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The structure of barium chlorite hydrate, Ba(ClO2)2·3.5H2O, has been determined by single-crystal X-ray analysis at 150 K. The structure is monoclinic, space group C2/c, with Z = 8. It contains layers of Ba2+ cations coordinated by ClO2- anions and water mol­ecules. There are also solvate water mol­ecules involved only in hydrogen bonding of the layers. Three solvate water O atoms are on sites of twofold symmetry, while all other atoms are in general positions. The full coordination environment of the Ba2+ cation consists of ten O atoms belonging to six chlorites and three water mol­ecules, forming a bicapped square antiprism.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010500925X/sq1204sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010500925X/sq1204Isup2.hkl
Contains datablock I

Comment top

The anhydrous alkaline earth metal chlorites, Ca(ClO2)2, Sr(ClO2)2 and Ba(ClO2)2, were first investigated crystallographically by Riganti & Garrini (1960). Because these compounds were obtained as microcrystalline powders, only powder diffraction patterns were obtained, which were not indexed. These authors proposed that Ca(ClO2)2 and Sr(ClO2)2 are isomorphic and have pseudo-cubic cells with similar parameters. However, the complete structures of all anhydrous alkaline- arth metal chlorites are still unknown. They also reported that barium chlorite may form a hydrate with 3.5 H2O molecules (unlike Ca and Sr chlorites), but its crystal structure was not determined because of its very low stability.

The purpose of the present investigation was to obtain structural data for the title hydrate. As the crystal structures of only some chlorites have been determined to date, a new contribution to the crystal chemistry of these simple compounds seemed useful. The present paper continues our research on chlorous acid salts, which has included LiClO2 and KClO2 (Smolentsev & Naumov, 2005a) and the redetermined structure of NH4ClO2 (Smolentsev & Naumov, 2005b).

In the structure of Ba(ClO2)2·3.5H2O, the coordination sphere of the Ba2+ cation includes ten O atoms (Fig. 1). Seven of these belong to the chlorite anions and the other three to the H2O molecules. The resultant coordination is a distorted bicapped square antiprism. By sharing edges, the antiprisms form layers parallel to the bc plane (Fig. 2). The layers are stacked in such way that adjacent layers are shifted along the b axis by 1/2 a unit translation.

The structure contains both H2O molecules coordinated to the Ba2+ cations and solvate water molecules, which are involved only in hydrogen bonding of the layers. Non-coordinated water of crystallization has not been found in other hydrated chlorites studied so far, viz. NaClO2·3H2O (Tarimci & Schempp, 1975), Mg(ClO2)2·6H2O (Okuda et al., 1990; Marsh, 1991), Zn(ClO2)2·2H2O (Pakkanen, 1979) and La(ClO2)3·3H2O (Castellani Bisi, 1984), in which all H2O molecules are coordinated to the metal cations. In this regard, Mg(ClO2)2·6H2O is outstanding: the water molecules form the complex cation [Mg(H2O)6]2+, which is then hydrogen bonded to ClO2 anions. A layered structure is found in Zn(ClO2)2·2H2O, while the sodium salt contains chains, and both magnesium and lanthanum salts have three-dimensional frameworks. Unlike these other hydrated chlorites, the title compound has one more feature, i.e. two independent ClO2 groups with symmetry non-equivalent O atoms. Anions of the first type (O11—Cl1—O12) serve as tetradentate bridging ligands between the Ba2+ cations and are not included in the hydrogen-bond system. The O atoms of the second anion type (O21—Cl2—O22) have different environments. They are both coordinated to the same Ba2+ cation and involved in hydrogen bonding. However, atom O21 is also coordinated to the neighbouring cation and forms a hydrogen bond with only one coordinated H2O molecule within the layer, while atom O22 is hydrogen-bonded to two interlayer H2O molecules.

Due to the non-equivalence of the ClO2 anions, their geometric parameters are slightly different. Nevertheless, they are in good agreement with the values determined for other chlorites. Comparison can be made with the average Cl—O distance and O—Cl—O angle calculated from the corresponding values reported previously (Tarimci & Schempp, 1975; Tarimci et al., 1976; Pakkanen, 1979; Castellani Bisi, 1984; Okuda et al., 1990; Marsh, 1991; Smolentsev & Naumov, 2005a,b), which are 1.571 (14) Å and 110 (2)°, respectively.

