5-(4-Cyano-5-dicyanomethylene-2,2-dimethyl-2,5-dihydro-3-furyl)-3-(1-methyl-1,4-dihydropyridin-4-ylidene)pent-4-enyl 3,5-bis(benzyloxy)benzoate acetonitrile 0.25-solvate: a synchrotron radiation study

The title compound, C42H36N4O5·0.25CH3CN, crystallizes with a partial twofold disordered (1/4) acetonitrile solvent of crystallization. The linking atoms to the 3,5-bis(benzyloxy)benzoic acid are disordered between two conformations in the ratio 0.780 (6):0.220 (6). In the crystal, the molecules pack using mainly C—H⋯N(cyano) interactions coupled with weak C—H⋯O(ether) interactions and C—H⋯π interactions. A brief comparison is made between a conventional and this synchrotron data collection.


Comment
The title compound (I) was synthesized as part of a continuing research programme involving the development of organic nonlinear optical (NLO) chromophores. Due to the highly polar nature of these compounds they have a strong tendency to aggregate, a phenomenon that often leads to a reduction in the macroscopic nonlinearity. We have previously reported the crystallographic parameters for two chromophores containing a quinolinylidene donor coupled to a cyanodicyanomethylidenedihydrofuran (CDFP) electron acceptor group . In both instances an examination of the unit cell packing showed plane to plane stacking of the chromophores via the interaction of the donor end of one molecule with the acceptor end of another. This is clear evidence for potentially deleterious H-aggregation occurring between the compounds.
However, it has been reported that the introduction of bulky substituents near the centre of NLO chromophores leads to a significant reduction in the observed aggregation (Kim et al., 2007). Consequently we were interested to make modifications to the core structure of our compounds to see whether the introduction of a bulky 3,5-bis(benzyloxy) benzoate group would lead to any change in the unit cell packing. We report here on the structural properties of a chromophore containing a pyridinylidene donor, CDFP acceptor and bulky side group. While a direct comparison between the compounds studied earlier  and one also containing a quinolinylidene donor would be preferable, this wasn't feasible from synthetic viewpoint. An initial report based on the earlier conventional data collection has been given .
The asymmetric unit of crystals of (I) contains one independent copy of the molecule and a partial (1/4) acetonitrile molecule disordered around a twofold symmetry site ( Figure 1). The linking atoms to the 3,5-bis-benzyloxy-benzoic acid (C20,C21,O2) are disordered over two conformations with refined occupancies of 0.780:0.220 (6). The CDFP ring (atoms C4/C5/O1/C6/C7) and the cyano groups appended to C2 are coplanar ( Table 2). The geometric parameters are consistent with the localized electron configuration shown in the scheme with ony subtle differences to the closely related quinoline molecules (NAJKUT & NOJLAA, Gainsford et al., 2008); the similarity is reflected in the bond length alternation (Marder et al., 1993) BLA values of -0.042 (here) and -0.015 & -0.042 respectively. The interplanar angles (Table 2) show the overall moleculear non-planarity of the adjacent planar entities.
An opportunity arose to recollect data on the Australian synchrotron, which is the data presented here. The conventional laboratory results are quite similar but that data did not support refinement of the partial acetonitrile solvent molecule. There were about 2.5 times more observed data in the synchrotron data set (collected in 5% of the conventional time) giving supplementary materials sup-2 smaller su (by ~70%) values, but overall both datasets gave similar agreement factors. Given the overall agreement data statistics (see exptl_refinement) and the different crystal used, further comparison seems unwarranted.

Experimental
The title compound was synthesized by a published procedure (Clarke et al., 2009). Black crystals suitable for X-ray structure determination were grown in acetonitrile by slow evaporation of the solvent at room temperature.

Refinement
A total of 12 outlier reflections were omitted from the processed set, from which 16 intense reflections with poor internal agreement had been removed. An examination of the data did not establish definitively that these latter data, with F o >> F c , represented data from a multiple crystal fragment or were subject to twinning.