INTRODUCTION

Five-membered heterocycles are increasingly important in medical chemistry. Especially 1,2,4-triazole derivatives have a wide spectrum of biological activity, including anti-tuberculosis, antimalarial, antioxidant, antimicrobial, anti-inflammatory, antiviral, cytotoxic, anticonvulsant, antiproliferative, antidepressant, hypoglycemic, anticancer, antipyretic and analgesic activities [1–4]. In addition, flucanazole and itraconazole, which have a triazole nucleus, are effective against fungal growth in biological systems [5]. Due to the importance of the items researched in this work, the results of experimental and theoretical studies were compared to determine the structure details.

EXPERIMENTAL

Synthesis

The compounds were synthesized according to [6].

X-Ray Data Collection

X-ray diffraction patterns were obtained on a Bruker diffractometer [7, 8]. Single crystals of compounds I and II were grown in the form of blocks. Crystals with approximate sizes of 0.500 × 0.300 × 0.200 mm for I and 0.55 × 0.50 × 0.45 mm for II were chosen for further measurements (MoKα radiation, λ = 0.71073 Å, ω scan technique at 293 K). Data reduction was performed using the APEX2 [8] and SAINT software [7]. The crystal structures of the title compounds were solved and refined by direct methods and full-matrix least square procedure using the SHELXS-97 [9, 10] and SHELXL-97 programs [9, 10]. The ORTEP-3 program [11] for MS Windows has been preferred for the visualization of figures. WinGX [11] was used to prepare data for publication.

The parameters of all atoms of compounds I and II, except hydrogen, were refined in the anisotropic approximation of atomic displacements. The H1 atoms attached to N1 and N2 atoms were localized from difference Fourier map and their parameters were refined in the isotropic approximation. Other H atoms were positioned with idealized geometry and refined using isotropic temperature factors and C–H distances of 0.93–0.96–0.97 Å with Uiso(H) = 1.2Ueq(C) and 1.5Ueq(C). Crystallographic data, structure solution and refinement results are listed in Table 1, the CCDC reference numbers are 1957024 and 1957025 for crystals I and II, respectively.

Table 1.   Crystal data, details of data collection, and results of structure refinement for the compounds C13H17N3O2 (I) and C14H19N3O2 (II)
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Theoretical Analysis

The geometry was optimized for the compounds I and II of triazole derivatives in gas phases using the density functional theory (DFT) with the B3YLP functional and Hartree–Fock (HF) approximation with the 6-31G+(d) basis [12–15]. Theoretical calculations were performed using the Gaussian03 program [16]. For this aim, X-ray diffraction (XRD) data are used as initial atomic parameters in theoretical calculations.

RESULTS AND DISCUSSION

X-Ray Diffraction Study

The molecular structures of compounds I and II were obtained by single crystal XRD technique. Compound I crystallizes in the monoclinic sp. gr. P21 with Z = 2, while compound II crystallizes in the sp. gr. P21/c with Z = 4. The asymmetric unit in both compounds contains one molecule (Fig. 1). The bond lengths and angles in I and II have normal values [17, 18]. In I, the triazole ring is twisted by 63.17(1)° with respect to the benzene ring, whereas in compound II the corresponding dihedral angle is only 2.71(1)°, which indicates that both ring systems are almost coplanar.

Fig. 1.
figure 1

Molecules of (a) C13H17N3O2 and (b) C14H19N3O2.

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In I, the crystal packing is consolidated by the N–H⋅⋅⋅O and C–H⋅⋅⋅O hydrogen bonds, namely, N2–H1⋅⋅⋅O1, C5–H5A⋅⋅⋅O1, C6–H6A⋅⋅⋅O2, and C8–H8⋅⋅⋅O1, which generate eight-membered ring, producing \(R_{2}^{2}(9)\) and \(R_{2}^{1}(7)\) motifs [17] (Table 2). In II, molecules are joined by hydrogen bonds of the N–H⋅⋅⋅O type (Table 3), namely, N2–H1⋅⋅⋅O1 (symmetry code: –x – 1, –y – 2, –z – 1), which links molecules into centrosymmetric pairs, forming a \(R_{2}^{2}(8)\) motif [19]. The molecule packing in both compounds is shown in Fig. 2.

Table 2.   Hydrogen bond geometry for compound I
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Table 3.   Hydrogen bond geometry for compound II
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Fig. 2.
figure 2

Packing of the molecules of (a) C13H17N3O2 and (b) C14H19N3O2.

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Optimized Geometry

Geometric parameters, such as bond lengths, bond angles, and torsion angles, were tested with the basis set 6-31G+(d) using DFT/B3YLP and HF methods to determine if they are compatible with the experimental values. The results showed that, although most of the parametric values were almost close to the experimental data, the bridge C7–C6–C5–N3 torsion angle in compound I was calculated as 60.68° and 59.40° using DFT/BYLP and HF, respectively. The bridge torsion angle N3–C3–C4–C5 in compound II was calculated as 177.03° and 177.96° using DFT/BYLP and HF, respectively. The XDR values of these torsion angles are 63.3(4)° and 172.47(15)° for compounds I and II, respectively.

The root mean square errors were calculated for bond lengths and angles. The calculated values with the selected basis set of DFT/B3YLP and HF methods were 0.014 Å and 0.88°, 0.015 Å and 0.87° for compound I, 0.019 Å and 0.59°, 0.016 Å and 0.57° for compound II, respectively. The results showed that the HF method gives the best results for the studied molecular structures, although both methods give approximate results. Some selected geometric parameters are shown in Tables 4 and 5.

Table 4.   The experimental and calculated values of selected bond lengths (Å), bond angles, and torsion angles (deg) for I
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Table 5.   The experimental and calculated values of selected bond lengths (Å), bond angles, and torsion angles (deg) for II
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The structure determined by XRD and geometry optimized by DFT/B3YLP and HF methods with the 6-31G+(d) basis set are superimposed in Fig 3. Although the overall superimposition is in good agreement, most deviations from the superimposition were observed in the triazole ring for compound I. These deviations are assumed to occur because the theoretical calculations are based on the gas phase of the compound, while the experimental results are based on its solid phase.

Fig. 3.
figure 3

Superimposed images of the structures of compounds (a, c) I and (b, d) II according to XRD (black) and theoretical values (grey) obtained using (a, b) DFT and (c, d) HF.

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