Experimental top

The title compound appears as a thin crystalline film on the surface of a concentrated aqueous solution of barium chlorite during evaporation at room temperature. Thus, the main difficulty resides in selection of a crystal suitable for X-ray diffraction. It is also necessary to note that this hydrate is very unstable and without the mother solution it completely decomposes to the anhydrous salt, even in a few minutes. In contrast, at low temperatures the crystals are quite stable. Anhydrous Ba(ClO2)2 was previously synthesized by reacting an aqueous suspension of BaO2 with chlorine dioxide, followed by precipitation from solution by adding a 3:1 mixture of ethanol and diethyl ether. Unlike the hydrate, it is one of the most stable salts of chlorous acid.

Refinement top

The H atoms were located in difference electron-density maps and refined with O—H distances constrained to 0.82 (1) Å.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Bruker, 2004); program(s) used to refine structure: SHELXTL; molecular graphics: BS (Ozawa & Kang, 2004) and POV-RAY (Cason, 2002); software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. The coordination environment of the Ba2+ cation. Displacement ellipsoids are plotted at the 50% probability level. [Symmetry codes: (i) 1/2 − x, 1/2 − y, 1 − z; (ii) x, y, 1 + z; (iii) x, −y, 1/2 + z; (iv) 1/2 − x, 1/2 − y, 2 − z.]
[Figure 2] Fig. 2. A perspective packing diagram of the Ba(ClO2)2·3.5H2O structure, viewed along the c axis. Thin lines represent hydrogen bonds.
Barium chlorite hydrate top
Crystal data top
Ba(ClO2)2·3.5H2OF(000) = 1256
Mr = 335.30Dx = 2.797 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 3491 reflections
a = 18.4801 (5) Åθ = 2.3–33.5°
b = 13.5715 (4) ŵ = 5.65 mm1
c = 6.6904 (2) ÅT = 150 K
β = 108.364 (1)°Plate, colourless
V = 1592.52 (8) Å30.15 × 0.13 × 0.02 mm
Z = 8
Data collection top
Bruker Nonius X8Apex CCD area-detector
diffractometer
2821 independent reflections
Radiation source: fine-focus sealed tube2321 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.022
Detector resolution: 25 pixels mm-1θmax = 32.6°, θmin = 2.3°
ϕ scansh = 2727
Absorption correction: multi-scan
(SADABS; Bruker, 2004)
k = 2012
Tmin = 0.484, Tmax = 0.895l = 98
7807 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.020Hydrogen site location: difference Fourier map
wR(F2) = 0.051H atoms treated by a mixture of independent and constrained refinement
S = 1.05 w = 1/[σ2(Fo2) + (0.0234P)2]
where P = (Fo2 + 2Fc2)/3
2821 reflections(Δ/σ)max = 0.002
118 parametersΔρmax = 1.55 e Å3
16 restraintsΔρmin = 0.54 e Å3
Crystal data top
Ba(ClO2)2·3.5H2OV = 1592.52 (8) Å3
Mr = 335.30Z = 8
Monoclinic, C2/cMo Kα radiation
a = 18.4801 (5) ŵ = 5.65 mm1
b = 13.5715 (4) ÅT = 150 K
c = 6.6904 (2) Å0.15 × 0.13 × 0.02 mm
β = 108.364 (1)°
Data collection top
Bruker Nonius X8Apex CCD area-detector
diffractometer
2821 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2004)
2321 reflections with I > 2σ(I)
Tmin = 0.484, Tmax = 0.895Rint = 0.022
7807 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.02016 restraints
wR(F2) = 0.051H atoms treated by a mixture of independent and constrained refinement
S = 1.05Δρmax = 1.55 e Å3
2821 reflectionsΔρmin = 0.54 e Å3
118 parameters
Special details top

