Hexaaqua­chromium(III) pyridine-2,4,6-tricarboxyl­ate dihydrate

Mariam, I.; Rauf, A.; Sharif, S.; Khan, I.U.; Ng, S.W.

doi:10.1107/S1600536810023767

metal-organic compounds

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ISSN: 2056-9890

Volume 66| Part 7| July 2010| Page m843

doi:10.1107/S1600536810023767

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Hexaaquachromium(III) pyridine-2,4,6-tricarboxylate dihydrate

Irfana Mariam,^a Abdul Rauf,^a Shahzad Sharif,^a Islam Ullah Khan ^a and Seik Weng Ng ^b ^*

^aDepartment of Chemistry, Government College University, 54000 Lahore, Pakistan, and ^bDepartment of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
^*Correspondence e-mail: seikweng@um.edu.my

(Received 10 June 2010; accepted 19 June 2010; online 26 June 2010)

The chromium(III) atom in the title salt, [Cr(H₂O)₆](C₈H₂NO₆)·2H₂O, has an octahedral coordination geometry. In the crystal, the cation, anion and uncoordinated water molecules, both of which are disordered over two positions in a 1:1 ratio, are linked by O—H⋯O hydrogen bonds.

Related literature

For the crystal structure of hexaaquachromium(III) acetate, see: Eshel & Bino (2001 ). For the synthesis of 2,4,6-pyridinetricarboxylic acid, see: Syper et al. (1980 ).

Experimental

Crystal data

[Cr(H₂O)₆](C₈H₂NO₆)·2H₂O
M_r = 404.23
Monoclinic, P 2₁ /c
a = 7.8610 (3) Å
b = 16.9269 (5) Å
c = 11.6823 (4) Å
β = 100.649 (1)°
V = 1527.70 (9) Å³
Z = 4
Mo Kα radiation
μ = 0.83 mm⁻¹
T = 293 K
0.11 × 0.07 × 0.05 mm

Data collection

Bruker Kappa APEXII diffractometer
Absorption correction: multi-scan (SADABS; Sheldrick, 1996 ) T_min = 0.915, T_max = 0.960
14299 measured reflections
3507 independent reflections
2486 reflections with I > 2σ(I)
R_int = 0.060

Refinement

R[F² > 2σ(F²)] = 0.050
wR(F²) = 0.152
S = 0.98
3507 reflections
235 parameters
H-atom parameters constrained
Δρ_max = 0.64 e Å⁻³
Δρ_min = −0.54 e Å⁻³

Table 1
Selected bond lengths (Å)

Cr1—O1w	1.964 (2)
Cr1—O2w	1.957 (2)
Cr1—O3w	1.941 (2)
Cr1—O4w	1.947 (2)
Cr1—O5w	1.977 (3)
Cr1—O6w	1.952 (3)

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1w—H11⋯O1	0.84	1.78	2.592 (3)	164
O1w—H12⋯O5ⁱ	0.84	1.93	2.757 (3)	167
O2w—H21⋯O2	0.84	1.75	2.565 (3)	164
O2w—H22⋯O4ⁱⁱ	0.84	1.82	2.662 (3)	177
O3w—H31⋯O1ⁱⁱⁱ	0.84	1.86	2.670 (3)	164
O3w—H32⋯O6ⁱⁱⁱ	0.84	1.85	2.667 (3)	163
O4w—H41⋯O6ⁱ	0.84	1.74	2.555 (4)	162
O4w—H42⋯O7w^iv	0.84	2.05	2.798 (6)	149
O4w—H42⋯O8w′^iv	0.84	1.69	2.448 (7)	149
O5w—H51⋯O3^iv	0.84	2.38	3.070 (5)	140
O5w—H52⋯O8w^v	0.84	2.01	2.812 (6)	161
O6w—H61⋯O3ⁱⁱ	0.84	1.70	2.533 (4)	172
O6w—H62⋯O7w^vi	0.84	1.78	2.600 (6)	165
O6w—H62⋯O7w′^vi	0.84	2.04	2.780 (7)	148
O7w—H72⋯O2	0.84	2.13	2.860 (6)	146
O7w—H71⋯O8w	0.84	2.32	2.865 (8)	123
O8w—H82⋯O4ⁱⁱ	0.84	1.83	2.649 (6)	164
O8w—H81⋯O5^vii	0.84	2.06	2.896 (8)	178
O7w′—H73⋯O2	0.84	2.02	2.840 (7)	167
O7w′—H74⋯O4ⁱⁱ	0.84	2.17	2.993 (7)	167
O8w′—H83⋯O3	0.84	1.89	2.729 (6)	179
O8w′—H84⋯O7w′	0.84	1.91	2.744 (9)	171
Symmetry codes: (i) $[-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ ; (ii) $[-x, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iii) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (iv) $[-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (v) $[x+1, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (vi) $[x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (vii) -x, -y+1, -z+1.

