Sodium selenite, Na₂SeO₃

The title compound, Na₂SeO₃, contains two crystallograph­ically different Na⁺ ions, Na1 and Na2. Na1 is coordinated by four monodentate and one chelating SeO₃^2- group, while two monodentate and two chelating selenite ions are attached to Na2. For both Na⁺ ions, a strongly distorted octahedral coordination results. The [NaO₆] octahedra are linked via common edges. The SeO₃^2- ion shows a pyramidal shape, due to the lone electron pair of the Se atom.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Se-O) = 0.004 Å
• R factor = 0.031
• wR factor = 0.072
• Data-to-parameter ratio = 14.7

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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Computing details

Data collection: X-AREA (Stoe & Cie, 2001); cell refinement: X-AREA; data reduction: X-RED (Stoe & Cie, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2001); software used to prepare material for publication: SHELXL97.

disodium oxoselenate(IV)

Crystal data

Na2SeO3	F(000) = 320
Mr = 172.94	Dx = 3.413 Mg m^−3
Monoclinic, P21/c	Melting point: not measured K
Hall symbol: -P 2ybc	Mo Kα radiation, λ = 0.71073 Å
a = 4.9089 (13) Å	Cell parameters from 2000 reflections
b = 10.0072 (15) Å	θ = 3.0–28.0°
c = 6.8535 (15) Å	µ = 11.22 mm^−1
β = 91.11 (3)°	T = 293 K
V = 336.61 (13) Å^3	Column, colourless
Z = 4	0.25 × 0.17 × 0.11 mm

Data collection

Stoe IPDS-I diffractometer	808 independent reflections
Radiation source: fine-focus sealed tube	571 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.069
Detector resolution: not measured pixels mm^-1	θmax = 28.1°, θmin = 3.6°
oscillation scans	h = −6→6
Absorption correction: numerical via crystal shape optimization (X-SHAPE; Stoe & Cie, 1999)	k = −12→13
Tmin = 0.115, Tmax = 0.291	l = −9→8
3856 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Primary atom site location: structure-invariant direct methods
R[F^2 > 2σ(F^2)] = 0.031	Secondary atom site location: difference Fourier map
wR(F^2) = 0.072	w = 1/[σ^2(Fo^2) + (0.0349P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max < 0.001
808 reflections	Δρmax = 0.90 e Å^−3
55 parameters	Δρmin = −1.32 e Å^−3

Special details

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. 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.

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

	x	y	z	Uiso*/Ueq
Na1	0.2431 (4)	0.7470 (3)	0.4151 (3)	0.0190 (5)
Na2	0.7397 (4)	0.9133 (3)	0.6526 (3)	0.0179 (5)
Se1	0.77619 (10)	0.91566 (6)	0.18757 (7)	0.01143 (17)
O1	0.7517 (7)	1.0567 (4)	0.3253 (6)	0.0163 (8)
O2	0.7152 (8)	0.7920 (4)	0.3523 (5)	0.0169 (9)
O3	1.1158 (7)	0.8996 (4)	0.1645 (5)	0.0169 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Na1	0.0183 (12)	0.0174 (11)	0.0213 (11)	−0.0018 (10)	0.0037 (8)	0.0041 (12)
Na2	0.0159 (11)	0.0148 (11)	0.0229 (11)	−0.0013 (10)	0.0011 (8)	−0.0036 (11)
Se1	0.0112 (2)	0.0095 (3)	0.0136 (2)	0.0005 (3)	0.00239 (15)	−0.0002 (3)
O1	0.0131 (19)	0.015 (2)	0.0213 (18)	0.0000 (16)	0.0039 (14)	−0.0016 (17)
O2	0.019 (2)	0.013 (2)	0.019 (2)	0.0006 (16)	0.0035 (16)	0.0024 (15)
O3	0.0168 (19)	0.016 (2)	0.0184 (18)	0.0017 (17)	0.0049 (14)	0.0016 (16)

Geometric parameters (Å, º)

Na1—O3^i	2.347 (4)	Na2—O2	2.391 (5)
Na1—O3^ii	2.373 (4)	Na2—O1^iv	2.438 (4)
Na1—O2	2.408 (4)	Na2—O2^vii	2.473 (5)
Na1—O1^iii	2.518 (5)	Na2—O1^vi	2.516 (4)
Na1—O1^iv	2.650 (4)	Na2—O1	2.664 (4)
Na1—O2^ii	2.657 (5)	Na2—Se1^vi	3.110 (2)
Na1—Se1^ii	3.224 (2)	Na2—Se1	3.196 (2)
Na1—Na2	3.348 (3)	Na2—Se1^iv	3.263 (2)
Na1—Se1^iii	3.390 (3)	Na2—Se1^vii	3.306 (3)
Na1—Se1^i	3.400 (2)	Se1—O3	1.685 (4)
Na1—Na2^ii	3.418 (4)	Se1—O1	1.703 (4)
Na1—Na2^v	3.427 (3)	Se1—O2	1.705 (4)
Na2—O3^vi	2.354 (5)
O3^i—Na1—O3^ii	149.2 (2)	O2—Na2—O1^iv	94.74 (15)
O3^i—Na1—O2	121.21 (16)	O3^vi—Na2—O2^vii	112.55 (15)
O3^ii—Na1—O2	89.49 (14)	O2—Na2—O2^vii	92.99 (12)
O3^i—Na1—O1^iii	90.58 (16)	O1^iv—Na2—O2^vii	90.51 (14)
O3^ii—Na1—O1^iii	91.10 (15)	O3^vi—Na2—O1^vi	65.47 (13)
O2—Na1—O1^iii	90.14 (14)	O2—Na2—O1^vi	98.37 (15)
O3^i—Na1—O1^iv	88.48 (14)	O1^iv—Na2—O1^vi	164.4 (2)
O3^ii—Na1—O1^iv	90.43 (15)	O2^vii—Na2—O1^vi	97.16 (16)
O2—Na1—O1^iv	89.12 (14)	O3^vi—Na2—O1	90.50 (16)
O1^iii—Na1—O1^iv	178.29 (18)	O2—Na2—O1	63.27 (13)
O3^i—Na1—O2^ii	87.20 (13)	O1^iv—Na2—O1	91.38 (14)
O3^ii—Na1—O2^ii	62.04 (13)	O2^vii—Na2—O1	156.25 (16)
O2—Na1—O2^ii	151.44 (19)	O1^vi—Na2—O1	87.04 (15)
O1^iii—Na1—O2^ii	92.55 (14)	O3—Se1—O1	102.22 (18)
O1^iv—Na1—O2^ii	88.84 (14)	O3—Se1—O2	100.35 (18)
O3^vi—Na2—O2	150.65 (17)	O1—Se1—O2	102.66 (18)
O3^vi—Na2—O1^iv	99.06 (16)

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