Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105000569/ga1037sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270105000569/ga1037Isup2.hkl |
CCDC reference: 268091
A sample of hexanitroazobenzene was obtained from the Explosive Component Division of (our) Sandia National Laboratories; the compound was prepared by reacting purified picryl chloride with hydrazine and potassium acetate in ethanol followed by acidification with hydrochloric acid. This yield of crude hexanitrohydrazobenzene was subsequently oxidized with nitric acid to give orange crystals of HNAB. About 70% of the crystals from this preparation were form I crystals, the balance being form II. Larger crystals of forms I and II may be obtained by recrystallization from nitromethane at room temperature, and those of form III from hot nitromethane. Morphological characteristics for forms I and II were described previously. Equant crystals of form I consist of rhombohedra with monoclinic symmetry and well developed dipyramid {111} faces and {l00} basal pinacoids; form II crystals consist of long, obliquely truncated rods with {110} prism and {001} basal pinacoids; form III mostly consists of flat bladed crystals of apparent orthorhombic symmetry bound by {100} and {110} prism and {101} basal pinacoids along the long direction.
Atom N1B was fixed at y = 0.0. H atoms were constrained (C—H = 0.93 Å), with their Uiso(H) values set to 1.2Ueq(C). An independent refinement (conducted by A. D. Rae) used similarly constrained H atoms at 0.93 Å; however, in this case, these H atoms were given the same atom displacement parameters as the atom to which they were attached. In Rae's refinement, the origin along y was fixed by setting the mean y coordinate of the two pairs of central N atoms to y = 0.625.
Data collection: SMART (Bruker, 1997); cell refinement: SMART; data reduction: SAINT (Bruker , 1997) and SADABS (Sheldrick, 1999); program(s) used to solve structure: XM in SHELXTL (Bruker, 1998); program(s) used to refine structure: XL in SHELXTL; molecular graphics: XP and XSHELL in SHELXTL; software used to prepare material for publication: XCIF in SHELXTL.
C12H4N8O12 | F(000) = 912 |
Mr = 452.23 | Dx = 1.703 Mg m−3 |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2yb | Cell parameters from 770 reflections |
a = 15.4015 (8) Å | θ = 2.8–22.2° |
b = 5.5240 (3) Å | µ = 0.16 mm−1 |
c = 22.1182 (11) Å | T = 298 K |
β = 110.367 (2)° | Acicular, orange |
V = 1764.13 (16) Å3 | 0.40 × 0.10 × 0.08 mm |
Z = 4 |
Bruker SMART CCD area-detector diffractometer | 6076 independent reflections |
Radiation source: fine-focus sealed tube | 4219 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.028 |
ϕ and ω scans | θmax = 26.0°, θmin = 2.0° |
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1999) | h = −19→10 |
Tmin = 0.94, Tmax = 0.99 | k = −6→6 |
10081 measured reflections | l = −26→27 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.038 | H-atom parameters constrained |
wR(F2) = 0.086 | w = 1/[σ2(Fo2) + (0.004P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.02 | (Δ/σ)max = 0.004 |
6076 reflections | Δρmax = 0.16 e Å−3 |
