3.4. ANÁLISIS E INTERPRETACIÓN DE RESULTADOS
4.1.1 Datos obtenidos mediante la aplicación de encuestas a las
synthetic procedures to compounds 1–5 are summarized in
Scheme 1.
Molecular Structures
To determine the molecular structures of1–5in the crystal-
line state an Oxford Xcalibur3 diffractometer with a Spellman generator (voltage 50 kV, current 40 mA) and a KappaCCD detector was used. The data collections at 173 K were per-
formed using the CrysAlis CCD software,[4] the data re-
ductions with the CrysAlis RED software.[5]The solution and
refinement of all structures were performed using the programs
Table 1.X-ray data and parameters.
1 2 3 4 5
formula BeC2H10N8O5 MgC2H18N8O9 CaC2H10N8O5 SrC8H22N10O6 BaC2H8N8O4
form. mass /g·mol–1 235.19 322.55 266.26 441.98 345.49
crystal system monoclinic monoclinic monoclinic orthorhombic triclinic space group P21/c(No. 14) P21/n(No. 14) P21/c(No. 14) Pcca(No. 54) P1¯ (No. 2)
color / habit colorless plate colorless rod colorless block colorless plate colorless rod size /mm 0.23⫻0.22⫻0.08 0.30⫻0.20⫻0.20 0.25⫻0.20⫻0.10 0.23⫻0.22⫻0.10 0.17⫻0.10⫻0.10 a/Å 11.5764(8) 12.117(4) 6.7848(2) 22.378(5) 7.4679(5) b/Å 11.8368(7) 6.955(5) 13.6768(3) 5.8533(9) 7.5004(5) c/Å 7.1908(6) 16.081(6) 10.8009(2) 13.940(3) 9.4148(7) α/° 90 90 90 90 73.119(6) β/° 99.035(7) 93.413(5) 91.147(2) 90 70.842(7) γ/° 90 90 90 90 81.251(5) V/Å3 973.11(12) 1352.8(12) 1002.06(4) 1825.9(6) 475.73(6) Z 4 4 4 4 2 ρcalcd./g·cm–3 1.605 1.584 1.765 1.608 2.412 μ/mm–1 0.145 0.192 0.654 3.000 4.189 F(000) 488 680 552 904 328 λ(Mo-Kα) /Å 0.71073 0.71073 0.71073 0.71073 0.71073 T/K 173 173 173 173 173 θmin-max /° 4.5, 26.0 4.2, 26.0 4.2, 25.7 4.2, 25.0 4.2, 26.0 dataseth; k; l –12:14;-14:14;-8: 7 –14:14;-5:8;-18:19 –8:8; –16:16; –13:13 –17: 26;-6: 6;-16:16 –9: 9;-9: 9;-11:11 reflect. coll. 4876 6818 14722 7853 4862 independ. refl. 1888 2647 1908 1598 1866 Rint 0.032 0.027 0.024 0.023 0.041 reflection obs. 295 1996 1678 1245 1648 No. Parameters 185 253 185 134 168 R1(obs) 0.0289 0.0294 0.0202 0.0230 0.0219 wR2(all data) 0.0503 0.0677 0.0566 0.0662 0.0488 S 0.77 0.91 1.03 1.06 0.98
resd. dens. /e·Å–3 –0.14, 0.19 –0.18, 0.28 –0.23, 0.30 –0.46, 0.35 –0.89, 0.48
device type Oxford Xcalibur3 Oxford Xcalibur3 CCD Oxford Xcalibur3 CCD Oxford Xcalibur3 Oxford Xcalibur3
CCD CCD CCD
solution SHELXS-97 SIR-92 SIR-92 SIR-92 SIR-92 refinement SHELXL-97 SHELXL-97 SHELXL-97 SHELXL-97 SHELXL-97 absorpt. corr. multi-scan multi-scan multi-scan multi-scan multi-scan
CCDC 827503 827502 827501 827504 827500
SIR-92,[6]SHELXS-97,[7]and SHELXL-97[8]implemented in
the WinGX software package[9] and finally checked with the
PLATON software.[10] In all crystal structures the hydrogen
atoms were located and refined. The absorptions were cor-
rected with the SCALE3 ABSPACK multi-scan method.[11]
Selected data and parameters of the X-ray determinations are given in Table 1.
