8,10-Diiodo-2,6-dioxo-4λ³-ioda-3,5-dioxatricyclo­[5.3.1.0^4,11]undeca-1(11),7,9-triene-9-carb­oxy­lic acid

In the title compound, C₉HI₃O₆·2H₂O, the mol­ecule is located on a twofold axis that gives rise to disorder of the carboxyl group. This disorder is correlated with the disorder of one of the H atoms of the water mol­ecule. The carboxyl group is twisted relative to the attached benzene ring by 75.1 (4)°. The intra­molecular I...O distance is 2.112 (6) Å. Mol­ecules are linked via O—H...O hydrogen bonding, C—I...O halogen bonding, with I...O distances in the range 3.156 (5)–3.274 (6) Å, and dipolar C=O...C=O inter­actions between the carboxyl and carboxyl­ate groups, with an O...C distance of 2.944 (10) Å.

Key indicators

• Single-crystal X-ray study
• T = 130 K
• Mean [sigma](C-C) = 0.010 Å
• R factor = 0.042
• wR factor = 0.097
• Data-to-parameter ratio = 16.6

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT431_ALERT_2_B Short Inter HL..A Contact  I2     ..  O2      ..       3.15 Ang.
PLAT782_ALERT_2_B Unusual geometry for C-CO2   moiety involving ..         C6

Alert level C
PLAT342_ALERT_3_C Low Bond Precision on  C-C Bonds ...............     0.0098 Ang
PLAT369_ALERT_2_C Long   C(sp2)-C(sp2) Bond  C5     -   C6     ...       1.54 Ang.
PLAT431_ALERT_2_C Short Inter HL..A Contact  I2     ..  O1      ..       3.27 Ang.
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.600          5
PLAT912_ALERT_4_C Missing # of FCF Reflections Above STh/L=  0.600         13
PLAT975_ALERT_2_C Positive Residual Density at 1.01A from O1     .       0.63 eA-3
PLAT975_ALERT_2_C Positive Residual Density at 0.86A from O1W    .       0.59 eA-3
PLAT976_ALERT_2_C Negative Residual Density at 0.74A from O1W    .      -0.66 eA-3
PLAT976_ALERT_2_C Negative Residual Density at 1.01A from O1W    .      -0.59 eA-3

Alert level G
PLAT007_ALERT_5_G Note: Number of Unrefined D-H Atoms ............          4
PLAT083_ALERT_2_G SHELXL Second Parameter in WGHT Unusually Large.      40.78
PLAT432_ALERT_2_G Short Inter X...Y Contact  O3     ..  C4      ..       2.94 Ang.

   0 ALERT level A = Most likely a serious problem - resolve or explain
   2 ALERT level B = A potentially serious problem, consider carefully
   9 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   3 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
  10 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   1 ALERT type 4 Improvement, methodology, query or suggestion
   1 ALERT type 5 Informative message, check

---

S1. Comment

Iodine-based compounds have always been used as contrast agents for X-ray imaging (Morin et al., 1987). The 1,3,5-triiodo-benzene core has been the basis of many contrast agents (Yu & Watson, 1999). In this paper, we present the crystal structure of a new compound based on 1,3,5-triiodobenzene core.

In the title compound the organic molecule is located on a twofold axis what results in disorder of the carboxylic group (Fig. 1). In the crystal structure, there are hydrogen bonds between symmetry related water molecules as well as between the water molecule and the carboxylic group. It indicates that one of the hydrogen atoms of the water molecule has to be disordered and this disorder is evidently correlated with the disorder of the carboxylic group. The hydrogen atom and the oxygen atom forming hydrogen bond between the water molecule and the carboxylic group are either from the water molecule or the carboxylic group. There is also a hydrogen bond between the water molecule and the carboxylate O1 atom. Hydrogen atom involved in this interaction has full occupancy. The dihedral angle between the plane of the carboxyl group and the benzene ring is 75.1 (4)°.

In addition to hydrogen bond, the structure is stabilized by halogen bonding between the I2 atom and the carboxylate group O1 and O2 atoms. There is also a halogen bond between the water molecule and I1 atom (Fig. 2). A dipolar interaction between carboxyl C6—O3 and carboxylate C4 also is observed (C···O 2.95 Å) (Fig. 3).

Related literature

For general background to 1,3,5-triiodobenzene derivatives, see: Morin et al. (1987); Yu & Watson (1999). For information on the related compound 1,3,5-triiodo-2,4,6-trimethylbenzene, see: Bosch & Barnes (2002); Boudjada et al. (2001); Reddy et al. (2006). For the crystal structures of 5-amino-2,4,6-triiodoisophthalic acid monohydrate and 5-amino-2,4,6-triiodoisophthalic acid–4,4'-bipyridine N,N'-dioxide–water, see: Beck & Sheldrick (2008); Zhang et al. (2011).