578 parameters | Δρmin = −0.17 e Å−3 |
1 restraint | Extinction correction: Bruker SHELXTL (XL), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: dual space recycling | Extinction coefficient: 0.0028 (6) |
C12H4N8O12 | V = 1764.13 (16) Å3 |
Mr = 452.23 | Z = 4 |
Monoclinic, P21 | Mo Kα radiation |
a = 15.4015 (8) Å | µ = 0.16 mm−1 |
b = 5.5240 (3) Å | T = 298 K |
c = 22.1182 (11) Å | 0.40 × 0.10 × 0.08 mm |
β = 110.367 (2)° |
Bruker SMART CCD area-detector diffractometer | 6076 independent reflections |
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1999) | 4219 reflections with I > 2σ(I) |
Tmin = 0.94, Tmax = 0.99 | Rint = 0.028 |
10081 measured reflections |
R[F2 > 2σ(F2)] = 0.038 | 1 restraint |
wR(F2) = 0.086 | H-atom parameters constrained |
S = 1.02 | Δρmax = 0.16 e Å−3 |
6076 reflections | Δρmin = −0.17 e Å−3 |
578 parameters |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 'Atom1' 'Atom2' 'Symm. op. 1' 'Symm. op. 2' 'Length Å' 'H3A' 'O9B' '1 − x,1/2 + y,-z' '1 + x,-1 + y,z' '2.462' 'O12B' 'H5BA' 'x,y,z' '1 − x,-1/2 + y,1 − z' '2.491' 'O9A' 'H11B' '∓x,1 + y,z' '∓x,1 + y,z' '2.516' 'N1A' 'O6A' '1 − x,1/2 + y,1 − z' '1 − x,1/2 + y,1 − z' '2.582' 'O6B' 'N1B' '1 − x,-1/2 + y,1 − z' '1 − x,1/2 + y,1 − z' '2.590' 'O4A' 'H3BA' '1 − x,1/2 + y,-z' '1 − x,1/2 + y,1 − z' '2.594' 'O3B' 'H11A' '1 − x,-1/2 + y,1 − z' 'x,∓y,∓z' '2.598' 'O1B' 'H9BA' 'x,y,z' '-x,-1/2 + y,1 − z' '2.615' 'O1A' 'H9A' '1 − x,1/2 + y,-z' '1 + x,y,z' '2.616' 'H5A' 'O12A' '1 − x,1/2 + y,1 − z' '∓x,1 + y,1 + z' '2.617' 'H9A' 'O7A' '∓x,1 + y,z' '-x,1.5 + y,-z' '2.627' 'O7B' 'H9BA' '1 − x,-1/2 + y,1 − z' '1 + x,-1 + y,z' '2.692' 'N5A' 'O12A' '∓x,1 + y,z' '∓x,1 + y,z' '2.700' 'N5B' 'O12B' '1 − x,1/2 + y,1 − z' '1 − x,-1/2 + y,1 − z' '2.738' 'O1A' 'O7A' '∓x,1 + y,z' '∓x,1 + y,z' '2.771' 'O1B' 'N1B' '1 − x,-1/2 + y,1 − z' '1 − x,1/2 + y,1 − z' '2.816' 'O1B' 'O7B' 'x,y,z' 'x,y,z' '2.833' 'O9A' 'O1A' '∓x,1 + y,z' '-x,1.5 + y,-z' '2.850' 'O6A' 'O5A' '1 − x,1/2 + y,-z' 'x,y,z' '2.869' 'N1A' 'O1A' 'x,y,1 + z' 'x,y,1 + z' '2.916' 'O5A' 'N4A' '∓x,1 + y,z' '1 − x,1.5 + y,-z' '2.919' 'O1B' 'O9B' 'x,y,z' '-x,-1/2 + y,1 − z' '2.921' 'O1B' 'N5B' 'x,y,z' 'x,1 + y,z' '2.931' 'O1A' 'N5A' '1 − x,1/2 + y,-z' '1 − x,1/2 + y,-z' '2.935' 'O10A' 'C11B' '1 − x,1/2 + y,-z' '1 − x,-1/2 + y,-z' '2.954' 'O5B' 'O6B' 'x,y,z' '1 − x,1/2 + y,1 − z' '2.968' 'O5B' 'N4B' 'x,y,z' '1 − x,1/2 + y,1 − z' '2.969' 'O3A' 'C3B' '1 − x,1/2 + y,1 − z' '1 − x,-1/2 + y,2 − z' '2.969' 'C11A' 'O3B' '∓x,1 + y,z' '1 − x,1/2 + y,1 − z' '2.979' 'O8B' 'O7B' 'x,y,z' '-x,1/2 + y,1 − z' '2.998' 'C7A' 'O8A' '1 − x,1/2 + y,1 − z' '1 − x,-1/2 + y,1 − z' '3.005' 'N1A' 'O7A' 'x,y,1 + z' 'x,y,1 + z' '3.025' 'O12A' 'O4A' '1 − x,1/2 + y,-z' 'x,∓y,z' '3.035' 'O7A' O8A' 'x,y,1 + z' '-x,-1/2 + y,1 − z' '3.036' 'N1B' 'O7B' '1 − x,1/2 + y,1 − z' '1 − x,-1/2 + y,1 − z' '3.037' 'N1B' 'O7B' 'x,1 + y,z' 'x,y,z' '3.037' 'O10B' 'C3A' 'x,y,z' '-x,1/2 + y,-z' '3.052' 'O8A' 'N5A' '∓x,1 + y,z' '∓x,2 + y,z' '3.053' 'C7B' 'O8B' '1 − x,-1/2 + y,1 − z' '1 − x,-1.5 + y,1 − z' '3.069' 'O2A' 'C1A' '1 − x,1/2 + y,-z' '1 − x,-1/2 + y,-z' '3.085' 'O8A' 'C12A' '1 − x,1/2 + y,-z' '1 − x,1.5 + y,-z' '3.109' 'O11B' 'C8B' 'x,y,z' 'x,-1 + y,z' '3.161' 'O11A' 'C8A' '∓x,1 + y,z' '∓x,∓y,z' '3.182' 'C2B' 'O3A' '1 − x,-1/2 + y,1 − z' '1 − x,1/2 + y,-z' '3.183' 'C12B' 'O8B' 'x,y,z' 'x,-1 + y,z' '3.183' 'C1B' 'O2B' 'x,1 + y,z' 'x,1 + y,z' '3.210' |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. The independent refinement employed RAELS2000 (Rae, 2000). |
