research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890

Crystal structure of magnesium selenate hepta­hydrate, MgSeO4·7H2O, from neutron time-of-flight data

aDepartment of Earth Sciences, University College London, Gower Street, London WC1E 6BT, England, bDepartment of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London WC1E 7HX, England, and cISIS Facility, STFC Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Chilton, Didcot, Oxfordshire OX11 0QX, England
*Correspondence e-mail: andrew.fortes@ucl.ac.uk

Edited by M. Weil, Vienna University of Technology, Austria (Received 6 August 2014; accepted 18 August 2014; online 23 August 2014)

MgSeO4·7H2O is isostructural with the analogous sulfate, MgSO4·7H2O, consisting of isolated [Mg(H2O)6]2+ octa­hedra and [SeO4]2− tetra­hedra, linked by O—H⋯O hydrogen bonds, with a single inter­stitial lattice water mol­ecule. As in the sulfate, the [Mg(H2O)6]2+ coordination octa­hedron is elongated along one axis due to the tetra­hedral coordination of the two apical water mol­ecules; these have Mg—O distances of ∼2.10 Å, whereas the remaining four trigonally coordinated water mol­ecules have Mg—O distances of ∼2.05 Å. The mean Se—O bond length is 1.641 Å and is in excellent agreement with other selenates. The unit-cell volume of MgSeO4·7H2O at 10 K is 4.1% larger than that of the sulfate at 2 K, although this is not uniform; the greater part of the expansion is along the a axis of the crystal.

1. Chemical context

Since their discovery almost two hundred years ago, the hepta­hydrates of divalent metal selenates have received scant attention. This is in stark contrast with the M2+SeO4 hexa­hydrates, which have been extensively characterized, including studies of their morphology and optical properties (Topsøe & Christiansen, 1874[Topsøe, H. & Christiansen, C. (1874). Ann. Chim. Phys. 5e Série, 1, 5-99.]), their crystal structures (Stadnicka et al., 1988[Stadnicka, K., Glazer, A. M. & Koralewski, M. (1988). Acta Cryst. B44, 356-361.]; Kolitsch, 2002[Kolitsch, U. (2002). Acta Cryst. E58, i3-i5.]), their formation of isomorphous solution series (e.g., Ojkova et al., 1990[Ojkova, T., Balarew, C. & Staneva, D. (1990). Z. Anorg. Allg. Chem. 584, 217-224.]: Stoilova et al., 1995[Stoilova, D., Ojkova, T. & Staneva, D. (1995). Cryst. Res. Technol. 30, 3-7.]) and their dehydration properties (Nabar & Paralkar, 1975[Nabar, M. A. & Paralkar, S. V. (1975). Thermochim. Acta, 13, 93-95.]: Stoilova & Koleva, 1995[Stoilova, D. & Koleva, V. (1995). Thermochim. Acta, 255, 33-38.]). In part this may be due to the fact that the hepta­hydrates must be prepared at lower temperatures. Nevertheless, it is striking that the only information concerning their crystal structures, namely their apparent isomorphism with the M2+SO4 hepta­hydrates, has remained largely unaltered since the observations made prior to 1830 by Berzelius and his student Mitscherlich, which is that MgSeO4·7H2O forms deliquescent four-sided prismatic crystals below 288 K (e.g., Berzelius, 1818[Berzelius, J. (1818). J. Chem. Phys. 23, 430-484.], 1829[Berzelius, J. (1829). Jahres-Bericht über die Fortschritte der Physichen Wissenschaften. Tübingen.]). The only known goniometric data relate to FeSeO4·7H2O and CoSeO4·7H2O (Wohlwill, 1860[Wohlwill, E. (1860). Über isomorphe Mischungen der selensauren Salze. Dissertation, Georg-August Universität Göttingen, Germany.]: Topsøe, 1870[Topsøe, H. (1870). Krystallografisk-kemiske Undersøgelser over de selensure salte. Dissertation, København, Denmark.]: Tutton, 1918[Tutton, A. E. H. (1918). Proc. Roy. Soc. London. A, 94, 352-361.]), which are isomorphous with the monoclinic series of M2+SO4 hepta­hydrates. It is worth stating that MgMoO4·5H2O is isomorphous with both the sulfate, chromate and selenate analogues but is not isostructural with them [Bars et al., 1977[Bars, O., Le Marouille, J.-Y. & Grandjean, D. (1977). Acta Cryst. B33, 1155-1157.]; see also Lima-de-Faria et al. (1990[Lima-de-Faria, J., Hellner, E., Liebau, F., Makovicky, E. & Parthé, E. (1990). Acta Cryst. A46, 1-11.]) for further discussion of these nomenclature], so the occurrence of MgSeO4·7H2O as acicular rhombic prisms is no guarantee that it is isostructural with the sulfate salt. Additional confusion arises from conflicting observations of the MgSeO4–H2O binary phase diagram (Meyer & Aulich, 1928[Meyer, J. & Aulich, W. (1928). Z. Anorg. Allg. Chem. 172, 321-343.]: Klein, 1940[Klein, A. (1940). Ann. Chim. 14, 263-317.]), including our own recent discovery of hitherto unknown hydrates (containing 9H2O and 11H2O) below 273 K (Fortes, 2014[Fortes, A. D. (2014). Powder Diffr. Submitted.]).

As part of a wider study into low-temperature crystal hydrates of MgSeO4 and related compounds (Fortes et al., 2013[Fortes, A. D., Wood, I. G. & Gutmann, M. J. (2013). Acta Cryst. C69, 324-329.]) we synthesised the title compound and carried out a single-crystal neutron diffraction experiment in order to determine its structure.