S2. Experimental

A mixture of 1,3,5-triiodo-2,4,6-trimethylbenzene (5 g) and excess of potassium permanganate (80 g) was dissolved in pyridine (60 ml) and heated under reflux for 24 h to produce the title compound (m.p. 573 K, decompose). Crystallization was carried out from a mixture of water and methanol (v/v 1:2). Colorless crystals suitable for X-ray single-crystal diffraction were obtained by slow evaporation method.

S3. Refinement

H atom of the carboxylic group was placed in geometrically calculated position and refined using a riding model the the occupantion factor of 0.5. Positions of H atoms from the water molecule were calculated after analysis of possible hydrogen-bond interactions. The occupantion factors of H1W and H2W were assigned as 0.5.

The isotropic displacement parameters of all H atoms were set to 1.5 times the equivalent displacement parameter of their parent O atoms.

Computing details

Data collection: APEX2 (Bruker, 2007); cell refinement: APEX2 (Bruker, 2007); data reduction: APEX2 (Bruker, 2007); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: publCIF (Westrip, 2010).

Figures

	Fig. 1. Molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level. Symmetry code: (i) 1 - x, y, 1.5 + z.
	Fig. 2. Partial view of the crystal structure. Molecules are linked by O—H···O (green dashed lines) and O—H···I hydrogen bonds (purple dashed lines).
	Fig. 3. Packing of the title compound, hydrogen atoms are omitted for clarity. Hydrogen bonds (green), halogen bonds (purple) and dipolar interaction (blue) are shown as dashed lines.

8,10-diiodo-2,6-dioxo-4λ³-ioda-3,5-dioxatricyclo[5.3.1.0^4,11]undeca- 1(11),7,9-triene-9-carboxylic acid

Crystal data

C9HI3O6·2H2O	F(000) = 1128
Mr = 621.83	Dx = 3.016 Mg m^−3
Monoclinic, C2/c	Melting point: 573 K
Hall symbol: -C 2yc	Mo Kα radiation, λ = 0.71069 Å
a = 14.7667 (8) Å	Cell parameters from 3350 reflections
b = 11.9890 (6) Å	θ = 2.4–27.4°
c = 9.7419 (5) Å	µ = 6.88 mm^−1
β = 127.4236 (5)°	T = 130 K
V = 1369.68 (12) Å^3	Prism, colourless
Z = 4	0.32 × 0.14 × 0.12 mm

Data collection

Bruker APEXII CCD area-detector diffractometer	1547 independent reflections
Radiation source: fine-focus sealed tube	1515 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.016
ϕ and ω scans	θmax = 27.4°, θmin = 2.4°
Absorption correction: multi-scan (APEX2; Bruker, 2007)	h = −10→19
Tmin = 0.217, Tmax = 0.492	k = −14→15
4078 measured reflections	l = −12→12

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.042	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.097	H-atom parameters constrained
S = 1.23	w = 1/[σ^2(Fo^2) + (0.0157P)^2 + 40.7765P] where P = (Fo^2 + 2Fc^2)/3
1547 reflections	(Δ/σ)max < 0.001
93 parameters	Δρmax = 2.36 e Å^−3
0 restraints	Δρmin = −2.23 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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	Occ. (<1)
C1	0.5000	0.3381 (8)	0.7500	0.0216 (19)
C2	0.4147 (5)	0.3903 (6)	0.5979 (8)	0.0207 (13)
C3	0.4155 (6)	0.5066 (6)	0.5979 (9)	0.0249 (14)
C4	0.3340 (6)	0.3120 (6)	0.4528 (9)	0.0248 (14)
C5	0.5000	0.5629 (8)	0.7500	0.0222 (19)
C6	0.5000	0.6916 (8)	0.7500	0.027 (2)
I1	0.5000	0.16946 (5)	0.7500	0.02526 (18)
I2	0.29502 (5)	0.59994 (5)	0.37929 (8)	0.0469 (2)
O1	0.2532 (5)	0.3419 (5)	0.3093 (7)	0.0386 (14)
O2	0.3559 (5)	0.2049 (5)	0.4946 (7)	0.0313 (12)
O3	0.5338 (6)	0.7375 (5)	0.6751 (9)	0.0474 (16)
H3	0.5308	0.8054	0.6818	0.071*	0.50
O1W	0.4370 (6)	0.9449 (6)	0.5383 (9)	0.0494 (16)
H1W	0.4763	0.8910	0.5958	0.074*	0.50
H2W	0.4756	0.9896	0.5303	0.074*	0.50
H3W	0.3831	0.9240	0.4416	0.074*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.021 (4)	0.019 (4)	0.021 (5)	0.000	0.011 (4)	0.000
C2	0.017 (3)	0.024 (3)	0.012 (3)	0.000 (2)	0.004 (2)	−0.001 (2)
C3	0.021 (3)	0.030 (4)	0.017 (3)	0.005 (3)	0.008 (3)	0.004 (3)
C4	0.021 (3)	0.031 (4)	0.015 (3)	−0.002 (3)	0.007 (3)	−0.003 (3)
C5	0.026 (5)	0.018 (4)	0.029 (5)	0.000	0.020 (4)	0.000
C6	0.039 (6)	0.012 (4)	0.035 (6)	0.000	0.025 (5)	0.000
I1	0.0282 (3)	0.0169 (3)	0.0269 (3)	0.000	0.0148 (3)	0.000
I2	0.0427 (4)	0.0392 (3)	0.0341 (3)	0.0125 (2)	0.0104 (3)	0.0160 (2)
O1	0.031 (3)	0.042 (3)	0.019 (3)	0.000 (3)	0.003 (2)	−0.004 (2)
O2	0.030 (3)	0.029 (3)	0.024 (3)	−0.008 (2)	0.011 (2)	−0.008 (2)
O3	0.074 (5)	0.028 (3)	0.069 (5)	0.000 (3)	0.058 (4)	0.005 (3)
O1W	0.050 (4)	0.044 (4)	0.048 (4)	−0.008 (3)	0.026 (3)	−0.002 (3)

