1-Ethyl-5-iodoindoline-2,3-dione

There are two independent molecules in the asymmetric unit of the title compound, C10H8INO2, which differ in the degree of planarity. The iodoindoline-2,3-dione skeleton of molecule 1 is essentially planar [mean deviation = 0.003 (2) Å for the nine non-H atoms of the indoline core, with a maximum deviation of 0.033 (1) Å for the I atom]. The I atom and O atom in the 3-position of molecule 2 deviate by 0.195 (1) and 0.120 (2) Å, respectively, from the least-squares plane through the nine non-H atoms of the indoline core. Molecules 1 and 2 are roughly coplanar, the mean planes through their cores making a dihedral angle of 6.84 (1)°. This coplanarity results in a layer-like structure parallel to (6,11,17) in the crystal, the distance between adjacent least-squares planes through the cores of molecules 1 and 2 being 3.37 (1) Å. In such a layer, molecules 1 and 2 are linked by C—H⋯O hydrogen bonds, forming chains along [11-1]. The chains are further coupled to construct a kind of double-chain structure via I⋯O interactions [3.270 (2) Å].


Comment
To date, isatin and its derivatives have received much attention due to their potential applications in biomedicine and agrochemical industries (Silva et al., 2001). In this paper, we report the synthesis and structure of a new isatin derivative, namely 1-ethyl-5-iodoindoline-2,3-dione.
There are two molecules in the asymmetric unit of the unit cell as depicted in Fig. 1. The two molecules are essentially planar. All non-hydrogen atoms, except the terminal methyl C atom, are in a same plane. The iodoindoline-2,3-dione skeleton of molecule 1 has a perfect planarity (mean deviation is 0.003 (2) Å, maximum deviation is 0.033 (1) Å for I1 for the least-squares plane through the 9 non-hydrogen atoms of the indoline core). In molecule 2, two large deviations exist [0.195 (1) (I2) and 0.120 (2) Å (O3)], and the mean deviation is relatively larger [0.022 (2) Å]. Molecules 1 and 2 are virtually co-planar with a small dihedral angle of 6.84 (1) ° between both best planes. This co-planarity results in a layer-like structure of the crystal (Figs. 2 and 3). Considering this co-planarity, the least-squares plane through the 18 non-hydrogen atoms of the two indoline cores of the two molecules shows a mean deviation of 0.064 (3) Å. The distance between two such adjacent best planes or layers is 3.37 (1) Å.
Several intermolecular interactions can be found in a layer. The C-H···O hydrogen bonds (Table 1) help to build onedimensional chains and the I1···O3 [-x, 1 -y, 1 -z] [3.270 (2) Å] short contact helps to construct a kind of double-chain structure.

Experimental
We synthesized the title compound by the similar method reported by Ji et al. (2010). KI (1.27 g), hexadecyl trimethyl ammonium bromide (0.410 g) and 5-iodoisatin (3.75 g) were dissolved in 20 ml DMSO, and the mixture was stirred in N 2 atmosphere while 2.7 ml iodoethane was quickly added via a syringe. Then 5 ml aqueous KOH solution (17.8 mol/L) was dropwise added into the brown solution at 30 °C and the colour rapidly became black. After another 3 ml iodoethane was added, the heating temperature was raised to 45 °C. The mixture was stirred for 5 h, then 1.6 ml iodoethane was added.
The reaction continued for 1 h at 45°C. The mixture was then poured into water, and extracted with dichloromethane. The organic phase was seperated and dried over anhydrous Na 2 SO 4 . The solvent was evaporated under reduced pressure, the crude product was purified by column chromatography [V (dichloromethane)/ V (petroleum ether) = 1:1] obtaining 47.4% yield. Crystals suitable for X-ray diffraction were obtained by slow evaporation of a dichloromethane solution of the compound.

Refinement
H atoms bound to aromatic C atoms were located in difference maps and freely refined leading to C-H distances from 0.88 (3) to 0.99 (3) Å. Other H atoms were placed at calculated positions and treated by the riding model with C-H distances = 0.97 (methylene C) or 0.96 Å (methyl C) and U iso (H) = 1.2 U eq (methylene C) or 1.5 U eq (methyl C).    A view of the uniform layered structure, the spacing between neighboring layers is 3.37 (1) Å.

Special details
Experimental. Scan width 0.5° ω and φ, Crystal to detector distance 5.964 cm, exposure time 20 s, 19 h for data collection 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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.