oxadiazole Derivatives Featuring the ... - Wiley Online Library

DOI: 10.1002/chem.201406436

Communication

& Structure Elucidation

Synthesis, Characterisation and Crystal Structures of Two Bi-oxadiazole Derivatives Featuring the Trifluoromethyl Group Marcos A. Kettner, Thomas M. Klapçtke,* Tomasz G. Witkowski, and Felix von Hundling[a] Abstract: The synthesis, characterisation, and crystal structure determination of the closely related compounds 3,3’-bi-(5-trifluoromethyl-1,2,4-oxadiazole) and 5,5’-bi-(2trifluoromethyl-1,3,4-oxadiazole) are reported. These two compounds are known for their bioactivity; however, in this study they serve as model compounds to evaluate the suitability of the heterocyclic oxadiazole ring system for energetic materials when the fluorine atoms in the exocyclic CF3 groups are substituted successively by nitro groups. Quantum chemical calculations for the bi-1,3,4oxadiazole derivatives with difluoronitromethyl, fluorodinitromethyl, and trinitromethyl groups have been carried out and predict promising energetic performances for both explosive and propulsive applications.

Scheme 1. Syntheses of compounds 1[8] and 2.[9, 10]

The heterocyclic class of oxadiazoles includes four different isomers. They find application as ingredients for drugs,[1] dyestuffs,[2] ionic liquids,[3] and scintillators.[4] The bi-oxadiazoles form two further isomers, owing to the asymmetry of the 1,2,3- and 1,2,4-oxadiazoles, which can be linked at two different carbon atoms. In the area of energetic materials, largely only 1,2,5-oxadiazole (furazane) derivatives have been exhaustively investigated.[5] In contrast 1,2,3-, 1,2,4-, and 1,3,4oxadiazoles have only been explored sparsely with respect to derivatives in which energetic moieties such as polynitro groups or azides are attached.[6] Furazanes or furoxanes are not necessarily the thermally and chemically most stable derivatives of this class, but are favored due to their positive heats of formation and high densities.[5h] Herein we summarise the synthetic pathways for 3,3’-bi-(5trifluoromethyl-1,2,4-oxadiazole) (TFM2-1,2,4BOD, 1) and the analogous 5,5’-bi-(2-trifluoromethyl-1,3,4-oxadiazole) (TFM21,3,4 BOD, 2) and compare the density and thermal behaviour of the two compounds. The trifluoromethyl group serves as a non-energetic moiety, in which fluorine atoms can be [a] M. A. Kettner, Prof. Dr. T. M. Klapçtke, T. G. Witkowski, F. von Hundling Department of Inorganic Chemistry Ludwig-Maximilian University of Munich (LMU) Butenandtstr. 5–13, 81377 Munich (Germany) E-mail: [email protected] Homepage: http://www.hedm.cup.uni-muenchen.de Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201406436. The general procedures as well as computational and X-ray diffraction details and predictions calculated with the ICT-Thermodynamic Code can be found in the Supporting Information. Chem. Eur. J. 2015, 21, 4238 – 4241

substituted stepwise by nitro groups, as reported previously for several 3,3’-bi-(5-polynitromethyl-1,2,4-oxadiazole) derivatives.[6b,c, 7] The synthetic routes used are depicted in Scheme 1. Compound 1 was synthesised according to a slightly modified literature procedure in which trifluoromethyl acetic acid anhydride acts as both the solvent and reactant, resulting in an increase in the yield by 11 % in comparison with the previously reported yield.[8] Compound 2[9] was synthesised using a convenient literature method for the formation of bi-1,3,4-oxadiazoles. The conversion of bi-5,5’-tetrazoles into the oxadiazoles with formation of N2 results in very high yields (93 %) and a high purity of the target compound.[10] IR and Raman spectra show the expected bands for the two title molecules.[11, 12] The characteristic stretching modes (sym. and asym.) of the CF3 groups are observed in the IR spectra at 1212 and 1171 cm 1 (1), and at 1227 and 1169 cm 1 (2), respectively. Additionally, some characteristic vibrations of the ring systems could be assigned according to the literature (see Experimental Section).[12] The 13C NMR spectra show the expected 1 J(C,F) and 2J(C,F) coupling constants.[12, 13] In addition, 19F and 15 N NMR spectra were obtained showing the chemical shifts for the ring nitrogen atoms of the 1,2,4- and 1,3,4-oxadiazole derivatives as well as their 3J(15N,19F) coupling constants (Table 1). According to differential scanning calorimetry (DSC) measurements, compound 1 melts at 98 8C and boils at 142 8C, whereas compound 2 melts at 169 8C and boils at 199 8C. Both compounds showed no decomposition until a temperature of 400 8C in a closed aluminium vessel in the DSC measurements. Compounds 1 and 2 crystallised from ethanol as very thin colourless plates, or by sublimation as thin needles (1) or blocks (2). Both compounds crystallise in the monoclinic space group P21/c with two molecules per unit cell and show remarkably high densities of 2.01 g cm 3 (1) and 1.98 g cm 3 (2) at 173 K. Figure 1 depicts the molecular structures of both TFM2-BODs viewed perpendicular to the ring systems, which