Geometric parameters (Å, º)

C1—C2^i	1.380 (8)	C5—C3^i	1.400 (8)
C1—I1	2.022 (9)	C5—C6	1.543 (13)
C2—C3	1.394 (10)	C6—O3	1.237 (7)
C2—C4	1.501 (9)	I1—O2	2.113 (5)
C3—C5	1.400 (8)	O3—H3	0.8200
C3—I2	2.085 (7)	O1W—H1W	0.8201
C4—O1	1.216 (9)	O1W—H2W	0.8200
C4—O2	1.326 (9)	O1W—H3W	0.8201
C4···O3^ii	2.944 (10)	I2···O2^iv	3.156 (5)
I1···O1W^iii	3.173 (7)	I2···O1^iv	3.274 (6)
C2^i—C1—C2	126.1 (9)	C3—C5—C3^i	122.3 (9)
C2^i—C1—I1	117.0 (5)	C3—C5—C6	118.8 (5)
C2—C1—I1	117.0 (5)	O3^i—C6—O3	127.1 (10)
C1—C2—C3	116.8 (6)	O3—C6—C5	116.5 (5)
C1—C2—C4	114.3 (6)	C1—I1—O2	78.38 (15)
C3—C2—C4	128.9 (6)	O2^i—I1—O2	156.8 (3)
C2—C3—C5	119.0 (7)	C4—O2—I1	116.1 (4)
C2—C3—I2	122.3 (5)	C6—O3—H3	109.5
C5—C3—I2	118.7 (6)	H1W—O1W—H2W	109.6
O1—C4—O2	121.6 (7)	H1W—O1W—H3W	109.5
O1—C4—C2	124.1 (7)	H2W—O1W—H3W	109.6
O2—C4—C2	114.2 (6)
C2^i—C1—C2—C3	0.5 (5)	I2—C3—C5—C3^i	−179.6 (5)
I1—C1—C2—C3	−179.5 (5)	C2—C3—C5—C6	−179.5 (5)
C2^i—C1—C2—C4	179.7 (6)	I2—C3—C5—C6	0.4 (5)
I1—C1—C2—C4	−0.3 (6)	C3—C5—C6—O3^i	105.1 (5)
C1—C2—C3—C5	−0.9 (9)	C3—C5—C6—O3	−74.9 (5)
C4—C2—C3—C5	180.0 (6)	C3^i—C5—C6—O3	105.1 (5)
C1—C2—C3—I2	179.1 (4)	C2^i—C1—I1—O2	179.6 (4)
C4—C2—C3—I2	0.1 (11)	C2—C1—I1—O2	−0.4 (4)
C1—C2—C4—O1	179.7 (7)	O1—C4—O2—I1	180.0 (6)
C3—C2—C4—O1	−1.3 (13)	C2—C4—O2—I1	−1.5 (8)
C1—C2—C4—O2	1.2 (9)	C1—I1—O2—C4	1.1 (5)
C3—C2—C4—O2	−179.7 (7)	O2^i—I1—O2—C4	1.1 (5)
C2—C3—C5—C3^i	0.5 (5)

Symmetry codes: (i) −x+1, y, −z+3/2; (ii) −x+1, −y+1, −z+1; (iii) x, y−1, z; (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
O3—H3···O1W	0.82	2.08	2.772 (9)	142
O1W—H1W···O3	0.82	1.98	2.772 (9)	163
O1W—H2W···O1W^v	0.82	1.94	2.730 (14)	160
O1W—H3W···O1^iv	0.82	2.24	3.053 (9)	172

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