N,N′-Bis[(E)-(6-methyl-2-pyridyl)methylene]hexane-1,6-diamine

The title compound, C20H26N4, is composed of two (6-methyl-2-pyridyl)methylene units linked by a 1,6-diamine hexane chain. The molecule has Ci symmetry with the inversion center situated at the mid-point of the central C—C bond. The alkyl chain has an all-trans conformation, with all the non-H atoms sharing the same plane [maximum deviation 0.004 (3) Å]. The pyridylmethylene groups are also planar [maximum deviation 0.009 (3) Å], making an angle of 53.78 (19)° with the hexane chain plane. In the crystal, the molecules assemble in layers, stacking along the a axis. The stacks are hold together by attractive interactions between π electron systems.

The title compound, C 20 H 26 N 4 , is composed of two (6-methyl-2-pyridyl)methylene units linked by a 1,6-diamine hexane chain. The molecule has C i symmetry with the inversion center situated at the mid-point of the central C-C bond. The alkyl chain has an all-trans conformation, with all the non-H atoms sharing the same plane [maximum deviation 0.004 (3) Å ]. The pyridylmethylene groups are also planar [maximum deviation 0.009 (3) Å ], making an angle of 53.78 (19) with the hexane chain plane. In the crystal, the molecules assemble in layers, stacking along the a axis. The stacks are hold together by attractive interactions between electron systems.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: SU2109). Comment Schiff bases and their complexes (salen ligands) continue to raise interest, even after a hundred years of research, due to their novel structures, their application in reversible binding of oxygen, their catalytic activity in hydrogenation of olefins, intermolecular transfer of amino groups, and their complexing ability towards some toxic metals (Cozzi, 2004;Li et al., 2007;Renehan et al.;2005, Mohamed et al., 2006. Two important examples are, copper(I)-salen complexes investigated as antitumor agents, and ruthenium-salen complexes studied as protein kinase inhibitors by mimicking the structure of organic indolocarbazoles (Wu & Gorden, 2007). Salen complexes have also been used to form metal-organic frameworks (MOFs), which are intensively sought for the storage of hydrogen and carbon dioxide (Berga & Arean, 2008).

Structure Reports Online
The title compound was synthesized to be used as a ligand/spacer in the construction of MOFs. For such purposes long-chain bidentate ligands may be useful to alter the cavity size, as reported by Bu et al., who showed that in some Cu(II) coordination compounds, the cavity size depends on the chain length of bis-sulfinyl ligands used.
The title compound is illustrated in Fig. 1 In the crystal structure the molecules assemble in layers stacked along the a axis, as shown in Fig. 2.
Experimental 5.5 mmol of 1,6-diamine was added to 11 mmol of 6-methyl-pyridil-2-aldehyde in toluene (50 ml). The mixture was stirred at 160°C with reflux in a Dean-Stark system until all the water was removed (~2 h). The solution was washed with diluted HCl (30 ml) and NaHCO 3 (15 ml) and dried with NaSO 4 anhydrous (5 g). Solvent was evaporated in a stirring water bath at 40°C under nitrogen. The product was recrystallized from CH 2 Cl 2 to give the title compound in 40% yield.

Refinement
The crystals of the title compound diffracted very poorly, displaying broad weak reflections, hence the ratio of observed/  Fig. 1. ORTEPII (Johnson, 1976) plot of the title compound. Displacement ellipsoids are drawn at the 50% probability level.

Data collection
Bruker APEX CCD area-detector diffractometer 2308 independent reflections 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 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.