Magnetic hexamers interacting in layers in the (Na,K)2_2Cu3_3O(SO4)3_4)_3 minerals

Magnetic properties and underlying magnetic models of the synthetic A$_2$Cu$_3$O(SO$_4)_3$ fedotovite (A = K) and puninite (A = Na) minerals, as well as the mixed euchlorine-type NaKCu$_3$O(SO$_4)_3$ are reported. We show that all these compounds contain magnetic Cu$_6$ hexamer units, which at temperatures below about 100 K act as single spin-1 entities. Weak interactions between these magnetic molecules lead to long-range order below $T_N$ = 3.4 K (A = Na), 4.7 K (A = NaK), and about 3.0 K (A = K). The formation of the magnetic order is elucidated by ab initio calculations that reveal two-dimensional inter-hexamer interactions within crystallographic $bc$ planes. This model indicates the presence of a weakly distorted square lattice of $S=1$ magnetic ions and challenges the earlier description of the A$_2$Cu$_3$O(SO$_4)_3$ minerals in terms of Haldane spin chains.Comment: published version, re-worked compared to the initial submissio

Oxocentered Cu(II) lead selenite honeycomb lattices hosting Cu(I)Cl2 groups obtained by chemical vapor transport reactions

Chemical vapor transport (CVT) reactions were used to prepare three modular mixed-valent Cu(I)-Cu(II) compounds, (Pb2Cu(2+)9O4)(SeO3)4(Cu(+)Cl(2))Cl5 (1), (PbCu(2+)5O2)(SeO3)2(Cu(+)Cl2)Cl3 (2), and (Pb(x)Cu(2+)(6-x)O2)(SeO3)2(Cu(+)Cl2)K(1-x)Cl(4-x) (x = 0.20) (3). In their crystal structures chains of anion-centered (OCu(2+)4) and (OCu(2+)3Pb) tetrahedra form honeycomb-like double layers with cavities occupied by linear [Cu(+)Cl2](-) groups

Immersion into the fascinating world of anion-centered units

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Complémentarité DRX / MET / RMN (ordre vs. désordre dans les nouveaux oxyphosphates de bismuth)

Ce travail de thèse porte sur la description d'une nouvelle série de composés désordonnés: les oxyphosphate de bismuth et de métaux de transition qui sont constitués de rubans polycationiques [M4Bi2n-2O2n]x+ formés par association de tétraèdres OBi4. Dans cette formule, n correspond au nombre de tétraèdres associés: n= 1, 2, 3, 4... L'interpolation de n à l'infini conduit à une couche bidimensionnelle analogue aux feuillets [Bi202]2+ des phases d'Aurivillius. Dans les composés constitués de rubans, une nomenclature basée sur cet arrangement entre rubans D(= double), T(= triple), Q'(= quadruples), P'(= pentavalent) et H'(= sextuple) (le > indique la présence de deux atomes supplémentaires liés aux rubans n> 3) et tunnels t a été établie pour différencier l'ensemble des composés mis en évidence. Pour les composés contenant des plans [Bi2O2]2+ infinis, les polyèdres PO4 et MOx sont isolés entre les feuillets. La caractérisation structurale de ces composés utilise la complémentarité DRX/HREM grâce à un code d'interprétation des images établies à partir de structures connues et applicables aux nouvelles. Il permet la prédiction et la formulation de nouvelles phases contenues dans des échantillons multi-phasés.Le désordre important de la zone inter-rubans est la conséquence des sites mixtes situés en bouts de rubans, qui correspond à une orientation des PO4 et une occupation des tunnels (espace entre deux rubans distants de 7Å et partiellement occupé de cation M2+), Ainsi, la caractérisation du désordre par diffraction des neutrons, RMN 31p IR et ED montre que le caractère complexe du désordre (occupation mixte Bi3+/M2+ des sites mixtes -> influence sur l'orientation de PO4 -> influence sur l'occupation des tunnels) implique intuitivement de très légers gradients de composition et donc de mise en ordre qui peut intervenir entre différents grains, voire différents domaines d'un même monocristal, le réseau polycationique restant géométriquement inchangé. La complémentarité RMN/RX permet d'approfondir l'étude des phases désordonnées en utilisant des techniques de RMN 31P, 112Cd et 17O. Afin de mieux connaître les parametres influençant les spectres obtenus, des études préliminaires ont été réalisées sur des solutions solides, permettant de montrer les effets de paramètres de maille, de cation et de seconds voisins,LILLE1-BU (590092102) / SudocSudocFranceF

“TEM investigation of microporous compounds”

poste

TEM investigation of the microporous compound VSB-1: Building units and crystal growth mechanisms

Surface fine structure and structural defects in the open framework material VSB-1 have been investigated by electron microscopy. Crystal growth phenomena are proposed by a building unit model: (i) a unit is formed by two building units; (ii) they are linked to form first channels; and (iii) the whole network is grown via a layer-by-layer growth mechanism. A planar defect was observed in highresolution transmission electron microscope (HRTEM) image taken with the [0001] incidence, and diffuse streaks related to the presence of defects were observed in a series of electron diffraction (ED) patterns. The microstructure model derived from the defect structure gives information on crystal growth. These defects highlight an open site that could be the pillar of a new crystal growth process. The study of defects and crystal growth is important in understanding physical properties such as catalytic or magnetic properties, and in synthesising a new open framework structure

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

HREM: a Useful Tool to Formulate New Members of the Wide Bi3+/M2+ Oxide Phosphate Series

A number of double Bi3+/M2+ oxide phosphates have been isolated and structurally described using variable arrangements of isolated [Bi-M-O]n+ polycations surrounded by PO4 groups. The relationship between them leads to suspecting a great number of new arrangements within new compounds. In this work, the use of electron diffraction associated with high resolution imaging has considerably facilitated the prospecting. On the basis of the strong contrast observed by HREM between polycations of variable width and the interspace, a high-resolution image code and formulation rules have been established. This has allowed the formulation of original compounds, first detected in multiphased samples, yielding the synthesis of single-phased materials essential for the structural and physical characterization. This paper illustrates the complementarity between X-ray diffraction and electron microscopy studies to be especially well suited in this family of materials

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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