Journal of Physical and Theoretical Chemistry of Islamic Azad University of Iran, 12 (1) 33-43: Spring 2015 (J. Phys. Theor. Chem. IAU Iran) ISSN 1735-2126 DFT Study of 1H-tetrazolyl derivatives of tetrahedrane Mehdi Nabati and Mehrdad Mahkam* Chemistry Department, Faculty of Science, Azarbaijan Shahid Madani University, Tabriz, Iran Received January 2015; Accepted February 2015 ABSTRACT Tetrazole-containing compounds have been the subject of much recent research because of their potential as high energy density materials (HEDMs). In this work, theoretical studies on the 1H- tetrazolyl derivatives of tetrahedrane were done at the density functional theory (DFT) method with the 6-31G(d) basis set without any symmetrical restrictions in order to find the structural and energetically properties. Geometric and electronic structures, natural bond orbitals (NBOs) population, aromaticity of tetrazole rings, thermodynamic properties and detonation performances of these molecules have been studied using mentioned level of theory. Nucleus independent chemical shift (NICS) calculations show the tetrazole rings on the tetrahedrane system are aromatic. The heat of formation (HOF) values of all structures has been calculated by a proper isodesmic reaction. The HOFs are found to be correlative with the number of tetrazole groups. According to the results of the calculations, only tri-substituted derivative of tetrahedrane can be a viable candidate of high energy materials. Keywords: Tetrahedrane; Tetrazole; Theoretical study; Detonation properties; Heat of formation INTRODUCTION 1Tetrahedrane is a platonic hydrocarbon produces under decomposition [3]. The with tetrahedral structure [1]. It is a most nitrogen-rich groups such as tetrazole rings highly strained hydrocarbon and has an can increase the detonation properties of important role in the extension of the strain the explosive compounds [4]. Synthesis of concept in organic chemistry. Due to this these materials is very difficult and reason, this molecule is unstable and dangerous, but knowing of the structural experimental data on it have been hard to and energetic properties of explosives obtain [2]. It can be used from this makes easy the preparation of them [5]. In property to design of novel high energy the present work, we report the theoretical density materials (HEDMs). The explosive study of the 1H-tetrazolyl derivatives of function is dependent on many things such tetrahedrane. A particularly important as density, volume of explosion, velocity method is to model a molecular system of detonation, pressure of explosion and prior to synthesizing that molecule in the the number of moles and molecular weight laboratory [6]. This is very useful mean of the gaseous products that one explosive because synthesizing a compound could *Corresponding author: [email protected] Mehdi Nabati and Mehrdad Mahkam /J. Phys. Theor. Chem. IAU Iran, 12 (1) 33-43: Spring 2015 need months of labor and raw materials, RESULTS AND DISCUSSION and generates toxic waste [7]. A second use of computational chemistry is in Structural properties study of the understanding a problem more completely molecules [8]. In this paper we studied 1H-tetrazolyl derivatives of tetrahedrane system. The COMPUTATIONAL METHODS studied molecules are depicted in Figure 1. All theoretical studies were carried out As mentioned above, we were successful with the Gaussian 03 computational in computing the structural properties of package [9]. The computational method the molecules with DFT method at 298.15 employed for the tetrahedrane derivatives K and 1 atmosphere; therefore, we use the calculations is the same as that used DFT method for computing the properties previously for tetraherane: B3LYP/6- of the structures. The geometric structures 31G(d) level of theory. The term of of the studied molecules are shown in B3LYP consists of the Vosko, Wilk, Figure 2. All calculations were performed Nusair (VWN3) local correlation at B3LYP/6-31G(d) level of theory. As functional [10] and Lee, Yang, Parr (LYP) seen from the Table 1, the dipole moment correlation correction functional [11]. The (µ) order is T2>T1>T3>T4>tetrahedrane geometry of structures was optimized for the structures. The bond lengths and without any structural or symmetry angles data of the molecules have been restrictions in the gas phase. Vibrational given in Table 2. It is observed that the frequencies were calculated to determine length of C-H bond of tetrahedrane the nature of the stationary points as well backbone does not change by increasing of as the zero point and heat capacity 1H-tetrazole number on the system (MC- corrections. Prediction the heat of H=1.075A°). As seen from the data, the formation (HOF) of the molecules was length of CT-CT bond is longer than the studied via the isodesmic reactions [12]. length of CH-CT bond. The results of the To calculate the density of structures, the calculations showed that the longest C-C molecular volume data was required. The bond among all the structures corresponds molecular volume V was defined as inside to CT-CT bond of molecule T4, which is a contour of 0.001 electrons/bohr3 density. 