Beryllium 5,5⬘-bistetrazolate pentahydrate (1) (Figure 1)
crystallizes in the monoclinic space groupP21/cwith four mo-
lecules in the unit cell. The N–N bond lengths in the two C– C linked tetrazolate rings are between N–N single bonds (1.454 Å) and N=N double bonds (1.245 Å). The shortest dis- tance is between the atoms N2–N3 (1.3094(17)Å), the longest between the atoms N1–N2 1.3445(17) Å. The C–C bond length (1.4629(19) Å) is closer to a single bond (1.52 Å) than
to a double bond (1.32 Å). In comparison to neutral 5,5⬘-biste-
trazole there are no significant changes regarding the bond lengths (N2–N3 = 1.2976(14) Å, N1–N2 = 1.3439(14) Å, C1–
C2 = 1.4535(15) Å). The bond angle in 1 N2–N1–C1 is
smaller (104.40(11)°) than in 5,5⬘-bistetrazole (108.37(9)°),[12]
whereas the angle N1–N2–N3 is larger (109.70(11)°) than in
the free acid (106.46(10)°). The five membered 6π electron
angle N1–N2–N3–N4 = 0.05(12)) as well as for its alkaline earth metal salts (torsion angle N1–N2–N3–N4 = 0.03(16)°). Exact bond lengths and angles are listed in Table 2. In this structure beryllium is coordinated tetrahedral by four water molecules with bond lengths between 1.60 Å and 1.61 Å and
Figure 1. Molecular unit of 1. Thermal ellipsoids of non-hydrogen atoms represent the 50 % probability level.
Table 2.Selected bond lengths /Å, angles /° and torsion angles /° of the anions of compounds1–5.
5,5BT Be-BT (1) Mg-BT (2) Ca-BT (3) Sr-BT (4) Ba-BT (5) Atom 1–2 /Å d(1–2) d(1–2) d(1–2) d(1–2) d(1–2) d(1–2) N1–N2 1.3439(14) 1.3445(17) 1.343(2) 1.3483(15) 1.349(3) 1.349(5) N2–N3 1.2976(14) 1.3094(17) 1.315(2) 1.3107(15) 1.313(3) 1.316(4) N3–N4 1.3583(14) 1.3430(17) 1.343(2) 1.3512(15) 1.352(3) 1.345(4) N4–C1 1.3178(14) 1.3307(18) 1.332(2) 1.3353(15) 1.329(3) 1.346(5) N1–C1 1.3289(14) 1.3333(18) 1.336(2) 1.3332(15) 1.331(3) 1.338(5) C1–C2 1.4535(15) 1.4629(19) 1.461(2) 1.4549(16) 1.465(4) 1.466(5) N5–C2 1.3178(14) 1.3333(18) 1.332(2) 1.3334(16) 1.331(5) N5–N6 1.3583(14) 1.3466(17) 1.347(2) 1.3495(15) 1.342(5) N6–N7 1.2976(14) 1.3032(17) 1.314(2) 1.3126(14) 1.316(4) N7–N8 1.3439(14) 1.3446(17) 1.346(2) 1.3460(14) 1.342(5) N8–C2 1.3289(14) 1.3299(18) 1.333(2) 1.3362(15) 1.328(5) Atoms 1–2–3 /° ⬍(1–2–3) ⬍(1–2–3) ⬍(1–2–3) ⬍(1–2–3) ⬍(1–2–3) ⬍(1–2–3) N2–N1–C1 108.37(9) 104.40(11) 104.23(12) 104.81(10) 104.02(19) 103.9(3) N1–N2–N3 106.46(10) 109.70(11) 109.90(12) 109.11(9) 109.7(2) 110.1(3) N2–N3–N4 110.57(10) 109.28(11) 109.08(12) 109.92(10) 109.3(2) 109.5(3) N3–N4–C1 105.52(9) 104.80(11) 104.85(12) 104.13(9) 104.16(19) 104.2(3) N6–N5–C2 105.52(9) 104.50(11) 104.66(12) 103.88(9) 104.9(3) N5–N6–N7 110.57(10) 109.68(11) 109.24(12) 110.05(9) 108.7(3) N6–N7–N8 106.46(10) 109.36(11) 109.62(12) 109.22(9) 110.1(3) N7–N8–C2 108.37(9) 104.89(11) 104.49(12) 104.46(9) 104.2(3) N1–C1–N4 109.07(10) 111.82(12) 111.94(13) 112.03(10) 112.8(2) 112.3(3) N4–C1–C2 126.23(10) 