2. Structural commentary

The crystal structure (Fig. 1[link]) is isostructural with that of the sulfate, having isolated [Mg(H2O)6]2+ octa­hedra and [SeO4]2− tetra­hedra linked by a framework of moderately strong hydrogen bonds (H⋯O from 1.692 to 1.946 Å; Table 1[link]). The seventh water mol­ecule is coordinated to neither Mg nor Se, occupying a `void' between the polyhedral ions and donating comparatively weak (i.e., long and non-linear) hydrogen bonds (Fig. 2[link], Table 1[link]). The [Mg(H2O)6]2+ octa­hedron is slightly elongated along the OW2 – Mg – OW5 axis, the respective Mg—O distances being 2.101 Å (average) compared with 2.046 Å (average) for the other four `equatorial' water mol­ecules (Table 2[link]). This distortion was also noted in the sulfate by Baur (1964[Baur, W. H. (1964). Acta Cryst. 17, 1361-1369.]) and is manifested in subsequent neutron single-crystal and powder diffraction studies (Ferraris et al., 1973[Ferraris, G., Jones, D. W. & Yerkess, J. (1973). J. Chem. Soc. Dalton Trans. 8, 816-821.]: Fortes et al., 2006[Fortes, A. D., Wood, I. G., Alfredsson, M., Vočadlo, L. & Knight, K. S. (2006). Eur. J. Min. 18, 449-462.]). The difference is due to the tetra­hedral coordination of OW2 and OW5; both of these water mol­ecules (in addition to being Mg-coordin­ated) donate two hydrogen bonds and accept one hydrogen bond, from OW7 and OW6 respectively. The four `equatorial' water mol­ecules donate but do not accept any hydrogen bonds. In the sulfate at 2 K (Fortes et al., 2006[Fortes, A. D., Wood, I. G., Alfredsson, M., Vočadlo, L. & Knight, K. S. (2006). Eur. J. Min. 18, 449-462.]), the average equatorial Mg—O distances were found to be 2.029 Å and the average axial Mg—O distances to be 2.100 Å (2.056 and 2.102 Å at room temperature; Ferraris et al., 1973[Ferraris, G., Jones, D. W. & Yerkess, J. (1973). J. Chem. Soc. Dalton Trans. 8, 816-821.]; Calleri et al., 1984[Calleri, M., Gavetti, A., Ivaldi, G. & Rubbo, M. (1984). Acta Cryst. B40, 218-222.]).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
OW1—H1A⋯O3i 0.969 (16) 1.692 (16) 2.659 (9) 175.4 (13)
OW1—H1B⋯O4ii 0.968 (16) 1.757 (15) 2.724 (9) 175.1 (11)
OW2—H2A⋯O2i 0.983 (14) 1.781 (15) 2.757 (9) 171.0 (11)
OW2—H2B⋯O4iii 0.984 (11) 1.753 (11) 2.732 (7) 172.4 (10)
OW3—H3A⋯O2ii 0.976 (13) 1.889 (13) 2.861 (8) 174.5 (12)
OW3—H3B⋯O3iv 0.985 (9) 1.708 (9) 2.692 (6) 177.4 (14)
OW4—H4A⋯O1iii 0.976 (14) 1.720 (15) 2.688 (9) 170.9 (11)
OW4—H4B⋯O2v 0.964 (13) 1.927 (11) 2.861 (7) 162.3 (15)
OW5—H5A⋯O4 0.976 (14) 1.874 (14) 2.839 (8) 169.6 (10)
OW5—H5B⋯OW7 0.967 (15) 1.786 (14) 2.742 (9) 169.4 (10)
OW6—H6A⋯OW5i 0.976 (10) 1.875 (10) 2.841 (6) 170.3 (12)
OW6—H6B⋯OW7vi 0.982 (14) 1.809 (13) 2.787 (8) 173.4 (11)
OW7—H7A⋯O1iv 0.973 (10) 1.858 (12) 2.790 (7) 159.5 (14)
OW7—H7B⋯OW2vii 0.955 (13) 1.946 (16) 2.866 (8) 161.2 (15)
Symmetry codes: (i) [-x+{\script{3\over 2}}, -y+1, z-{\script{1\over 2}}]; (ii) [-x+{\script{3\over 2}}, -y+1, z+{\script{1\over 2}}]; (iii) [-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]; (iv) [-x+1, y+{\script{1\over 2}}, -z+{\script{3\over 2}}]; (v) [x-{\script{1\over 2}}, -y+{\script{1\over 2}}, -z+1]; (vi) x, y, z-1; (vii) [-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}].

Table 2
Selected bond lengths (Å)

Se1—O1 1.630 (6) Mg1—OW1 2.045 (6)
Se1—O3 1.631 (8) Mg1—OW3 2.046 (10)
Se1—O2 1.642 (4) Mg1—OW6 2.058 (9)
Se1—O4 1.661 (7) Mg1—OW5 2.097 (8)
Mg1—OW4 2.037 (6) Mg1—OW2 2.104 (8)
[Figure 1]
Figure 1
Asymmetric unit of MgSeO4·7H2O with anisotropic displacement ellipsoids drawn at the 50% probability level (75% for Mg and the selenate O atoms to aid visibility). Dashed rods indicate hydrogen bonds. The superscripts (i) and (ii) denote, respectively, the symmetry operations [1 − x, [{1\over 2}] + y, [{3\over 2}] − z] and [[{3\over 2}] − x, 1 − y, [{1\over 2}] + z].
[Figure 2]
Figure 2
Packing of the polyhedra and inter­stitial water in MgSeO4·7H2O viewed down the c-axis. The polyhedral ions have been blurred in order to emphasize the location of the inter­stitial water mol­ecules.

The [SeO4]2− tetra­hedron exhibits a similar property in that the bond lengths are influenced by the hydrogen-bond coord­ination. Two of the oxygen atoms (O1 and O3) accept two hydrogen bonds and have mean Se—O bond lengths of 1.631 Å, whereas the other two oxygen atoms (O2 and O4) accept three hydrogen bonds and have a mean Se—O bond length of 1.652 Å. This distinction is not readily apparent in any of the data pertaining to the sulfate, but it is worth observing that the neutron scattering cross-section of selenium is almost three times greater than that of sulfur so our result should be considered more accurate. The mean Se—O bond length of 1.641 Å is in excellent agreement with other similar high-precision analyses of selenate crystals (Kolitsch, 2001[Kolitsch, U. (2001). Acta Cryst. E57, i104-i105.], 2002[Kolitsch, U. (2002). Acta Cryst. E58, i3-i5.]; Weil & Bonneau, 2014[Weil, M. & Bonneau, B. (2014). Acta Cryst. E70, 54-57.]).

Overall, the unit-cell volume of the selenate at 10 K is 4.1% larger than the sulfate analogue (deuterated) at 2 K. This expansion is not isotropic, however, with the greatest proportion being along the a axis of the crystal. We find that the a axis is 2.7% longer, the b axis 1.0% longer, and the c axis 0.3% longer in the selenate than the sulfate. It is not readily apparent from examination of the structure why this should be so. The magnitude of the volumetric strain is virtually identical to that found in MgSeO4·11H2O (4.1% larger than the sulfate analogue; Fortes, 2014[Fortes, A. D. (2014). Powder Diffr. Submitted.]) and somewhat less than is observed in, for example, CuSeO4·5H2O (5.1% larger than the equivalent sulfate; Kolitsch, 2001[Kolitsch, U. (2001). Acta Cryst. E57, i104-i105.]) or MgSeO4·6H2O (5.2%; Kolitsch, 2002[Kolitsch, U. (2002). Acta Cryst. E58, i3-i5.]).

