1,2-Dimethyl-4,4-triafulvenedicarbonitrile

Abstract

Abstract. C8H6N 2, M, = 130.1, monoclinic, P21/n; a = 7.414(1), b = 15.572(1), c = 7.478(1) A, fl = 118.19 (1)°; D e = 1.136 g cm -3 for Z = 4; Mo K~t diffractometer data. Final R = 0.041. The endocyclic C=C distance of 1.327 A is ca 0.02 A less than the value found in diphenyltriafulvenes, a difference which appears to be characteristic of the change in the threemembered-ring substituents from phenyl to alkyl. There are no significant differences between the other structural parameters of the 1,2-dimethyl-and 1,2-diphenyl-4,4-triafulvenedicarbonitriles.Introduction. A sample of 1,2-dimethyl-4,4-triafulvenedicarbonitrile (Ia), prepared in the laboratories of T. Eicher, crystallized from ethanol in the form of colorless blocks. A cube-shaped crystal, ca 0.4 mm in all dimensions, mounted parallel to a, was used for all X-ray measurements. The space group was established with oscillation and Weissenberg photographs with Cu radiation. All lattice-parameter and intensity measurements were made with a Picker FACS-I diffractometer with Mo radiation [graphite monochromator, 2(Mo K~t) = 0.71069 A] with the crystal aligned to place a* paral!el to the instrument's ~p axis. The final unit-cell parameters were obtained by least-squares calculations from the Bragg angles of 12 reflections manually centered at +20 (average of120 o20el = 0.003°).Intensities were measured with the 0-20 scan method, with a 20 scan rate of 2.0 ° min -~, and with 20 s backgrounds. Three standard reflections were counted at 100-reflection intervals. 1575 data were measured to a 20 maximum of 50 ° giving 1340 unique reflections (excluding 63 systematically absent data); 880 of these were 3a above background. The structure was solved by direct methods with the XRAY system (Stewart, Kruger, Ammon, Dickinson & Hall, 1972) subprogram PHASE. The phasing required the calculation of four E maps (corresponding to the four + combinations of two