Sulfate Tetrahedra Research Articles

Sodium lanthanum(III) sulfate monohydrate, NaLa(SO4)2.H2O

The structure of NaLaIII(SO4)2.H2O consists of distorted Na-O6 octahedra, La-O9 complexes in the form of distorted tricapped trigonal prisms, and slightly irregular tetrahedral sulfate ions. All bond distances fall within normal limits. The sulfate ions manifest rigid-body behavior but this is not the case for either of the cation complexes. The single water molecule is modelled as having O-atom disorder but an ordered H atom. Hydrogen bonds involve only sulfate O atoms as acceptors. The absolute structure has been determined.

The Structures of Some Zirconium(IV) Chromium(III) Basic Sulfates Containing New Heteropolyanions

Three complexes (A)-(C), MI4 [Zr6Cr4O8(OH)8(SO4)8(H2O)4].yH2O, where MI4 is Cs2.78- Na1.22 (A), Na4 (B) or not present (C), in which (A) and (B) contain the same ZrIV-CrIII heteropolyanion and (C) contains a structural isomer of it, have been crystallographically characterized with varying degrees of refinement. A fourth complex (D), [Zr6Cr4O8(OH)8(SO4)5(DL-α-Ala)4(H2O)4]n+ hydrate, in which some of the sulfate groups that form part of the heteropolyanion have been replaced by alanine (Ala) molecules, is also described. The heteropolyanion [it has 4 crystallographic symmetry in (A), no symmetry in (B)] is best described as an octahedron of eight-coordinate ZrIV ions (intermediate between square-antiprismatic and dodecahedral stereochemistry) with CrIII octahedra and sulfate tetrahedra bound to it. In (C), two CrIII octahedra and two sulfate groups have been rotated with respect to the octahedron of zirconium ions leaving an unsymmetrical heteropolyanion, while in (D) the heteropolyanion has twofold symmetry and is similar to that in (A) and (B) except for the presence of alanine in place of some sulfate groups.

The role of orientational disorder in the pressure-induced amorphization of lithium potassium sulphate

Raman scattering investigations of lithium potassium sulphate at high pressures have revealed that the sulphate tetrahedra are orientationally disordered in the high-pressure phases. In order to understand the nature of the disorder, the temperature dependence of the relative intensities of Raman lines associated with the sulphate internal modes are investigated. The results suggest a frozen-in static disorder rather than dynamic equilibrium between the occupancies of different orientations. The behaviour of the Raman linewidths up to a pressure of 250 kbar indicates successively broader distributions of the sulphate orientations. A mechanism of amorphization involving disorder in cation sublattices induced by the orientational disorder of sulphate is proposed.

Adsorption of O 2, SO 2, and SO 3, on Nickel Oxide: Mechanism for Sulfate Formation

Calculations based on the atom superposition and electron delocalization molecular orbital (ASED‐MO) technique suggest that will adsorb preferentially end‐on at an angle 45° from normal on a nickel cation site on the (100) surface of . adsorption is also stronger on the nickel site; bonds through the sulfur atom in a plane perpendicular to the surface. Adsorption energies for on the nickel and oxygen sites are comparable in the preferred orientation in which the plane is parallel to the surface. The calculations suggest that the strength of adsorption varies as . On activation, adsorbed to an O2− site forms a trigonal pyramidal species which yields, with a low barrier, a tetrahedral sulfate anion. Subsequently the anion reorients on the surface. Alternative mechanisms which require the formation of Ni3+ or O− are discussed. thus formed may play a passivating role for the corrosion of Ni at low temperatures in the atmospheres and an active role at high temperatures, as discussed in the experimental literature.