3. Synthesis and crystallization

In our initial attempts to make MgSeO4 we employed the widely cited method of reacting basic Mg-carbonate with aqueous selenic acid (e.g., Stoilova & Koleva, 1995[Stoilova, D. & Koleva, V. (1995). Thermochim. Acta, 255, 33-38.]), but this was found to leave a substantial amount of acid in solution, giving a pink-coloured viscous liquid with a sour odour, which yielded an intimate mixture of MgSeO4·6H2O and Mg(HSeO3)2·4H2O crystals (cf., Kolitsch, 2002[Kolitsch, U. (2002). Acta Cryst. E58, i3-i5.]; Mička et al., 1996[Mička, Z., Němec, I. & Vojtíšek, P. (1996). J. Solid State Chem. 122, 338-342.]) even after repeated re-crystallization and treatment with aqueous H2O2. Consequently, we prepared an aqueous solution of magnesium selenate by stirring MgO into a solution of H2SeO4 (Sigma–Aldrich 481513, 40%wt diluted further in its own weight of distilled water) heated to 340 K. This reaction is much less dramatic than is the case when Mg-carbonate is used and the only clear indication that it has run to completion is the pH of the solution, which changed from 0.11 to 8.80. After a period of evaporation in the open air, the solution precipitates cm-sized crystals of MgSeO4·6H2O. After a further round of recrystallization from distilled water the phase purity of the hexa­hydrate was verified both by X-ray powder diffraction and Raman spectroscopy.

Finally, crystalline MgSeO4·6H2O was dissolved in distilled water to a concentration of 35%wt MgSeO4 at 333 K, and this liquid was left to evaporate in a refrigerated workshop at 269 K. After two days, slender prismatic crystals indistinguishable in habit from MgSO4·7H2O, appeared. One of these was removed from the liquid, dried on filter paper and cut into a pair of fragments each with dimensions 1 x 1 x 4 mm. The two fragments were placed side-by-side in an aluminium foil pouch suspended inside a standard thin-walled vanadium sample can (6 mm inner diameter). The lid of the can was sealed with indium wire and was then transported to the ISIS neutron source immersed in liquid nitro­gen.

The sample can was screwed onto a standard centre stick and inserted into a pre-cooled Closed-Cycle Refrigerator (CCR) already mounted on the SXD beam-line (Keen et al., 2006[Keen, D. A., Gutmann, M. J. & Wilson, C. C. (2006). J. Appl. Cryst. 39, 714-722.]). Initial data collection as the sample was cooled from 200 K down to 10 K revealed strong reflections from both crystals that could be indexed with an ortho­rhom­bic unit cell of similar shape but roughly 4% larger than that of MgSO4·7H2O. After cooling to 10 K data were collected with the crystals in four discrete orientations with respect to the incident beam, optimizing the coverage of reciprocal space, with integration times of 1600 µAhr each (roughly 10 h per frame at typical ISIS beam intensity). The peaks were indexed and integrated using the instrument software, SXD2001 (Gutmann, 2005[Gutmann, M. J. (2005). SXD2001. ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire, England.]) and exported in a format suitable for analysis using SHELX2014 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]; Gruene et al., 2014[Gruene, T., Hahn, H. W., Luebben, A. V., Meilleur, F. & Sheldrick, G. M. (2014). J. Appl. Cryst. 47, 462-466.]).

Upon completion of the experiment, crystals of the title compound that had been stored in a glass vial at 253 K for ten days were analysed by means of X-ray powder diffraction. This measurement, carried out on a custom Peltier cold stage (Wood et al., 2012[Wood, I. G., Hughes, N. J., Browning, F. & Fortes, A. D. (2012). J. Appl. Cryst. 45, 608-610.]) at 253 K, revealed that the hepta­hydrate had transformed completely to the newly reported MgSeO4·9H2O (Fortes, 2014[Fortes, A. D. (2014). Powder Diffr. Submitted.]), thus providing some initial insight into the relative stability of the two compounds.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3[link]. Structure refinement with SHELXL using the model obtained at 2 K for the deuterated MgSO4 analogue (Fortes et al., 2006[Fortes, A. D., Wood, I. G., Alfredsson, M., Vočadlo, L. & Knight, K. S. (2006). Eur. J. Min. 18, 449-462.]) based on earlier work (Baur, 1964[Baur, W. H. (1964). Acta Cryst. 17, 1361-1369.]: Ferraris et al., 1973[Ferraris, G., Jones, D. W. & Yerkess, J. (1973). J. Chem. Soc. Dalton Trans. 8, 816-821.]: Calleri et al., 1984[Calleri, M., Gavetti, A., Ivaldi, G. & Rubbo, M. (1984). Acta Cryst. B40, 218-222.]) yielded a good fit with no density residuals larger than 4.5% of the nuclear scattering density due to a hydrogen atom. No restraints were used and all anisotropic temperature factors were refined independently.

Table 3
Experimental details

Crystal data
Chemical formula [Mg(H2O)6](SeO4)(H2O)
Mr 293.38
Crystal system, space group Orthorhombic, P212121
Temperature (K) 10
a, b, c (Å) 12.234 (4), 12.020 (4), 6.809 (3)
V3) 1001.3 (6)
Z 4
Radiation type Neutron, λ = 0.48–7.0 Å
μ (mm−1) 0.48 + 0.0036 * λ
Crystal size (mm) 1.00 × 1.00 × 4.00
 
Data collection
Diffractometer SXD diffractometer
Absorption correction Numerical. The linear absorption coefficient is wavelength dependent and is calculated as: μ = 0.4823 + 0.0036 * λ [mm−1] as determined by Gaussian integration in SXD2001 (Gutmann, 2005[Gutmann, M. J. (2005). SXD2001. ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire, England.])
No. of measured, independent and observed [I > 2σ(I)] reflections 4337, 4337, 4337
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.072, 0.197, 1.08
No. of reflections 4337
No. of parameters 252
H-atom treatment All H-atom parameters refined
  w = 1/[σ2(Fo2) + (0.1399P)2 + 21.2928P] where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (fermi Å−3) 2.06, −1.72
Absolute structure All f′′ are zero, so absolute structure could not be determined
Computer programs: SXD2001 (Gutmann, 2005[Gutmann, M. J. (2005). SXD2001. ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire, England.]), SHELXS2014 and SHELXL2014 (Gruene et al., 2014[Gruene, T., Hahn, H. W., Luebben, A. V., Meilleur, F. & Sheldrick, G. M. (2014). J. Appl. Cryst. 47, 462-466.]), DIAMOND (Putz & Brandenburg, 2006[Putz, H. & Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany.]) and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Supporting information


