2,4-Diiodoaniline

The structure of the title compound, C6H5I2N, shows a weak intermolecular amine–amine N—H⋯N hydrogen-bonding interaction, giving a helical chain which extends along the a axis. An intramolecular N—H⋯I hydrogen bond is also observed.

The structure of the title compound, C 6 H 5 I 2 N, shows a weak intermolecular amine-amine N-HÁ Á ÁN hydrogen-bonding interaction, giving a helical chain which extends along the a axis. An intramolecular N-HÁ Á ÁI hydrogen bond is also observed.

Experimental
Crystal data

Comment
Although the crystal structures of a number of nitro-substituted iodoanilines including 3-nitro-2,4-diodoaniline have been reported (Garden et al., 2002), that of the title compound 2,4-diiodoaniline C 6 H 6 I 2 N (I) has not been determined and the structure is reported here. The compound was isolated as the major crystalline product in the attempted synthesis of an adduct of 4,5-dichlorophthalic acid with 4-iodoaniline in aqueous ethanol. This conversion of 4-iodoaniline to 2,4-diiodoaniline has been reported previously (Dains et al., 1935), where solid 4-iodoaniline was observed to undergo a ca 25% conversion to the diiodo analogue in a sealed container over a period of three years. Hodgson & Marsden (1937) also reported the ready formation of the diiodo derivative along with 4-iodoaniline from the reaction of aniline with iodine.

Experimental
The title compound was formed in the attempted synthesis of a proton-transfer salt of 4,5-dichlorophthalic acid with 4-iodoaniline by heating together under reflux for 10 minutes 1 mmol quantities of the two reagents in 50 ml of 50% ethanolwater. After concentration to ca 30 ml, partial room temperature evaporation of the hot-filtered solution gave colourless needle prisms of 2,4-diiodoaniline [m.p. 368-389 K (O'Neil, 2001)] as the major product. This conversion of 4-iodoaniline to 2,4-diiodoaniline in the solid state has been reported previously (Dains et al., 1935).

Refinement
The hydrogen atoms of the amino group were located in a difference Fourier map and their positional and isotropic displacement parameters were refined freely. Other H-atoms were included in the refinement in calculated positions [C-H = 0.93 Å) and treated using a riding model approximation, with U iso (H) = 1.2U eq (C).
supplementary materials sup-2 Figures   Fig. 1. Molecular configuration and atom naming scheme for (I). Displacement ellipsoids are drawn at the 50% probability level.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles 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 Rfactors(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.