4238

2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication Table 1. 13C, [D6]DMSO.

15

N, and

19

F NMR chemical shifts of compounds 1 and 2 in

Table 2. Crystallographic data for compounds 1 and 2. Compound

Nucleus

Assignment

1

2

13

C

Coxadiazole CC CF3

166.5 (q) 159.3 (s) 115.4 (q)

155.3 (q) 153.8 (s) 115.7 (q)

15

N

CNC/3-N ONC/4-N

134.8 (q) 9.3 (s)

64.2 (q) 64.6 (s)

19

F

CF3

65.14 (br)

1

formula formula weight [g mol 1] crystal dimensions [mm] crystal description crystal system space group a [] b [] c [] a,g [8] b [8] V [3] Z 1calc [g cm 3] m [mm 1] F(000) temperature [K] q range [8] index ranges

64.65 (br)

(s) singlet; (q) quartet; (br) broad.

reflections measured reflections independent reflections unique R(int) R1, wR2 (2s data) R1, wR2 (all data) data/restraints/parameters GoF on F2 residual electron density

Figure 1. Single crystal structures of 3,3’-bi-(5-trifluoromethyl-1,2,4-oxadiazole) (1, left) and 5,5’-bi-(2-trifluoromethyl-1,3,4-oxadiazole) (2, right); bond lengths [] and angles [8]: 1) O1 C2 1.332(2), O1 N2 1.405(2), N1 C2 1.285(2), N1 C3 1.380(2), N2 C3 1.301(2), average F C1 1.315(2), C3 C3’ 1.458(3), C2 C1 1.510(2); average F-C1-F 108.2(2), C2-C1-F 110.8(3), N2-C3-N1 115.7(1), O1-N2-C3-C3’ 178.6(2), N2-O1-C2-C1 178.7(1); 2) O1 C2 1.350(2), O1 C3 1.353(2), N2 C3 1.288(2), N2 N1 1.405(2), N1 C2 1.278(2), average F C1 1.306(2), C3 C3’ 1.446(3), C2 C1 1.504(2); average F-C1-F 107.9(2), C2C1-F 111.0(2), N2-C3-O1 114.1(1), C2-O1-C3 100.8(1), N1-N2-C3-C3’ 179.1(2), N2-N1-C2-C1 178.3(2).

are planar in both molecules. Table 2 lists the crystallographic data. The structures exhibit some short intermolecular contacts that are well below the sum of van der Waals radii. For example, in the structure of compound 1, N2···C3i 3.105(2) and O1···C3i 3.122(2) [symmetry operator i) x, 1=2 + y, 1=2 z], and in the structure of compound 2, N1···C3i 3.062(2) and N2···C3i’ 2.984(2) [symmetry operator i) 1 x, 1=2 + y, 11=2 z; (van Chem. Eur. J. 2015, 21, 4238 – 4241

www.chemeurj.org

2

C6N4O2F6 274.10 0.404 0.291 0.067 0.550 0.338 0.188 colourless platelet colourless block monoclinic P21/c 11.1575(8) 10.9970(5) 4.7619(2) 5.1570(3) 8.7461(6) 8.2190(5) 90.0 103.142(7) 99.428(5) 452.52(5) 459.82(4) 2 2.012 1.980 0.230 0.227 268 268 173(2) 4.67–28.27 4.38–28.27 14 h 14 14 h 14 3k6 6k6 11 l 10 10 l 10 3724 4399 1104 1133 876 922 0.0245 0.0206 0.0390, 0.0977 0.0437, 0.1107 0.0530, 0.1097 0.0544, 0.1201 1104/0/82 1133/0/82 1.026 1.074 0.298/0.261 0.421/0.377

