Synthesis, Crystal Structure and Spectroscopic Studies of 1-(p- Bromphenyl)-3,5 Diphenylformazan

In this study, novel 1-substituted-phenyl-3,5-diphenylformazans were synhesized with –Br group at p-positions. Their structures were elucidated by elemental analyses, UV–vis and IR spectroscopy and X-ray single crystal structure determination. Their UV–vis spectra indicated that their λmax showed a shift amount of which was dependent upon the position of the substituent on the ring. The title compound, 1-(p-bromphenyl)-3,5 diphenylformazan, crystallizes in the orthorombic P bca space group, with a=7.9526(9)Å, b=18.611(2) Å, c=23.099(2) Å. The final cycle of refinement was converged to R = 0.0703. The big part of the molecule is coplanar. The molecular conformation is maintained by an intramolecular N-HN hydrogen bond. Keywords: Formazan, X-ray, organic compound, crystal
structure.

 INTRODUCTION Formazans are compounds containing the characteristic azohydrazone group (-N=N-C=N-NH-), which is a good carrier of π -bonding and chelating properties. They are widely used as dyes, as ligands in complex formation reactions, and as analytical reagents, where their deep colour makes them good indicators of redox reactions [1, 2]. Formazans form salts and complexes with several metal ions, and especially the transition metal ions. Their derivatives with electron donating and withdrawing group attached to 1,3,5phenyl ring were synthesized and the effects of substituents on the absorption λmax values were examined. They are also biologically active and there is much interest in their biological applications [3]. Various 1 and 3-substituted formazans were synthesized and, the effect of substituents evaluated by using UV-vis and IR spectra [4, 5]. The biological activity of formazan makes the knowledge of its oxidation potentials and possible mechanisms very important. In the present study, a noval formazan complex with substituent on 1-phenyl ring has been synthesized and its structure was determined using the X-ray diffraction method and characterized with spectroscopic techniques. The structure of formazan complex molecule is given in Fig. (1). MATERIALS AND METHODOLOGY General Procedures and Materials All starting reagents and solvents were purchased from Merck, Sigma-Aldrich Chemical Co. and used without further purification. IR spectrum was recorded on a MATTSON 1000 FT-IR spectrophotometer with range 4000–625 cm *Address correspondence to this author at the Science Education Department, Faculty of Education, Aksaray University, Aksaray, Turkey; Tel: +90 506 5057102; Fax: +90 382 2801180; E-mail: [email protected] using KBr pellets. Absorption spectra were obtained with UNICAM UV2-100 UV–vis spectrophotometer using 1 cm quartz cells in 10 mol l methanol in the range of 192.2– 600 nm. Elemental analyses for (C, H, N) were performed using a LECO CHNS 932 elemental analyzer. Fig. (1). Chemical diagram of 1-(p-bromphenyl)-3,5 diphenylformazan. Synthesis of 1-(p-Bromphenyl)-3,5 Diphenylformazan For the synthesis, dissolved Benzaldehyde (2.12 g, 0.02 mol) in 12.5 ml methanol was gradually added to phenylhydrazine (2.16g, 0.02 mol) with constant stirring at pH 5-6. The procedure was completed in 45 min. The resulting white hydrazone was left on the bench over night and was then filtered and recrystallized from methanol. The benzaldehyde phenylhydrazone (1.06 g, 0.01 mol) was dissolved in methanol (50ml). By constant stirring under reflux and buffer solution (prepared as before). In another flask, p-brombenzendiazonium chloride solution was prepared using pbromaniline (1.7203 g, 0.01 mol) concentrated HCl (2.5ml) and sodium nitrite (0.75g) at 0-5 ̊C. This solution was added to the benzaldehyde phenylhydrazone solutions dropwise with constant stirring to form compound. The solution stirred to 2h at the same temperature and kept in a cupboard for 2 days. Dye was filtered and then washed water and methanol. The compound was recrystallised from diclormethane. Red colored crystal; m.p 189 C; yield 74%. Analysis calculated for C19H15BrN4 (%): C, 60.16; H, 3.96; Br, 21.11; N, 14.76. Found (%): C, 60.12; H, 3.90; Br, 21.20; N, 14.79. C Br N N N H N Synthesis, Crystal Structure and Spectroscopic Studies The Open Crystallography Journal, 2010, Volume 3 55 RESULTS AND DISCUSSION IR and UV–VIS Spectra of 1-(p-Bromphenyl)-3,5 Diphenylformazan The most characteristics bands of the complex is summarized in Table 1. As seen from Table 1, v(C=N) bands at 1520-1500 cm and v(N=N) bands at 1450-1410 cm were observed in the complex. These results are in agreement with literature [4, 5]. The v(N-N) valans vibration bands observed in the region 1080, 1055 and 1030 cm. Other aromatic v(CH), v(C=C), v(CNNC) skeleton stretching bands in the compound were observed in their expecting regions. Table 2 list all peaks observed in the UV-vis spectra of 1-(pbromphenyl)-3,5 diphenylformazan and the values of literature of 1, 3, 5 triphenylformazan at same solvent [6]. The chemical shift values (Δ λmax) were compared by taking the difference between the λmax1 values of the p-Br substituted formazan with the λmax value of TPF in this study. The peaks listed as λmax1 in Table 2 are the broad peaks which are characteristic of the formazan skeleton. They are generally observed at 410–500 nm depending upon structure. These peaks are due to π–π* electronic transitions in the formazan skeleton. The sharp λmax2 peaks which appear at 300–350 nm correspond to n–π* electronic transitions of the – N=N– group. The λmax3 peaks observed at 210– 300 nm originate from n–π* transitions of –C=N– groups. As seen from Table 2, the λmax1 value of TPF at 483 nm, shifts to 489 nm when the 1-phenyl ring is substituted with a –Br at the p-positions. Description of the Crystal Structure of 1-(pBromphenyl)-3,5 Diphenylformazan A needle red crystal with a size of 0.5x0.04x0,04 mm was used for diffraction experiments. Diffraction measurements were made at room temperature on a Stoe IPDS II CCD X-ray diffractometer using graphite-monochromated MoKα radiation using w-scan mode [7]. Unit-cell dimensions were determined and refined by using the angular settings of 25 automatically centered reflections in the 1.76 < θ< 26 range. The empirical absorption corrections were applied by the multiscan method via X-RED32 software. Data collection, cell refinement and data reduction performed using STOE X-AREA and STOE X-RED [7,8]. The structure was solved by direct methods and refinement using the programs SHELXS97 and SHELXL97, respectively [9] in the WinGX package [10]. The quality of crystals obtained was always poor and this fact may underlie both low proportion of the reflection labelled “observed” at room temperature and fairly high merging index. A full-matrix least-squares refinement on F converged at R = 0.0703. All non-hydrogen atoms were refined anisotropically. Hydrogen atom of the N3 atom is taken from a difference Fourier map and fixed its thermal parameter, while the other hydrogen atoms were in calculated positions using the riding method with Uiso(H)=1.2 Ueq(C). Hydrogen bond and molecular packing geometry of the title molecule was calculated with PLATON [11]. The graphical representations of the structure were made with ORTEP [12] (see Fig. 2) and MERCURY [13]. The crystal and instrumental parameters used in the unit cell determination and data collection are summarized in Table 3. Selected bond lengths and angles are given in Table 4. ORTEP drawing of the molecule with 20% probability displacement thermal ellipsoids and atom-labeling scheme are shown in Fig. (2). CONCLUSION The molecule of the title compound has C=N and N=N double bond [C13-N4=1.324(10), N1-N2=1.300(10) Å]. The exocyclic C-C-N bond angles around the C1 atom are asymmetrical. The C6-C1-N1 angle [111.2(8)°] is significantly smaller than the C2-C1-N1 angle [128.2(8)°]. C13N2-N1 [122.7(9)°] and C13-N4-N3 [121.0(8)°] angles around the N2, N4 atoms are almost equal to each other. The aromatic rings in the molecule as expected have usual bond lengths and angles. The title compound has a strong intramolecular N3-H⋅⋅⋅N1 hydrogen bond with D-H, D⋅⋅⋅A and H⋅⋅⋅A distances of 0.96(5), 2.405(11) and 1.59(6) Ǻ, respectively, and D-HA angle of 140(8)° as shown Fig. (3a). This bond turns the molecule in to a chelate structure, which is responsible for its tautomerism. This hydrogen bond possibly influences the relative orientation of the phenyl rings. Tautomerism of 1,3,5 triphenylformazan was also seen Table 1. The IR Data of 1-(p-Bromphenyl)-3,5 Diphenylformazan (in KBr, cm) Aromatic C-H Aromatic C=C C=N N=N N-N Valans Vibration CNNC Structural Vibration 310