Chemical context top

Since their discovery almost two hundred years ago, the heptahydrates of divalent metal selenates have received scant attention. This is in stark contrast with the M2+SeO4 hexahydrates, which have been extensively characterized, including studies of their morphology and optical properties (Topsøe & Christiansen, 1874), their crystal structures (Stadnicka et al., 1988; Kolitsch, 2002), their formation of isomorphous solution series (e.g., Ojkova et al., 1990: Stoilova et al., 1995) and their dehydration properties (Nabar & Paralkar, 1975: Stoilova & Koleva, 1995). In part this may be due to the fact that the heptahydrates must be prepared at lower temperatures. Nevertheless, it is striking that the only information concerning their crystal structures, namely their apparent isomorphism with the M2+SO4 heptahydrates, has remained largely unaltered since the observations made prior to 1830 by Berzelius and his student Mitscherlich, which is that MgSeO4·7H2O forms deliquescent four-sided prismatic crystals below 288 K (e.g., Berzelius, 1818,1829). The only known goniometric data relates to FeSeO4·7H2O and CoSeO4·7H2O (Wohlwill, 1860: Topsøe, 1870: Tutton, 1918), which are isomorphous with the monoclinic series of M2+SO4 heptahydrates. It is worth stating that MgMoO4·5H2O is isomorphous with both the sulfate, chromate and selenate analogues but is not isostructural with them [Bars et al., 1977; see also Lima-de-Faria et al. (1990) for further discussion of these nomenclature], so the occurrence of MgSeO4·7H2O as acicular rhombic prisms is no guarantee that it is isostructural with the sulfate salt. Additional confusion arises from conflicting observations of the MgSeO4–H2O binary phase diagram (Meyer & Aulich, 1928: Klein, 1940), including our own recent discovery of hitherto unknown hydrates (containing 9H2O and 11H2O) below 273 K (Fortes, 2014).

As part of a wider study into low-temperature crystal hydrates of MgSeO4 and related compounds (Fortes et al., 2013) we synthesised the title compound and carried out a single-crystal neutron diffraction experiment in order to determine its structure.

Structural commentary top

The crystal structure (Fig. 1) is isostructural to that of the sulfate, having isolated [Mg(H2O)6]2+ o­cta­hedra and [SeO4]2- tetra­hedra linked by a framework of moderately strong hydrogen bonds (H···O from 1.692 to 1.946 Å; Table 1). The seventh water molecule is coordinated to neither Mg nor Se, occupying a `void' between the polyhedral ions and donating comparatively weak (i.e., long and non-linear) hydrogen bonds (Fig. 2, Table 2). The [Mg(H2O)6]2+ o­cta­hedron is slightly elongated along the OW2 – Mg – OW5 axis, the respective Mg—O distances being 2.101 Å (average) compared with 2.046 Å (average) for the other four `equatorial' water molecules (Table 2). This distortion was also noted in the sulfate by Baur (1964) and is manifested in subsequent neutron single-crystal and powder diffraction studies (Ferraris et al., 1973: Fortes et al., 2006). The difference is due to the tetra­hedral coordination of OW2 and OW5; both of these water molecules (in addition to being Mg-coordinated) donate two hydrogen bonds and accept one hydrogen bond, from OW7 and OW6 respectively. The four `equatorial' water molecules donate but do not accept any hydrogen bonds. In the sulfate at 2 K (Fortes et al., 2006), the average equatorial Mg—O distances were found to be 2.029 Å and the average axial Mg—O distances to be 2.100 Å (2.056 and 2.102 Å at room temperature; Ferraris et al., 1973; Calleri et al., 1984).

The [SeO4]2- tetra­hedron exhibits a similar property in that the bond lengths are influenced by the hydrogen-bond coordination. Two of the oxygen atoms (O1 and O3) accept two hydrogen bonds and have mean Se—O bond lengths of 1.631 Å, whereas the other two oxygen atoms (O2 and O4) accept three hydrogen bonds and have a mean Se—O bond length of 1.652 Å. This distinction is not readily apparent in any of the data pertaining to the sulfate, but it is worth observing that the neutron scattering cross-section of selenium is almost three times greater than that of sulfur so our result should be considered more accurate. The mean Se—O bond length of 1.641 Å is in excellent agreement with other similar high-precision analyses of selenate crystals (Kolitsch, 2001,2002; Weil & Bonneau, 2014).

Overall, the unit-cell volume of the selenate at 10 K is 4.1% larger than the sulfate analogue (deuterated) at 2 K. This expansion is not isotropic, however, with the greatest proportion being along the b axis of the crystal. We find that the a axis is 2.7% longer, the b axis 1.0% longer, and the c axis 0.3% longer in the selenate than the sulfate. It is not readily apparent from examination of the structure why this should be so. The magnitude of the volumetric strain is virtually identical to that found in MgSeO4·11H2O (4.1% larger than the sulfate analogue; Fortes, 2014) and somewhat less than is observed in, for example, CuSeO4·5H2O (5.1% larger than the equivalent sulfate; Kolitsch, 2001) and MgSeO4·6H2O (5.2%; Kolitsch, 2002).

Synthesis and crystallization top

In our initial attempts to make MgSeO4 we employed the widely cited method of reacting basic Mg-carbonate with aqueous selenic acid (e.g., Stoilova & Koleva, 1995), but this was found to leave a substantial amount of acid in solution, giving a pink-coloured viscous liquid with a sour odour, which yielded an intimate mixture of MgSeO4·6H2O and Mg(HSeO3)·4H2O crystals (cf., Kolitsch, 2002; Mička et al., 1996) even after repeated re-crystallization and treatment with aqueous H2O2. Consequently, we prepared an aqueous solution of magnesium selenate by stirring MgO into a solution of H2SeO4 (Sigma–Aldrich 481513, 40%wt diluted further in its own weight of distilled water) heated to ~340 K. This reaction is much less dramatic than is the case when Mg-carbonate is used and the only clear indication that it has run to completion is the pH of the solution, which changed from 0.11 to 8.80. After a period of evaporation in the open air, the solution precipitates cm-sized crystals of MgSeO4·6H2O. After a further round of re-crystallization from distilled water the phase purity of the hexahydrate was verified both by X-ray powder diffraction and Raman spectroscopy.

Finally, crystalline MgSeO4·6H2O was dissolved in distilled water to a concentration of ~35%wt MgSeO4 at 333 K, and this liquid was left to evaporate in a refrigerated workshop at 269 K. After two days, slender prismatic crystals indistinguishable in habit from MgSO4·7H2O, appeared. One of these was removed from the liquid, dried on filter paper and cut into a pair of fragments each with dimensions 1 x 1 x 4 mm. The two fragments were placed side-by-side in an aluminium foil pouch suspended inside a standard thin-walled vanadium sample can (6 mm inner diameter). The lid of the can was sealed with indium wire and was then transported to the ISIS neutron source immersed in liquid nitro­gen.