der Waals radii): N,C = 3.25 ; O,C = 3.22 ].[14] These short contacts may be responsible for the high densities observed for compounds 1 and 2. The bi-1,2,4-oxadiazole derivatives featuring the trinitromethyl and fluorodinitromethyl moieties have been reported previously and revealed good detonation and combustion properties, whereas the trinitromethyl compound shows a relatively low thermal stability, decomposing at 124 8C.[6c, 7] For the bi-1,3,4-oxadiazole derivatives that are assumed to be thermally more stable, the heats of formation for compounds containing the difluoronitromethyl (3), fluorodinitromethyl (4), and trinitromethyl (5) groups attached were computed by ab initio calculations using the GAUSSIAN 09 program package[15] at the CBS-4M level of theory (Figure 2).[16] The heat of formation of compound 2 (DHf8 = 1191 kJ mol 1) was calculated to be slightly more negative than that of compound 1 (DHf8 = 1135 kJ mol 1). The effect of C F bonds on the heat of formation can clearly be observed in this series of polyfluoro/polynitro compounds. Using these values and an estimated density of 1.90 g cm 3 (minimumestimation supported by previous work)[6c, 7] the detonation and combustion parameters were calculated using the EXPLO5 (V6.02) computer code (Table 3)[17] and the ICT-Thermodynamic Code (see the Supporting Information).[20] Providing the thermal stability of the non-fused heterocyclic system is not decreased too much by the trinitromethyl moiety, compound 5 would be a suitable candidate as oxidiser in solid rocket propellants.[18]

4239


Communication Table 3. Calculated detonation and combustion parameters for predicted energetic compounds 3, 4 and 5 depicted in Figure 2.

Formula weight [g mol 1] N + O [%][a] WCO [%][b] WCO2 [%][c] 1est [g cm 3][d] DHf0 [kJ mol 1][e]

Figure 2. Molecular structures of 5,5’-bi-(2-difluoronitromethyl-1,3,4-oxadiazole) (3), 5,5’-bi-(2-fluorodinitromethyl-1,3,4-oxadiazole) (4) and 5,5’-bi-(2trinitromethyl-1,3,4-oxadiazole) (5) with successive substitution of the fluorine atoms by nitro groups.

Detonation parameters[17] DexU8 [kJ kg 1][f] Tex [K][g] DV [m s 1][h] pCJ [kbar][i] V0 [L kg 1][j]

From this comparative study on CF3-substituted bi-1,2,4- and bi-1,3,4-oxadiazoles the following conclusions can be drawn: · ·

·

Bi-1,2,4-oxadiazole 1 has only a slightly higher density than bi-1,3,4-oxadiazole 2. In comparing the bi-1,2,4-oxadiazole with the bi-1,3,4-oxadiazole ring system, the heats of formation are barely affected by the position of the oxygen atom in the oxadiazole rings. The calculations on bi-1,3,4-oxadiazoles with difluoronitromethyl, fluorodinitromethyl, and trinitromethyl groups predict promising properties for these compounds for both explosive and propulsive applications. Work on the syntheses of these and various related compounds is already in progress within our group.

5,5’-Bi-(2-trifluoromethyl-1,3,4-oxadiazole) (2): To a stirred suspension of 5,5’-bi-2 H-tetrazole (2.15 g, 15.56 mmol) in p-xylene (30 mL), a solution of trifluoroacetic acid anhydride (5.56 mL, 8.40 g, 40 mmol) in p-xylene (12 mL) was added dropwise. The reaction mixture was stirred at 100 8C until N2 no longer evolved. The mixture was allowed to cool to room temperature and was then adjusted to pH 9 using a saturated NaHCO3 solution. The white precipitate was filtered off, washed with water (200 mL), and Chem. Eur. J. 2015, 21, 4238 – 4241

www.chemeurj.org

4

5

C6N6O6F4 328.09 54.87 29.3 0.0 1.90 685

C6N8O10F2 382.11 71.20 16.8 8.4 1.90 212

C6N10O14 436.12 83.48 29.3 7.3 1.90 231

1606 2220 6898 248 597

4316 3647 8440 297 677

5893 4633 8764 332 677

Combustion parameters, chamber pressure 70 bar vs. atmosphere[17] Isp (neat) [s][k] 203 (2894 K) 244 (3581 K) 252 (3562 K) 236 (3750 K) 260 (4455 K) 260 (4447 K) Isp (15 % Al) [s][l] Isp (16 % Al, 14 % PBAN) [s][m] 221 (2908 K) 238 (2952 K) 253 (2957 K) 225 (2908 K) 248 (3220 K) 267 (3867 K) Isp (10 % Al, 10 % PBAN) [s][n] [a] Combined nitrogen and oxygen content; [b] oxygen balance assuming the formation of CO and HF; [c] oxygen balance assuming the formation of CO2 and HF; [d] estimated density; [e] heat of formation calculated at the CBS-4M level of theory;[16] [f] heat of detonation; [g] temperature of the explosion gases; [h] detonation velocity; [i] detonation pressure; [j] volume of gaseous detonation products (assuming only gaseous products); [k] specific impulse of the neat compound; [l] specific impulse of a mixture with 15 % aluminium; [m] the specific impulse for the composition with 16 % aluminium, 6 % polybutadiene acrylic acid, 6 % polybutadiene acrylonitrile, and 2 % bisphenol A ether; the according mixture with 70 % ammonium perchlorate as the NASA Space Shuttle used was calculated to Isp = 260 s;[19] [n] specific impulse for the composition with 10 % aluminium, 4 % polybutadiene acrylic acid, 4 % polybutadiene acrylonitrile, and 2 % bisphenol A ether; [k–o] isobaric combustion temperature in parenthesis.

Experimental Section 3,3’-Bi-(5-trifluoromethyl-1,2,4-oxadiazole) (1):[8] N,N’-Dihydroxyoxal amidine (1.00 g, 8.47 mmol) was added to trifluoroacetic anhydride (10 mL) and stirred at 35 8C for 3 h. The solution was kept under reduced pressure and the acid was collected into an external cooling trap ( 78 8C). On cooling, the crude product precipitated and was removed by filtration using a glass frit (porosity 4). The white precipitate was recrystallised from hot ethanol yielding compound 1 (1.72 g, 6.27 mmol, 75 %) as colourless crystals. Alternatively, the crude compound can be purified by sublimation. DSC (5 8C min 1, Tonset): Tmelt = 98; Tboil = 142 8C; 13C NMR ([D6]DMSO): d = 166.5 (q, 2J(C,F) = 44.8 Hz, OCN), 159.3 (CC), 115.4 ppm (q, J(C,F) = 273.4 Hz, CF3); 15N NMR ([D6]DMSO): d = 9.3 (ONC), 134.8 ppm (q, 3J(15N,19F) = 1.9 Hz, CNC); 19F NMR ([D6]DMSO): d = 65.1 ppm (br, CF3); IR: n = 1605 (w, nC=N), 1453 (vw), 1431 (w), 1334 (m), 1276 (vw), 1212 (s, nsym C F), 1171 (vs, nasym,C F), 1138 (vs), 996 (m), 951 (w), 911 (m, n2N O), 758 (s), 668 cm 1 (m); Raman (200 mW): n (rel. int.) = 1615 (17), 1601 (100), 1432 (12), 1329 (4), 1185 (5, nasym C F), 1150 (4), 1022 (9), 994 (38), 923 (8, n2N O), 766 (22), 737 cm 1 (10); MS (DCI + ): m/z: 275.2 [M + H + ]; MS (DEI + ): m/z: 274.2 [M + ]; elemental analysis calcd (%) for C6N8O10F2 : C 26.29, N 20.44; found: C 26.29, N 20.60.

3

dried under reduced pressure yielding pure product 2 (3.97 g, 14.48 mmol, 93 %). The compound could be further purified by sublimation. DSC (5 8C min 1, Tonset): Tmelt = 169; Tboil = 199 8C; 13 C NMR ([D6]DMSO): d = 155.3 (q, 2J(C,F) = 44.7 Hz, OCN), 153.8 (CC), 115.7 ppm (q, J(C,F) = 271.9 Hz, CF3); 15N NMR ([D6]DMSO): d = 64.6 ppm (4-N); 19F NMR 64.2 (q, 3J(15N,19F) = 1.5 Hz, 3-N), ([D6]DMSO): d = 64.7 ppm (br, CF3); IR: n = 1579 (w, nC=N), 1476 (s, nC=N), 1378 (s), 1227 (w, nsym C F), 1169 (vs, nasym C F), 1118 (vs, nC O), 1005 (vs), 974 (s, nC O), 950 (s), 755 (s), 735 (s), 674 cm 1 (s); Raman (200 mW): n(rel. int.) = 1651 (64), 1580 (4, nC=N), 1037 (11), 973 (7), 764 (5), 721 cm 1 (4); MS (DEI + ): m/z: 274.1 [M + ]; elemental analysis calcd (%) for C6N8O10F2 : C 26.29, N 20.44; found: C 26.21, N 20.33.

