Tetra­yttrium(III) tris­ulfide disilicate

Tetra­yttrium(III) tris­ulfide disilicate, Y4S3(Si2O7), crystallizes in the Sm4S3(Si2O7) structure type. The structure consists of isolated (Si2O7)6− units (2mm. symmetry) and two crystallo­graphically independent Y3+ cations bridged by one S and one O atom. The first Y atom (site symmetry .m.) is coordinated by three O atoms and three S atoms in a trigonal–prismatic arrangement whereas the second Y atom (site symmetry ..2) is coordinated by six O atoms and three S atoms in a tricapped trigonal–prismatic arrangement

Dicaesium hexa­mercury hepta­sulfide

The title compound, Cs2Hg6S7, crystallizes in a new structure type that is closely related to that of K2Zn6O7. The structure comprises a three-dimensional mercury sulfide network that is composed of channels. These channels, which are along [001], are of two different diameters. The crystal structure contains one Cs, two Hg, and three S atoms in the asymmetric unit. The Cs, one Hg, and one S atom are at sites of symmetry m, whereas a second S atom is at a site of symmetry 2mm. The Hg atoms are bound to the S atoms in both three- and four-coordinate geometries. The caesium cations occupy the central spaces of the larger diameter channels and exhibit a coordination number of 7

The nature of the hydrogen bond in the bifluoride ion

Neutron diffraction data, obtained from single crystals of NaHF2 and NaDF2, have been analyzed in terms of several models for the bifluoride ion geometry. In sodium acid fluoride the bifluoride ion must be linear and the two fluorine atoms equivalent. The F-H-F distance is 2.264 ± 0.003 Å, the F-D-F distance is 2.265 ± 0.007 Å. The neutron diffraction data obtained by Peterson and Levy from a single crystal of KHF2 have been refined in an attempt to settle the question of the geometry of the bifluoride ion in KHF2. The F-H-F distance is 2.277 ± 0.006 Å. In neither sodium acid fluoride nor potassium acid fluoride is it possible from the diffraction data alone to distinguish between a symmetric model for the bifluoride ion and one in which the potential for the hydrogen (or deutérium) along the bond has two equal minima on either side of the center, even when these minima are 0.15 Å or so from the center. However, in both cases from a comparison between the differences in mean-square amplitudes of vibration along the bond of hydrogen (or deuterium) and fluorine as obtained from the analysis of the diffraction data and as calculated from the spectroscopic frequencies it is concluded that the bifluoride ion is indeed symmetric.Les intensités de diffraction neutronique de monocristaux de NaHF 2 et de NaDF2 ont été analysées sur la base de plusieurs modèles proposés pour la géométrie de l'ion bifluorure. Dans le fluorure acide de sodium, l'ion bifluorure doit être linéaire et les deux atomes F doivent être équivalents. La distance F-H-F est 2,264 ± 0,003 A, la distance F-D-F est 2,265 ± 0,007 Å. Les données de diffraction neutronique obtenues par Peterson et Levy dans leur étude d'un monocristal de KHF2 ont été raffinees pour essayer de résoudre le problème de la géométrie de l'ion bifluorure dans KHF2. La distance F-H-F est 2,277 ± 0,006 Å. Ni dans le fluorure acide de sodium, ni dans celui de potassium, il n'est possible de distinguer sur la seule base de données de diffraction, entre un modele symétrique de l'ion bifluorure et un modèle dans lequel le potentiel de l'hydrogène (ou de deutérium) le long de la liaison aurait deux minima égaux de chaque côté du centre, même si ces minima sont à une distance de l'ordre de 0,15 A du centre. Cependant, en comparant les différences, pour H et F, de leurs carrés moyens d'amplitude de vibration le long de la liaison, déduites soit de l'analyse des données de diffraction, soit des fréquences spectroscopiques, on conclut dans les deux cas que l'ion bifluorure est symetrique

Myoglobin models and steric origins of the discrimination between O 2 and CO

 Synthetic models of the myoglobin active site have provided much insight into factors that affect CO and O 2 binding in the proteins. "Capped" and "pocket" metal porphyrin systems have been developed to probe how steric factors affect ligand binding and ultimately to elucidate important aspects of the mechanism of CO discrimination in the proteins. These model porphyrins are among the most thoroughly characterized systems to date. From the twenty-one known crystal structures, analysis of the types of distortion that occur upon ligand binding under the cap, including porphyrin doming and ruffling, lateral and horizontal movement of the cap, and bending and tilting of the Fe–C–O bond, provides an indication of how steric interactions will affect structure in Hb and Mb. The model porphyrin systems discussed range from those that discriminate against O 2 binding compared to biological systems to those with similar CO and O 2 binding strength to myoglobin, and also to those that bind both O 2 and CO very weakly or not at all. The primary type of distortion observed upon CO binding is vertical or lateral movement of the cap and some ruffling of the porphyrin plane. Minimal bending or tilting of the M–C–O bond is observed, suggesting that the Fe–C–O bending that has been found from crystal structures of the hemoproteins is unlikely.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42324/1/775-2-4-521_70020521.pd

Manganese(II) octa­uranium(IV) hepta­deca­sulfide

Single crystals of manganese(II) octa­uranium(IV) hepta­deca­sulfide, MnU8S17, were grown from the reaction of the elements in a RbCl flux. MnU8S17 crystallizes in the space group C2/m in the CrU8S17 structure type. The asymmetric unit is composed of the following atoms with site symmetries shown: U1 (1), U2 (m), U3 (m), Mn1 (2/m), S1 (1), S2 (1); S3 (m), S4 (m), S5 (m), S6 (m) and S7 (2/m). The three UIV atoms are each coordinated by eight S atoms in a bicapped trigonal–prismatic arrangement. The MnII atom is coordinated by six S atoms in a distorted octa­hedral arrangement

The β-polymorph of uranium phosphide selenide

β-UPSe was synthesized from the reaction of U2Se3, P and Se in a CsCl flux in a fused-silica tube. It crystallizes with four formula units in the tetra­gonal space group I4/mmm in the UGeTe structure type. The asymmetric unit comprises one U (site symmetry 4mm), one Se (4mm), and one P (mmm.) atom. The U atom is coordinated in a monocapped square-anti­prismatic arrangement, where the square face is formed by P atoms and the other five vertices are Se atoms. The P site is disordered about a mirror plane, showing half-ocupancy for each of the two resulting P atoms. The title structure is related to that of α-UPSe, which crystallizes with two formula units in the tetra­gonal space group P4/nmm in the PbFCl structure type

The crystal structure of uytenbogaardtite, Ag3AuS2, and its relationships with gold and silver sulfides-selenides

The file attached is the Accepted/final draft post-refereeing version of the article

X-ray scattering intensities of water at extreme pressure and temperature

We have calculated the coherent x-ray scattering intensity of several phases of water at 1500 and 2000 K under high pressure, using ab initio Density Functional Theory (DFT). Our calculations span the molecular liquid, ice VII, and superionic solid phases, including the recently predicted symmetrically hydrogen bonded region of the superionic phase. We show that wide angle x-ray scattering intensity could be used to determine phase boundaries between these high pressure phases, and we compare the results for ice VII and superionic water. We compute simulated spectra and provide new atomic scattering form factors for water at extreme conditions, which take into account frequently neglected changes in ionic charge and electron delocalization. We show that our modifed atomic form factors allow for a nearly exact comaprison to the total x-ray scattering intensities calculated from DFT. Finally, we analyze the effect our new form factors have on determination of the oxygen-oxygen radial distribution function