The sample can was screwed onto a standard centre stick and inserted into a pre-cooled Closed-Cycle Refrigerator (CCR) already mounted on the SXD beam-line (Keen et al., 2006). Initial data collection as the sample was cooled from ~200 K down to 10 K revealed strong reflections from both crystals that could be indexed with an orthorhombic unit cell of similar shape but roughly 4% larger than that of MgSO4·7H2O. After cooling to 10 K data were collected with the crystals in four discrete orientations with respect to the incident beam, optimizing the coverage of reciprocal space, with integration times of ~1600 µA hr each (roughly 10 hours per frame at typical ISIS beam intensity). The peaks were indexed and integrated using the instrument software, SXD2001 (Gutmann, 2005) and exported in a format suitable for analysis using SHELX2014 (Sheldrick, 2008; Gruene et al., 2014).

Upon completion of the experiment, crystals of the title compound that had been stored in a glass vial at 253 K for ten days were analysed by means of X-ray powder diffraction. This measurement, carried out on a custom Peltier cold stage (Wood et al., 2012) at 253 K revealed that the heptahydrate had transformed completely to the newly reported MgSeO4·9H2O (Fortes, 2014), thus providing some initial insight into the relative stability of the two compounds.

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 3. Structure refinement with SHELXL using the model obtained at 2 K for the deuterated MgSO4 analogue (Fortes et al., 2006) based on earlier work (Baur, 1964: Ferraris et al., 1973: Calleri et al., 1984) yielded a good fit with no density residuals larger than 4.5% of the nuclear scattering density due to a hydrogen atom. No restraints were used and all anisotropic temperature factors were refined independently.

Related literature top

For related literature, see: Bars et al. (1977); Baur (1964); Berzelius (1818, 1829); Calleri et al. (1984); Ferraris et al. (1973); Fortes (2014); Fortes et al. (2006, 2013); Gruene et al. (2014); Gutmann (2005); Keen et al. (2006); Klein (1940); Kolitsch (2001, 2002); Lima-de-Faria, Hellner, Liebau, Makovicky & Parthé (1990); Meyer & Aulich (1928); Mička et al. (1996); Nabar & Paralkar (1975); Ojkova et al. (1990); Sheldrick (2008); Stadnicka et al. (1988); Stoilova & Koleva (1995); Stoilova, Ojkova & Staneva (1995); Topsøe (1870); Topsøe & Christiansen (1874); Tutton (1918); Weil & Bonneau (2014); Wohlwill (1860); Wood et al. (2012).

Computing details top

Data collection: SXD2001 (Gutmann, 2005); cell refinement: SXD2001 (Gutmann, 2005); data reduction: SXD2001 (Gutmann, 2005); program(s) used to solve structure: SHELXS2014 (Gruene et al., 2014); program(s) used to refine structure: SHELXL2014 (Gruene et al., 2014); molecular graphics: DIAMOND (Putz & Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top
[Figure 1] Fig. 1. Asymmetric unit of MgSeO4·7H2O with anisotropic displacement ellipsoids drawn at the 50% probability level (75% for Mg and the selenate O atoms to aid visibility). Dashed rods indicate hydrogen bonds. The superscripts (i) and (ii) denote, respectively, the symmetry operations [1 - x, 1/2 + y, 3/2 - z] and [3/2 - x, 1 - y, 1/2 + z].
[Figure 2] Fig. 2. Packing of the polyhedra and interstitial water in MgSeO4·7H2O viewed down the c-axis. The polyhedral ions have been blurred in order to emphasize the location of the interstitial water molecules.
Hexaaquamagnesium(II) selenate monohydrate top
Crystal data top
[Mg(H2O)6](SeO4)(H2O)F(000) = 592
Mr = 293.38Dx = 1.946 Mg m3
Orthorhombic, P212121Neutron radiation, λ = 0.48–7.0 Å
a = 12.234 (4) ÅCell parameters from 550 reflections
b = 12.020 (4) ŵ = 0.48 + 0.0036 * λ mm1
c = 6.809 (3) ÅT = 10 K
V = 1001.3 (6) Å3Rhomboid, colourless
Z = 44.00 × 1.00 × 1.00 mm
Data collection top
SXD
diffractometer
4337 independent reflections
Radiation source: ISIS neutron spallation source4337 reflections with I > 2σ(I)
time–of–flight LAUE diffraction scansθmax = 84.5°, θmin = 0.001°
Absorption correction: numerical
The linear absorption coefficient is wavelength dependent and is calculated as: µ = 0.4823 + 0.0036 * λ [mm-1] as determined by Gaussian integration in SXD2001 (Gutmann, 2005)
h = 3230
Tmin = ?, Tmax = ?k = 3120
4337 measured reflectionsl = 116
Refinement top
Refinement on F2Hydrogen site location: difference Fourier map
Least-squares matrix: fullAll H-atom parameters refined
R[F2 > 2σ(F2)] = 0.072 w = 1/[σ2(Fo2) + (0.1399P)2 + 21.2928P]
where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.197(Δ/σ)max < 0.001
S = 1.08Δρmax = 2.06 e Å3
4337 reflectionsΔρmin = 1.72 e Å3
252 parametersExtinction correction: SHELXL2014 (Gruene et al., 2014), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraintsExtinction coefficient: 0.0026 (3)
Primary atom site location: structure-invariant direct methodsAbsolute structure: All f" are zero, so absolute structure could not be determined
Crystal data top
[Mg(H2O)6](SeO4)(H2O)V = 1001.3 (6) Å3
Mr = 293.38Z = 4
Orthorhombic, P212121Neutron radiation, λ = 0.48–7.0 Å
a = 12.234 (4) ŵ = 0.48 + 0.0036 * λ mm1
b = 12.020 (4) ÅT = 10 K
c = 6.809 (3) Å4.00 × 1.00 × 1.00 mm
Data collection top
SXD
diffractometer
4337 measured reflections
Absorption correction: numerical
The linear absorption coefficient is wavelength dependent and is calculated as: µ = 0.4823 + 0.0036 * λ [mm-1] as determined by Gaussian integration in SXD2001 (Gutmann, 2005)
4337 independent reflections
Tmin = ?, Tmax = ?4337 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.072All H-atom parameters refined
wR(F2) = 0.197 w = 1/[σ2(Fo2) + (0.1399P)2 + 21.2928P]
where P = (Fo2 + 2Fc2)/3
S = 1.08Δρmax = 2.06 e Å3
4337 reflectionsΔρmin = 1.72 e Å3
252 parametersAbsolute structure: All f" are zero, so absolute structure could not be determined
0 restraints
Special details top

Experimental. For peak integration a local UB matrix refined for each frame, using approximately 50 reflections from each of the 11 detectors. Hence _cell_measurement_reflns_used 550 For final cell dimensions a weighted average of all local cells was calculated Because of the nature of the experiment, it is not possible to give values of theta_min and theta_max for the cell determination. The same applies for the wavelength used for the experiment. The range of wavelengths used was 0.48–7.0 Angstroms, BUT the bulk of the diffraction information is obtained from wavelengths in the range 0.7–2.5 Angstroms. The data collection procedures on the SXD instrument used for the single-crystal neutron data collection are most recently summarized in the Appendix to the following paper Wilson, C. C. (1997). J. Mol. Struct. 405, 207–217

Geometry. All e.s.d.s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.s are taken into account individually in the estimation of e.s.d.s in distances, angles and torsion angles; correlations between e.s.d.s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.s is used for estimating e.s.d.s involving l.s. planes.

