A new polymorph of barium chloro­anilate trihydrate

Single crystals of a new polymorph of the title compound, barium(II) 3,6-di­chloro-2,5-di­hydroxy-1,4-benzo­quinone tri­hydrate, Ba²⁺·C₆Cl₂O₄^2-·3H₂O, have been grown in sodium metasilicate gel. Each Ba²⁺ cation is coordinated by eight O atoms. The Ba²⁺ cations are bridged by an O atom of a ligand around the centre of symmetry at Wyckoff position 4a and by the O atom of a water mol­ecule around the centre of symmetry at Wyckoff position 4b, forming a sheet parallel to the (100) plane. Loose contacts are found around one of the water mol­ecules, as observed in the Cmca form.

S1. Comment

It has been reported that barium chloranilate trihydrate (barium 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone trihydrate) and its 3,6-dibromo analogue crystallize in the orthorhombic space group Cmca (Robel & Weiss, 1986). In the crystal there are water molecules which may be removed reversibly (Robel & Weiss, 1986). The existence of loosely bound water molecules has also been reported for the crystal of copper(II) chloranilate trihydrate (Cueto et al., 1992). The presence of such water molecules is of interest from the point of view of topochemical and/or surface reactions in the crystalline state, especially because barium chloranilate particles are used in a flow-injection analysis method for the spectrophotometric determination of sulfate ion concentration in natural water (Ueno et al., 1992). We report here the structure of a new polymorph of barium chloranilate trihydrate, (I). \sch

The bond lengths within the chloranilate anion are characteristic of the double π system, as exemplified by the long bond lengths for C1—C2 and C4—C5 [1.553 (10) and 1.561 (10) Å, respectively; Benchekroun & Savariault, 1995). Each Ba cation is coordinated by eight O atoms, with the Ba···O distances in the range 2.719 (5)–2.934 (6) Å (Figs. 1 and 2; Table 1). The Ba cations related by a centre of symmetry at Wyckoff position 4 b are bridged by O4 and those related by a centre of symmetry at Wyckoff position 4a are bridged by O7^vi [symmetry code: (vi) 1/2 - x, 1 - y, 1/2 + z], forming a sheet parallel to the (100) plane. In this sheet, the anions related by a twofold screw axis along c overlap and are nearly parallel, with short C···C contacts in the range 3.266 (10)–3.368 (10) Å (Table 2). The sheets are stacked along a, forming rather short Cl···Cl contacts and a rather long contact between O6 and O5^vi of the water molecules (Table 2). Atom O6 possibly takes part in a weak hydrogen bond, because the angle of 90.9 (2)° for O5^vi···O6···O7ⁱⁱ [symmetry code: (ii) 1 - x, 1 - y, 1 - z] satisfies a geometrical requirement for hydrogen bonding. Atom O2 does not participate in coordination with the cation, in contrast with the case of the Cmca form, while it makes rather short O···O contacts with two water molecules (Table 2). Query symmops.

The space group Pbca of (I) is a non-isomorphic subgroup of Cmca [Z = 8, a = 16.901 (3), b = 6.5234 (8) and c = 19.262 (2) Å, and V = 2123.7 ų; Robel & Weiss, 1986]. The unit cell volume of (I) is smaller than that of the Cmca form by 0.9%. There is a similarity in the arrangements of the anions in the sheet for both forms, i.e., the arrangement of the anion related by a c glide plane in (I) corresponds to that related by a b glide plane perpendicular to the a axis in the Cmca form. The arrangement of anions related by a twofold screw axis is seen in the sheets of both forms, being along the b axis for (I) and along the a axis for the Cmca form. In both forms, the sheets related by a glide plane are stacked, along an a glide plane in (I) and a c glide plane in the Cmca form. Thus, the a, b and c axes of (I) correspond to the c, a and b axes, respectively, of the Cmca form.

Our measurement of differential scanning calorimetry performed for (I) in the temperature range 273–443 K showed broad endothermic anomalies at around 363 and 403 K on heating. Since these thermal anomalies are irreversible, they are attributable to dehydration. This dehydration phenomenon corresponds to that observed at temperatures of 313–363 K and 368–383 K for the bromo analogue from thermogravimetry measurements (Robel & Weiss, 1986). This shows that the water molecules in (I) are more tightly bound than in the bromo analogue. The lower and higher temperature regions have been assigned to the hydration of one and two water molecules per formula unit, respectively (Robel & Weiss, 1986).

