Synthesis, Crystal Structure, and DFT Study of N′-(2,4-Dinitrophenyl)-2-Fluorobenzohydrazide

Abstract

A new hydrazide derivative N′-(2,4-dinitrophenyl)-2-fluorobenzohydrazide was synthesized and characterized by NMR and IR spectroscopy. The molecular structure was also studied by X-ray diffraction, and the results of the optimized molecular structure are presented and compared with density functional methods with 631-G basis set. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters, for example, bond lengths and angles show good agreement with the experimental data.

1. Introduction

Hydrazides are an important class of biologically active compounds exhibiting a variety of biological activities notably, antituberculosis [1], antibacterial [2], antifungal [3], antimalarial [4], antiproliferative and antitumour [5, 6]. Several clinical drugs like the antituberculosis drug, isoniazid, antihypertensive and peripheral vasodilator drug hydralazine, and benserazide used for treatment of restless legs syndrome are hydrazides in nature. Furthermore, metallic complexes of hydrazides show potent fungicidal and antibacterial activities [7].

In addition, benzohydrazides are also used for the construction of heterocyclic rings due to the presence of carbonyl functionality as well as two nitrogens which can behave like nucleophiles in a number of reactions [8]. Examples of heterocycles include indoles, carbazoles, pyrazoles, triazines, indazolones, and indazoles [9–15].

We have already reported on the synthesis and crystal structure of (2,4-dinitrophenyl) benzohydrazide [16]. Herein, we wish to report the synthesis of N′-(2,4-dinitrophenyl)-2-fluorobenzohydrazide (Scheme 1). The chemical structure of compound was confirmed by FT-IR, ¹H NMR, ¹³C NMR, elementary analysis, and X-ray single-crystal determination.

Scheme 1 

Synthesis of title compound.

Density functional theory (DFT) has been very popular for calculations in theoretical modelling since the 1970s. DFT predicts a great variety of molecular properties like molecular structures, vibrational frequencies, atomization energies, ionization energies, electric and magnetic properties, and reaction paths. The molecular structure parameters of the title compound have been calculated by density functional theory (B3LYP) with 6-31G basis set. The calculated molecular structure parameters have been analyzed and compared with obtained experimental data.

2. Results and Discussion

2.1. Crystal Structure

The PhC(O)NNPh core moiety (Figure 1) is similar to that of N-anilino-4-nitrobenzamide [17] and N-(3,5-dinitrobenzoyl)-N′-phenylhydrazine [18] with different ring substitution patterns. The molecular conformation is determined by the intramolecular N1–H⋯O5 and N4–H⋯F hydrogen bonds with H⋯O5 2.02 and H⋯F 2.10 Å. Associated torsion angles are N4–C1–C2–C7 = 9.9(3)° and N4–N1–C8–C13 = −170.9(2)°. The two aromatic ring planes make a dihedral angle of 88.65(5)°. Intermolecular hydrogen bond interactions N1–H⋯O1 (𝑥+1,𝑦,𝑧) with H⋯O 2.25(3) Å and N–H⋯O 139(2)° as well as C5–H⋯O4 (𝑥−1,𝑦+1,𝑧) with H⋯O 2.44 Å and C–H⋯O 132° link molecules into zigzag chains extended along the b-axis (Figure 2).

Figure 1 

The molecular structure of the title molecule (1), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level, and H atoms are shown as small spheres of arbitrary radii.

Figure 2 

Crystal packing is viewed approximately along a-axis with H-bonding as dashed lines. H atoms not involved are omitted.

2.2. Molecular Geometry and Optimized Structures

The optimized geometrical parameters, namely, bond lengths and angles experimental and calculated by B3LYP/6-31G level listed in Table 2. From the theoretical results, expected fluctuations of the calculated values against the experimental ones were observed. Comparing experimental bond lengths and angles with theoretical bond lengths and bond angles it is of notice that the bond lengths calculated are always higher than experimental values. Optimized structures yields identical bond lengths for the C–C bonds on the Aryl rings and calculated values by 631G basis set are finest closed to experimental. The calculated bond lengths of the C–C bond in benzene ring is between 1.365 and 1.509 Å, while experimentally, it ranges 1.365–1.500 Å which is much shorter than the typical C–C single bond (1.54 Å) and longer than the C=C double bond (1.34 Å) [19, 20].

