Magnesium selenite dihydrate, MgSeO₃·2H₂O

Hydro­thermally prepared MgSeO₃·2H₂O consists of pairs of edge-sharing MgO₆ (4O, 2H₂O) octahedra [d_av(Mg-O) = 2.095 (2) Å]. These are linked by pyramidal SeO₃ units [d_av(Se-O) = 1.697 (2) Å] and hydrogen bonds forming a three-dimensional network.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Mg-O) = 0.002 Å
• R factor = 0.023
• wR factor = 0.061
• Data-to-parameter ratio = 19.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



PLAT_354  Alert C Short O-H Bond (0.82A)     O(4)   -   H(1)   =       0.67 Ang.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

MgSeO₃·2H₂O is isostructural with the mineral cobaltomenite (Leider & Gattow, 1967) and the syntheic compounds CoSeO₃·2H₂O and NiSeO₃·2H₂O (Wildner, 1990).

The magnesium cation adopts a slightly distorted octahedral coordination with Mg—O distances typical of other magnesium selenites (Mueller & Unterweide, 1996; Kohn & Inoue, 1976). The bond valence sum (BVS; Brown, 1996) for Mg of 2.04 is close to the expected value of 2.00. O4 and O5 are water molecules and have a significant role in hydrogen bonding.

The SeO₃ unit adopts its usual pyramidal coordination (Hawthorne & Groat, 1987; Harrison, 1999) with BVS for Se = 4.09 (expected 4.00).

The MgO₆ octahedra form edge sharing, Mg₂O₁₀H₈ pairs (Fig. 1), with each pair connected to six SeO₃ pyramids. Each SeO₃ unit links three octahedral pairs. When viewed down to [001] (Fig. 2), the octahedral pairs are situated at the unit-cell corners (UCC) and body centre (BC). This also shows the twisting of the BC Mg₂O₁₀H₈ pair relative to the UCC pairs.

Hydrogen bonding, which has been described in detail elsewhere (Wildner, 1990), completes the three-dimensional framework. All four H atoms are involved (Table 2). O4 is a donor, whilst O5 both donates and accepts hydrogen bonds.

S2. Experimental

Direct reaction of MgCO₃ (0.759 g, 9 mmol) and SeO₂ (1.333 g, 12 mmol) and 15 ml of water. The reactants were placed in a 23-ml-capacity sealed teflon-lined steel bomb in an oven at 413 K. The bomb was removed after 26 d and cooled over 3 h. Upon opening, the bomb was seen to contain a clear solution and very large (ca 1.5 × 0.5 × 0.5 mm maximum) white single crystals. The crystals were recovered by suction filtration and washing with water.

S3. Refinement

The highest difference peak is 0.71 Å from Se1 and the deepest difference hole is 0.71 Å from Se1.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SMART; data reduction: SMART); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and ATOMS (Shape Software, 1999); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Fragment of the MgSeO3·2H2O structure (50% displacement ellipsoids). H atoms are shown as white spheres. Symmetry codes as in Table 1, with the addition of (v) 1/2 + x, 3/2 - y, 1/2 + z and (vi) 1 + x, y, z.
	Fig. 2. Slice of MgSeO3·2H2O viewed down [001], with MgO6 groups represented as orange octahedra and Se (yellow) atoms represented by spheres of arbitrary radii.

(I)

Crystal data

MgSeO3·2H2O	Dx = 2.891 Mg m^−3
Mr = 187.30	Melting point: not measured K
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 6.4818 (3) Å	Cell parameters from 3192 reflections
b = 8.7975 (5) Å	θ = 3.6–32.5°
c = 7.6367 (4) Å	µ = 8.77 mm^−1
β = 98.753 (1)°	T = 293 K
V = 430.40 (4) Å^3	Chunk, colourless
Z = 4	0.52 × 0.18 × 0.15 mm
F(000) = 360.0

Data collection

Bruker SMART1000 CCD area-detector diffractometer	1545 independent reflections
Radiation source: fine-focus sealed tube	1426 reflections with I > σ(I)
Graphite monochromator	Rint = 0.030
area detector scans	θmax = 32.5°, θmin = 3.6°
Absorption correction: multi-scan (SADABS; Bruker, 1999)	h = −9→7
Tmin = 0.118, Tmax = 0.268	k = −13→12
4223 measured reflections	l = −10→11

Refinement

Refinement on F^2	Hydrogen site location: difference Fourier map
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.023	w = 1/[σ^2(Fo^2) + (0.0447P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.061	(Δ/σ)max = 0.001
S = 1.02	Δρmax = 0.92 e Å^−3
1545 reflections	Δρmin = −0.91 e Å^−3
81 parameters	Extinction correction: SHELXL (Sheldrick, 1997)
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.92 (4)
Secondary atom site location: difference Fourier map

