2-{3-Cyano-5,5-dimethyl-4-[6-(pyrrolidin-1-yl)hexa-1,3,5-trienyl]-2,5-dihydro-2-furylidene}malononitrile

The title compound, C20H20N4O, is packed into a three-dimensional ‘herringbone’ matrix using two different types of attractive C—H⋯N(cyano) interactions. The bond-length alternation, caused by delocalization of charge between the donor N atoms and the cyano acceptor groups, is compared with related compounds.

The title compound, C 20 H 20 N 4 O, is packed into a threedimensional 'herringbone' matrix using two different types of attractive C-HÁ Á ÁN(cyano) interactions. The bond-length alternation, caused by delocalization of charge between the donor N atoms and the cyano acceptor groups, is compared with related compounds.

Table 2
Selected bond lengths and angles (Å , ) in the title compound and related compounds.
We thank Dr J. Wikaira and Dr C. Fitchett of the University of Canterbury, New Zealand, for their assistance with the data collection.

Comment
We have previously reported on the synthesis of a number of high figure of merit chromophores for nonlinear optics (Kay et al., 2004), and the X-ray crystallographic and structural properties of crucial dye precursors used [Gainsford et al., 2007;Gainsford et al., 2008a (hereafter III); Gainsford et al., 2008b (hereafter II)]. We report here the crystallographic data of another molecule derived from a chromophore precursor and summarize the structural details of this and closely related compounds.
The polyene C-H attractive interactions with adjacent cyano nitrogen atom N3 (principally entry 1, Table 1), commonly observed for these molecules (Gainsford et al., 2008a), link adjacent molecules which lie parallel to each other and the 0,1,-2 plane. The other two main methylene H···N (cyano) interactions (entries 3 & 4, Table 2) link to the other (herringbone) planes which are parallel to the 0,1,2 plane.
supplementary materials sup-2 Refinement All methyl and other H atoms were refined with U iso 1.5 & 1.2 times respectively that of the U eq of their parent atom using riding models. All non-hydrogen atoms were refined with anisotropic thermal parameters. Fig. 1. Molecular structure of the asymmetric unit (Farrugia, 1997); displacement ellipsoids are shown at the 50% probability level.   Refinement. An extinction parameter was refined. 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.