Acknowledgements Financial support for this work by the Ludwig-Maximilian University of Munich (LMU), the U.S. Army Research Laboratory (ARL) under grant no. W911NF-09-2-0018, the Armament Research, Development and Engineering Center (ARDEC) under grant nos. W911NF-12-1-0467 and W911NF-12-1-0468, and the Office of Naval Research (ONR) under grant nos. ONR.N0001410-1-0535 and ONR.N00014-12-1-0538 is gratefully acknowl-

4240


Communication edged. The authors acknowledge collaborations with Dr. Mila Krupka (OZM Research, Czech Republic) in the development of new testing and evaluation methods for energetic materials and with Dr. Muhamed Suceska (Brodarski Institute, Croatia) in the development of new computational codes to predict the detonation and propulsion parameters of novel explosives. We are indebted to and thank Drs. Betsy M. Rice and Brad Forch (ARL, Aberdeen, Proving Ground, MD) for many inspiring discussions. T.G.W. is supported by the Research Grants for Doctoral Candidates and Young Scientists and Academics project, which is financed by German Academic Exchange Service (DAAD). We thank Dr. Burkhard Krumm for multinuclear NMR measurements, and the X-ray team around Prof. Dr. Konstantin Karaghiosoff is gratefully thanked for the single crystal measurements. Keywords: oxadiazoles · quantum chemistry · ring-closure · structure elucidation · thermal analysis [1] a) M. Heitzmann, Sandoz AG, CH Pat 661270, 1987; b) T. Kim, J. W. Suh, J. C. Ryu, B. C. Chung, J. Park, J. Chromatogr. B 1996, 687, 79 – 83. [2] a) D. V. Nightingale, R. M. Brooker, J. Am. Chem. Soc. 1950, 72, 5539 – 5543; b) K.-H. Kim, H.-J. Lee, U.S. Pat. 20140231757 (A1 20140821), 2014. [3] a) A. Pace, P. Pierro, Org. Biomol. Chem. 2009, 7, 4337 – 4348; b) J. A. Pedro, J. R. Mora, E. Westphal, H. Gallardo, H. D. Fiedler, F. Nome, J. Mol. Struct. 2012, 1016, 76 – 81; c) E. Westphal, D. Henrique da Silva, F. Molin, H. Gallardo, RSC Adv. 2013, 3, 6442 – 6454. [4] a) J. B. Birks, Pat. GB 1286622 19720823, 1972; b) M. Hyman, Jr., Pat. U.S. 4017738 A 19770412, 1977; c) V. Rimbau Barreras, Pat. ES 551136 A1 19870316, 1987; d) F. Dubois, R. Knochenmuss, R. Zenobi, Int. J. Mass Spectrom. Ion Processes 1997, 169/170, 89 – 98. [5] a) D. Chavez, L. Hill, M. Hiskey, S. Kinkead, J. Energ. Mater. 2000, 18, 219 – 236; b) D. Fischer, T. M. Klapçtke, M. Reymann, J. Stierstorfer, Chem. Eur. J. 2014, 20, 6401 – 6411; c) A. B. Sheremetev, J. Heterocycl. Chem. 1995, 32, 371 – 385; d) P. W. Leonard, D. E. Chavez, P. F. Pagoria, D. L. Parrish, Propellants Explos. Pyrotech. 2011, 36, 233 – 239; e) R. Wang, Y. Guo, Z. Zeng, B. Twamley, J. M. Shreeve, Chem. Eur. J. 2009, 15, 2625 – 2634; f) V. Zelenov, A. Lobanova, S. Sysolyatin, N. Sevodina, Russ. J. Org. Chem. 2013, 49, 455 – 465; g) A. M. Churakov, S. L. Ioffe, V. A. Tartakovsky, Mendeleev Commun. 1995, 5, 227 – 228; h) N. N. Makhova, Proceedings of Seminar on New Trends in Research of Energetic Materials, Part 2, (NTREM), Pardubice, Czech Republic, April 9 – 11th, 2014, pp. 647 – 652. [6] a) L. Zhanxiong, O. Yuxiang, C. Boren, http://www.mdpi.org/cji/cji/2001/ 033013ne.htm (accessed: 06.11.2014), Chem. J. Internet 2001, 3, 13; b) T. M. Klapçtke, N. Mayr, J. Stierstorfer, M. Weyrauther, Chem. Eur. J. 2014, 20, 1410 – 1417; c) M. A. Kettner, K. Karaghiosoff, T. M. Klapçtke, M. Sucéska, S. Wunder, Chem. Eur. J. 2014, 20, 7622 – 7631; d) V. Thottempudi, J. Zhang, C. He, J. M. Shreeve, RSC Adv. 2014, 4, 50361 – 50364.