124.20(13) 123.94(13) 126.94(11) 124.1(2) 122.1(3) N1–C1–C2 124.67(9) 123.98(13) 124.10(13) 121.02(10) 123.1(2) 125.4(3) N5–C2–C1 126.23(10) 124.20(13) 123.63(13) 121.89(10) 124.2(3) N8–C2–C1 124.67(9) 124.22(13) 124.34(13) 125.69(11) 123.6(3) N5–C2–N8 109.07(10) 111.58(12) 112.00(13) 112.40(10) 112.2(3) Atoms 1–2–3–4 /° ⬍(1–2–3–4) ⬍(1–2–3–4) ⬍(1–2–3–4) ⬍(1–2–3–4) ⬍(1–2–3–4) ⬍(1–2–3–4) N1–C1–C2–N5 –1.94(18) 0.9(2) –18.9(2) 0.80(18) 0.1(4) –9.9(6) N1–C1–C2–N8 –180.00(11) –179.60(13) 163.35(14) 178.57(11) 178.6(2) 173.6(4)
bond angles between 105.1° and 115.1°. The packing is affec-
ted by layers of 5,5⬘-BT anions connected by strong hydrogen
bonds involving all water hydrogen atoms (Figure 2).
Figure 2.Hydrogen bonding in the structure of 1 forming layers of 5,5⬘-BT dianions connected by the tetrahedrally solvated beryllium cations.
Basically all of the metal atoms are coordinated by crystal water molecules and partly by the bistetrazolate dianions. The coordination numbers follow an increasing trend by raising the
period (CN: Be2+ = 4, Mg2+= 6, Ca2+= 6, Sr2+ = 8, Ba2+=
9). The densities do not follow a corresponding trend (ρ(5)⬎
ρ(3)⬎ρ(4)⬎ρ(1)⬎ρ(2)), due to the varying water content.
Magnesium 5,5⬘-bistetrazolate nonahydrate (2) crystallizes
ties in the unit cell. The magnesium dications are coordinated octahedrally by water molecules, with bond lengths in the range of 2.1 Å (Figure 3). Additionally, there are three free
water molecules in each molecular unit. The packing of2can
be described as a vertical layer structure along theaaxis, with
alternating alignments of octahedrally coordinated Mg2+-cat-
ions as well as the 5,5⬘-BT anions and free water molecules
(Figure 4).
Figure 3. Molecular unit of 2. Thermal ellipsoids of non-hydrogen atoms represent the 50 % probability level. Coordination distances /Å: Mg–O1 2.067(2), Mg–O2 2.069(2), Mg–O3 2.037(2), Mg–O4 2.089(2), Mg–O5 2.086(2), Mg–O6 2.0745(19).
Figure 4.Packing of the magnesium salt 2, showing the alternating layers within thea,bplane.
Calcium 5,5⬘-bistetrazolate pentahydrate (3) crystallizes in
the monoclinic space groupP21/cwith four molecular moieties
in the unit cell. Calcium is coordinated sixfold by four water molecules, with shorter bond lengths (Ca–O1 = 2.3576(11) Å, Ca–O2 = 2.3955(10) Å, Ca–O3 = 2.3770(10) Å, Ca–O4 = 2.3263(11) Å], and two nitrogen atoms of two different 5,5- BT anions, with longer bond lengths (Ca–N1 = 2.5049(11) Å,
Ca–N6i = 2.5293(10) Å) (Figure 5). A further contact, indi-
cated in Figure 6, is formed by Ca–N5 with a distance of
2.8739(10) Å, which is slightly above the sum of thevan der
Waalsradii. The packing along thecaxis can be described as a horizontal alternating layer structure between the coordinated cations and the anions with the free water molecules. Within
theb,c planes the structure shows alternating vertical layers.