S2. Experimental

The formation of crystals of (I) was accomplished by the reaction of BaCl₂ and C₆H₂Cl₂O₄ in sodium metasilicate gel. Chloranilic acid was dissolved in NaOH aqueous solution in equal concentrations of 0.1 M. The solution (20 ml) was mixed with 0.5 M Na₂SiO₃·9H₂O solution (20 ml). The mixed solution was placed in a test tube of length 200 mm and inner diameter 30 mm. For gelation, 2 M acetic acid (about 10 ml) was then added to the solution. The gelation period was 24 h. After the gel had set, 0.1 M BaCl₂·2H₂O solution (30 ml) was carefully layered on the top of the set gel. The test tube was kept at 313 K for 30 d. Dark-red prismatic crystals of (I) were obtained in the gel.

S3. Refinement

The H atoms of the water molecules were not found in a difference Fourier map and were not included in the refinement. The maximum Δρ was 2.60 e Å^-3 at 0.74 Å from Ba1. Calculations were carried out at the Centre of Instrumental Analysis, Okayama University.

Computing details

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1990); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN for Windows (Molecular Structure corporation, 1997-1999); program(s) used to solve structure: DIRDIF92 (Beurskens et al., 1992); program(s) used to refine structure: TEXSAN for Windows; molecular graphics: ORTEP-3 for Windows (Farrugia, 1997).

Figures

	Fig. 1. ORTEP-3 for Windows (Farrugia, 1997) drawing of the asymmetric unit of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and the water molecules are not shown.
	Fig. 2. The arrangement of the chloroanilate anions and the coordination around the Ba cations in (I), viewed down the a axis. The arrangement related by an a glide plane is omitted for clarity. Symmetry codes are given in Table 1.

(I)

Crystal data

[Ba(C6Cl2O4)]·3H2O	F(000) = 1504
Mr = 398.35	Dx = 2.514 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 25 reflections
a = 17.258 (4) Å	θ = 10.2–11.0°
b = 17.614 (4) Å	µ = 4.29 mm^−1
c = 6.925 (2) Å	T = 298 K
V = 2105.1 (8) Å^3	Prismatic, dark red
Z = 8	0.46 × 0.21 × 0.09 mm

Data collection

Rigaku AFC-5R diffractometer	2110 reflections with I > 0.5σ(I)
Radiation source: Rigaku rotating anode	Rint = 0.023
Graphite monochromator	θmax = 27.5°, θmin = 4.0°
ω/2θ scans	h = −2→22
Absorption correction: ψ scans (North et al., 1968)	k = −2→22
Tmin = 0.351, Tmax = 0.680	l = −1→8
3563 measured reflections	3 standard reflections every 97 reflections
2415 independent reflections	intensity decay: none

Refinement

Refinement on F	0 constraints
Least-squares matrix: full	H-atom parameters not defined
R[F^2 > 2σ(F^2)] = 0.060	Weighting scheme based on measured s.u.'s w = 1/[σ^2(Fo) + 0.00063|Fo|^2]
wR(F^2) = 0.065	(Δ/σ)max < 0.001
S = 1.61	Δρmax = 2.60 e Å^−3
2110 reflections	Δρmin = −1.78 e Å^−3
146 parameters	Extinction correction: Zachariasen (1967), equ(3) Acta Cryst. (1968) A24, p213.
0 restraints	Extinction coefficient: 2.14 (7) × 10^-6

Special details

Experimental. The scan width was (1.00 + 0.30tanθ)° with an ω scan speed of 4° per min (up to 2 scans to achieve I/σ(I) > 10). Stationary background counts were recorded at each end of the scan, and the scan time:background time ratio was 2:1.