Refinement. The variable wavelength nature of the data collection procedure means that sensible values of _diffrn_reflns_theta_min & _diffrn_reflns_theta_max cannot be given instead the following limits are given _diffrn_reflns_sin(theta)/lambda_min 0.06 _diffrn_reflns_sin(theta)/lambda_max 1.38 _refine_diff_density_max/min is given in Fermi per angstrom cubed not electons per angstrom cubed. Another way to consider the _refine_diff_density_ is as a percentage of the scattering density of a given atom: _refine_diff_density_max = 4.5% of hydrogen _refine_diff_density_min = -3.8% of hydrogen Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. For comparison, the calculated R-factor based on F is 0.0578 for the 1606 unique reflections obtained after merging to generate the Fourier map.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Se10.72001 (19)0.1764 (3)0.4966 (7)0.0005 (6)
O10.6727 (3)0.0565 (4)0.4240 (10)0.0045 (10)
O20.8540 (3)0.1781 (4)0.4840 (10)0.0039 (10)
O30.6788 (3)0.2016 (4)0.7201 (10)0.0032 (9)
O40.6714 (3)0.2769 (4)0.3540 (10)0.0037 (10)
Mg10.5841 (3)0.6050 (4)0.4601 (11)0.0028 (11)
OW10.7361 (3)0.6719 (5)0.5016 (11)0.0053 (10)
OW20.5312 (3)0.7470 (4)0.3064 (10)0.0046 (10)
OW30.5370 (3)0.6718 (5)0.7231 (10)0.0052 (10)
OW40.4319 (3)0.5399 (4)0.4219 (10)0.0049 (11)
OW50.6304 (3)0.4595 (4)0.6082 (10)0.0042 (10)
OW60.6434 (3)0.5384 (4)0.2028 (11)0.0059 (11)
OW70.5042 (3)0.4328 (4)0.9377 (11)0.0048 (10)
H1A0.7663 (8)0.7214 (10)0.403 (2)0.019 (2)
H1B0.7660 (8)0.6934 (9)0.628 (2)0.017 (3)
H2A0.5789 (8)0.7721 (9)0.199 (2)0.017 (2)
H2B0.4571 (7)0.7511 (9)0.251 (2)0.016 (2)
H3A0.5772 (7)0.7242 (9)0.805 (2)0.018 (3)
H3B0.4584 (7)0.6826 (10)0.748 (2)0.018 (2)
H4A0.3879 (7)0.5493 (9)0.304 (2)0.017 (2)
H4B0.4068 (8)0.4717 (9)0.481 (2)0.020 (3)
H5A0.6362 (7)0.3931 (9)0.526 (2)0.019 (3)
H5B0.5863 (8)0.4406 (9)0.721 (2)0.018 (2)
H6A0.7205 (7)0.5302 (10)0.170 (3)0.026 (3)
H6B0.5992 (8)0.4994 (10)0.104 (2)0.019 (3)
H7A0.4395 (7)0.4789 (9)0.953 (2)0.021 (3)
H7B0.4843 (8)0.3642 (9)0.998 (3)0.023 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Se10.0004 (7)0.0005 (10)0.0006 (18)0.0001 (7)0.0003 (10)0.0002 (15)
O10.0057 (12)0.0042 (19)0.004 (3)0.0009 (12)0.0004 (16)0.0005 (19)
O20.0013 (10)0.0051 (18)0.005 (3)0.0001 (11)0.0015 (14)0.002 (2)
O30.0041 (13)0.0042 (19)0.001 (3)0.0006 (11)0.0013 (15)0.0011 (19)
O40.0046 (13)0.0025 (18)0.004 (3)0.0004 (12)0.0005 (15)0.0016 (19)
Mg10.0027 (12)0.0021 (17)0.003 (3)0.0008 (11)0.0005 (14)0.0019 (19)
OW10.0046 (12)0.008 (2)0.003 (3)0.0021 (12)0.0007 (17)0.001 (3)
OW20.0038 (12)0.0028 (19)0.007 (3)0.0004 (11)0.0016 (16)0.000 (2)
OW30.0038 (11)0.007 (2)0.005 (3)0.0004 (13)0.0005 (15)0.001 (2)
OW40.0042 (13)0.006 (2)0.005 (3)0.0011 (13)0.0017 (14)0.000 (2)
OW50.0057 (13)0.0010 (19)0.006 (3)0.0000 (12)0.0002 (14)0.001 (2)
OW60.0046 (13)0.006 (2)0.007 (3)0.0001 (13)0.0006 (16)0.002 (2)
OW70.0064 (14)0.0040 (19)0.004 (3)0.0009 (12)0.0009 (15)0.000 (2)
H1A0.022 (4)0.020 (5)0.016 (7)0.005 (3)0.004 (4)0.002 (5)
H1B0.020 (4)0.019 (5)0.013 (8)0.006 (3)0.004 (4)0.002 (5)
H2A0.019 (4)0.014 (4)0.018 (7)0.002 (3)0.007 (4)0.004 (5)
H2B0.013 (3)0.017 (4)0.018 (7)0.001 (3)0.000 (3)0.003 (5)
H3A0.015 (3)0.019 (5)0.019 (7)0.003 (3)0.001 (4)0.012 (5)
H3B0.009 (3)0.024 (5)0.021 (7)0.001 (3)0.005 (3)0.002 (5)
H4A0.016 (3)0.021 (5)0.013 (7)0.001 (3)0.006 (3)0.002 (5)
H4B0.022 (4)0.016 (4)0.021 (8)0.007 (3)0.001 (4)0.005 (5)
H5A0.021 (3)0.014 (4)0.021 (8)0.002 (3)0.003 (4)0.004 (5)
H5B0.020 (4)0.022 (5)0.011 (7)0.001 (3)0.002 (4)0.001 (5)
H6A0.009 (3)0.030 (6)0.039 (10)0.002 (3)0.004 (4)0.001 (6)