Chem. Eur. J. 2015, 21, 4238 – 4241

www.chemeurj.org

[7] M. A. Kettner, T. M. Klapçtke, Chem. Commun. 2014, 50, 2268 – 2270. [8] V. G. Andrianov, V. G. Semenikhina, A. V. Eremeev, Chem. Heterocycl. Compd. 1994, 30, 475 – 477. [9] G. Seitz, C. H. Gerninghaus, Pharmazie 1994, 49, 102 – 106. [10] L. I. Vereshchagin, A. V. Petrov, V. N. Kizhnyaev, F. A. Pokatilov, A. I. Smirnov, Russ. J. Org. Chem. 2006, 42, 1049 – 1055. [11] G. Socrates, Infrared and Raman Characteristic Group Frequencies: Tables and Charts, 3rd ed., John Wiley & Sons, Chichester, 2004. [12] a) K. Hemming in Comprehensive Heterocyclic Chemistry III, Vol. 5 (Eds.: A. R. Katritzky, C. A. Ramsden, E. F. V. Scriven, R J. K. Taylor) Elsevier, Amsterdam, 2008, pp. 243 – 314; b) J. Suwin´ski, W. Szczepankiewicz in Comprehensive Heterocyclic Chemistry III, Vol. 5 (Eds.: A. R. Katritzky, C. A. Ramsden, E. F. V. Scriven, R J. K. Taylor) Elsevier, Amsterdam, 2008, pp. 397 – 466. [13] H.-O. Kalinowski, S. Berger, S. Braun, 13 C NMR Spektroskopie, Thieme, Stuttgart, New York, 1984. [14] A. Bondi, J. Phys. Chem. 1964, 68, 441 – 451. [15] a) Gaussian 09, Revision C.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, . Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian, Inc., Wallingford, CT, 2009; b) GaussView 5, V5.0.8, T. K. R. Dennington, J. Millam, Semichem Inc., Shawnee Mission, 2009. [16] a) J. J. A. Montgomery, M. J. Frisch, J. W. Ochterski, G. A. Petersson, J. Chem. Phys. 2000, 112, 6532 – 6542; b) J. W. Ochterski, G. A. Petersson, J. J. A. Montgomery, J. Chem. Phys. 1996, 104, 2598 – 2619. [17] a) M. Sucéska, Version 6.02, Zagreb, Croatia, 2014; b) M. Sucéska, Propellants Explos. Pyrotech. 1991, 16, 197 – 202; c) M. Sucéska, Propellants Explos. Pyrotech. 1999, 24, 280 – 285; d) M. Suceska, H. G. Ang, H. Y. Chan, Mater. Sci. Forum 2011, 673, 47 – 52. [18] a) T. M. Klapçtke, Chemie der Hochenergetischen Materialien, de Gruyter GmbH & Co. KG, Berlin, New York, 2009; b) T. M. Klapçtke, Chemistry of High-Energy Materials, de Gruyter GmbH & Co. KG, Berlin, New York, 2011. [19] a) NASA, Space Shuttle News Reference, 2 – 20 – 22 – 21, http://de.scribd.com/doc/17005716/NASA-Space-Shuttle-News-Reference-1981 (accessed: 13.11.2014); b) NASA, press release: STS-122 The Voyage of Columbus, 2008, 82 – 84, http://www.nasa.gov/pdf/203212mainsts122presskit2.pdf (accessed: 13.11.2014). [20] F. Volk, H. Balthet, The ICT-Thermodynamic Code (ICT-Code), 27th International Annual Conference of ICT, Karlsruhe, Germany, 92/1 – 16, 1996.

Received: December 11, 2014 Published online on February 3, 2015

4241