The one layer is made up of the 5,5⬘-BT anions, the calcium
cations as well as the free water molecule, while the other one contains just the water coordination sphere of the calcium cat- ion. The packing is affected by several strong hydrogen bonds.
Figure 5. View on the molecular unit of 3 indicating the distorted octahedral coordination sphere of the calcium cations. Thermal ellip- soids represent the 50 % probability level. Symmetry code: (i)x, 0.5– y, 0.5+z.
Figure 6.Structural motive within3. Top: Strings of Ca2+and 5,5⬘-
BT anions alongc; bottom: View alongcaxis showing the alternating layers formed by the strings.
Strontium 5,5⬘-bistetrazolate (4) could only be obtained
crystalline as its tetrahydrate with two additional DMF mole- cules per molecular unit. It crystallizes in the orthorhombic
space groupPcca, with four molecular moieties in its unit cell.
The bond lengths and angles in the 5,5⬘-BT anion are similar
to the other alkaline earth metal salts. The strontium cations are coordinated eightfold by two water molecules and two ni-
oxygen and nitrogen atoms are doubled by symmetry. The Sr– O bond lengths are shorter (Sr–O1 = 2.579(19) Å, Sr–O2 = 2.594(2) Å) than the Sr–N bond lengths (Sr–N1 = 2.802(2) Å,
Sr–N4i = 2.787(19) Å) (Figure 7). The packing along the a
axis could be described as a stacking of alternating layers of
the strontium 5,5⬘-bistetrazolate tetrahydrate and the DMF mo-
lecules, which are connected by strong hydrogen bonds e.g.
O2–H2A•••O3: D–A = 2.688(3), 175(2)°. A view along the
c axis shows the angulated packing of two 5,5⬘-bistetrazolate
moieties above each other (Figure 8).
Figure 7.View on the molecular unit of4. Thermal ellipsoids repre- sent the 50 % probability level. Symmetry code: (i) = 0.5–x, 1 –y,z.
Figure 8.View along the b- andcaxis in the crystal structure of4 showing the alternating layers.
Barium 5,5⬘-bistetrazolate tetrahydrate (5) crystallizes in the
triclinic space group P1¯ with two molecular moieties in the
unit cell. A view on the molecular unit is shown in Figure 9. The bond lengths are in agreement to the previously discussed structures and given in Table 2. The barium atoms are coordi- nated ninefold, by six oxygen and three nitrogen atoms, as shown in Figure 9 (Ba–O1 = 2.830(3) Å, Ba–O2 = 2.712(4) Å,
Ba–O3 = 2.829(3) Å, Ba–O4 = 2.702(4) Å, Ba–N1 =
2.984(3) Å, Ba–N3i= 2.975(3) Å, Ba–O3ii= 2.919(3) Å, Ba–
Oiii= 2.892(3) Å, Ba–N2iii= 2.912(3) Å). The packing along
the c axis shows an alternating horizontal layer structure be-
tween tilted 5,5⬘-BT anions and barium cations with its water
coordination sphere. A view along theaaxis (Figure 10) pres-
ents vertical rows of 5,5⬘-BT, which are separated from each
other through a zig-zag pattern of coordinated barium atoms.
Again the structure of5is stabilized by various strong hydro-
gen bonds.
Figure 9. Molecular unit of 5. Thermal ellipsoids of non-hydrogen atoms represent the 50 % probability level. Symmetry codes: (i) x, –1+y,z, (ii) 1 –x, –y, –z, (iii) 1 –x, 1 –y, -z.
Figure 10.View along theaaxis showing columns of staggered 5,5⬘- BT dianions.