Data collection: APEX2 (Bruker, 2009 ); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001 ); software used to prepare material for publication: publCIF (Westrip, 2010 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810023767/jh2167sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536810023767/jh2167Isup2.hkl

checkCIF report

Comment top

The pyridine-2,4,6-tricarboxylate anion is a multifunctional ligand having nitrogen-donor as well as several oxygen-donor sites. Chelation to chromium is expected. However, its reaction with the chromium(III) ion gave instead a salt in which the cation is coordinated by water molecules only (Scheme I, Fig. 1). Interestingly, the only report of a hexaaquachromium carboxylate crystal structure appears to be that of the acetate, an industrially important chemical (Eshel & Bino, 2001). There are no lattice water molecules in the crystal structure.

Related literature top

For the crystal structure of hexaaquachromum(III) acetate, see: Eshel & Bino (2001). For the synthesis of 2,4,6-pyridinetricarboxylic acid, see: Syper et al. (1980).

Experimental top

Pyridine-2,4,6-tricarboxylicacid was prepared by the oxidation of 2,4,6-trimethylpyridine with potassium permanganate(Syper et al., 1980). Chromium chloride hexahydrate (0.03 g, 0.13 mmol) was dissolved in water (10 ml) and this was mixed with the acid (0.11 g, 0.50 mmol) dissolved in water (10 ml). The solution was briefly heated and then set aside for the growth of light purple crystals over several days.

Computing details top

Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT (Bruker, 2009); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures top

Fig. 1. Thermal ellipsoid plot (Barbour, 2001) of [Cr(H₂O)₆](C₈H₂NO₆)^.2H₂O at the 50% probability level; hydrogen atoms are drawn as spheres of arbitrary radius.

Hexaaquachromium(III) pyridine-2,4,6-tricarboxylate dihydrate top

Crystal data top

[Cr(H₂O)₆](C₈H₂NO₆)·2H₂O	F(000) = 836
M_r = 404.23	D_x = 1.758 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 2431 reflections
a = 7.8610 (3) Å	θ = 2.6–24.6°
b = 16.9269 (5) Å	µ = 0.83 mm⁻¹
c = 11.6823 (4) Å	T = 293 K
β = 100.649 (1)°	Prism, purple
V = 1527.70 (9) Å³	0.11 × 0.07 × 0.05 mm
Z = 4

Data collection top

Bruker Kappa APEXII diffractometer	3507 independent reflections
Radiation source: fine-focus sealed tube	2486 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.060
ϕ and ω scans	θ_max = 27.5°, θ_min = 2.1°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −10→10
T_min = 0.915, T_max = 0.960	k = −21→21
14299 measured reflections	l = −15→14

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.050	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.152	H-atom parameters constrained
S = 0.98	w = 1/[σ²(F_o²) + (0.0867P)² + 0.7924P] where P = (F_o² + 2F_c²)/3
3507 reflections	(Δ/σ)_max = 0.001
235 parameters	Δρ_max = 0.64 e Å⁻³
0 restraints	Δρ_min = −0.54 e Å⁻³

Crystal data top

[Cr(H₂O)₆](C₈H₂NO₆)·2H₂O	V = 1527.70 (9) Å³
M_r = 404.23	Z = 4
Monoclinic, P2₁/c	Mo Kα radiation
a = 7.8610 (3) Å	µ = 0.83 mm⁻¹
b = 16.9269 (5) Å	T = 293 K
c = 11.6823 (4) Å	0.11 × 0.07 × 0.05 mm
β = 100.649 (1)°

Data collection top

Bruker Kappa APEXII diffractometer	3507 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	2486 reflections with I > 2σ(I)
T_min = 0.915, T_max = 0.960	R_int = 0.060
14299 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.050	0 restraints
wR(F²) = 0.152	H-atom parameters constrained
S = 0.98	Δρ_max = 0.64 e Å⁻³
3507 reflections	Δρ_min = −0.54 e Å⁻³
235 parameters

