2-[4-(2-{5-tert-Butyl-2-chloro-3-[2-(3-pentyl-1,3-benzothiazol-2-ylidene)ethylidene]cyclohex-1-enyl}ethenyl)-3-cyano-5,5-dimethylfuran-2-ylidene]malononitrile

In the title molecule, C36H39ClN4OS, the non-aromatic part of the cyclohex-1-enyl ring and the attached tert-butyl group are disordered over two conformations with occupancy ratios of 0.52 (3):0.48 (3) and 0.53 (3):0.47 (3), respectively. The polyene chain single- and double-bond dimensions contrast with a closely related compound [Bouit et al. (2007 ▶). Chem. Mater. 19, 5325–5335] with an approximate 19° twist between donor and acceptor ends of the molecule, related to the additional intramolecular C—H⋯S interaction. In the title compound, the molecules pack into dimeric units about centres of symmetry utilizing weak C—H⋯N(cyano) and C—H⋯O attractive interactions, building both chain and ring motifs about the centres [R 2 2(8) and R 2 2(9)]. Adjacent dimeric sets then form a herringbone configuration.


Comment
The title compound, C 36 H 39 ClN 4 OS (3, Figure 1) was synthesized as part of our ongoing research involving the development of organic nonlinear optical (NLO) chromophores. As part of this we have previously reported the crystallographic parameters for chromophores containing an indoline donor coupled to a 2-(3-cyano-4,5,5-trimethyl-5Hfuran-2-ylidene)-malononitrile electron acceptor group (Bhuiyan et al., 2011). Compound 3 was synthesized to check the impact of using a benzothiazole based donor as this should influence both the degree of both length alternation (viz. bond order) as well as the crystal packing. Compound 3 was conveniently prepared in good yield by the condensation of Npentyl-2-methylbenzothiazolinium iodide 1 with precursor 2 (Figure 1). Compound 2 was prepared by the procedure previously reported in the literature (Kay et al., 2004).
These twists in the adjacent near-planar moieties contrasts with the closely related molecule HITVIQ (Bouit et al.,2007) where the benzothiazole entity is replaced by a 1-benzyl-3,3-dimethyl-1,3-dihydro-2H-indol-2-ylidene: here the CDFP and terminal donor rings make an angle of ~10°. As in HITVIQ, there are close intramolecular H···Cl interactions involving the adjacent polyene hydrogen atoms (entries 7 & 8, The different deviation from molecular planarity is also reflected in a significant difference between the two structures in the alternation of double and single bonds beginning at the C2-C6 CDFP bond (Table 2). This alternation is described by the BLA parameter , reflecting the average change in bond length alternation. A related sodium salt (with the CDFP ring at both ends of the molecule EGOSOJ, Bouit et al., 2008)) appears to be have intermediate BLA values between the two.

Experimental
A mixture of compound 2 (5.26 g, 10 mmol) and 3-pentyl-2-methylbenzothiazolum iodide (4.51 g, 13 mmol) was stirred in the minimum amount of acetic anhydride (c. 20 ml). To this suspension, and at room temperature, was added one equivalent of triethylamine (1.4 ml, 20 mmol). The mixture was then allowed to reflux for 3 hrs, by which time its colour had changed to deep greenish black. The solvent was removed in vacuum and the residue washed with diethylether. The oily residue was then dissolved in hot isopropyl ether and kept in a fridge overnight whereupon a solid separated out.

Refinement
Nine reflections affected by the backstop and 12 others which were clearly outlier data (mostly at low angle) were omitted from the refinements (using OMIT). The 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. All H atoms bound to carbon were constrained to their expected geometries (C-H 0.95, 0.98 & 0.99 Å).

Figure 2
Molecular structure of the asymmetric unit (Farrugia, 1999); displacement ellipsoids are shown at the 35% probability level. The minor conformations (b) in the cyclohex-1-enyl ring and bound tert-butyl ring are shown with dotted bonds without labels to avoid confusion.  Packing diagram [Mercury, Macrae et al.,(2008)] of the unit cell. Close contacts are indicated by dotted lines. Symmetry

Data collection
Bruker-Nonius APEXII CCD area-detector diffractometer Radiation source: fine-focus sealed tube Graphite monochromator Detector resolution: 8.333 pixels mm -1 φ and ω scans Absorption correction: multi-scan (Blessing, 1995) and SADABS (Bruker, 2005)  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. 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.