x | y | z | Uiso*/Ueq | ||
N1B | 0.2686 (3) | 0.0000 | 0.52485 (19) | 0.0418 (11) | |
C1B | 0.3580 (3) | 0.9303 (13) | 0.5717 (2) | 0.0358 (13) | |
C2B | 0.3681 (4) | 0.7414 (15) | 0.6169 (3) | 0.0427 (14) | |
C3B | 0.4520 (4) | 0.6759 (15) | 0.6594 (3) | 0.0492 (16) | |
H3BA | 0.4572 | 0.5455 | 0.6870 | 0.059* | |
C4B | 0.5291 (4) | 0.8045 (15) | 0.6611 (3) | 0.0528 (16) | |
C5B | 0.5239 (4) | 0.9946 (14) | 0.6198 (3) | 0.0498 (15) | |
H5BA | 0.5764 | 1.0818 | 0.6216 | 0.060* | |
C6B | 0.4386 (4) | 1.0505 (14) | 0.5758 (2) | 0.0422 (14) | |
N2B | 0.2862 (4) | 0.6146 (15) | 0.6215 (2) | 0.0536 (15) | |
O1B | 0.2195 (3) | 0.7344 (13) | 0.6168 (2) | 0.0712 (15) | |
O2B | 0.2949 (4) | 0.3970 (12) | 0.6324 (3) | 0.0857 (17) | |
N3B | 0.6199 (4) | 0.7253 (19) | 0.7067 (3) | 0.097 (2) | |
O3B | 0.6234 (4) | 0.5239 (19) | 0.7319 (3) | 0.162 (3) | |
O4B | 0.6835 (3) | 0.8712 (16) | 0.7183 (2) | 0.116 (2) | |
N4B | 0.4333 (3) | 1.2488 (13) | 0.5282 (2) | 0.0529 (12) | |
O5B | 0.4958 (3) | 1.3981 (13) | 0.5452 (2) | 0.0857 (15) | |
O6B | 0.3726 (3) | 1.2481 (13) | 0.4775 (2) | 0.0893 (18) | |
N5B | 0.2336 (3) | 0.8231 (14) | 0.48988 (18) | 0.0427 (11) | |
C7B | 0.1455 (3) | 0.8825 (14) | 0.4411 (2) | 0.0364 (13) | |
C8B | 0.0798 (4) | 1.0445 (14) | 0.4445 (2) | 0.0383 (13) | |
C9B | −0.0026 (4) | 1.0777 (14) | 0.3948 (2) | 0.0433 (15) | |
H9BA | −0.0444 | 1.1957 | 0.3970 | 0.052* | |
C10B | −0.0214 (4) | 0.9301 (14) | 0.3413 (3) | 0.0479 (16) | |
C11B | 0.0394 (4) | 0.7564 (14) | 0.3361 (3) | 0.0444 (14) | |
H11B | 0.0244 | 0.6555 | 0.3003 | 0.053* | |
C12B | 0.1223 (4) | 0.7367 (14) | 0.3850 (3) | 0.0397 (14) | |
N6B | 0.0926 (3) | 1.1940 (12) | 0.5024 (2) | 0.0430 (12) | |
O7B | 0.0900 (3) | 1.0931 (12) | 0.55023 (17) | 0.0611 (12) | |
O8B | 0.1052 (4) | 1.4080 (11) | 0.4985 (2) | 0.0699 (13) | |
N7B | −0.1085 (4) | 0.9668 (15) | 0.2868 (2) | 0.0677 (16) | |
O9B | −0.1437 (4) | 1.1668 (15) | 0.2803 (2) | 0.107 (2) | |
O10B | −0.1388 (4) | 0.7941 (15) | 0.2508 (2) | 0.115 (2) | |
N8B | 0.1951 (4) | 0.5763 (15) | 0.3770 (2) | 0.0530 (13) | |
O11B | 0.1754 (4) | 0.3636 (12) | 0.3668 (2) | 0.0755 (14) | |
O12B | 0.2670 (3) | 0.6695 (13) | 0.3823 (3) | 0.0810 (16) | |
N1A | 0.2495 (2) | 0.2591 (15) | −0.0195 (2) | 0.0419 (11) | |
C1A | 0.2892 (4) | 0.2011 (13) | −0.0680 (3) | 0.0401 (14) | |
C2A | 0.2552 (3) | 0.0231 (14) | −0.1140 (3) | 0.0385 (14) | |
C3A | 0.2929 (4) | −0.0224 (16) | −0.1617 (3) | 0.0505 (16) | |
H3A | 0.2706 | −0.1461 | −0.1917 | 0.061* | |
C4A | 0.3645 (4) | 0.1240 (16) | −0.1624 (3) | 0.0551 (17) | |
C5A | 0.4021 (4) | 0.3076 (16) | −0.1186 (3) | 0.0527 (16) | |
H5A | 0.4503 | 0.4040 | −0.1209 | 0.063* | |
C6A | 0.3633 (4) | 0.3404 (14) | −0.0704 (3) | 0.0448 (15) | |
