Ethyl 9-dicyanomethylene-2,5,7-trinitro- fluorene-4-carboxylate

The title compound, C19H9N5O8, has a warped fluorene ring system due to steric repulsion between the 4-ethoxy­carbonyl and 5-nitro groups.

The title compound, (I), has been obtained in the course of our studies of electron acceptors of the fluorene series and their charge-transfer complexes and radical ion salts withelectron donors, e.g. tetrathiafulvalene family donors (Perepichka et al., 1998(Perepichka et al., , 2000Batsanov et al., 2001Batsanov et al., , 2002Kuz'mina et al., 2002).
The diffraction was rather weak, with a mean I/(I) ratio of 5.2. The methyl group was refined as a rigid body (C-H = 0.98 Å ) rotating around the C-C bond, with a common (refined) U iso value for all three H atoms. Other H atoms were treated as riding in idealized positions, with Csp 3 -H = 0.99 Å and Csp 2 -H = 0.95 Å , and U iso (H) = 1.3U eq (C) and 1.2U eq (C), respectively.
The authors thank Professor M. R. Bryce for fruitful advice.

Special details
Experimental. The data collection nominally covered over a hemisphere of reciprocal space, by a combination of 4 sets of ω scans; each set at different φ and/or 2θ angles and each scan (46.5 sec exposure) covering 0.3° in ω. Crystal to detector distance 6.03 cm.

sup-2
Acta Cryst. (2006). E62, o885-o887 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.