H6B0.018 (3)0.023 (5)0.015 (8)0.005 (3)0.002 (4)0.004 (5)
H7A0.015 (3)0.018 (5)0.030 (9)0.007 (3)0.001 (4)0.007 (5)
H7B0.026 (4)0.016 (5)0.028 (9)0.003 (3)0.002 (5)0.013 (6)
Geometric parameters (Å, º) top
Se1—O11.630 (6)OW2—H2A0.983 (14)
Se1—O31.631 (8)OW2—H2B0.984 (11)
Se1—O21.642 (4)OW3—H3A0.976 (13)
Se1—O41.661 (7)OW3—H3B0.985 (9)
Mg1—OW42.037 (6)OW4—H4B0.964 (13)
Mg1—OW12.045 (6)OW4—H4A0.976 (14)
Mg1—OW32.046 (10)OW5—H5B0.967 (15)
Mg1—OW62.058 (9)OW5—H5A0.976 (14)
Mg1—OW52.097 (8)OW6—H6A0.976 (10)
Mg1—OW22.104 (8)OW6—H6B0.982 (14)
OW1—H1B0.968 (16)OW7—H7B0.955 (13)
OW1—H1A0.969 (16)OW7—H7A0.973 (10)
O1—Se1—O3109.7 (3)OW5—Mg1—OW2177.3 (3)
O1—Se1—O2110.5 (3)H1B—OW1—H1A107.8 (12)
O3—Se1—O2110.8 (4)H1B—OW1—Mg1124.8 (9)
O1—Se1—O4109.8 (4)H1A—OW1—Mg1119.5 (9)
O3—Se1—O4107.4 (3)H2A—OW2—H2B104.2 (12)
O2—Se1—O4108.6 (3)H2A—OW2—Mg1115.9 (7)
OW4—Mg1—OW1179.2 (5)H2B—OW2—Mg1121.0 (7)
OW4—Mg1—OW390.3 (3)H3A—OW3—H3B108.0 (11)
OW1—Mg1—OW388.9 (4)H3A—OW3—Mg1127.8 (8)
OW4—Mg1—OW693.7 (3)H3B—OW3—Mg1118.5 (10)
OW1—Mg1—OW687.2 (3)H4B—OW4—H4A105.5 (11)
OW3—Mg1—OW6175.7 (3)H4B—OW4—Mg1124.4 (8)
OW4—Mg1—OW589.3 (3)H4A—OW4—Mg1124.5 (8)
OW1—Mg1—OW590.9 (3)H5B—OW5—H5A107.7 (11)
OW3—Mg1—OW589.0 (4)H5B—OW5—Mg1115.3 (7)
OW6—Mg1—OW589.4 (3)H5A—OW5—Mg1115.3 (10)
OW4—Mg1—OW288.1 (3)H6A—OW6—H6B109.0 (13)
OW1—Mg1—OW291.7 (3)H6A—OW6—Mg1125.2 (11)
OW3—Mg1—OW291.7 (3)H6B—OW6—Mg1125.1 (8)
OW6—Mg1—OW290.0 (4)H7B—OW7—H7A103.7 (11)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
OW1—H1A···O3i0.969 (16)1.692 (16)2.659 (9)175.4 (13)
OW1—H1B···O4ii0.968 (16)1.757 (15)2.724 (9)175.1 (11)
OW2—H2A···O2i0.983 (14)1.781 (15)2.757 (9)171.0 (11)
OW2—H2B···O4iii0.984 (11)1.753 (11)2.732 (7)172.4 (10)
OW3—H3A···O2ii0.976 (13)1.889 (13)2.861 (8)174.5 (12)
OW3—H3B···O3iv0.985 (9)1.708 (9)2.692 (6)177.4 (14)
OW4—H4A···O1iii0.976 (14)1.720 (15)2.688 (9)170.9 (11)
OW4—H4B···O2v0.964 (13)1.927 (11)2.861 (7)162.3 (15)
OW5—H5A···O40.976 (14)1.874 (14)2.839 (8)169.6 (10)
OW5—H5B···OW70.967 (15)1.786 (14)2.742 (9)169.4 (10)
OW6—H6A···OW5i0.976 (10)1.875 (10)2.841 (6)170.3 (12)
OW6—H6B···OW7vi0.982 (14)1.809 (13)2.787 (8)173.4 (11)
OW7—H7A···O1iv0.973 (10)1.858 (12)2.790 (7)159.5 (14)
OW7—H7B···OW2vii0.955 (13)1.946 (16)2.866 (8)161.2 (15)
Symmetry codes: (i) x+3/2, y+1, z1/2; (ii) x+3/2, y+1, z+1/2; (iii) x+1, y+1/2, z+1/2; (iv) x+1, y+1/2, z+3/2; (v) x1/2, y+1/2, z+1; (vi) x, y, z1; (vii) x+1, y1/2, z+3/2.
Selected bond lengths (Å) top
Se1—O11.630 (6)Mg1—OW12.045 (6)
Se1—O31.631 (8)Mg1—OW32.046 (10)
Se1—O21.642 (4)Mg1—OW62.058 (9)
Se1—O41.661 (7)Mg1—OW52.097 (8)
Mg1—OW42.037 (6)Mg1—OW22.104 (8)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
OW1—H1A···O3i0.969 (16)1.692 (16)2.659 (9)175.4 (13)
OW1—H1B···O4ii0.968 (16)1.757 (15)2.724 (9)175.1 (11)
OW2—H2A···O2i0.983 (14)1.781 (15)2.757 (9)171.0 (11)
OW2—H2B···O4iii0.984 (11)1.753 (11)2.732 (7)172.4 (10)
OW3—H3A···O2ii0.976 (13)1.889 (13)2.861 (8)174.5 (12)
OW3—H3B···O3iv0.985 (9)1.708 (9)2.692 (6)177.4 (14)
OW4—H4A···O1iii0.976 (14)1.720 (15)2.688 (9)170.9 (11)
OW4—H4B···O2v0.964 (13)1.927 (11)2.861 (7)162.3 (15)
OW5—H5A···O40.976 (14)1.874 (14)2.839 (8)169.6 (10)
OW5—H5B···OW70.967 (15)1.786 (14)2.742 (9)169.4 (10)
OW6—H6A···OW5i0.976 (10)1.875 (10)2.841 (6)170.3 (12)
OW6—H6B···OW7vi0.982 (14)1.809 (13)2.787 (8)173.4 (11)
OW7—H7A···O1iv0.973 (10)1.858 (12)2.790 (7)159.5 (14)
OW7—H7B···OW2vii0.955 (13)1.946 (16)2.866 (8)161.2 (15)
Symmetry codes: (i) x+3/2, y+1, z1/2; (ii) x+3/2, y+1, z+1/2; (iii) x+1, y+1/2, z+1/2; (iv) x+1, y+1/2, z+3/2; (v) x1/2, y+1/2, z+1; (vi) x, y, z1; (vii) x+1, y1/2, z+3/2.