Vibrational Spectroscopy
IR- as well as Raman spectroscopy are suitable methods for
the detection of the 5,5⬘-bistetrazolates 1–5. After deproton-
ation of the free acid, the N–H stretching vibration disappears. The values for the stretching and deformation vibrations in the IR and Raman spectra of the examined substances were
compared to values found in literature.[13–15]The most inten-
stretching mode between the C–C linked tetrazole rings at
around 1576 cm–1and a typical tetrazole ring deformation vi-
bration at around 1143 cm–1. The most intensive absorption
bands in the IR spectra can be assigned to asymmetrical
⬎C=N– stretching modes of the tetrazole ring system in the
range of 1690 and 1640 cm–1. Further, O-H stretching vi-
brations of the crystal water, which is contained in all com-
pounds, are found in the range of 3600–3100 cm–1. Apart from
⬎C=N– stretching modes at 1690 and 1640 cm–1further sets
of tetrazole ring stretching and deformation vibrations in a
range of 1390–700 cm–1 [ν(NCN), ν(NN), δ(ring), δ(NCN),]
can be identified.
Physico-Chemical Properties
Thermal Behavior
Differential scanning calorimetry (DSC) measurements to
determine the melt- and decomposition temperatures of 1–5
(about 1.5 mg of each energetic material) were performed in covered aluminum containers with a hole (0.1 mm) in the lid for gas release and a nitrogen flow of 20 mL per minute with
a Linseis PT 10 DSC[16]calibrated by standard pure indium
and zinc at a heating rate of 5 °C·min–1.
In the DSC curves of the salts 1–5 several endothermic
peaks between 92 °C and 190 °C can be detected, which can be assigned to the stepwise dehydration of the salts. Except from the strontium salt all compounds show two endothermic peaks, the first one of which is due to the loss of water mole-
cules, which are not coordinated by the metal atoms (1:
123 °C,2: 138 °C,3: 98 °C,4: 130 °C,5: 92 °C). The second
endothermic peaks, which are observed for1,2,3 and5can
be assigned to the loss of the hydration shells of the metal
centers (1: 186 °C,2: 148 °C, 3: 190 °C,5: 166 °C). For the
determination of the exact amount of released water thermo- gravimetrical measurements had to be accomplished. Despite
the high nitrogen content of the investigated 5,5⬘-bistetrazolate
salts, no exothermic decomposition of any of the compounds could be observed in a temperature range up to 400 °C.
Water Solubility
From recrystallization attempts in water and NMR measure- ments, which were carried out in deuterium oxide, a trend of
the water solubility of the salts1–5could be observed. For the
salts2to5the water solubility decreases rapidly with increas-
ing molecular weight of the cation just as it also is observed for the alkaline earth metal sulfates. In this context, the beryl- lium salt plays a special role, since, against expectations from the above mentioned trend, its solubility in water is similar to that of the barium salt. A possible explanation for this behavior could be the same argumentation as it is applied for diagonal relationships in the periodic table saying that lithium salts be- have like magnesium salts rather than the other alkali salts or beryllium salts behave like aluminum salts rather than other alkaline earth metal salts because of the similar charge to dia- meter ratio of the diagonally related ions.
Sensitivities
The impact sensitivity tests were carried out according to
STANAG 4489[17]modified instruction[18]using a BAM (Bun-
desanstalt für Materialforschung) drophammer.[19]The friction
sensitivity tests were carried out according to STANAG
4487[20]modified instruction[21]using the BAM friction tester.
The classification of the tested compounds results from the “UN Recommendations on the Transport of Dangerous
Goods”.[22] All compounds were tested upon the sensitivity
towards electrical discharge using the Electric Spark Tester
ESD 2010 EN.[23]Apart from the beryllium salt, the sensitivi-
ties of all alkaline earth metal salts were determined. To dehy- drate the compounds, all substances were dried at 200 °C pre- viously to sensitivity testing. Also for the sensitivities, a trend from lower to higher molecular weight of the cation can be observed. The impact sensitivities are in a range from 40 J to
30 J with the higher values for the lighter elements (2: 40 J,
3: 40 J, 4: 35 J,5: 30 J). Therefore, the dry magnesium and
calcium salts can be considered as insensitive, the strontium salt as less sensitive and the barium salt as sensitive. Also the sensitivity towards electrical discharge shows the same trend. The values reach from 0.30 J for the magnesium salt to 0.15 J
for both, the strontium and the barium salt (2: 0.30 J,3: 0.20
J, 4: 0.15 J, 5: 0.15 J). Only the friction sensitivities do not
change within the row of the alkaline earth metal salts and were determined to 360 N for all compounds. They can there- fore be considered as less sensitive towards friction.