By comparison of the results obtained by DFT calculations by 63-1G basis set and the experimental data in Table 2, several observations can be made. The experimental C9–C10 bond length is 1.366 Å; this value was calculated as 1.379. The N2–C11 and N3–C13 bond lengths are 1.454 and 1.449 Å, respectively, which are in good agreement with the experimental values 1.453 and 1.449 and smaller than the normal C–N single bond length of about 1.47 Å [21]. From the calculation results of bond angles which are analyzed in the present work, it can be obtained that the calculated bond angles are very close to their experimental data except F1–C7–C6 and C7–C2–C1; both were underestimated, and C12–C13–N3 is the only one which is overestimated. While most of the calculated angles for 1 at 631-G basis set differ only in the decimal with the experimental values. These results indicate that the calculated angles are very similar to the crystal structure of titled compound 1. When the X-ray structure of the title compound is compared with its optimised counterparts (see Figure 3), minor conformational discrepancies are observed between them. A logical method for globally comparing the structures obtained with the theoretical calculations is by superimposing the molecular skeleton with that obtained from X-ray diffraction.

Figure 3 

Atom-by-atom superimposition of the structures calculated (blue) by B3LYP/6-31G on the X-ray structure (black) of the title compound.

3. Experimental and Computational Details

3.1. Materials and Analyses

All chemicals were of reagent grade and used as commercially purchased without additional purification. All solvents were dried and distilled before use. For TLC analysis, precoated plates of silica gel 60 F254 were used. The ¹H NMR spectra were recorded on a Brucker AM_300 instrument, and chemical shifts are reported in parts per million (ppm). The melting point was determined on Staurt SMP3 apparatus and is uncorrected. The FT-IR spectrum was recorded using a Shimadzu IR 460 instrument by attenuated total reflectance (ATR) method. The CHN elemental analysis was performed on LECO CHNS-932 analyser.

3.2. Synthesis

2,4-Dinitrophenyl hydrazine (2.8 mmol) in dry CHCl₃ (10 mL) was treated with 2-fluorobenzoyl chloride (2.8 mmol), and the mixture was refluxed for 2 hours. On completion of reaction, the mixture was allowed to cool, and the solvent was evaporated under reduced pressure. Yellow prisms of the title compound were recrystallized from ethanol by slow evaporation at room temperature (m.p 190–192°C). IR: 3418 ((C=O)NH), 3293 (NH), 1675 (C=O), 3101 (C_SP²–H), cm⁻¹. ¹H-NMR (300 MHz, CDCl₃): δ 7.23–7.39 (m, 3H, Ar-H), 7.59 (m, 1H, Ar-H), 8.07 (ddd, 1H, Ar-H), 8.32 (dd, 1H, Ar-H), 8.94 (d, 1H, Ar-H), 9.71 (s, 1H, CONH), 11.24 (s, 1H, NH); ¹³C-NMR (75 MHz, CDCl₃): δ 164.5, 154.6, 148.1, 137.1, 133.5, 133.1, 130.3, 129.8, 129.5, 127.0, 126.6, 119.3, 116.0, 115.8.

3.3. X-Ray Structure Determination

Data were collected at 130(2) K on a Bruker [22] AXS SMART APEX CCD diffractometer using MoKα radiation. The structure was solved by direct methods [18] and refined on F² by full-matrix least-squares [23] with 215 parameters and 1806 unique intensities. All nonhydrogen atoms were refined anisotropically. All H atom positions were clearly derived from difference Fourier maps and refined on idealized positions with U_iso=1.2U_eq(C/N), C–H distances of 0.95 Å. H(N) positions were refined freely. The title compound crystallizes in the noncentrosymmetric space group P 2₁2₁2₁; however, in the absence of significant anomalous scattering effects, the Flack parameter is essentially meaningless. Accordingly, Friedel pairs were merged. Experimental data are listed in Table 1.

Table 1 

Parameter for data collection and structure refinement of 1.

Table 2 

The bond lengths (Å) and bond angles [°] for title compound (1) determined by X-ray diffraction and DFT calculations using 63-1G basis set.

3.4. Computational Method

Optimized molecular structure of the title compound (1) in the ground state (S₀) was computed with PC GAMESS/Firefly version 7.1.G [24] (based in part on the codes of the GAMESS program (USA)) [25] together with the Gabedit [26] graphical interface by using density functional theory (DFT) Becke-3-Lee-Yang-Parr (B3LYP) functional [27, 28]. Furthermore, experimental molecular geometry was used as the initial guess for optimization.

4. Conclusion

In this study, we have synthesized a novel compound N′-(2,4-dinitrophenyl)-2-fluorobenzohydrazide, C₁₃H₉FN₄O₅, characterized by spectroscopic (FT-IR, NMR) and structural (XRD) techniques. Theoretical geometrical parameters by DFT were compared with experimental data results and seemed to be in a good agreement with experimental ones. The X-ray structure is found to be very slightly different from it optimized counterpart, and the crystal structure is stabilized by N–H⋯O and N–H⋯F type hydrogen bonds. It is noted here that the experimental results are for the solid phase and the theoretical calculations are for the gaseous phase. The geometry of the solid state structure is subject to intermolecular forces, such as van der Waals interactions and crystal packing forces.