Experimental details

Crystal data
Chemical formula[Mg(H2O)6](SeO4)(H2O)
Mr293.38
Crystal system, space groupOrthorhombic, P212121
Temperature (K)10
a, b, c (Å)12.234 (4), 12.020 (4), 6.809 (3)
V3)1001.3 (6)
Z4
Radiation typeNeutron, λ = 0.48–7.0 Å
µ (mm1)0.48 + 0.0036 * λ
Crystal size (mm)4.00 × 1.00 × 1.00
Data collection
DiffractometerSXD
diffractometer
Absorption correctionNumerical
The linear absorption coefficient is wavelength dependent and is calculated as: µ = 0.4823 + 0.0036 * λ [mm-1] as determined by Gaussian integration in SXD2001 (Gutmann, 2005)
No. of measured, independent and
observed [I > 2σ(I)] reflections
4337, 4337, 4337
Rint?
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.072, 0.197, 1.08
No. of reflections4337
No. of parameters252
H-atom treatmentAll H-atom parameters refined
w = 1/[σ2(Fo2) + (0.1399P)2 + 21.2928P]
where P = (Fo2 + 2Fc2)/3
Δρmax, Δρmin (e Å3)2.06, 1.72
Absolute structureAll f" are zero, so absolute structure could not be determined

Computer programs: SXD2001 (Gutmann, 2005), SHELXS2014 (Gruene et al., 2014), SHELXL2014 (Gruene et al., 2014), DIAMOND (Putz & Brandenburg, 2006), publCIF (Westrip, 2010).

 

Acknowledgements

The authors thank the STFC ISIS facility for beam-time access and ADF acknowledges financial support from STFC, grant Nos. PP/E006515/1 and ST/K000934/1.

References

First citationBars, O., Le Marouille, J.-Y. & Grandjean, D. (1977). Acta Cryst. B33, 1155–1157.  CrossRef CAS IUCr Journals Web of Science Google Scholar
First citationBaur, W. H. (1964). Acta Cryst. 17, 1361–1369.  CrossRef CAS IUCr Journals Web of Science Google Scholar
First citationBerzelius, J. (1818). J. Chem. Phys. 23, 430–484.  Google Scholar
First citationBerzelius, J. (1829). Jahres-Bericht über die Fortschritte der Physichen Wissenschaften. Tübingen.  Google Scholar
First citationCalleri, M., Gavetti, A., Ivaldi, G. & Rubbo, M. (1984). Acta Cryst. B40, 218–222.  CrossRef CAS Web of Science IUCr Journals Google Scholar
First citationFerraris, G., Jones, D. W. & Yerkess, J. (1973). J. Chem. Soc. Dalton Trans. 8, 816–821.  CrossRef Web of Science Google Scholar
First citationFortes, A. D. (2014). Powder Diffr. Submitted.  Google Scholar
First citationFortes, A. D., Wood, I. G., Alfredsson, M., Vočadlo, L. & Knight, K. S. (2006). Eur. J. Min. 18, 449–462.  Web of Science CrossRef CAS Google Scholar
First citationFortes, A. D., Wood, I. G. & Gutmann, M. J. (2013). Acta Cryst. C69, 324–329.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationGruene, T., Hahn, H. W., Luebben, A. V., Meilleur, F. & Sheldrick, G. M. (2014). J. Appl. Cryst. 47, 462–466.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationGutmann, M. J. (2005). SXD2001. ISIS Facility, Rutherford Appleton Laboratory, Oxfordshire, England.  Google Scholar
First citationKeen, D. A., Gutmann, M. J. & Wilson, C. C. (2006). J. Appl. Cryst. 39, 714–722.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationKlein, A. (1940). Ann. Chim. 14, 263–317.  CAS Google Scholar
First citationKolitsch, U. (2001). Acta Cryst. E57, i104–i105.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationKolitsch, U. (2002). Acta Cryst. E58, i3–i5.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationLima-de-Faria, J., Hellner, E., Liebau, F., Makovicky, E. & Parthé, E. (1990). Acta Cryst. A46, 1–11.  CrossRef CAS IUCr Journals Google Scholar
First citationMeyer, J. & Aulich, W. (1928). Z. Anorg. Allg. Chem. 172, 321–343.  CrossRef CAS Google Scholar
First citationMička, Z., Němec, I. & Vojtíšek, P. (1996). J. Solid State Chem. 122, 338–342.  Google Scholar
First citationNabar, M. A. & Paralkar, S. V. (1975). Thermochim. Acta, 13, 93–95.  CrossRef CAS Web of Science Google Scholar
First citationOjkova, T., Balarew, C. & Staneva, D. (1990). Z. Anorg. Allg. Chem. 584, 217–224.  CrossRef Web of Science Google Scholar
First citationPutz, H. & Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany.  Google Scholar
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationStadnicka, K., Glazer, A. M. & Koralewski, M. (1988). Acta Cryst. B44, 356–361.  CrossRef CAS Web of Science IUCr Journals Google Scholar
First citationStoilova, D. & Koleva, V. (1995). Thermochim. Acta, 255, 33–38.  CrossRef CAS Web of Science Google Scholar
First citationStoilova, D., Ojkova, T. & Staneva, D. (1995). Cryst. Res. Technol. 30, 3–7.  CrossRef CAS Web of Science Google Scholar
First citationTopsøe, H. (1870). Krystallografisk-kemiske Undersøgelser over de selensure salte. Dissertation, København, Denmark.  Google Scholar
First citationTopsøe, H. & Christiansen, C. (1874). Ann. Chim. Phys. 5e Série, 1, 5–99.  Google Scholar
First citationTutton, A. E. H. (1918). Proc. Roy. Soc. London. A, 94, 352–361.  CrossRef CAS Google Scholar
First citationWeil, M. & Bonneau, B. (2014). Acta Cryst. E70, 54–57.  CSD CrossRef CAS IUCr Journals Google Scholar
First citationWestrip, S. P. (2010). J. Appl. Cryst. 43, 920–925.  Web of Science CrossRef CAS IUCr Journals Google Scholar
First citationWohlwill, E. (1860). Über isomorphe Mischungen der selensauren Salze. Dissertation, Georg-August Universität Göttingen, Germany.  Google Scholar
First citationWood, I. G., Hughes, N. J., Browning, F. & Fortes, A. D. (2012). J. Appl. Cryst. 45, 608–610.  Web of Science CrossRef CAS IUCr Journals Google Scholar

This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Follow Acta Cryst. E
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds