Disorder of a Trigonally Planar Coordinated Water Molecule in Cobalt Sulfate Heptahydrate, C oS04 • 7 D20 (Bieberite)* Thomas Kellersohn*. Robert G. Delaplane, and Ivar Olovsson** Institute of Chemistry. Department of Inorganic Chemistry, University of Uppsala, P.O. Box 531, S-75121 Uppsala Z. Naturforsch. 46b, 1635- 1640 (1991); received June 4. 1991 Cobalt Sulfate Heptahydrate. Bieberite. Disordered Structure. Hydrogen Bonding, Crystal Structure Cobalt sulfate heptahydrate (d-14), CoS04-7D:0 . Mr = 294.99. monoclinic, P2,/c, a = 1404.8(1), b = 649.41(6), c = 1092.5(2) pm,/? = 1057232(8) , V = 961.66- 106pm3, Z = 4. D v = 2.073 Mg-m"3, A(MoKa) = 71.073 pm. [(sin0)/x]max = 0.7035• 10"2 pm"1, ft = 20.26 cm ', F(000) = 580, T = 298 K. R(F) = 0.0264 for 2339 observed unique reflections. CoS04- 7 D:0 is shown to be isotypic to FeS04- 7 H ,0 (Melanterite). The deuterated compound is stable at am­ bient conditions in contrast to the normal hydrate. Its structure is built up by [Co(D:0 )6]2+ octahedra, S042~ tetrahedra, and “lattice” water molecules. One water molecule, which is al­ most exactly trigonally planar coordinated in its average position, exhibits a distinct oxygen disorder. The ‘lattice” water molecule accepts two strong hydrogen bonds and donates a li­ near and a bifurcated one. The hydrogen-bond lengths (O 0 distances) are in the range 271 - 302 pm. Introduction hydrates when the mother liquor is removed, and, A large number of divalent metal sulfates are hence, it is extremely difficult to handle. The com­ known to form heptahydrates. Two different mercial product, upon closer examination, turned out to be a mixture of different phases. On prepar­ structure types are known [ 1 ]: the monoclinic ing C oS0 4 ■ 6 D20 for an electron density study [ 8 ], FeS0 4 - 7 H20 (Melanterite) type with M = Fe, Mn (Mallardite), Cu (Boothite), Zn (Zincmelanterite), we obtained single crystals of CoS0 4 -7D 20 as a by-product. The deuterated from was found to be and Co (Bieberite), and the orthorhombic much more stable than the normal hydrate so that M gS0 4 -7H 20 (Epsomite) type with M = Mg, Ni (Morenosite) and Zn (Goslarite). Common basic a structure determination could be performed. features of both structure types are [M"(H 2 0 ) 6]2+ Experimental octahedra and one additional "lattice” water mo­ Deep red crystals of CoS0 4 -7D20 were ob­ lecule, not coordinated to a metal ion. tained by slow evaporation of a neutral D20 solu­ However, precise structure determinations are tion of previously dried (600 K, 24 h) C oS0 4 at up to now only available for the two respective room temperature. A suitable, approximately te- principal minerals [2-6]. Therefore, no detailed trahedrally shaped fragment with maximum di­ comparative discussion could be given. mensions of 0.45x0.36x0.32 mm was broken Despite the fact that "CoS0 4 -7H 2 0 ” is availa­ from a larger crystal. It was quickly sealed in a ble as a commercial product, its crystal structure glass capillary tube and mounted on a STOE has not been previously determined. This is ob­ AED 2 four-circle diffractometer. viously due to experimental difficulties: although Cell parameters were determined from 16 well- the heptahydrate has been described to be the sta­ centered reflections with 35° < 20 < 45 and are given in the Abstract. The intensities of 5238 re­ ble hydrate at room temperature [7], it rapidly de­ flections were measured in step-scans in the a ; - 2 0 - mode with a step width of Aco = 0.012 and a mini­ + Hydrogen Bond Studies 156. Part 155: R. G. Dela­ mum number of 70 steps/scan. A maximum count­ plane, R. Tellgren, and I. Olovsson. Acta Crystal­ ing time of 3.0 s/step was employed, range of hki. logr. B46, 361 (1990). * On leave from Universität GH Siegen, Inorganic -2 0 < h < 20, - 2 < k < 10, 0 < / < 15. Six moni­ Chemistry I, P.O. Box 101240. D-W-5900 Siegen. tor reflections were measured every 3 h and exhib­ FRG. ited an average total intensity decrease of 2.5% for ** Reprint requests to Prof. Dr. I. Olovsson. the 260 h of data collection. A linear decay correc­ Verlag der Zeitschrift für Naturforschung, D-7400 Tübingen tion was therefore applied. Averaging over 202 re­ 0932 - 0776/91 /1200 - 163 5/$ 01.00/0 peatedly measured reflections gave an internal R = 1636 Th. Kellersohn et al. • Cobalt Sulfate Heptahydratc, CoSQ4 