Synthesis , characterization and single crystal X-ray analysis of azobenzene-4 , 4 ′-dicarbonyl chloride

Abstract The title compound azobenzene-4, 4′-dicarbonyl chloride has been synthesized in distilled dichlomethane and characterized by elemental analysis (C, H, N), IR and NMR (H & C) studies. The crystal and molecular structure was further confirmed using single crystal X-ray diffraction analysis. It was crystallized in triclinic crystal system with space group P-1. The centrosymmetrically related molecules held together via C–H---O secondary interaction result in molecular aggregation of the compound.


Introduction
The synthesis of new and novel materials has long been recognized as essential step in the development of advance technology.It is becoming increasingly urgent to produce materials designed to perform highly specific and cooperative functions.In this context, the design and synthesis of azo (-N=N-) group containing compounds has led remarkable developments in that direction owing to their potential applications in the construction of metal-organic frameworks (Chen et al., 2008), as chemosensors (Lee et al., 2007) and photoactive materials (Park et al., 2012).The azo fuctionalised MOFs are exploited as materials for selective capture of CO2 (Nagaraja et al., 2012).The azoloaded chemosensors are used to detect cations (Arabahmadi & Amani, 2013), anions (Lee et al., 2001) and neutral molecules (Goshwami et al., 1999) while the azo-based photoactive materials are used for photoresponsive molecular recognition (Hunter et al., 2004), light driven fluorescence enhancement (Man & Hara, 2005), design of molecular photoswitches (Willner & Rubin,1996) and photoinduced release of adsorbed CO2 (Park et al., 2012).The azo-based systems have also been exploited as photoactive DNA cleavage agents (Panja et al., 2011).
In 1937, G. S. Hartley published a study of the influence of light on the configuration of N=N double bonds (Hartley, 1937).The exposure of light to a solution of azobenzene in acetone to light allowed the discovery of the cis isomer.This finding was the starting point of the development of one of the best organic molecular switches described so far.
In recent years, the photochromic properties of azobenzenes have attracted great interest owing to the isomerization of N=N bonds that occurs readily in the presence of a light

Research Article
source (Ross & Blanc, 1971).The introduction of an azobenzene fragment in a molecule with biological activity, can allow the spatial and temporal control of a variety of biological processes.The isomerization of azo-compounds has been used as a synthetic tool to control the opening and closing of pores in cellular membranes, essential for the transport of ions (Banghart, 2004).
Considering these aspects, the present article is thought to be of worth as it deals with the synthesis and characterization of azobenzene-4, 4′-dicarbonyl chloride.It also includes single crystal X-ray analysis to confirm the molecular structure of the compound.

Experimental Section
All reagents and solvents were commercially available and used as received.The carbon, nitrogen, and hydrogen contents of the compounds were determined by Carbo-Erba elemental analyzer 1108.The infrared spectra of the compounds were recorded on a Varian 3100 FT-IR spectrometer (4000−400cm −1 ) using KBr disks. 1 H and 13 C NMR spectra of compounds were recorded using JEOL AL 300 MHz spectrometer.The starting compound azobenzene-4, 4′-dicarboxylic acid 1 and azobenzene-4, 4′dicarbonyl chloride 2 were synthesized following reported methods used (Ghosh et al., 2008).

Scheme 1. Synthetic strategy of 1 & 2
Single crystal X-ray analysis of 2: For X-ray Crystallographic Study, the X-ray diffraction data were collected by mounting a single crystal of the sample on glass fibers.Oxford diffraction XCALIBUR-EOS diffractometer was used for the determination of cell parameters and intensity data collection at room temperature.Monochromating Mo Kα radiation (λ = 0.71073 Å) was used for the measurements.The crystal structures were solved by direct methods using SHELXS-97 Program (Sheldrick, 1997) and were refined by full matrix leastsquares SHELXL-97 (Sheldrick, 1990).Drawings were carried out using MERCURY (Bruno et al., 2002) and special computations were carried out with PLATON (Spek, 2003).

Results and Discussion
The infrared spectra of 1 and 2 show peaks at 1683 and 1776 cm -1 due to C=O stretching vibrations respectively.The peaks at 1600 and 1601 cm -1 correspond to N=N stretching vibrations of 1 and 2. 1 H NMR spectra exhibit peaks at δ = 13.3 due to COOH proton of 1. 13 C NMR spectra of 1 and 2 exhibit peaks at δ = 166 and 167 ppm due to C=O carbon respectively.
Crystallographic data and refinement details for the structural analyses of 2 are summarized in Table 1.Selected bond lengths and bond angles with their estimated standard deviations are presented in Table 2, while selected parameters for weak interactions are listed in Table 3. Crystallographic data for the title compound 2 reported in this paper have been deposited with the Cambridge data centre.The deposition number is CCDC 1846836.These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/.The X-ray single-crystal structure determination of compound 2 suggested that it was crystallized in triclinic crystal system with space group P-1.The distances Cl(05)−C(20) (1.780(4) Å) and C(20)−O(03) (1.178(4) Å) fall in the reported range.The dihedral angles between two phenyl rings is 15.3°.It is interesting to note that, centrosymmetrically related molecules connected via C-H---O secondary interaction of 2.651 Å (Table 3) lead to supramolecular associations of molecules in the crystal structure (Fig. 2).

Conclusion
The synthesis and chacterization of azobenzene-4, 4′dicarbonyl chloride is descried.Single crystal X-ray analysis was carried out to confirm the molecular structure of the compound.It was crystallized in triclinic crystal system with space group P-1.The crystal structure of the compound reveals that the bond lengths and bond angles are in reported range.Additionally, C-H---O intermolecular interactions have also been observed between two symmetry related molecules.