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Cr1	0.54053 (7)	0.15648 (3)	0.39171 (4)	0.02536 (19)
O1	0.4502 (3)	0.36658 (14)	0.53968 (19)	0.0282 (6)
O2	0.3235 (4)	0.37338 (16)	0.3540 (2)	0.0408 (7)
O3	−0.0565 (4)	0.6012 (2)	0.2197 (2)	0.0684 (11)
O4	−0.1258 (3)	0.68517 (15)	0.3489 (2)	0.0386 (7)
O5	0.2467 (3)	0.66964 (13)	0.7612 (2)	0.0307 (6)
O6	0.3712 (4)	0.55364 (15)	0.8057 (2)	0.0395 (7)
O1w	0.5769 (4)	0.22599 (15)	0.5287 (2)	0.0506 (9)
H11	0.5517	0.2740	0.5268	0.076*
H12	0.6408	0.2148	0.5921	0.076*
O2w	0.4111 (3)	0.23657 (14)	0.29037 (19)	0.0293 (6)
H21	0.3912	0.2786	0.3235	0.044*
H22	0.3194	0.2204	0.2483	0.044*
O3w	0.5096 (3)	0.08414 (13)	0.26061 (19)	0.0313 (6)
H31	0.4765	0.1051	0.1954	0.047*
H32	0.4470	0.0448	0.2675	0.047*
O4w	0.6735 (4)	0.07453 (15)	0.4853 (2)	0.0419 (7)
H41	0.6514	0.0580	0.5487	0.063*
H42	0.7368	0.0418	0.4592	0.063*
O5w	0.7577 (3)	0.19559 (15)	0.3495 (2)	0.0378 (6)
H51	0.7938	0.1565	0.3170	0.057*
H52	0.8217	0.2030	0.4145	0.057*
O6w	0.3271 (4)	0.11722 (18)	0.4342 (2)	0.0448 (7)
H61	0.2418	0.1082	0.3810	0.067*
H62	0.2997	0.1085	0.4991	0.067*
N1	0.3130 (3)	0.50687 (15)	0.5851 (2)	0.0211 (6)
C1	0.3554 (4)	0.39985 (19)	0.4552 (3)	0.0236 (7)
C2	0.2751 (4)	0.47842 (18)	0.4768 (3)	0.0216 (7)
C3	0.1641 (4)	0.5174 (2)	0.3883 (3)	0.0245 (7)
H3	0.1417	0.4968	0.3132	0.029*
C4	0.0871 (4)	0.58741 (19)	0.4134 (3)	0.0234 (7)
C5	0.1272 (4)	0.61709 (19)	0.5264 (3)	0.0232 (7)
H5	0.0778	0.6639	0.5462	0.028*
C6	0.2426 (4)	0.57513 (18)	0.6089 (3)	0.0215 (7)
C7	0.2909 (4)	0.60201 (19)	0.7341 (3)	0.0250 (7)
C8	−0.0413 (5)	0.6290 (2)	0.3203 (3)	0.0308 (8)
O7w	0.2400 (7)	0.4369 (3)	0.1235 (4)	0.0362 (12)	0.50
H71	0.1349	0.4321	0.1275	0.054*	0.50
H72	0.3062	0.4247	0.1859	0.054*	0.50
O8w	−0.0236 (8)	0.3188 (3)	0.0680 (5)	0.0536 (16)	0.50
H81	−0.0888	0.3236	0.1171	0.080*	0.50
H82	0.0266	0.2751	0.0814	0.080*	0.50
O7w'	0.1532 (10)	0.3598 (4)	0.1183 (6)	0.0642 (19)	0.50
H73	0.2043	0.3716	0.1857	0.096*	0.50
H74	0.1374	0.3107	0.1159	0.096*	0.50
O8w'	0.0632 (8)	0.5126 (4)	0.0562 (5)	0.0511 (15)	0.50
H83	0.0262	0.5402	0.1062	0.077*	0.50
H84	0.0855	0.4667	0.0819	0.077*	0.50

