Crystal structure of 1,1′-{(dodecane-1,12-diyl)bis[(azaniumylylidene)methanylylidene]}bis(naphthalen-2-olate)

The title compound, C34H40N2O2, exists in an extended conformation and has crystallographically imposed centrosymmetry. The crystal packing can be described as being composed of parallel layers stacked along [010]. The zwitterionic structure is stabilized by an intramolecular N—H⋯O hydrogen-bond interaction.


Ultrasonication method
A reaction flask containing 0.344g (2mmol) of 2-hydroxy-1-naphthaldehyde and 0.508g (1mmol) of 1,12-diaminododecane, mixed and ground to a fine powder in a mortar, was immersed in an ultrasonic bath containing water at a temperature of 50 °C. The reaction mixture was exposed to ultrasound irradiation for 40 min. Upon completion, based on TLC analysis (silica gel, CH 2 Cl 2 /MeOH, 9.5/0.5, V/V) the product was washed with methanol (3 x 3 mL) and diethyl ether (3 x 3 mL) and filtered. Single crystals, suitable for X-ray diffraction, were obtained after 2 days of crystallization

Conventional method
To a solution of 0.172 g (1mmol) of 2-hydroxy-1-naphthaldehyde in 5 mL of methanol was added 0.254 g (0.5 mmol) of 1,2-diaminododecane dissolved in 5 mL of the same solvent.The mixture was stirred and refluxed for 3 hours under a nitrogen atmosphere. At completion, based on TLC analysis, the resulting compound was filtered and washed with methanol and diethyl ether to afford pure product in 62% yield.

S0.2. Refinement
The iminium H atom was located from a difference Fourier map and refined isotropically. C-bound H atoms were included in calculated positions and treated as riding atoms: C-H = 0.95 Å (CH) or 0.99 Å (CH 2 ) with Uiso(H) = 1.2Ueq (C-Har.).
The synthesis via ultrasound irradiation is an efficient, fast, high yielding method and is a more economical synthetic process for the preparation of the Schiff base compound than the conventional method.

Figure 1
The title compound with atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are represented as small spheres of arbitrary radius.

Figure 2
Crystal packing of the title compound viewed along the c axis.