7DoO 0.0137 (on F2). A numerical absorption correction FeS0 4 -7H20 [4], a refinement with 0 5 on a split using Gaussian integration was performed where position was performed, which gave a small, but the crystal shape was approximated by four significant improvement, final R = 0.0264. The oc­ boundary planes; the transmission factor varied cupancy of each site was kept at 0.5. However, it between 0.780 and 0.892. Averaging over symme­ was not possible to include the corresponding hy­ try equivalent reflections gave R = 0.0490. drogen atoms in this refinement. The same space group (P2,/c, no. 14 [9]) and the In the final cycle, 187 parameters were refined, close resemblance of the lattice parameters to including an isotropic extinction coefficient, type those of FeS0 4 • 7 H20 were taken as a strong indi­ II with a Gaussian distribution of mosaic blocks cation that CoS0 4 -7D20 is isotypic. Therefore, according to Becker and Coppens [10] with a final the atomic coordinates as reported by Baur [4] were value of 1.07(4)-105. Seven low-angle reflections taken as starting values for the subsequent refine­ were obviously severely affected by extinction ments. In order to facilitate the comparison be­ (more than 50% difference) and were excluded. tween the two structures, the established atomic 2339 reflections with F 2 > 3<r(F2) were used, final numbering scheme has been largely maintained in wR = 0.0388 with w = [l/cr2 (F) + 0.035 F2], good­ the present study, but the positions of some atoms ness of fit: S = 1.002. A J7?-plot according to had to be altered to symmetry equivalents in order Abrahams and Keve [11] had a slope of 1.06 and to match the recommendations for cell standardi­ an ordinate intercept of -0.06, thus indicating that zation as far as possible. the standard deviations were adequately estimat­ After a conventional full-matrix least-squares ed. All calculations were performed with the DU- refinement of positional and anisotropic displace­ PALS [12] system. The final atomic coordinates ment parameters for Co, S, and O, all hydrogen and equivalent isotropic displacement parameters atoms could be localized from difference Fourier are given in Table I, selected bond lengths and an­ syntheses. They were included in the refinement gles in Table II*. with isotropic displacement parameters which gave R = 0.0272. Since one water oxygen, 0 5, ex­ * Additional material to this paper can be ordered refer­ ring to the no. CSD 55222, names of the authors and hibited an abnormally large anisotropy of the vi­ citation of the paper at the Fachinformationszentrum brational ellipsoid, as had also been observed pre­ Karlsruhe GmbH, D-7514 Eggenstein-Leopoldsha- viously for the corresponding water molecule in fen, FRG. Table I. Fractional atomic coordinates and Atom .Y y z Ueq/A2 equivalent isotropic temperature factors for CoS0 4-7D-,0. Asterisks indicate isotropically Co(l) 0.0 0.0 0.0 0.0211(2) refined atoms. The occupancy of 0 5a and 0 5 b Co(2) 0.5 0.5 0.0 0.0208(2) was set to 0.5. The U have been estimated ac­ S 0.22675(2) 0.47241(5) 0.17647(3) 0.0196(2) cording to Ueq = 1 /3 EjjUya^a 0(1) 0.20467(8) 0.47122(16) 0.03652(10) 0.0289(5) 0(2) 0.13814(7) 0.54217(17) 0.21371(10) 0.0315(5) 0(3) 0.30951(2) 0.61333(17) 0.22694(10) 0.0327(5) 0(4) 0.25251(7) 0.26351(16) 0.22663(10) 0.0309(5) 0(5 a ) 0.1229(4) 0.4045(12) 0.4434(8) 0.031(2) 0(5 b) 0.0992(5) 0.3642(13) 0.4231(9) 0.041(3) 0(6) 0.09718(9) 0.96137(20) 0.18159(12) 0.0362(6) 0(7) 0.02906(8) 0.79182(17) 0.43215(11) 0.0337(5) 0(8) 0.47956(9) 0.44943(20) 0.17767(10) 0.0306(5) 0(9) 0.43148(8) 0.27931(18) 0.44138(11) 0.0329(5) 0(10) 0.35744(7) 0.85773(18) 0.44239(11) 0.0339(5) 0(11) 0.36435(10) 0.00542(19) 0.11696(14) 0.0338(6) D(51) 0.138(2) 0.293(4) 0.455(2) 0.040(5)* D(52) 0.117(2) 0.432(4) 0.369(3) 0.053(6)* D(61) 0.114(2) 0.850(4) 0.199(2) 0.059(7)* D(62) 0.145(2) 1.035(4) 0.209(2) 0.046(6)* D(71) 0.077(2) 0.866(3) 0.462(2) 0.031(4)* D(72) -0.010(2) 0.859(4) 0.389(2) 0.060(7)* D(81) 0.428(2) 0.514(3) 0.187(3) 0.050(7)* D(82) 0.522(2) 0.474(4) 0.225(3) 0.058(8)* D(91) 0.380(2) 0.281(4) 0.377(3) 0.071(8)* D(92) 0.420(2) 0.340(4) 0.486(3) 0.065(8)* D(101) 0.307(2) 0.923(4) 0.455(3) 0.063(7)* D (102) 0.341(2) 0.792(4) 0.379(2) 0.061(7)* D (lll) 0.324(2) 0.067(4) 0.139(2) 0.043(6)* D( 112) 0.347(2) -0.088(4) 0.096(2) 0.052(7)* Th.