition the samples crystallize in two space groups (S.G.) Fd3̄m (0 ≤ x ≤ 0.40 and x = 1) and P4 3 32 (0.50 ≤ x ≤ 0.875). Samples crystallizing in the S.G. P4 3 32 are ordered spinels with a cation ordering of the 13 type at octahedral 4b and 12d sites. The cation ordering in octahedral sites is full in the sample with x = 0.75 (Li and Ti occupy 4b and 12d sites, respectively) and decreases for samples with higher/smaller x. Changes of the extinction conditions and nonlinearities in the concentration dependence of the lattice parameter in the regions 0.40 andlt; x andlt; 0.50 and 0.875 andlt; x andlt; 1 indicate changes of the crystal symmetry (Fd3̄m ↔ P4 3 32). The partially ordered spinel x = 0.50 has a convergent, reversible, order-disorder phase transition at T c = (1083 ± 10) K. Samples with x = 0.875 and 0.75 have an order - disorder phase transition out of our experimental ranges with T C (x = 0.875) andlt; 973 K and T C (x = 0.75) andgt; 1173 K. The mechanism of the phase transition is based on cation migration

Crystallographic Statistical Study of Decavanadate Anion Based-Structures: Toward a Prediction of Noncovalent Interactions

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Structural modifications in H3PW12O40·6H2O heteopolyacid

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Non-Photochemical Laser-induced nucleation in Microfluides device

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Etude préliminaire de la densité de charge d'un complexe cyanoguanidine de cuivre

International audienceLe ligand de type cyanoguanidine (NaCbNgCd(NeR 2) 2) est une molécule mono ou bidentate pouvant former des complexes métalliques variés. Du point de vue pharmacologique, la cyanoguanidine est connue pour favoriser le passage extra-cellulaire du potassium et est utilisée comme médicament antihypertenseur. Cette activité est très certainement liée à la structure originale de cette molécule présentant une grande variété de longueurs de liaison C-N (voir tableau ci-dessous) et un mode de coordination s 1 (linéaire ou coudée) ou µ(s 1-s 3). De plus, le complexe cuivre-cyanoguanidine possède un intérêt biologique. En effet, lorsque les complexes sont dinucléaires, chaque atome de cuivre est en coordination 3. Cette arrangement métal-ligand facilite alors l'établissement de liaison avec O 2 favorisant ainsi le transport de l'oxygène et la réduction de l'oxygène de l'eau. Une étude de diffraction des rayons X à 100 K a été menée sur le complexe Cu-cyanoguanidine [Cu{Et 2 N)(NH 2)CNCN} 2 {H 2 O} 2 Cl]Cl cristallisant dans le système orthorhombique (groupe d'espace P2 1 2 1 2 1) avec des paramètres de maille : a = 9,1186(4), b = 12,4878(7), c = 18,902(2) Å. Les données ont été enregistrées sur un diffractomètre Siemens (Bruker) à détecteur CCD en utilisant la longueur d'onde du Molybdène. Le tableau suivant donne les principales distances de liaison (Å) obtenues après l'affinement de la structure

Crystal structure of a copper (I) cyanoguanidne complex

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