Configuration of the SO=4 ion in the cubic phase of Li2SO4 from band shape studies of the ν3 mode

A Raman spectroscopic study of the molecular ν3 band in the plastic phase of Li2SO4 is presented. The analysis of the band shape and the depolarization ratio vs frequency suggests a prevalence of C3v configurations around the sulfate tetrahedra. Spectroscopic evidence from the pretransitional region in the monoclinic phase and a similar analysis of the ν3 band in the melt reinforce this hypothesis. These data are compared with structural results and a computer modeling of the possible orientational distribution of the SO2−4 tetrahedra in the plastic phase.

A computer simulation of LiKSO4

Molecular-dynamics computer-simulation of an ionic molecular solid LiKSO4 has been carried out at 300 and 1000 K using the atom-atom potentials obtained from lattice dynamical studies. We observe hopping of lithium ions to interstitial positions which is related to reorientations of sulphate tetrahedra.

Esr study of (SO 4) 2− dynamics in relation to the ferroelectric phase transition in ammonium sulfate

Ferroelectric phase transition in ammonium sulfate has been studied by ESR of CrO 4 3− radical substituting for SO 4 2− ion in (NH 4) 2SO 4. In addition to discontinuous changes at T c , certain continuous changes are observed in ESR parameters of this probe below T c , which reflect the role of the sulfate ion in the phase transition. A microscopic mechanism of the phase transition is proposed and discussed in terms of the change of orientation of the sulfate tetrahedron through a finite angle. The degree of the change of orientation below T c is thought to be the possible order parameter of the phase transition.

X-Ray and neutron diffraction study of alums

Abstract The crystal structure of the alums, (NH3CH3)Al(SO4)2 · 12H2O and (NH4)Al(SO4)2 · 12H2O, has been determined and refined from X-ray and neutron diffraction data. The compounds crystallize cubic in space group Pa3 (Z = 4) with a 0 = 12.322(3) Å and a 0 = 12.242(1) Å respectively. The positional and thermal parameters of all atoms including hydrogens have been refined by full matrix least-squares analysis resulting in Rw values from the X-ray and neutron data of 0.030 and 0.029 respectively for the methylammonium alum and of 0.024 and 0.014 respectively for the ammonium alum. The atoms of the cation groups (NH3CH3)+ and (NH4)+ are distributed on 8(c) and 24(d) positions in two orientations of equal probability on and around the [111] direction related to each other by an inversion centre. The disorder in the cation groups is explained by a quantized rotation. Disorder in the sulfate groups has been determined to 4.2% for the methylammonium alum and to about 17% for the ammonium alum. The disordered sulfate tetrahedra are distorted and in a reversed orientation along the threefold axis. The system of the hydrogen bonds is discussed.

Structure of a new uranyl sulfate hydrate .alpha.-2UO2SO4.cntdot.7H2O

Atomic distances, parameters, and angles are tabulated. The uranium is at the center of a pentagonal bipyramid arrangement of oxygen atoms. These are joined in an infinite chain along the b axis by sulfate tetrahedra. The ..beta..-form also contains chains made up of very similar units of two bipyramids and two tetrahedra; both forms are illustrated for comparison. The overall structures of these chains are different; in the chain in the ..cap alpha.. form the units are repeated according to the b-axis translation, while in the ..beta.. form the replication is by a glide plane. As a result, alternate units in the latter case have reversed orientations. The interatomic distances and angles are comparable in these two forms. The molecular form is 2% smaller in the ..cap alpha.. form indicating a very slightly more efficient packing. All the water molecules are hydrogen bonded, and distances and angles for these bonds are also tabulated. 1 figure, 3 tables.

Structural analysis of some molten materials by X-ray diffraction. Part 2.—Li2SO4, Na2SO4 and the mixed system

The structures of molten Li2SO4, Na2SO4 and their mixtures have been examined by consideration of the radial distribution function and the molar volume. The existence of tetrahedral sulphate ions in these molten salts has been demonstrated. S—O and O—O distances for the sulphate ion in the molten state are 1.500 and 2.450Å, respectively. A close packed arrangement of sulphate ions appears to be the configuration realized in molten Li2SO4; the calculated correlation function based on this structural model is qualitatively in good agreement with the observed one. In molten Na2SO4, sodium ions probably occupy a position intermediate between the edge and face sites of the sulphate ion; the nearest-neighbour distances of Na—S and Na—O pairs are 2.8 and 2.33 Å, respectively.