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

	x	y	z	Uiso*/Ueq
Ba1	0.424214 (18)	0.543160 (16)	0.25324 (5)	0.01760 (10)
Cl1	0.24079 (8)	0.27894 (8)	0.2144 (2)	0.0227 (3)
Cl2	0.58369 (8)	0.28470 (8)	0.5382 (2)	0.0226 (4)
O1	0.4889 (3)	0.1502 (2)	0.4384 (6)	0.0240 (11)
O2	0.3428 (3)	0.1458 (2)	0.3072 (7)	0.0264 (11)
O3	0.3411 (3)	0.4124 (2)	0.2794 (6)	0.0236 (11)
O4	0.4814 (2)	0.4171 (2)	0.4422 (6)	0.0210 (10)
O5	0.2829 (3)	0.5933 (3)	0.1033 (7)	0.0344 (13)
O6	0.3102 (3)	0.5448 (2)	0.5604 (8)	0.0365 (14)
O7	0.5831 (3)	0.5065 (2)	0.1349 (7)	0.0251 (11)
C1	0.4562 (3)	0.2122 (3)	0.4117 (8)	0.0174 (13)
C2	0.3717 (3)	0.2095 (3)	0.3346 (8)	0.0165 (13)
C3	0.3351 (3)	0.2795 (3)	0.2986 (7)	0.0150 (12)
C4	0.3706 (3)	0.3503 (3)	0.3196 (8)	0.0162 (13)
C5	0.4535 (3)	0.3520 (3)	0.4099 (8)	0.0169 (13)
C6	0.4897 (3)	0.2838 (3)	0.4477 (8)	0.0173 (13)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ba1	0.0124 (2)	0.0195 (2)	0.0208 (2)	−0.00157 (11)	−0.00172 (16)	0.00032 (13)
Cl1	0.0099 (6)	0.0292 (6)	0.0292 (7)	−0.0012 (5)	−0.0046 (6)	0.0001 (6)
Cl2	0.0086 (6)	0.0309 (7)	0.0284 (8)	0.0012 (6)	−0.0032 (6)	−0.0031 (6)
O1	0.019 (2)	0.0230 (19)	0.030 (2)	0.0059 (17)	0.002 (2)	−0.0022 (17)
O2	0.020 (2)	0.021 (2)	0.039 (3)	−0.0007 (17)	−0.005 (2)	−0.0038 (18)
O3	0.016 (2)	0.0201 (19)	0.034 (3)	0.0000 (15)	−0.0049 (19)	0.0028 (17)
O4	0.014 (2)	0.0221 (19)	0.027 (2)	−0.0021 (16)	−0.0109 (19)	−0.0007 (16)
O5	0.022 (3)	0.049 (3)	0.032 (3)	0.013 (2)	−0.002 (2)	0.001 (2)
O6	0.028 (3)	0.037 (3)	0.045 (3)	0.004 (2)	0.006 (3)	−0.004 (2)
O7	0.020 (2)	0.025 (2)	0.031 (2)	−0.0024 (17)	0.002 (2)	−0.0002 (18)
C1	0.019 (3)	0.021 (3)	0.012 (3)	0.001 (2)	0.008 (2)	−0.0019 (19)
C2	0.013 (3)	0.021 (3)	0.015 (3)	0.000 (2)	0.003 (2)	−0.001 (2)
C3	0.011 (3)	0.021 (2)	0.013 (2)	−0.001 (2)	−0.000 (2)	−0.003 (2)
C4	0.009 (3)	0.021 (3)	0.018 (3)	0.004 (2)	0.001 (2)	−0.004 (2)
C5	0.009 (3)	0.023 (3)	0.018 (3)	−0.001 (2)	0.006 (2)	0.003 (2)
C6	0.011 (3)	0.027 (3)	0.014 (3)	−0.000 (2)	−0.003 (2)	0.000 (2)

Geometric parameters (Å, º)

