(E,E)-1,2-Bis[3-methoxy-4-(prop-2-yn-1-yloxy)benzylidene]hydrazine

The complete molecule in the title compound, C22H20N2O4, is generated by the application of an inversion centre. With the exception of the terminal acetylene groups [C—O—C—C = −78.02 (17)°], the remaining atoms constituting the molecule are essentially coplanar. The configuration around the C=N bond [1.282 (2) Å] is E. The formation of supramolecular chains mediated by C—H⋯O interactions, occurring between methylene H and methoxy O atoms, is the most notable feature of the crystal packing.

The complete molecule in the title compound, C 22 H 20 N 2 O 4 , is generated by the application of an inversion centre. With the exception of the terminal acetylene groups [C-O-C-C = À78.02 (17) ], the remaining atoms constituting the molecule are essentially coplanar. The configuration around the C N bond [1.282 (2) Å ] is E. The formation of supramolecular chains mediated by C-HÁ Á ÁO interactions, occurring between methylene H and methoxy O atoms, is the most notable feature of the crystal packing.

Comment
Molecules combining an azine functionality and/or a diimine linkage have been investigated in terms of their crystallography and coordination chemistry (Xu et al., 1997;Zheng et al., 2005;Kundu et al., 2005). In this connection the title compound, (I), was studied.
The most prominent feature of the crystal packing is the presence of C-H···O interactions, occurring between methylene-H and the methoxy-O atoms, which serve to link molecules into supramolecular chains mediated by centrosymmetric 12-membered {···HCOC 2 O} 2 synthons, Table 1 and Fig. 2. Chains pack in the ac plane and interdigitate along the b axis., Fig. 3. Each acetylene-H atom is orientated towards an imino-N atom, being separated by 2.77 Å, i.e. outside the standard criteria to be considered significant (Spek, 2009).

Experimental
Vanillinazine (2.0 g, 6.7 mmol) in dry acetone and anhydrous K 2 CO 3 (1.84 g, 13.3 mmol) was stirred at room temperature for about 20 min. Then, an excess of propargyl bromide (1.74 g, 14.7 mmol) was added drop wise. The mixture was refluxed for 48 h. The solvent was evaporated under reduced pressure and the product extracted with 100 ml diethyl ether. The organic layer was washed with brine and dried over MgSO 4 . The yellow compound was recrystallized from ethyl acetate/methanol (1/1) solution to yield yellow needles of (I); yield 72% and M.pt. 460 K.

Refinement
Carbon-bound H-atoms were placed in calculated positions (C-H 0.95 to 0.99 Å) and were included in the refinement in the riding model approximation with U iso (H) = 1.2-1.5U eq (C).

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.