A Comparative X-Ray Diffraction Study of Aqueous MnSO₄ and Crystals of MnSO₄·5H₂O

Abstract

X-ray single crystal analysis of MnS04 • 5H2O shows that the manganese atoms are octahedral ly coordinated by oxygen atoms, four of which belong to water molecules and two to sulphate groups.A model derived from the crystal structure was fitted to the X-ray scattering intensities from aqueous MnS04. Good agreement with experimental data is achieved using a model in which Mn(H20)6-2(0S03)z +2 " 2z interacts with about ten water molecules and each sulphate ion with about seven water molecules.Analysis of X-ray [1-3] and neutron [4] diffraction data from concentrated aqueous salt solutions gives details about the environment of the ions and information about the geometry of the coordination polyhedra. This is particularly useful in the case of direct interaction between the anion and the cation, since information about their relative orientation cannot be obtained through other experimental techniques than diffraction; in the last several years contributions to the knowledge of complex-formation in solution have been provided by the analysis of halogen salt solutions [1,3,5] and recently by that of some sulphate salts, i.e. Shapovalow and Radchenko [10] examined diffraction data of dilute MnS04 solutions; their analysis was, however, limited to the first hydration sphere and no mention was made of cation-anion interaction, although an indication for its presence is suggested by the values of equilibrium constants [11]. We therefore undertook a detailed analysis of the diffraction data of two concentrated MnS04 solutions, which is reported in this paper, together with the single crystal structure determination of MnS04-5H20. Experimental and Data ProcessingMnS04 • H20 (Merck reagent grade) was dissolved in water to give a 2M (Sol. A) and a saturated Reprints request to Dr. Ruggero Caminiti, Istituto Chimico, Universitä di Cagliari, Via Ospedale 72, 09100 Cagliari, Italy.(Sol. B) solution. Mn + + and SO^-contents were determined by titrations with standard EDTA [12] and with a cation exchange resin (Dowex 50W-X8). The analytical results are given in Table 1. X-ray scattering data were obtained at 20i 1°C on a $ -& diffractometer using Moka radiation (wavelength X = 0.7107 Ä). A divergent beam was diffracted at the horizontal surface of the sample and then monochromatized by reflection from a curved quartz crystal. The observed range of scattering angles (2$) was from 3° to 134°, corresponding to the range 0.46 Ä -1 ^ 16.3 A -1 , where s= (4tt/A) sin $ is the scattering variable. The measured intensities were corrected for background, polarization and absorption [13], and smoothed by fourth differences [14], The Compton contribution was evaluated by a semiempirical method [15] in order to account for the monochromator discrimination. The corrected intensities were scaled to the independent scattering factor for the solution using both the analytical method

The Arrangement of First- and Second-Sphere Water Molecules in Divalent Magnesium Complexes: Results from Molecular Orbital and Density Functional Theory and from Structural Crystallography

“…First, all the crystal structures in the Cambridge Structural Database (CSD) 88 that contain a hexahydrated Mg 2+ ion have all six water molecules in the inner shell (octahedral coordination) . Second, solutions containing Mg 2+ ions have been widely investigated using X-ray diffraction methods and these experiments have consistently found the inner shell surrounding these ions to contain six water molecules. ,− ,,− Third, computational studies of gas-phase hexahydrated Mg 2+ ions have been reported at several computational levels, ,,, and the global minimum on the potential energy surface (PES) has been identified as Mg[H 2 O] 6 2+ with T h symmetry. In this arrangement, the water dipoles point directly toward the magnesium ion (see Figure ), indicative of a strong metal ion−water dipole interaction that also minimizes the water−water repulsion.…”

Langbeinite-type (NH4)2Mn2(SO4)3

“…The development of microporous materials has led to investigations of the factors governing the amine-templated syntheses of metal sulfates (Behera et al, 2004). The present report on a new ammonium manganese sulfate, which was obtained unexpectedly in a hydrothermal synthesis intended for this purpose, is a contribution to the limited number of structural studies of inorganic manganese sulfate compounds, such as, for example, Mn(HSO 4 ) 2 , Mn(HSO 4 ) 2 ÁH 2 O and Mn(HSO 4 ) 2 (H 2 SO 4 ) (Stiewe et al,1998), MnSO 4 ÁH 2 O (Le Fur et al, 1966) (Chang et al, 1983), MnSO 4 Á5H 2 O (Caminiti et al, 1982), MnSO 4 ÁH 2 O (Wildner & Giester, 1991), and MnSO 4 Á4H 2 O (Held & Bohatý, 2002). The sulfatomanganate(II) dianion can exist as a distinct entity, as noted in histidinium tetraaquadisulfatomanganate (Wojtczak & Jaskó lski, 1989) and ethylenediammonium tetraaquadisulfatomanganate (Chaabouni et al, 1996); both salts have monodentate sulfate groups only.…”