Pyrotechnical Compositions
Nitrogen-rich compounds are promising substances in the development of ecologically friendly coloring agents in pyro- technical formulations. The formation of mainly gaseous prod- ucts like nitrogen is an important requirement for smokeless combustion, therefore the investigation of nitrogen-rich com- pounds as coloring substances is focused. For this reason sev- eral pyrotechnical formulations with the barium and strontium salts of 5,5⬘-bistetrazole were tested.
The pyrotechnic mixtures were prepared by mixing all sub- stances, except the binder, in a mortar. Then the binder, a solu- tion of 25 % vinyl alcohol acetate resin (VAAR), was added. The mixture was formed by hand and dried under high vacuum for three hours. The controlled burn down was filmed with a digital video camera recorder (SONY, DCR-HC37E). The performance of each composition has been evaluated with re- spect to color emission (subjective impression), smoke genera- tion and the amount of solid residues. As red and green color- ing agents the strontium and barium salts (MBT) were used. In all pyrotechnic formulations ammonium nitrate served as oxidizer. Magnesium and amorphous boron in the case of the formulations with the barium salt were used as fuels. Polyvinyl chloride (PVC) was added to a barium formulation and served as chlorine source for the generation of the green-emitting spe-
cies BaCl2. In Table 3 the content of the compositions (mass
Table 3.Composition of pyrotechnical mixtures containing4and5. Formulations Sr-BT_1 Sr-BT_2 Ba-BT_1 Ba-BT_2 Ba-BT_3 MBT /wt.-% 35 39 35 30 40 NH4NO3/wt.-% 40 44 40 35 44 Mg /wt.-% 18 10 – 11 – B /wt.-% – – 18 – 9 PVC /wt.-% – – – 17 – VAAR /wt.-% 7 7 7 7 7
The pyrotechnic composition Sr-BT_1 consists of 35 % Sr-
BT, 40 % NH4NO3, 18 % magnesium and 7 % VAAR. The ob-
served flame color is intense red and the combustion occurs fast and smokeless and no residues were observed. Formula- tion Sr-BT_2 with an increased oxidizer and Sr-BT content of
44 % NH4NO3 and 39 % Sr-BT and a decreased amount of
10 % magnesium burned smokeless with an orange-red flame color (Figure 11). The combustion velocity was slower than that of composition Sr-BT_1 and some magnesium sparks and solid residues could be observed.
Figure 11.Flame colors of Sr-BT_1 (top left), Sr-BT_2 (top right), Ba-BT_1 (bottom left) and Ba-BT_3 (bottom right).
Both formulations Ba-BT_1 and Ba-BT_3 with 35 % Ba-
BT, 40 % NH4NO3, 18 % boron, 7 % VAAR and 40 % Ba-BT,
44 % NH4NO3, 9 % boron, 7 % VAAR respectively burned fast
with an intense green flame color and no residues remained, however a slight generation of smoke was observed for both compositions. The composition Ba-BT_2 containing 30 % Ba-
BT, 35 % NH4NO3, 11 % magnesium, 17 % PVC and 7 %
VAAR combusted fast with an intense white flame color with- out smoke and no solid residues remained.
Conclusions
5,5⬘-Bistetrazole was deprotonated in aqueous solution
using the alkaline earth metal hydroxides or, in case of the magnesium salt, the basic carbonate to synthesize the corre-
sponding alkaline earth metal salts 2,3,4, and5. Due to the
low solubility of the alkaline earth metal hydroxides in water, the yields of the described reactions are not quantitative. The
beryllium salt1 of 5,5⬘-bistetrazole was synthesized in a me-
tathesis reaction using the barium salt of 5,5⬘-bistetrazole and
beryllium sulfate.
The water solubility of the alkaline earth metal salts of 5,5⬘- bistetrazole in water drops with increasing molecular weight of the cation. As an exception, the solubility of the beryllium
salt1is almost as low as the solubility of the barium salt5.