N2A | 0.1727 (4) | −0.1217 (14) | −0.1189 (2) | 0.0517 (14) | |
O1A | 0.1043 (3) | −0.0072 (13) | −0.1177 (2) | 0.0700 (14) | |
O2A | 0.1777 (4) | −0.3374 (12) | −0.1246 (3) | 0.0878 (17) | |
N3A | 0.4041 (4) | 0.082 (2) | −0.2138 (3) | 0.094 (2) | |
O3A | 0.3888 (5) | −0.1144 (19) | −0.2394 (3) | 0.172 (4) | |
O4A | 0.4497 (4) | 0.2442 (18) | −0.2250 (2) | 0.131 (3) | |
N4A | 0.4048 (3) | 0.5248 (14) | −0.0218 (3) | 0.0644 (15) | |
O5A | 0.4383 (4) | 0.7029 (11) | −0.0378 (2) | 0.0990 (17) | |
O6A | 0.4036 (4) | 0.4898 (14) | 0.0317 (2) | 0.0880 (17) | |
N5A | 0.2418 (3) | 0.0763 (12) | 0.0111 (2) | 0.0419 (11) | |
C7A | 0.2020 (4) | 0.1295 (13) | 0.0597 (3) | 0.0355 (13) | |
C8A | 0.1337 (4) | 0.3007 (14) | 0.0548 (2) | 0.0374 (13) | |
C9A | 0.0979 (4) | 0.3385 (14) | 0.1039 (3) | 0.0479 (16) | |
H9A | 0.0555 | 0.4614 | 0.1012 | 0.058* | |
C10A | 0.1275 (4) | 0.1881 (15) | 0.1559 (3) | 0.0473 (15) | |
C11A | 0.1925 (4) | 0.0040 (15) | 0.1629 (3) | 0.0514 (16) | |
H11A | 0.2093 | −0.1016 | 0.1978 | 0.062* | |
C12A | 0.2309 (4) | −0.0120 (14) | 0.1142 (3) | 0.0404 (14) | |
N6A | 0.0927 (3) | 0.4484 (12) | −0.0033 (2) | 0.0456 (13) | |
O7A | 0.0443 (3) | 0.3469 (11) | −0.05259 (16) | 0.0642 (12) | |
O8A | 0.1045 (3) | 0.6679 (11) | 0.0026 (2) | 0.0707 (13) | |
N7A | 0.0909 (4) | 0.2207 (18) | 0.2093 (2) | 0.0786 (18) | |
O9A | 0.0708 (4) | 0.4297 (15) | 0.2175 (2) | 0.098 (2) | |
O10A | 0.0875 (5) | 0.0475 (17) | 0.2402 (3) | 0.134 (3) | |
N8A | 0.3082 (4) | −0.1806 (14) | 0.1253 (2) | 0.0563 (14) | |
O11A | 0.3024 (4) | −0.3852 (13) | 0.1448 (3) | 0.0892 (17) | |
O12A | 0.3773 (4) | −0.0999 (14) | 0.1156 (2) | 0.0851 (18) |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1B | 0.038 (2) | 0.047 (3) | 0.041 (2) | 0.004 (2) | 0.014 (2) | 0.000 (2) |
C1B | 0.026 (3) | 0.044 (3) | 0.034 (3) | 0.001 (2) | 0.006 (2) | −0.008 (2) |
C2B | 0.040 (3) | 0.052 (4) | 0.036 (3) | −0.001 (3) | 0.014 (3) | −0.003 (3) |
C3B | 0.042 (3) | 0.071 (4) | 0.037 (3) | −0.001 (3) | 0.015 (3) | 0.002 (3) |
C4B | 0.033 (3) | 0.085 (4) | 0.036 (3) | −0.003 (3) | 0.006 (2) | 0.013 (3) |
C5B | 0.036 (3) | 0.070 (4) | 0.045 (3) | −0.003 (3) | 0.017 (3) | −0.002 (3) |
C6B | 0.036 (3) | 0.059 (3) | 0.034 (3) | 0.001 (3) | 0.016 (2) | 0.000 (3) |
N2B | 0.036 (3) | 0.074 (4) | 0.045 (3) | −0.005 (3) | 0.007 (2) | −0.008 (3) |
O1B | 0.044 (2) | 0.106 (4) | 0.070 (3) | −0.004 (3) | 0.028 (2) | 0.006 (3) |
O2B | 0.083 (4) | 0.060 (3) | 0.104 (4) | −0.010 (3) | 0.021 (3) | 0.018 (3) |
N3B | 0.038 (3) | 0.190 (8) | 0.051 (3) | 0.001 (4) | −0.001 (3) | 0.042 (4) |
O3B | 0.069 (3) | 0.214 (7) | 0.156 (6) | 0.008 (4) | −0.019 (4) | 0.112 (6) |
O4B | 0.036 (2) | 0.217 (6) | 0.076 (3) | −0.016 (3) | −0.003 (2) | 0.047 (4) |
N4B | 0.043 (3) | 0.061 (3) | 0.061 (3) | −0.002 (3) | 0.026 (3) | −0.001 (3) |
O5B | 0.093 (3) | 0.087 (3) | 0.078 (3) | −0.042 (3) | 0.032 (3) | −0.003 (2) |
O6B | 0.052 (3) | 0.118 (5) | 0.084 (3) | 0.008 (3) | 0.006 (3) | 0.060 (3) |
N5B | 0.030 (2) | 0.051 (3) | 0.040 (2) | −0.002 (2) | 0.0041 (19) | −0.002 (2) |
C7B | 0.026 (3) | 0.047 (3) | 0.036 (3) | −0.003 (3) | 0.010 (2) | 0.004 (2) |