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Cr1	0.0390 (3)	0.0177 (3)	0.0159 (3)	0.0005 (2)	−0.0040 (2)	−0.0007 (2)
O1	0.0399 (14)	0.0225 (12)	0.0204 (12)	0.0080 (10)	0.0004 (10)	−0.0002 (9)
O2	0.0606 (18)	0.0325 (14)	0.0237 (13)	0.0142 (13)	−0.0072 (12)	−0.0098 (11)
O3	0.078 (2)	0.105 (3)	0.0187 (14)	0.061 (2)	0.0003 (14)	0.0002 (15)
O4	0.0399 (15)	0.0322 (14)	0.0374 (15)	0.0130 (12)	−0.0090 (12)	−0.0016 (12)
O5	0.0469 (16)	0.0169 (12)	0.0250 (12)	0.0030 (10)	−0.0022 (11)	−0.0040 (9)
O6	0.0665 (19)	0.0258 (13)	0.0215 (12)	0.0134 (12)	−0.0041 (12)	−0.0021 (10)
O1w	0.094 (2)	0.0261 (14)	0.0208 (13)	0.0157 (14)	−0.0177 (14)	−0.0072 (11)
O2w	0.0361 (14)	0.0213 (12)	0.0255 (12)	0.0018 (10)	−0.0077 (10)	−0.0021 (10)
O3w	0.0541 (16)	0.0202 (12)	0.0169 (11)	−0.0106 (11)	−0.0007 (11)	−0.0009 (9)
O4w	0.074 (2)	0.0245 (14)	0.0222 (12)	0.0123 (13)	−0.0027 (13)	0.0049 (10)
O5w	0.0334 (14)	0.0268 (14)	0.0489 (16)	−0.0008 (11)	−0.0039 (12)	−0.0021 (12)
O6w	0.0473 (17)	0.061 (2)	0.0250 (13)	−0.0072 (14)	0.0043 (12)	0.0031 (13)
N1	0.0249 (14)	0.0167 (13)	0.0201 (13)	−0.0004 (10)	0.0002 (11)	0.0011 (10)
C1	0.0268 (17)	0.0210 (16)	0.0221 (16)	−0.0021 (13)	0.0022 (13)	−0.0014 (13)
C2	0.0234 (16)	0.0192 (16)	0.0207 (15)	−0.0014 (13)	0.0005 (13)	0.0025 (12)
C3	0.0247 (17)	0.0285 (18)	0.0186 (15)	0.0015 (14)	−0.0001 (13)	−0.0018 (13)
C4	0.0233 (16)	0.0245 (17)	0.0212 (16)	−0.0009 (13)	0.0013 (13)	0.0063 (13)
C5	0.0235 (16)	0.0195 (16)	0.0262 (16)	0.0015 (13)	0.0032 (13)	−0.0005 (13)
C6	0.0232 (16)	0.0190 (16)	0.0210 (16)	−0.0056 (12)	0.0009 (13)	0.0001 (12)
C7	0.0310 (18)	0.0204 (16)	0.0221 (16)	−0.0020 (14)	0.0012 (13)	−0.0009 (13)
C8	0.0286 (18)	0.038 (2)	0.0249 (18)	0.0067 (15)	0.0019 (14)	0.0095 (15)
O7w	0.038 (3)	0.041 (3)	0.027 (3)	−0.005 (2)	0.001 (2)	0.002 (2)
O8w	0.052 (4)	0.036 (3)	0.063 (4)	0.005 (3)	−0.016 (3)	0.002 (3)
O7w'	0.095 (6)	0.051 (4)	0.046 (4)	0.003 (4)	0.012 (4)	0.008 (3)
O8w'	0.059 (4)	0.048 (4)	0.050 (3)	0.004 (3)	0.019 (3)	−0.006 (3)

Geometric parameters (Å, º) top

Cr1—O1w	1.964 (2)	O6w—H61	0.8391
Cr1—O2w	1.957 (2)	O6w—H62	0.8385
Cr1—O3w	1.941 (2)	N1—C6	1.332 (4)
Cr1—O4w	1.947 (2)	N1—C2	1.335 (4)
Cr1—O5w	1.977 (3)	C1—C2	1.513 (5)
Cr1—O6w	1.952 (3)	C2—C3	1.390 (4)
O1—C1	1.255 (4)	C3—C4	1.386 (5)
O2—C1	1.246 (4)	C3—H3	0.9300
O3—C8	1.251 (5)	C4—C5	1.392 (4)
O4—C8	1.240 (4)	C4—C8	1.514 (4)
O5—C7	1.254 (4)	C5—C6	1.391 (4)
O6—C7	1.254 (4)	C5—H5	0.9300
O1w—H11	0.8363	C6—C7	1.512 (4)
O1w—H12	0.8369	O7w—H71	0.8401
O2w—H21	0.8381	O7w—H72	0.8400
O2w—H22	0.8398	O8w—H81	0.8400
O3w—H31	0.8370	O8w—H82	0.8400
O3w—H32	0.8395	O7w'—H73	0.8400
O4w—H41	0.8393	O7w'—H74	0.8399
O4w—H42	0.8390	O8w'—H83	0.8400
O5w—H51	0.8387	O8w'—H84	0.8400
O5w—H52	0.8387