1.521A°, and the shortest C-C bond The computational molecular density H corresponds to CH-CH bond of molecule (H=M/V, where M = molecular weight) T1, which is 1.466A°. It is also observed was also calculated. The computational that the shortest angle corresponds to CT- molecular density H (H=M/V, where M = CH-CT angle of molecule T3, which is molecular weight) was also calculated. 59.615 degree. Oxygen balance (OB100) is an expression The molecular electrostatic potential that is used to indicate the degree to which (MEP) [14] is typically visualized through an explosive (CaHbOcNd) can be oxidized mapping its values onto the surface [13]. OB100 was calculated as follows: reflecting the molecules boundaries. The three-dimensional electrostatic potential ����� � maps of the structures are shown in Figure ��� � ����� ��� ���� �� � 3. The yellow-red loops and the blue loops indicate negative and positive charge where: a = number of atoms of carbon, b = development for a particular system number of atoms of hydrogen, c = number respectively. As can be seen from the of atoms of oxygen. figures the negative charge is located on 34 Mehdi Nabati and Mehrdad Mahkam /J. Phys. Theor. Chem. IAU Iran, 12 (1) 33-43: Spring 2015 the nitrogen elements of the tetrazole rings UV spectra of the molecules, respectively. as expected due to the electron withdrawing character of theirs and T1: IR [Harmonic frequencies (cm-1), positive charge is located on the intensities (KM/Mole)]: 134.05 (1.60), tetrahedrane backbone and hydrogen atom 136.20 (2.39), 368.82 (0.16), 427.04 that attached to the tetrazole rings. (0.44), 455.05 (9.77), 567.01 (72.54), The natural bond orbitals (NBOs) [15] data 603.45 (27.82), 695.66 (10.93), 724.33 of the structures are listed in Table 3. It can (4.99), 744.71 (2.84), 795.39 (22.83), be deduced from the data, the electron 810.98 (25.03), 836.29 (43.46), 873.88 occupancy order of the C-C bonds is CT- (3.85), 894.30 (5.43), 902.87 (0.91), CT<CT-CH<CH-CH for the molecules. It is 1013.42 (0.99), 1058.13 (0.27), 1061.87 also observed the C-C M-bonds and the C- (45.90), 1095.64 (11.39), 1136.93 (0.67), H M-bonds are p-rich and s-rich, 1168.85 (7.13), 1233.23 (1.18), 1271.33 respectively. We can see, the tetrazole (2.09), 1356.74 (47.16), 1401.19 (16.07), groups cause the carbon atoms use more p 1500.71 (36.78), 1701.73 (170.51), orbitals for formation of C-C bonds in 3352.43 (13.13), 3355.72 (15.52), 3383.11 tetrahedrane backbone. (8.41), 3654.48 (67.24). NMR [nucleus Aromatic character is not a directly shielding (ppm)]: H (22.4551, 28.7910, measurable or computable quantity [16]. 28.7911, 29.0900), C (49.0228, 200.1359, This character can be obtained by NMR 200.1374, 204.2996, 206.0690), N (- keyword in Gaussian software. Paul 147.6854, -102.3083, -72.3582, 39.5918). Schleyer and his coworkers proposed the UV: The wavelength of maximum use of nucleus independent chemical shift absorption (Pmax) is 221.13 nm. (NICS) computed with available quantum mechanics programs, as a new T2: IR [Harmonic frequencies (cm-1), aromaticity/antiaromaticity criterion [17]. intensities (KM/Mole)]: 35.64 (0.07), NICS calculations at the center of the rings 82.45 (6.69), 88.53 (13.72), 130.32 (1.51), were carried out on the molecule using the 147.20 (0.46), 187.32 (4.01), 313.09 gauge invariant atomic orbital (GIAO) (6.54), 381.98 (0.01), 396.43 (0.99), approach. NICS calculations were carried 419.50 (7.11), 483.16 (5.21), 583.97 out to determine the aromaticity of (86.90), 590.05 (1.66), 675.05 (0.48), tetrazole rings of the molecules [18]. The 691.39 (10.24), 713.04 (11.78), 728.04 results of calculations are shown in Table (7.49), 743.12 (0.01), 744.52 (1.18), 4. Negative and positive signs for NICS 820.02 (31.94), 823.92 (66.37), 849.95 indicate the aromatic and anti-aromatic (2.90), 880.79 (4.13), 888.20 (10.78), characters of the molecules, respectively. 1013.89 (1.62), 1024.57 (1.31), 1050.45 As can be seen from the data, tetrazole (1.86), 1061.47 (17.05), 1066.14 (14.67), rings of the molecules have been found to 1091.88 (31.59), 1098.36 (22.56), 1100.77 be aromatic. (17.06), 1143.99 (1.85), 1188.72 (6.21), 1250.47 (2.72), 1264.55 (27.58), 1283.55 IR, UV-VIS and NMR study of the (0.56), 1336.59 (26.35), 1405.84 (22.81), molecules 1422.43 (8.89), 1440.60 (1.27), 1515.12 Spectroscopy methods are widely used in (42.54), 1625.01 (287.29), 1750.45 all fields of chemistry for determination of (54.82), 3347.68 (20.82), 3366.56 (17.79), structure of molecules.