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Se1	0.10275 (2)	0.651353 (16)	0.33744 (2)	0.00948 (8)
Mg1	0.35091 (10)	0.36063 (6)	0.51565 (9)	0.01057 (13)
O1	0.1707 (2)	0.82366 (15)	0.26329 (17)	0.0131 (2)
O2	−0.0423 (2)	0.69826 (16)	0.49487 (18)	0.0143 (2)
O3	0.32793 (19)	0.59188 (14)	0.46361 (18)	0.0126 (2)
O4	0.4218 (3)	0.14290 (15)	0.5808 (2)	0.0180 (3)
O5	0.3813 (2)	0.43340 (16)	0.79156 (19)	0.0167 (3)
H1	0.515 (9)	0.143 (4)	0.632 (6)	0.057 (15)*
H2	0.339 (7)	0.094 (5)	0.624 (5)	0.045 (10)*
H3	0.465 (5)	0.496 (3)	0.795 (4)	0.025 (7)*
H4	0.428 (5)	0.364 (3)	0.875 (4)	0.018 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Se1	0.01148 (11)	0.00824 (11)	0.00874 (11)	−0.00001 (5)	0.00159 (6)	−0.00054 (5)
Mg1	0.0122 (3)	0.0084 (3)	0.0113 (3)	0.00013 (18)	0.0024 (2)	0.00108 (18)
O1	0.0167 (6)	0.0108 (5)	0.0119 (6)	−0.0003 (4)	0.0029 (5)	0.0033 (4)
O2	0.0135 (6)	0.0172 (6)	0.0134 (5)	−0.0017 (4)	0.0054 (5)	−0.0022 (4)
O3	0.0124 (5)	0.0095 (5)	0.0157 (6)	0.0016 (4)	0.0013 (4)	0.0028 (4)
O4	0.0203 (7)	0.0118 (6)	0.0214 (7)	0.0010 (5)	0.0011 (6)	0.0045 (4)
O5	0.0202 (6)	0.0156 (6)	0.0144 (6)	−0.0013 (5)	0.0028 (5)	0.0025 (5)

Geometric parameters (Å, º)

Se1—O1	1.6996 (13)	Mg1—O3	2.0739 (13)
Se1—O2	1.6864 (13)	Mg1—O3^iii	2.1054 (14)
Se1—O3	1.7042 (12)	Mg1—O4	2.0144 (14)
Mg1—O1^i	2.1383 (15)	Mg1—O5	2.1822 (16)
Mg1—O2^ii	2.0559 (14)
O2—Se1—O1	102.72 (7)	O3^iii—Mg1—O1^i	91.11 (6)
O2—Se1—O3	101.22 (6)	O4—Mg1—O5	93.27 (6)
O1—Se1—O3	102.65 (6)	O2^ii—Mg1—O5	93.20 (6)
O4—Mg1—O2^ii	87.37 (7)	O3—Mg1—O5	83.71 (6)
O4—Mg1—O3	170.79 (7)	O3^iii—Mg1—O5	85.77 (6)
O2^ii—Mg1—O3	101.46 (6)	O1^i—Mg1—O5	171.54 (6)
O4—Mg1—O3^iii	89.10 (7)	Se1—O1—Mg1^iv	119.11 (7)
O2^ii—Mg1—O3^iii	176.26 (6)	Se1—O2—Mg1^ii	123.73 (7)
O3—Mg1—O3^iii	82.02 (5)	Se1—O3—Mg1	116.10 (7)
O4—Mg1—O1^i	94.54 (6)	Se1—O3—Mg1^iii	137.18 (7)
O2^ii—Mg1—O1^i	90.39 (6)	Mg1—O3—Mg1^iii	97.98 (5)
O3—Mg1—O1^i	88.07 (6)

Symmetry codes: (i) −x+1/2, y−1/2, −z+1/2; (ii) −x, −y+1, −z+1; (iii) −x+1, −y+1, −z+1; (iv) −x+1/2, y+1/2, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H1···O1^iii	0.67 (6)	2.09 (6)	2.743 (2)	165 (5)
O4—H2···O5^v	0.80 (4)	2.18 (4)	2.965 (2)	171 (4)
O5—H3···O1^vi	0.77 (3)	2.11 (3)	2.8734 (19)	171 (3)
O5—H4···O2^v	0.90 (3)	1.85 (3)	2.741 (2)	167 (3)

Symmetry codes: (iii) −x+1, −y+1, −z+1; (v) −x+1/2, y−1/2, −z+3/2; (vi) x+1/2, −y+3/2, z+1/2.