O3w—Cr1—O4w	88.26 (11)	Cr1—O6w—H62	131.7
O3w—Cr1—O6w	89.85 (11)	H61—O6w—H62	109.5
O4w—Cr1—O6w	90.70 (13)	C6—N1—C2	118.8 (3)
O3w—Cr1—O2w	89.10 (10)	O2—C1—O1	124.8 (3)
O4w—Cr1—O2w	176.95 (11)	O2—C1—C2	117.2 (3)
O6w—Cr1—O2w	90.82 (11)	O1—C1—C2	118.0 (3)
O3w—Cr1—O1w	177.52 (10)	N1—C2—C3	122.2 (3)
O4w—Cr1—O1w	89.26 (11)	N1—C2—C1	116.6 (3)
O6w—Cr1—O1w	89.96 (13)	C3—C2—C1	121.2 (3)
O2w—Cr1—O1w	93.38 (10)	C4—C3—C2	119.2 (3)
O3w—Cr1—O5w	90.16 (11)	C4—C3—H3	120.4
O4w—Cr1—O5w	88.84 (12)	C2—C3—H3	120.4
O6w—Cr1—O5w	179.54 (12)	C3—C4—C5	118.6 (3)
O2w—Cr1—O5w	89.63 (10)	C3—C4—C8	120.3 (3)
O1w—Cr1—O5w	90.00 (13)	C5—C4—C8	121.1 (3)
Cr1—O1w—H11	124.3	C6—C5—C4	118.5 (3)
Cr1—O1w—H12	124.0	C6—C5—H5	120.8
H11—O1w—H12	110.1	C4—C5—H5	120.8
Cr1—O2w—H21	115.4	N1—C6—C5	122.8 (3)
Cr1—O2w—H22	115.0	N1—C6—C7	115.0 (3)
H21—O2w—H22	109.5	C5—C6—C7	122.1 (3)
Cr1—O3w—H31	115.0	O5—C7—O6	123.8 (3)
Cr1—O3w—H32	114.5	O5—C7—C6	119.1 (3)
H31—O3w—H32	109.5	O6—C7—C6	117.0 (3)
Cr1—O4w—H41	123.8	O4—C8—O3	125.3 (3)
Cr1—O4w—H42	124.0	O4—C8—C4	118.8 (3)
H41—O4w—H42	109.5	O3—C8—C4	115.8 (3)
Cr1—O5w—H51	103.2	H71—O7w—H72	112.7
Cr1—O5w—H52	103.1	H81—O8w—H82	106.5
H51—O5w—H52	109.4	H73—O7w'—H74	108.0
Cr1—O6w—H61	118.7	H83—O8w'—H84	110.0

C6—N1—C2—C3	−0.3 (5)	C2—N1—C6—C5	1.9 (5)
C6—N1—C2—C1	−178.7 (3)	C2—N1—C6—C7	179.1 (3)
O2—C1—C2—N1	−178.7 (3)	C4—C5—C6—N1	−1.7 (5)
O1—C1—C2—N1	0.5 (5)	C4—C5—C6—C7	−178.8 (3)
O2—C1—C2—C3	2.9 (5)	N1—C6—C7—O5	171.9 (3)
O1—C1—C2—C3	−177.8 (3)	C5—C6—C7—O5	−10.8 (5)
N1—C2—C3—C4	−1.3 (5)	N1—C6—C7—O6	−9.4 (5)
C1—C2—C3—C4	177.0 (3)	C5—C6—C7—O6	167.8 (3)
C2—C3—C4—C5	1.4 (5)	C3—C4—C8—O4	170.1 (3)
C2—C3—C4—C8	−176.9 (3)	C5—C4—C8—O4	−8.2 (5)
C3—C4—C5—C6	0.0 (5)	C3—C4—C8—O3	−7.7 (5)
C8—C4—C5—C6	178.3 (3)	C5—C4—C8—O3	174.0 (4)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1w—H11···O1	0.84	1.78	2.592 (3)	164
O1w—H12···O5ⁱ	0.84	1.93	2.757 (3)	167
O2w—H21···O2	0.84	1.75	2.565 (3)	164
O2w—H22···O4ⁱⁱ	0.84	1.82	2.662 (3)	177
O3w—H31···O1ⁱⁱⁱ	0.84	1.86	2.670 (3)	164
O3w—H32···O6ⁱⁱⁱ	0.84	1.85	2.667 (3)	163
O4w—H41···O6ⁱ	0.84	1.74	2.555 (4)	162
O4w—H42···O7w^iv	0.84	2.05	2.798 (6)	149
O4w—H42···O8w′^iv	0.84	1.69	2.448 (7)	149
O5w—H51···O3^iv	0.84	2.38	3.070 (5)	140
O5w—H52···O8w^v	0.84	2.01	2.812 (6)	161
O6w—H61···O3ⁱⁱ	0.84	1.70	2.533 (4)	172
O6w—H62···O7w^vi	0.84	1.78	2.600 (6)	165
O6w—H62···O7w′^vi	0.84	2.04	2.780 (7)	148
O7w—H72···O2	0.84	2.13	2.860 (6)	146
O7w—H71···O8w	0.84	2.32	2.865 (8)	123
O8w—H82···O4ⁱⁱ	0.84	1.83	2.649 (6)	164
O8w—H81···O5^vii	0.84	2.06	2.896 (8)	178
O7w′—H73···O2	0.84	2.02	2.840 (7)	167
O7w′—H74···O4ⁱⁱ	0.84	2.17	2.993 (7)	167
O8w′—H83···O3	0.84	1.89	2.729 (6)	179
O8w′—H84···O7w′	0.84	1.91	2.744 (9)	171