Ba1—O1^i	2.750 (5)	O1—C1	1.244 (8)
Ba1—O3	2.719 (5)	O2—C2	1.242 (8)
Ba1—O4	2.760 (5)	O3—C4	1.239 (8)
Ba1—O4^ii	2.755 (5)	O4—C5	1.263 (8)
Ba1—O5	2.794 (6)	C1—C2	1.553 (10)
Ba1—O6	2.898 (7)	C1—C6	1.410 (10)
Ba1—O7	2.934 (6)	C2—C3	1.407 (10)
Ba1—O7^iii	2.829 (6)	C3—C4	1.397 (10)
Cl1—C3	1.729 (7)	C4—C5	1.561 (10)
Cl2—C6	1.738 (7)	C5—C6	1.379 (9)
O2···O5^iv	2.750 (8)	C5···O2^vii	3.349 (9)
O2···O7^v	2.795 (7)	C6···C1^vii	3.266 (10)
O1···O7^v	2.865 (7)	C6···C2^vii	3.368 (10)
O6···O5^vi	2.931 (9)	C2···C3^vii	3.280 (10)
O6···O7^ii	2.943 (9)	Cl2···Cl1^viii	3.228 (3)
O1···C5^vii	3.322 (9)	Cl2···Cl1^ix	3.398 (3)
O1^i—Ba1—O3	154.20 (17)	O7—Ba1—O7^iii	73.05 (18)
O1^i—Ba1—O4	125.82 (16)	Ba1—O4—Ba1^ii	111.70 (16)
O1^i—Ba1—O4^ii	82.69 (16)	Ba1—O7—Ba1^iii	106.95 (18)
O1^i—Ba1—O5	94.56 (17)	O5^iv—O2—O7^v	98.0 (2)
O1^i—Ba1—O6	135.85 (16)	O5^vi—O6—O7^ii	90.9 (2)
O1^i—Ba1—O7	60.42 (15)	O2^x—O5—O6^xi	84.1 (2)
O1^i—Ba1—O7^iii	77.18 (16)	O2^i—O7—O6^ii	83.1 (2)
O3—Ba1—O4	58.39 (15)	O1^i—O7—O2^i	56.5 (2)
O3—Ba1—O4^ii	118.44 (15)	O1—C1—C2	116.8 (6)
O3—Ba1—O5	80.34 (17)	O1—C1—C6	125.0 (7)
O3—Ba1—O6	66.51 (16)	C2—C1—C6	118.3 (6)
O3—Ba1—O7	109.00 (15)	O2—C2—C1	117.2 (6)
O3—Ba1—O7^iii	77.15 (16)	O2—C2—C3	125.7 (7)
O4—Ba1—O4^ii	68.30 (16)	C1—C2—C3	117.1 (6)
O4—Ba1—O5	137.99 (17)	Cl1—C3—C2	118.6 (5)
O4—Ba1—O6	84.43 (16)	Cl1—C3—C4	116.9 (6)
O4—Ba1—O7	67.74 (15)	C2—C3—C4	124.5 (6)
O4—Ba1—O7^iii	102.55 (15)	O3—C4—C3	125.7 (7)
O4^ii—Ba1—O5	136.05 (16)	O3—C4—C5	116.7 (6)
O4^ii—Ba1—O6	80.60 (18)	C3—C4—C5	117.5 (6)
O4^ii—Ba1—O7	73.58 (16)	O4—C5—C4	116.0 (6)
O4^ii—Ba1—O7^iii	146.33 (16)	O4—C5—C6	125.7 (7)
O5—Ba1—O6	71.16 (18)	C4—C5—C6	118.3 (6)
O5—Ba1—O7	141.40 (17)	Cl2—C6—C1	117.1 (5)
O5—Ba1—O7^iii	72.89 (17)	Cl2—C6—C5	118.9 (6)
O6—Ba1—O7	147.34 (18)	C1—C6—C5	124.0 (7)
O6—Ba1—O7^iii	132.07 (18)
Cl1—C3—C2—O2	1.7 (10)	O2—C2—C3—C4	−175.9 (8)
Cl1—C3—C2—C1	−179.5 (5)	O3—C4—C3—C2	176.0 (7)
Cl1—C3—C4—O3	−1.6 (10)	O3—C4—C5—O4	3.2 (10)
Cl1—C3—C4—C5	175.6 (5)	O3—C4—C5—C6	−176.8 (7)
Cl2—C6—C1—O1	−0.6 (10)	O4—C5—C4—C3	−174.2 (6)
Cl2—C6—C1—C2	178.8 (5)	O4—C5—C6—C1	179.2 (7)
Cl2—C6—C5—O4	−2.9 (10)	C1—C2—C3—C4	2.9 (10)
Cl2—C6—C5—C4	177.2 (5)	C1—C6—C5—C4	−0.7 (10)
O1—C1—C2—O2	0.7 (10)	C2—C1—C6—C5	−3.2 (10)
O1—C1—C2—C3	−178.2 (6)	C2—C3—C4—C5	−6.8 (10)
O1—C1—C6—C5	177.3 (7)	C3—C2—C1—C6	2.3 (9)
O2—C2—C1—C6	−178.8 (7)	C3—C4—C5—C6	5.7 (10)

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