The salts crystallize in the common mono- and triclinic space groupsP21/c (1,3), P21/n (2), Pcca(4) and P1¯ (5) as
tetrahydrate (4,5), pentahydrate (1,3) or nonahydrate (2). Sin-
gle crystals of 4could only be obtained from DMF, where it
crystallizes with two molecules of DMF per molecular unit. All salts can be dehydrated at temperatures between 92 °C and 190 °C. They do not decompose at temperatures lower than 400 °C.
The impact and friction sensitivities were determined of pre-
viously dried substances. They reach from 30 J (5) to 40 J (2,
3) impact sensitivity. The friction sensitivity of all compounds
is 360 N. The salts therefore are comparatively insensitive towards impact and friction.
The strontium (4) and the barium salt (5) were tested in
pyrotechnical compositions as red respectively green colorants. Their color performance for the strontium salt was best in a
formulation containing 35 % Sr-BT, 40 % NH4NO3, 18 % mag-
nesium and 7 % VAAR. Regarding smokeless combustion, the best performing mixture for the barium salt consists of 40 %
Ba-BT, 44 % NH4NO3, 9 % boron and 7 % VAAR.
Experimental Section
All chemicals and solvents were employed as received (Sigma–Ald- rich, Fluka, Acros).1H and 13C spectra were recorded using a JEOL
Eclipse 270, JEOL EX 400 or a JEOL Eclipse 400 instrument. The chemical shifts quoted in ppm in the text refer to typical standards such as tetramethylsilane (1H,13C). To determine the melting and de-
composition temperatures of the described compounds a Linseis PT 10 DSC (heating rate 5 °C min–1) was used. Infrared spectra were
measured using a Perkin–Elmer Spectrum One FT-IR spectrometer as KBr pellets. Raman spectra were recorded with a Bruker MultiRAM Raman Sample Compartment D418 equipped with a Nd-YAG-Laser (1064 nm) and a LN-Ge diode as detector. Mass spectra of the de- scribed compounds were measured at a JEOL MStation JMS 700 using FAB technique. To measure elemental analyses a Netsch STA 429 si- multaneous thermal analyzer was employed.
Beryllium 5,5⬘-bistetrazolate pentahydrate (1):Barium bistetrazol- ate tetrahydrate (2.73 g, 10.0 mmol, 1 equiv.) was dissolved in boiling water (75 mL) and combined with beryllium sulfate tetrahydrate (1.77 g, 10.0 mmol, 1.0 equiv.), which previously was dissolved in hot water (25 mL). Barium sulfate precipitated instantly. Then the mixture was boiled for 20 min and filtered. To remove the remaining barium sulfate, the solution was centrifuged. Lastly, the water was evaporated and the colorless product was recrystallized from ethanol/water in 86 % yield (2.02 g).
DSC(5 °C·min–1): 123 °C (dehydr.), 186 °C (endoth.),⬎400 °C (no
dec.). IR (KBr):ν˜ = 2931 (s), 2235 (s), 1679 (m), 1593 (m), 1384 (m), 1339 (s), 1319 (m), 1229 (m), 1204 (s), 1167 (m), 1066 (s), 1054 (s), 1038 (vs), 983 (s), 880 (s), 788 (s), 719 (s), 675 (s), 533 (m), 488 (w) cm–1;Raman(1064 nm, 200 mW, 25 °C):ν˜ = 1595 (100), 1231
(15), 1159 (14), 1138 (31), 1101 (16), 782 (3), 540 (1), 489 (3), 426 (5), 392 (11) cm–1.1H NMR(D
2O, 95 °C):δ= 4.78 (H2O).13C NMR
(D2O, 95 °C): δ = 154.8 (CN4); m/z (FAB–) 137.0 [C2HN8–]; EA
(C2H10BeN8O5, 235.16): calcd.: C 10.21; H 4.29; N 47.65 %; found:
C 10.69; H 4.11; N 47.72 %.
Magnesium 5,5⬘-bistetrazolate nonahydrate (2): 5,5⬘-Bistetrazole (1.38 g, 9.99 mmol, 1.0 equiv.) was dissolved in hot water (20 mL) and combined with basic magnesium carbonate (Mg(OH)2·MgCO3)
(0.86 g, 12.06 mmol, 1.21 equiv.). The mixture was boiled for 40 min