C8B | 0.034 (3) | 0.047 (3) | 0.036 (3) | −0.003 (3) | 0.016 (2) | −0.002 (3) |
C9B | 0.036 (3) | 0.056 (4) | 0.041 (3) | 0.015 (3) | 0.017 (3) | 0.007 (3) |
C10B | 0.033 (3) | 0.076 (4) | 0.035 (3) | 0.006 (3) | 0.011 (3) | 0.010 (3) |
C11B | 0.048 (3) | 0.052 (3) | 0.034 (3) | 0.002 (3) | 0.016 (3) | 0.002 (3) |
C12B | 0.038 (3) | 0.049 (3) | 0.037 (3) | 0.010 (3) | 0.019 (3) | −0.002 (3) |
N6B | 0.031 (2) | 0.055 (3) | 0.044 (3) | −0.003 (2) | 0.016 (2) | −0.010 (3) |
O7B | 0.078 (3) | 0.069 (3) | 0.044 (2) | −0.001 (2) | 0.031 (2) | −0.011 (2) |
O8B | 0.098 (4) | 0.038 (3) | 0.073 (3) | −0.003 (2) | 0.029 (3) | −0.006 (2) |
N7B | 0.045 (3) | 0.109 (5) | 0.041 (3) | 0.014 (3) | 0.006 (2) | 0.002 (3) |
O9B | 0.091 (4) | 0.156 (6) | 0.056 (3) | 0.078 (4) | 0.001 (3) | 0.006 (3) |
O10B | 0.083 (4) | 0.126 (4) | 0.087 (4) | −0.003 (4) | −0.032 (3) | −0.015 (4) |
N8B | 0.052 (3) | 0.062 (3) | 0.042 (3) | 0.012 (3) | 0.012 (2) | 0.002 (3) |
O11B | 0.102 (4) | 0.049 (3) | 0.086 (3) | 0.010 (3) | 0.046 (3) | −0.012 (2) |
O12B | 0.048 (3) | 0.094 (4) | 0.109 (4) | 0.008 (3) | 0.037 (3) | −0.020 (3) |
N1A | 0.033 (2) | 0.054 (3) | 0.043 (2) | 0.000 (2) | 0.0186 (18) | 0.001 (2) |
C1A | 0.033 (3) | 0.050 (4) | 0.039 (3) | 0.001 (3) | 0.015 (2) | −0.008 (3) |
C2A | 0.032 (3) | 0.051 (3) | 0.035 (3) | 0.005 (3) | 0.016 (2) | 0.007 (3) |
C3A | 0.041 (3) | 0.076 (4) | 0.033 (3) | 0.003 (3) | 0.011 (3) | −0.003 (3) |
C4A | 0.038 (3) | 0.091 (5) | 0.040 (3) | 0.000 (3) | 0.018 (3) | −0.003 (3) |
C5A | 0.034 (3) | 0.078 (4) | 0.049 (3) | −0.002 (3) | 0.018 (3) | 0.019 (3) |
C6A | 0.029 (3) | 0.055 (4) | 0.049 (3) | −0.003 (3) | 0.011 (3) | −0.004 (3) |
N2A | 0.041 (3) | 0.069 (4) | 0.043 (3) | −0.014 (3) | 0.012 (2) | −0.009 (3) |
O1A | 0.046 (2) | 0.086 (4) | 0.077 (3) | −0.014 (3) | 0.021 (2) | −0.008 (3) |
O2A | 0.111 (4) | 0.052 (3) | 0.110 (4) | −0.011 (3) | 0.052 (3) | −0.001 (3) |
N3A | 0.065 (4) | 0.179 (8) | 0.053 (4) | −0.013 (5) | 0.039 (3) | −0.015 (4) |
O3A | 0.185 (7) | 0.246 (9) | 0.140 (6) | −0.064 (6) | 0.125 (6) | −0.110 (6) |
O4A | 0.084 (4) | 0.252 (8) | 0.074 (3) | −0.041 (5) | 0.049 (3) | 0.018 (4) |
N4A | 0.040 (3) | 0.059 (4) | 0.087 (4) | −0.001 (3) | 0.013 (3) | −0.011 (3) |
O5A | 0.087 (3) | 0.067 (3) | 0.114 (4) | −0.032 (3) | −0.003 (3) | 0.015 (3) |
O6A | 0.082 (3) | 0.110 (4) | 0.081 (3) | −0.040 (3) | 0.041 (3) | −0.052 (3) |
N5A | 0.039 (2) | 0.049 (3) | 0.038 (2) | 0.003 (2) | 0.015 (2) | −0.002 (2) |
C7A | 0.038 (3) | 0.038 (3) | 0.032 (3) | −0.003 (3) | 0.013 (2) | −0.008 (2) |
C8A | 0.038 (3) | 0.045 (3) | 0.030 (3) | −0.008 (3) | 0.013 (2) | −0.002 (3) |
C9A | 0.040 (3) | 0.057 (4) | 0.050 (3) | −0.003 (3) | 0.020 (3) | −0.005 (3) |
C10A | 0.041 (3) | 0.072 (4) | 0.033 (3) | 0.001 (3) | 0.018 (2) | −0.005 (3) |
C11A | 0.054 (4) | 0.069 (4) | 0.028 (3) | −0.016 (3) | 0.009 (3) | 0.000 (3) |
C12A | 0.038 (3) | 0.043 (3) | 0.035 (3) | −0.003 (3) | 0.006 (3) | −0.011 (3) |
N6A | 0.047 (3) | 0.042 (3) | 0.049 (3) | 0.004 (2) | 0.019 (3) | −0.003 (3) |
O7A | 0.060 (2) | 0.070 (3) | 0.049 (2) | 0.005 (2) | 0.001 (2) | −0.004 (2) |