Crystal structure and hydrogen bonding of copiapite

The structure of copiapite, MgFe4[(OH)2|(SO4)6] · 20H2O, is triclinic, space group P[unk], with a = 7.342 Å, b = 18.818 Å, c = 7.389 Å, α = 91.45°, β = 102.15°, and γ = 98.85°. Fe(O,OH,H2O)6 octahedra and sulfate tetrahedra are connected to form one-dimensional infinite complexes along [101]. Mg(H2O)6 octahedra and water molecules not bound to cations lie between the complexes. These structural groups are interconnected only by hydrogen bonds.

Crystal and molecular structure of thiocarbonohydrazide sulphate

Crystals of the title compound are orthorhombic, space group Pbca, with Z= 8 in a unit cell of dimensions: a= 10·80(1), b= 15·44(2), c= 8·26(1)A. The structure has been solved from diffractometer data by three-dimensional Patterson and Fourier methods, and refined by full matrix least-squares methods to R 0·047 for 1250 observed reflections. The structure consists of diprotonated cations, in a cis,cis-conformation, with tetrahedral sulphate anions. The distances and angles are comparable with those presented by thiocarbonohydrazide (I) in different conformations and crystals. Rotation angles of the two –[graphic omitted]H3 around N–N are somewhat different from one another. The whole cation possesses practically a binary axis of symmetry, through C–S. The –NH– and –[graphic omitted]H3 groups form several N–H ⋯ O hydrogen bonds with surrounding anions. The i.r. spectrum of the compound is compared with that of the simple molecule.

On the infra-red spectrum and thermal decomposition products of thaumasite, Ca3H2(CO3/SO4)SiO4.13H2O

SummaryThe infra-red spectrum of untreated thaumasite Ca3H2(CO3/SO4)SiO4.13H2O, as well as the spectra and X-ray diffraction patterns of thaumasite heated in air at 200, 360, 550, 725, 800, 900, and 1150° C were investigated. The release of CO2 and H2O upon heating was followed. It was established that thaumasite changes between 200 and 550° C to a glass-like, amorphous state. Ca2SiO4-polymorphs and anhydrite are formed upon heating at temperatures up to 800° C. From 900° C calcium silicosulphate and anhydrite are the thermal decomposition products. These results are used in the assignment of the IR-absorption bands under 1400 cm−1 of untreated thaumasite, which are shown to be of a composite nature, i.e. attributable to overlapping vibrations of both sulphate and silicate tetrahedra.

On the crystal chemistry of salt hydrates. V. The determination of the crystal structure of CuSO4.3H2O (bonattite)

CuSO4.3HzO crystallizes in space group Cc with a= 5.592, b= 13.029, c=7.341 A, B= 97°3 ', Z=4. The structure has been determined from Patterson and Fourier syntheses using three-dimensional data collected on a precession camera with Mo Ke radiation. The structure was refined by the method of least squares. The final R value for 936 observed structure factors is 0.069. The coordination polyhedra around the Cu2+ ions do not share any edges or corners with each other; they are connected by hydrogen bonds and via linking sulfate groups. The square planar coordination around the copper ion consists of three water oxygen atoms and one sulfate oxygen atom at an average distance of 1.96/~. Two more sulfate oxygen atoms at 2.40 and 2.45 A, complete the distorted octahedral coordination. The average S-O bond length in the sulfate tetrahedron is 1.472 A. The positions of the hydrogen atoms were not determined experimentally; they were calculated theoretically assuming that the hydrogen atoms are in positions of least electrostatic energy. Only four of the six crystallographically nonequivalent hydrogen atoms are involved in normal hydrogen bonds.