Crystal structure of 1-ethyl-5-iodoindolin-2-one

Molecules of 1-ethyl-5-iodoindolin-2-one are arranged in columns extending along the a axis and interact with the molecules in adjacent columns via intermolecular C—H⋯O hydrogen bonds and I⋯I short contacts. A one-dimensional zigzag iodine chain along the a axis can be recognized between two neighbouring columns.


Chemical context
Indolinone derivatives play an important role in the pharmaceutical industry and some of them show antineoplastic (Cane et al., 2000), antibacterial (Kumar et al., 2013) and anti-inflammatory (Mammone et al., 2006) activities. The indolinone skeleton can be also found in many known bioactive drugs, such as horsfiline (Murphy et al., 2005), rhynchophylline (Deiters et al., 2006) and the gelsemium alkaloids (Kitajima et al., 2006). In addition, indolinone derivatives are widely used in the spice industry and agriculture, as functional materials (Ji et al., 2010) and dye intermediates.
In recent years, the synthesis and crystal structures of many indolinone derivatives have been reported including 6-chloro-5-(2-chloroethyl)oxindole (Nadkarni & Hallissey, 2008). We have recently synthesized and reported the crystal structures of several indolin-2-one derivatives including 1-phenylindolin-2-one (Wang et al., 2015). As a continuation of our work in this field, we report here the synthesis and crystal structure of the title compound, 1-ethyl-5-iodoindolin-2-one.

Structural commentary
The title molecule is shown in Fig. 1

Supramolecular features
The crystal packing in the title compound is shown in Figs. 2 and 3. The molecules are face-to-face parallel-packed forming a column along the a axis withinteractions centroid-centroid distances = 4.130 (2) and 4.462 (2) Å ]. Molecules from neighbouring columns are connected by a C-HÁ Á ÁO hydrogen bond (Table 1) with the formation of a layer-type aggregate parallel to (001). There is an IÁ Á ÁI contact shorter than the sum (3.96 Å ) of the van der Waals radii [IÁ Á ÁI i 3.8986 (3) Å , C-IÁ Á ÁI i 173.3 (3) ; symmetry code: (i) x À 1 2 , Ày À 1 2 , Àz + 2] joining the columns of molecules in adjacent layers and forming a kind of 1-D zigzag chain along the a-axis direction (see Fig. 3). An important feature of the columns is that they are polar, i.e. all molecular dipole moments in the same column point in the same direction.
DFT/b3lyp/genecp calculations were carried out, which took the pseudopotential basis set LanL2DZ for the iodine atom and the 6-311g(d) basis set for the other atoms, to optimize the molecular geometry and calculate the dipole moment using the GAUSSIAN03 program (Frisch et al., 2003). The dipole moment of the title molecule (1.707 D) is much smaller than that of its precursor molecule, 1-ethyl-5-iodoindolin-2,3-dione (5.432 D). This difference may partly explain the non-centrosymmetry of the title crystal (space group P2 1 2 1 2 1 ) and the centrosymmetry of the crystal of the  Table 1 Hydrogen-bond geometry (Å , ). Symmetry code: (i) Àx þ 3; y À 1 2 ; Àz þ 3 2 .

Figure 2
The view of the structure along the a axis, showing the C-HÁ Á ÁO hydrogen bond between columns and the IÁ Á ÁI interactions between columns.

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level.
precursor (Wang et al.,2014). On the other hand, the noncentrosymmetry of the title crystal may be better explained by the IÁ Á ÁI intermolecular interactions, for there are no IÁ Á ÁI short contacts in the above centrosymmetric precursor crystal.

Database survey
A search of the Cambridge Structural Database (WebCSD, Version 5.36; last update April 2015; Groom & Allen, 2014) for 5-iodoindolin-2-one derivatives gave 15 hits. Of these 16 structures (with the title structure included), the number of non-centrosymmetric structures (9) is slightly greater than the number of centrosymmetric structures (7). In these 16 structures, there are four structures which exhibit IÁ Á ÁI short intermolecular contacts and all the four structures are noncentrosymmetric (three of them belong to the P2 1 2 1 2 1 space group and the other one belongs to the P6 3 space group; Takahashi et al., 2014). Therefore, the IÁ Á ÁI contacts seem to promote non-centrosymmetric packing in this kind of compound.

Synthesis and crystallization
The title compound was synthesized by reduction of the precursor with an 80% hydrazine hydrate (see reaction scheme) . 1-Ethyl-5-iodoindolin-2,3-dione precursor (1.714 g, 5.69 mmol) and 80% NH 2 NH 2 ÁH 2 O (19.0 mL) were added into a 50 mL flask and the mixture was stirred under reflux. The reaction progress was tracked by TLC. After 4.5 h, the reaction mixture was cooled down and poured into 100 mL water with precipitation of yellow solid. Then the mixture was extracted with CH 2 Cl 2 , the organic phase was washed with water and dried with MgSO 4 . The solvent was removed under reduced pressure and the crude product was purified by silica gel column chromatography with CHCl 3 as eluent. The title compound was obtained as a colorless solid (1.509 g, yield 92.3%). m.p. 403-404 K. Crystals suitable for X-ray diffraction were obtained by slow evaporation of a CHCl 3 solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms bound to aromatic C atoms and methylene C atoms were located in difference maps The view of the structure along the b axis, showing the one-dimensional columnar structure and the zigzag iodine chains along the a axis. and freely refined, leading to C-H distances of 0.91 to 1.02 Å .

1-Ethyl-5-iodoindolin-2-one
Crystal data Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0014 (3) Absolute structure: Flack (1983), 1183 Friedel pairs Absolute structure parameter: 0.02 (2) Special details Experimental. Scan width 0.4° ω, Crystal to detector distance 6.20 cm, exposure time 20 s, 17 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.