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 (Å2) top
xyzUiso*/Ueq
Ba10.255500 (6)0.124940 (7)0.754469 (15)0.00965 (4)
Cl10.35850 (3)0.12962 (3)0.34553 (8)0.01455 (10)
Cl20.09431 (2)0.03281 (3)0.35618 (7)0.01376 (9)
O110.30632 (8)0.19708 (9)0.4337 (2)0.0153 (3)
O120.30879 (8)0.05939 (10)0.1679 (2)0.0159 (3)
O210.17568 (7)0.04695 (10)0.3315 (2)0.0152 (3)
O220.08660 (8)0.11048 (10)0.5240 (2)0.0171 (3)
O1W0.33040 (8)0.30117 (10)0.9767 (2)0.0160 (3)
H110.3767 (6)0.2946 (16)1.039 (3)0.019*
H120.3287 (14)0.3467 (14)0.892 (3)0.019*
O2W0.41673 (9)0.11535 (10)0.8783 (3)0.0170 (3)
H210.4392 (13)0.1641 (13)0.852 (3)0.020*
H220.4322 (13)0.0721 (13)0.817 (3)0.020*
O3W0.50000.25403 (15)0.75000.0186 (4)
H30.5267 (12)0.2910 (14)0.841 (3)0.022*
O4W0.50000.03007 (16)0.25000.0187 (4)
H40.4741 (13)0.0624 (15)0.149 (3)0.022*
O5W0.50000.30284 (17)0.25000.0280 (5)
H50.4802 (15)0.3359 (17)0.321 (4)0.034*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ba10.01155 (6)0.00886 (7)0.00868 (6)0.00021 (3)0.00339 (4)0.00003 (3)
Cl10.01172 (19)0.0168 (2)0.0147 (2)0.00043 (15)0.00347 (16)0.00231 (16)
Cl20.01144 (18)0.0153 (2)0.01436 (19)0.00079 (15)0.00388 (15)0.00230 (17)
O110.0201 (7)0.0116 (6)0.0165 (7)0.0035 (5)0.0092 (5)0.0004 (5)
O120.0200 (7)0.0145 (7)0.0128 (6)0.0017 (5)0.0047 (5)0.0026 (5)
O210.0099 (6)0.0182 (7)0.0183 (7)0.0018 (5)0.0056 (5)0.0023 (6)
O220.0169 (7)0.0191 (7)0.0157 (7)0.0022 (5)0.0059 (6)0.0041 (6)
O1W0.0136 (6)0.0159 (7)0.0175 (7)0.0005 (5)0.0034 (5)0.0010 (6)
O2W0.0155 (7)0.0162 (8)0.0198 (8)0.0003 (5)0.0063 (6)0.0008 (6)
O3W0.0217 (10)0.0134 (10)0.0187 (10)0.0000.0036 (8)0.000
O4W0.0195 (10)0.0206 (11)0.0138 (10)0.0000.0023 (8)0.000
O5W0.0353 (13)0.0255 (13)0.0328 (13)0.0000.0247 (11)0.000
Geometric parameters (Å, º) top
Ba1—O12i2.7741 (14)Cl2—O211.5753 (13)
Ba1—O112.7781 (13)Cl2—O221.5787 (15)
Ba1—O11ii2.7960 (13)O1W—H110.829 (9)
Ba1—O12iii2.8148 (13)O1W—H120.831 (12)
Ba1—O2W2.8330 (15)O2W—H210.828 (12)
Ba1—O21iii2.8918 (13)O2W—H220.817 (12)
Ba1—O1W2.9241 (14)O3W—H3v0.822 (12)
Ba1—O1Wiv2.9254 (14)O3W—H30.822 (12)
Ba1—O212.9450 (14)O4W—H4vi0.823 (12)
Ba1—O223.0210 (15)O4W—H40.823 (12)
Cl1—O111.5728 (13)O5W—H5vi0.820 (12)
Cl1—O121.5737 (14)O5W—H50.820 (12)
O12i—Ba1—O11141.55 (4)O11—Ba1—O2164.73 (4)
O12i—Ba1—O11ii133.80 (4)O11ii—Ba1—O2182.42 (4)
O11—Ba1—O11ii62.44 (4)O12iii—Ba1—O2165.46 (4)
O12i—Ba1—O12iii83.27 (3)O2W—Ba1—O21115.25 (4)
O11—Ba1—O12iii85.92 (4)O21iii—Ba1—O2175.65 (3)
O11ii—Ba1—O12iii142.66 (4)O1W—Ba1—O21142.76 (4)
O12i—Ba1—O2W71.55 (4)O1Wiv—Ba1—O21120.62 (4)
O11—Ba1—O2W70.22 (4)O12i—Ba1—O22118.25 (4)
O11ii—Ba1—O2W114.47 (4)O11—Ba1—O22100.07 (4)
O12iii—Ba1—O2W67.38 (4)O11ii—Ba1—O2267.44 (4)
O12i—Ba1—O21iii66.69 (4)O12iii—Ba1—O22102.09 (4)
O11—Ba1—O21iii137.53 (4)O2W—Ba1—O22165.61 (5)
O11ii—Ba1—O21iii128.18 (4)O21iii—Ba1—O2262.33 (4)
O12iii—Ba1—O21iii63.31 (4)O1W—Ba1—O22124.07 (4)
O2W—Ba1—O21iii117.35 (4)O1Wiv—Ba1—O2270.28 (4)
O12i—Ba1—O1W78.04 (4)O21—Ba1—O2250.36 (4)
O11—Ba1—O1W83.32 (4)O11—Cl1—O12110.77 (8)
O11ii—Ba1—O1W65.36 (4)O21—Cl2—O22107.22 (8)
O12iii—Ba1—O1W133.74 (4)Ba1—O1W—H11114.5 (15)
O2W—Ba1—O1W66.62 (4)Ba1iv—O1W—H11113.9 (15)
O21iii—Ba1—O1W139.06 (4)Ba1—O1W—H12110.6 (17)
O12i—Ba1—O1Wiv65.67 (4)Ba1iv—O1W—H12104.6 (17)
O11—Ba1—O1Wiv137.32 (4)H11—O1W—H12103 (2)
O11ii—Ba1—O1Wiv75.92 (4)Ba1—O2W—H21116.9 (17)
O12iii—Ba1—O1Wiv136.38 (4)Ba1—O2W—H22112.9 (17)
O2W—Ba1—O1Wiv124.09 (4)H21—O2W—H22101 (2)
O21iii—Ba1—O1Wiv76.17 (4)H3v—O3W—H3105 (3)
O1W—Ba1—O1Wiv70.64 (4)H4vi—O4W—H4116 (3)
O12i—Ba1—O21139.10 (4)H5vi—O5W—H5113 (4)
Symmetry codes: (i) x, y, z+1; (ii) x+1/2, y+1/2, z+1; (iii) x, y, z+1/2; (iv) x+1/2, y+1/2, z+2; (v) x+1, y, z+3/2; (vi) x+1, y, z+1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1W—H11···O5Wi0.83 (1)2.27 (1)3.0913 (14)168 (2)
O1W—H12···O21ii0.83 (1)2.06 (1)2.8929 (19)176 (2)
O2W—H21···O3W0.83 (1)1.92 (1)2.735 (2)166 (2)
O2W—H22···O4Wvii0.82 (1)2.01 (1)2.798 (2)161 (2)
O3W—H3···O22viii0.82 (1)1.91 (1)2.730 (2)173 (2)
O4W—H4···O2Wix0.82 (1)1.92 (1)2.7352 (18)168 (2)
O5W—H5···O22ii0.82 (1)1.98 (1)2.7851 (17)166 (3)
Symmetry codes: (i) x, y, z+1; (ii) x+1/2, y+1/2, z+1; (vii) x+1, y, z+1; (viii) x+1/2, y+1/2, z+1/2; (ix) x, y, z1.

