1-(4-Bromophenyl)ferrocene

In the title compound, [Fe(C5H5)(C11H8Br)], the distance of the Fe atom from the centroids of the unsubstituted and substituted cyclopentadienyl (Cp) rings is 1.644 (1) and 1.643 (1) Å, respectively. The ferrocenyl moiety deviates from an eclipsed geometry, with marginally tilted Cp rings and an interplanar angle between the Cp and benzene rings of 13.0 (4)°. The crystal structure is stabilized by C—H⋯π interactions between a cyclopentadienyl H atom and the cyclopentadienyl ring of a neighbouring molecule.

In the title compound, [Fe(C 5 H 5 )(C 11 H 8 Br)], the distance of the Fe atom from the centroids of the unsubstituted and substituted cyclopentadienyl (Cp) rings is 1.644 (1) and 1.643 (1) Å , respectively. The ferrocenyl moiety deviates from an eclipsed geometry, with marginally tilted Cp rings and an interplanar angle between the Cp and benzene rings of 13.0 (4) . The crystal structure is stabilized by C-HÁ Á Á interactions between a cyclopentadienyl H atom and the cyclopentadienyl ring of a neighbouring molecule.
Cg1 is the centroid of the C1-C5 cyclopentadienyl ring.

Comment
Ferrocene compounds especially those synthesized by reacting a para-substituted phenylferrocene 4-Fc-C 6 H 4 -R (R = any atom or group) are of great interest in the field of material chemistry (Togni & Hayashi, 1995). They are employed as precursors in the synthesis of ferrocenomesogens with the ferrocenyl moiety incorporated as a terminal group (Imrie et al., 2002(Imrie et al., , 2003. Interest in these compounds stems from their potential use either as metathesis catalysts or therapeutic radiopharmaceuticals (Hor et al., 1991;Knoesen & Lotz, 1999). The compounds have also been used to synthesize non-linear optical materials containing molybdenum or tungsten redox centres (Coe et al.,1994).
In the title compound (I, Fig. 1), the distance of the Fe atom from the centroids of the unsubstituted (C1-C5) and the substituted (C6-C10) cyclopentadienyl rings are 1.644 (1) and 1.643 (1) Å respectively, indicating that the para-substitution (bromophenyl group) has little influence on Fe-Cp bonding interactions. The two Cp rings deviate from an eclipsed conformation with torsion angles around 11.0 (2)°. The rings are also marginally tilted towards each other with a tilt angle between the planes of the two rings of 0.83 (2)°. The interplanar angle between the Cp and the phenyl rings of (I) was 13.0 (4)°. This value is very close to the 12.  Table 1; Cg is the centroid of the C1-C5 cyclopentadienyl ring, symmetry code as in Fig. 2).

Experimental
The title compound (I) was synthesized via the diazonium reaction as follows: A solution of 4-bromobenzene diazonium sulfate was prepared by the reaction of 4-bromoaniline (20.02 g, 0.12 mol) in dilute sulfuric acid (100 cm 3 ) to which sodium nitrite (11.65 g, 0.17 mol) was slowly added in water at 278 K. The reaction temperature was continually monitored and held at 278 K during the addition. The resultant solution was filtered and the filtrate was immediately added to a cold, well stirred solution of ferrocene(24.60 g, 0.13 mol) in diethyl ether (450 cm 3 ). Stirring was continued at 278 K for 3 h and then at room temperature for a further 12 h. The ether layer was separated, washed with water, dried over anhydrous sodium sulfate and evaporated. The residue was purified by column chromatography on silica gel. Hexane was used to elute unreacted ferrocene and the product was eluted from the column using 1 : 1 hexane : dichloromethane mixture to yield 4.57 g, 11% of pure (I). mp 122-123 °C; Spectroscopic analysis: IR ν max (KBr/cm -1 ) 3086, 3053, 2925, 2853, 1588, 1509, 1446, 1406, 1383, 1278, 1103, 1088, 1066,1050, 1030, 1001, 884,  supplementary materials sup-2 Refinement All H atoms attached to C atoms were fixed geometrically and treated as riding with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). Fig. 1. Molecular structure of the title complex with the atom labelling scheme. Ellipsoids are drawn at the 50% probability level.

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 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 > 2sigma(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq