INTRODUCTION

Schiff bases and its derivatives are an important class of compounds which can be used in a variety of studies such as organic synthesis, catalysis, drug design, industry and the life sciences [1–3]. Schiff bases have received much attention because of their potential applications with some of these compounds exhibiting various pharmacological activities such as anticancer, anti-HIV, antibacterial and antifungal properties [4–7]. On the industrial scale, they have a wide range of applications, such as in dyes and pigments [8].

Due to the biological and industrial significance of the Schiff bases, we have synthesised derivatives of Schiff base, 6,6'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)bis(3-(octyloxy)phenol) (Fig. 1), for the first time. In this study, we present the structure of 6,6'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)bis(3-(octyloxy) phenol) was studied by using FTIR, 1H NMR, 13C NMR, and X-ray crystallographic techniques.

Fig. 1.
figure 1

Chemical diagram of 6,6'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)bis(3-(octyloxy)phenol).

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EXPERIMENTAL

Synthesis

6,6'-(1E,1'E)-(Ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)bis(3-(octyloxy)phenol) was prepared by refluxing a mixture of a solution containing 2-hydroxy-4-octyloxybenzophenone (10.4 mg, 0.07 mmol) in tetrahydrofurane (THF) (20 mL) and a solution containing 1,2-etylenediamine (18.0 mg, 0.07 mmol) in THF (20 mL). The reaction mixture was stirred for 5 h under reflux. The obtained cyrstal material was yellow and washed with ethanol, dried at room temperature (m.p. 379–381 K).

Spectral Studies

The IR spectrum of the title compound was recorded in the range 4000–400 cm–1 using a Vertex 80V Bruker FTIR spectrophotometer. 1H- and 13C-NMR spectra were obtained on a Bruker Ultra Shield Plus 500 MHz spectrometers using TMS as internal standard. The spectra were recorded in DMSO solutions.

Crystal Data and Structure Determination

All diffraction measurements were performed at room temperature (296 K) using graphite monochromated MoKα radiation (λ = 0.71073 Å) on a BRUKER APEX II diffractometer. Reflections were collected in the rotation mode and cell parameters were determined by using Bruker SAINT software [9]. Absorption correction was achieved by the integration method via Bruker SAINT software [9]. The structure was solved by direct methods using SHELXS 97 [10]. H atoms were positioned geometrically and treated using a riding model, fixing the bond lengths at 0.82, 0.93, 0.96, and 0.97 Å for OH, CH, CH3, and CH2 atoms, respectively. The ORTEP-3 program for windows has been used in the preparation of the figures [11]. The crystallographic data and refinement parameters for the structural analyses are as follows: C44H56N2O4, Mr = 676.91, prism and colourless, size 0.12 × 0.15 × 0.17 mm, space group C2/c, monoclinic, a = 33.750 (4) Å, b = 6.4978 (6) Å, с = 18.070 (2) Å, β = 100.248 (5)°, V = 3899.7 (7) Å3, Z = 4, Dx = 1.153 Mg m–3, μ = 0.07 mm–1, 3° ≤ θ ≤ 26°, measured reflections = 15085, reflections with I > 2σ(I) = 1846, Rint = 0.093, GOF = 1.00, R1 (I > 2σ(I)) = 0.0549, wR2 (I > 2 σ(I)) = 0.134, number of refined parameters = 234, – 41 ≤ h ≤ 41, –8 ≤ k ≤ 8, –22 ≤ l ≤ 22, Tmin/Tmax = 0.8592/0.9842, ∆ρmax/∆ρmin = 0.15/–0.18 e/Å3.

Crystallographic data for the structural analysis have been deposited with Cambridge Crystallographic Data Centre, CCDC reference number 1813286 Copies of this information can be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB12 1EZ, UK. Fax:+44(0)1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www.ccdc.cam.ac.uk.

RESULTS AND DISCUSSION

Crystal Structure

The title compound, an Ortep-3 view of which is shown in Fig. 2, crystallizes in the monoclinic space group C2/c with Z = 4. The asymmetric unit of the title compound, C44H56N2O4, contains one half-organic molecule. The molecule is located about a two-fold rotation axis which bisects the central C14–C14i bond (symmetry code (i): –x + 1, y, –z + 1/2). The title compound is not planar. The dihedral angle between the C1/C6 and C8/C13 rings is 68.46(11)°. The torsion angle of the bridge N–CH2–CH2–N group is 68.64°. The length of the C7=N1 double bond is 1.286 (2) Å, it is slightly longer than standart 1.28 Å value of C=N double bond and consistent with the related stuructures [12, 13]. The selected bond lengths and bond angles are given in Table 1. In the molecule, the bond lengths and angles are within normal ranges and they are comparable with those related structures [14–16].

Fig. 2.
figure 2

Ortep-3 diagram of the 6,6'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)bis(3-(octyloxy)phenol). Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. The intramolecular hydrogen bonds are shown as dashed lines.

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Table 1.   Selected molecular structure parameters
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The intramolecular O–H⋅⋅⋅N hydrogen bonds (Fig. 2) generates a six-membered ring, producing an S(6) ring motif [17]. The crystal structure is also stabilized by intermolecular C–H⋅⋅⋅π interactions (C16–H16A⋅⋅⋅Cg2 with symmetry code: x, 1 + y, z). Cg2 is the centroids of the C8–C13 ring. The details of the hydrogen bonds are summarized in Table 2. A packing diagram of the title compound is shown in Fig. 3.

Table 2.   Hydrogen-bond geometry (Å, deg)
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Fig. 3.
figure 3

Packing diagram of 6,6'-(1E,1'E)-(ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)bis(3-(octyloxy)phenol).

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IR Spectra

The infrared spectra of the title compound were recorded in Vertex 80V Bruker FTIR spectrometer using KBr pellets in the region of 4000–400 cm–1. The IR spectra contain some characteristic bands of the stretching vibrations of the O–H, C–H, C=N, C=C, and C–O groups. The broad band at 3441 cm–1 was assigned phenol OH stretching vibrations. The C–H aromatic stretchings were observed at 3027 cm–1. Besides, the stretching of imine C–H was found at 2920 cm–1. The strong band at 1601 cm–1 was assigned to azomethine C=N stretching vibration. The band at 1511 cm–1 is assigned to C=C stretchings. The C–O stretching band is observed at 1261 cm–1. The above conclusions are in good agreement with the related Schiff base compound [18–20].

NMR Spectra

1H chemical shift values of the title compound are observed to be 0.83–7.50 ppm. The aromatic C–H signals were observed to be 6.16–7.50 ppm. The OH proton is observed 3.92 ppm singlet. The –NCH2 and –OCH2 protons resonate at 3.45 and 3.30 ppm. The signals at 0.83–2.48 ppm are due to CH2 and CH3 protons.

13C NMR spectra of the compound show signal at 169.00 ppm due to the carbon C7 atom of the C=N group. The chemical shift value of C13 atom bounded the OH group is observed as 163.20 ppm. While the C14 atom of the –NCH2 group gave a singlet at 67.84 ppm, the carbons of the CH2 and CH3 groups are observed at 14.27–31.54 ppm. The aromatic carbons of phenyl ring are observed at 127.47–133.41 ppm. The 1H and 13C NMR spectra are in agreement with the X-ray structure of the title compound.

CONCLUSIONS

6,6'-(1E,1'E)-(Ethane-1,2-diylbis(azan-1-yl-1-ylidene))bis(phenylmethan-1-yl-1-ylidene)bis(3-(octyloxy)phenol) has been synthesized and characterized by FT-IR, 1H NMR, 13C NMR, and single-crystal X-ray diffraction analysis. The structure was unambiguously assigned by X-ray diffraction studies. The FT-IR and NMR spectroscopy and single crystal structure data confirm that the state of the ligand in solution and in the solid state corresponds to one form. In the crystal structure of the title compound, the intramolecular O–H⋅⋅⋅N hydrogen bonds generates a six-membered ring, producing an S(6) ring motif. The crystal structure is also stabilized by intermolecular C–H⋅⋅⋅π interactions.