Experimental details

Crystal data
Chemical formulaBa(ClO2)2·3.5H2O
Mr335.30
Crystal system, space groupMonoclinic, C2/c
Temperature (K)150
a, b, c (Å)18.4801 (5), 13.5715 (4), 6.6904 (2)
β (°) 108.364 (1)
V3)1592.52 (8)
Z8
Radiation typeMo Kα
µ (mm1)5.65
Crystal size (mm)0.15 × 0.13 × 0.02
Data collection
DiffractometerBruker Nonius X8Apex CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Bruker, 2004)
Tmin, Tmax0.484, 0.895
No. of measured, independent and
observed [I > 2σ(I)] reflections
7807, 2821, 2321
Rint0.022
(sin θ/λ)max1)0.757
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.020, 0.051, 1.05
No. of reflections2821
No. of parameters118
No. of restraints16
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)1.55, 0.54

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SAINT, SHELXTL (Bruker, 2004), SHELXTL, BS (Ozawa & Kang, 2004) and POV-RAY (Cason, 2002).

Selected geometric parameters (Å, º) top
Ba1—O12i2.7741 (14)Ba1—O223.0210 (15)
Ba1—O112.7781 (13)Cl1—O111.5728 (13)
Ba1—O2W2.8330 (15)Cl1—O121.5737 (14)
Ba1—O1W2.9241 (14)Cl2—O211.5753 (13)
Ba1—O212.9450 (14)Cl2—O221.5787 (15)
O11—Cl1—O12110.77 (8)O21—Cl2—O22107.22 (8)
Symmetry code: (i) x, y, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1W—H11···O5Wi0.830 (9)2.274 (10)3.0913 (14)168 (2)
O1W—H12···O21ii0.831 (12)2.063 (13)2.8929 (19)176 (2)
O2W—H21···O3W0.828 (12)1.924 (13)2.735 (2)166 (2)
O2W—H22···O4Wiii0.817 (12)2.012 (14)2.798 (2)161 (2)
O3W—H3···O22iv0.822 (12)1.913 (13)2.730 (2)173 (2)
O4W—H4···O2Wv0.823 (12)1.924 (13)2.7352 (18)168 (2)
O5W—H5···O22ii0.820 (12)1.983 (14)2.7851 (17)166 (3)
Symmetry codes: (i) x, y, z+1; (ii) x+1/2, y+1/2, z+1; (iii) x+1, y, z+1; (iv) x+1/2, y+1/2, z+1/2; (v) x, y, z1.
 

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