O8A | 0.091 (3) | 0.046 (3) | 0.078 (3) | −0.002 (2) | 0.033 (3) | 0.007 (2) |
N7A | 0.071 (4) | 0.128 (6) | 0.040 (3) | −0.013 (4) | 0.023 (3) | −0.015 (4) |
O9A | 0.102 (4) | 0.140 (6) | 0.054 (3) | 0.046 (4) | 0.032 (3) | −0.012 (3) |
O10A | 0.191 (7) | 0.154 (5) | 0.100 (4) | −0.039 (5) | 0.107 (5) | 0.008 (5) |
N8A | 0.061 (3) | 0.061 (4) | 0.041 (3) | 0.012 (3) | 0.011 (3) | −0.003 (3) |
O11A | 0.103 (4) | 0.057 (3) | 0.091 (3) | 0.015 (3) | 0.013 (3) | 0.018 (3) |
O12A | 0.069 (3) | 0.112 (5) | 0.081 (3) | 0.033 (3) | 0.035 (3) | 0.014 (3) |
N1B—N5Bi | 1.247 (7) | N8B—O11B | 1.215 (8) |
N1B—C1Bi | 1.457 (7) | N1A—N5A | 1.244 (6) |
C1B—C6B | 1.382 (8) | N1A—C1A | 1.442 (7) |
C1B—C2B | 1.415 (8) | C1A—C2A | 1.381 (8) |
C1B—N1Bii | 1.457 (7) | C1A—C6A | 1.393 (8) |
C2B—C3B | 1.356 (8) | C2A—C3A | 1.392 (8) |
C2B—N2B | 1.478 (8) | C2A—N2A | 1.474 (8) |
C3B—C4B | 1.372 (8) | C3A—C4A | 1.372 (8) |
C3B—H3BA | 0.9300 | C3A—H3A | 0.9300 |
C4B—C5B | 1.377 (8) | C4A—C5A | 1.384 (9) |
C4B—N3B | 1.477 (8) | C4A—N3A | 1.482 (8) |
C5B—C6B | 1.370 (8) | C5A—C6A | 1.403 (8) |
C5B—H5BA | 0.9300 | C5A—H5A | 0.9300 |
C6B—N4B | 1.502 (8) | C6A—N4A | 1.457 (8) |
N2B—O1B | 1.196 (7) | N2A—O2A | 1.204 (7) |
N2B—O2B | 1.224 (7) | N2A—O1A | 1.236 (7) |
N3B—O4B | 1.225 (8) | N3A—O3A | 1.207 (11) |
N3B—O3B | 1.237 (10) | N3A—O4A | 1.218 (10) |
N4B—O6B | 1.185 (6) | N4A—O6A | 1.205 (7) |
N4B—O5B | 1.222 (6) | N4A—O5A | 1.220 (7) |
N5B—N1Bii | 1.247 (7) | N5A—C7A | 1.441 (7) |
N5B—C7B | 1.447 (6) | C7A—C12A | 1.375 (8) |
C7B—C8B | 1.373 (8) | C7A—C8A | 1.391 (8) |
C7B—C12B | 1.416 (8) | C8A—C9A | 1.393 (7) |
C8B—C9B | 1.372 (7) | C8A—N6A | 1.467 (7) |
C8B—N6B | 1.478 (7) | C9A—C10A | 1.362 (8) |
C9B—C10B | 1.381 (8) | C9A—H9A | 0.9300 |
C9B—H9BA | 0.9300 | C10A—C11A | 1.397 (8) |
C10B—C11B | 1.373 (7) | C10A—N7A | 1.487 (7) |
C10B—N7B | 1.473 (7) | C11A—C12A | 1.400 (8) |
C11B—C12B | 1.360 (8) | C11A—H11A | 0.9300 |
C11B—H11B | 0.9300 | C12A—N8A | 1.464 (8) |
C12B—N8B | 1.488 (8) | N6A—O7A | 1.221 (5) |
N6B—O8B | 1.206 (5) | N6A—O8A | 1.227 (5) |
N6B—O7B | 1.209 (5) | N7A—O10A | 1.187 (8) |
N7B—O9B | 1.217 (7) | N7A—O9A | 1.224 (8) |
N7B—O10B | 1.226 (7) | N8A—O11A | 1.224 (8) |
N8B—O12B | 1.189 (7) | N8A—O12A | 1.239 (7) |
N5Bi—N1B—C1Bi | 109.3 (5) | N5A—N1A—C1A | 111.7 (5) |
C6B—C1B—C2B | 115.6 (5) | C2A—C1A—C6A | 118.0 (5) |
C6B—C1B—N1Bii | 121.6 (5) | C2A—C1A—N1A | 123.8 (5) |
C2B—C1B—N1Bii | 122.8 (5) | C6A—C1A—N1A | 118.1 (5) |
C3B—C2B—C1B | 122.1 (6) | C1A—C2A—C3A | 122.5 (6) |
C3B—C2B—N2B | 117.1 (5) | C1A—C2A—N2A | 122.4 (5) |
C1B—C2B—N2B | 120.8 (5) | C3A—C2A—N2A | 115.0 (5) |
C2B—C3B—C4B | 119.1 (6) | C4A—C3A—C2A | 116.8 (6) |
C2B—C3B—H3BA | 120.4 | C4A—C3A—H3A | 121.6 |
C4B—C3B—H3BA | 120.4 | C2A—C3A—H3A | 121.6 |
C3B—C4B—C5B | 121.8 (5) | C3A—C4A—C5A | 124.4 (6) |
C3B—C4B—N3B | 118.1 (6) | C3A—C4A—N3A | 117.5 (6) |
C5B—C4B—N3B | 120.1 (6) | C5A—C4A—N3A | 118.0 (6) |
C6B—C5B—C4B | 117.6 (5) | C4A—C5A—C6A | 116.3 (6) |
C6B—C5B—H5BA | 121.2 | C4A—C5A—H5A | 121.8 |
C4B—C5B—H5BA | 121.2 | C6A—C5A—H5A | 121.8 |
C5B—C6B—C1B | 123.8 (6) | C1A—C6A—C5A | 121.9 (6) |
C5B—C6B—N4B | 117.8 (5) | C1A—C6A—N4A | 120.8 (5) |