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

Experimental details

Crystal data
Chemical formula	[Cr(H₂O)₆](C₈H₂NO₆)·2H₂O
M_r	404.23
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	293
a, b, c (Å)	7.8610 (3), 16.9269 (5), 11.6823 (4)
β (°)	100.649 (1)
V (Å³)	1527.70 (9)
Z	4
Radiation type	Mo Kα
µ (mm⁻¹)	0.83
Crystal size (mm)	0.11 × 0.07 × 0.05

Data collection
Diffractometer	Bruker Kappa APEXII diffractometer
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996)
T_min, T_max	0.915, 0.960
No. of measured, independent and observed [I > 2σ(I)] reflections	14299, 3507, 2486
R_int	0.060
(sin θ/λ)_max (Å⁻¹)	0.650

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.050, 0.152, 0.98
No. of reflections	3507
No. of parameters	235
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.64, −0.54

Computer programs: APEX2 (Bruker, 2009), SAINT (Bruker, 2009), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), X-SEED (Barbour, 2001), publCIF (Westrip, 2010).

Selected bond lengths (Å) top

Cr1—O1w	1.964 (2)	Cr1—O4w	1.947 (2)
Cr1—O2w	1.957 (2)	Cr1—O5w	1.977 (3)
Cr1—O3w	1.941 (2)	Cr1—O6w	1.952 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1w—H11···O1	0.84	1.78	2.592 (3)	164
O1w—H12···O5ⁱ	0.84	1.93	2.757 (3)	167
O2w—H21···O2	0.84	1.75	2.565 (3)	164
O2w—H22···O4ⁱⁱ	0.84	1.82	2.662 (3)	177
O3w—H31···O1ⁱⁱⁱ	0.84	1.86	2.670 (3)	164
O3w—H32···O6ⁱⁱⁱ	0.84	1.85	2.667 (3)	163
O4w—H41···O6ⁱ	0.84	1.74	2.555 (4)	162
O4w—H42···O7w^iv	0.84	2.05	2.798 (6)	149
O4w—H42···O8w'^iv	0.84	1.69	2.448 (7)	149
O5w—H51···O3^iv	0.84	2.38	3.070 (5)	140
O5w—H52···O8w^v	0.84	2.01	2.812 (6)	161
O6w—H61···O3ⁱⁱ	0.84	1.70	2.533 (4)	172
O6w—H62···O7w^vi	0.84	1.78	2.600 (6)	165
O6w—H62···O7w'^vi	0.84	2.04	2.780 (7)	148
O7w—H72···O2	0.84	2.13	2.860 (6)	146
O7w—H71···O8w	0.84	2.32	2.865 (8)	123
O8w—H82···O4ⁱⁱ	0.84	1.83	2.649 (6)	164
O8w—H81···O5^vii	0.84	2.06	2.896 (8)	178
O7w'—H73···O2	0.84	2.02	2.840 (7)	167
O7w'—H74···O4ⁱⁱ	0.84	2.17	2.993 (7)	167
O8w'—H83···O3	0.84	1.89	2.729 (6)	179
O8w'—H84···O7w'	0.84	1.91	2.744 (9)	171

Acknowledgements

We thank GC University and the University of Malaya for supporting this study.

References

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