C1B—C6B—N4B | 118.4 (5) | C5A—C6A—N4A | 117.3 (6) |
O1B—N2B—O2B | 126.3 (6) | O2A—N2A—O1A | 126.6 (6) |
O1B—N2B—C2B | 117.4 (6) | O2A—N2A—C2A | 117.3 (6) |
O2B—N2B—C2B | 116.3 (6) | O1A—N2A—C2A | 116.1 (6) |
O4B—N3B—O3B | 126.3 (6) | O3A—N3A—O4A | 126.7 (7) |
O4B—N3B—C4B | 116.5 (7) | O3A—N3A—C4A | 115.8 (8) |
O3B—N3B—C4B | 117.1 (7) | O4A—N3A—C4A | 117.4 (8) |
O6B—N4B—O5B | 124.7 (6) | O6A—N4A—O5A | 124.6 (6) |
O6B—N4B—C6B | 119.6 (5) | O6A—N4A—C6A | 117.4 (6) |
O5B—N4B—C6B | 115.6 (5) | O5A—N4A—C6A | 118.0 (6) |
N1Bii—N5B—C7B | 112.1 (5) | N1A—N5A—C7A | 112.7 (5) |
C8B—C7B—C12B | 116.9 (5) | C12A—C7A—C8A | 117.3 (5) |
C8B—C7B—N5B | 128.6 (5) | C12A—C7A—N5A | 116.6 (5) |
C12B—C7B—N5B | 114.2 (5) | C8A—C7A—N5A | 126.0 (5) |
C9B—C8B—C7B | 122.5 (5) | C7A—C8A—C9A | 122.4 (5) |
C9B—C8B—N6B | 115.3 (5) | C7A—C8A—N6A | 121.9 (5) |
C7B—C8B—N6B | 122.2 (5) | C9A—C8A—N6A | 115.7 (5) |
C8B—C9B—C10B | 117.9 (5) | C10A—C9A—C8A | 117.3 (5) |
C8B—C9B—H9BA | 121.1 | C10A—C9A—H9A | 121.3 |
C10B—C9B—H9BA | 121.1 | C8A—C9A—H9A | 121.3 |
C11B—C10B—C9B | 122.5 (6) | C9A—C10A—C11A | 123.6 (5) |
C11B—C10B—N7B | 118.8 (6) | C9A—C10A—N7A | 119.3 (6) |
C9B—C10B—N7B | 118.7 (5) | C11A—C10A—N7A | 117.1 (6) |
C12B—C11B—C10B | 117.9 (6) | C10A—C11A—C12A | 116.0 (5) |
C12B—C11B—H11B | 121.1 | C10A—C11A—H11A | 122.0 |
C10B—C11B—H11B | 121.1 | C12A—C11A—H11A | 122.0 |
C11B—C12B—C7B | 122.2 (5) | C7A—C12A—C11A | 123.0 (6) |
C11B—C12B—N8B | 119.3 (5) | C7A—C12A—N8A | 120.2 (5) |
C7B—C12B—N8B | 118.2 (5) | C11A—C12A—N8A | 116.6 (5) |
O8B—N6B—O7B | 124.7 (5) | O7A—N6A—O8A | 124.8 (5) |
O8B—N6B—C8B | 117.5 (5) | O7A—N6A—C8A | 118.0 (4) |
O7B—N6B—C8B | 117.8 (4) | O8A—N6A—C8A | 117.0 (5) |
O9B—N7B—O10B | 125.3 (6) | O10A—N7A—O9A | 127.7 (7) |
O9B—N7B—C10B | 117.6 (6) | O10A—N7A—C10A | 117.7 (7) |
O10B—N7B—C10B | 117.2 (6) | O9A—N7A—C10A | 114.6 (7) |
O12B—N8B—O11B | 127.0 (6) | O11A—N8A—O12A | 124.5 (6) |
O12B—N8B—C12B | 116.4 (6) | O11A—N8A—C12A | 119.4 (6) |
O11B—N8B—C12B | 116.6 (6) | O12A—N8A—C12A | 116.1 (6) |
Symmetry codes: (i) x, y−1, z; (ii) x, y+1, z. |
Experimental details
Crystal data | |
Chemical formula | C12H4N8O12 |
Mr | 452.23 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 298 |
a, b, c (Å) | 15.4015 (8), 5.5240 (3), 22.1182 (11) |
β (°) | 110.367 (2) |
V (Å3) | 1764.13 (16) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.16 |
Crystal size (mm) | 0.40 × 0.10 × 0.08 |
Data collection | |
Diffractometer | Bruker SMART CCD area-detector diffractometer |
Absorption correction | Empirical (using intensity measurements) (SADABS; Sheldrick, 1999) |
Tmin, Tmax | 0.94, 0.99 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10081, 6076, 4219 |
Rint | 0.028 |
(sin θ/λ)max (Å−1) | 0.617 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.038, 0.086, 1.02 |
No. of reflections | 6076 |
No. of parameters | 578 |
No. of restraints | 1 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.16, −0.17 |
Computer programs: SMART (Bruker, 1997), SMART, SAINT (Bruker , 1997) and SADABS (Sheldrick, 1999), XM in SHELXTL (Bruker, 1998), XL in SHELXTL, XP and XSHELL in SHELXTL, XCIF in SHELXTL.
HNAB-I | |||
C1-N1-N1i-C1i | C1-C6 | ||
C1-C6 | 43.2 | ||
O1-N2-O2 | 129.6 | ||
O3-N3-O4 | 126.1 | ||
O5-N9-O6 | 148.3 | ||
HNAB-II | |||
C1-N1-N11-C11 | C1-C6 | C11-C61 | |
C1-C6 | 48.0 | ||
C11-C61 | 128.7 | 81.1 | |
O1-N2-O2 | 87.5 | ||
O3-N4-O4 | 1.4 | ||
O5-N6-O6 | 151.2 | ||
O11-N21-O21 | 52.4 | ||
O31-N41-O41 | 21.3 | ||
O51-N61-O61 | 143.4 | ||
HNAB-III | |||
C1A-N1A-N5A-C7A | C1A-C6A | C7A-C12A | |
C1A-C6A | 129.2 | ||
C7A-C12A | 32.0 | 97.3 | |
O1A-N2A-O2A | 130.0 | ||
O3A-N3A-O4A | 160.0 | ||
O5A-N4A-O6A | 148.1 | ||
O7A-N6A-O8A | 67.7 | ||
O9A-N7A-O10A | 31.6 | ||
O11A-N8A-O12A | 47.1 | ||
C1B-N1B-N5B-C7B | C1B-C6B | C7B-C12B | |
C1B-C6B | 122.6 | ||
C7B-C12B | 27.7 | 95.1 | |
O1B-N2B-O2B | 41.1 | ||
O3B-N3B-O4B | 16.7 | ||
O5B-N4B-O6B | 155.1 | ||
O7B-N6B-O8B | 70.8 | ||
O9B-N7B-O10B | 26.7 | ||
O11B-N8B-O12B | 123.3 | ||
HNS | |||
C11-C17-C17i-C11i | C11-C16 | ||
C11-C16 | 67.1 | ||
O12-N12-O13 | 5.5 | ||
O14-N14-O15 | 18.4 | ||
O16-N16-O17 | 48.7 | ||
C21-C27-C27i-C21i | C21-C26 | ||
C21-C26 | 108.0 | ||
O22-N22-O23 | 43.8 | ||
O24-N24-O25 | 21.7 | ||
O26-N26-O27 | 13.5 |
The labeling schemes are those of the original publications. Labels including the letter i signify inversion symmetry related atoms. |
2,2',4,4',6,6'-Hexanitroazobenzene (HNAB) is employed as an explosive and is extremely complex in its crystallographic behavior, as evidenced by the relationships among the various phases and their transformations. There are at least five crystallographic polymorphs of HNAB. Two of these structures, stable at ambient conditions, were solved over 30 years ago (HNAB-I and –II; Graeber & Morosin, 1974), while the third, the subject of the present study, eluded sporadic structure solution attempts over that time frame. The five crystalline polymorphs were initially identified by hot-stage optical microscopy (McCrone, 1967). Forms I and III are stable from room temperature to 458 K, and form II from room temperature to 478 K; above these temperatures, solid–solid transformations begin to occur. The very unstable forms IV and V are formed only from the melt on supercooling during recrystallization. Forms II and III also transform rapidly through the solution phase into form I. Bulk samples of HNAB, regardless of polymorphic forms present, melt at 496 K.
Historically, precession and Weissenberg photography were used to determine preliminary unit-cell dimensions and space-group extinctions and to inspect the diffraction images for satellites. These methods appeared to show very slight splitting at high diffraction angles for reflections down the short axis. There was a remarkable similarity with the precession photographs also taken along the short axis of a crystal of HNS, 2,2',4,4',6,6' -hexanitro-trans-1,2-diphenylethene, with the exception of the h0l's with odd l, as required by the c-glide in the latter compound. HNS is also known as 2,2',4,4',6,6'-hexanitrostilbene [P21/c, a = 22.351 Å, b = 5.572 Å, c = 14.668 Å and β = 110.05° (Duke, 1977); Duke commented on the remarkable structure similarities of his HNS results to those of the monoclinic form of TNT]. Systematic absences and the symmetry of the reciprocal lattice indicated the space group to be consistent with orthorhombic C2221 [a = 15.4015 (8) Å, b = 41.471 (18) Å, c = 5.5240 (3) Å, V = 3528.26 (32) Å3 and Z = 8], but possibly of monoclinic P21 or P21/m symmetry. Attempts to solve the structure using this orthorhombic cell with disordered molecules using various molecular packing models were unsuccessful.
The structure of HNAB-III was finally solved and refined as a pseudo-merohedral twin (monoclinic space group P21 emulating orthorhombic space group C2221) using a dual space recycling method (Sheldrick & Gould, 1995). Since Z = 4, space group P21 requires two structurally independent molecules, labeled A and B below, in the cell. The structure was also refined independently by one of the authors (Rae) using RAELS2000 (Rae, 2000), with essentially identical results. The SHELXTL (Bruker, 1998) results are principally given in this report, with the RAELS2000 results also indicated where appropriate. The twin ratio for reflections h, k, l and h, −k, −h-l related by a twofold axis parallel to the a axis was refined to a value 0.551 (1)/0.449 using the program RAELS2000 compared with 0.552/0.448 determined by SHELXTL. Reflections with even h + k values were approximately three times more intense than the others. Reflections were monitored according to the parity of h and k, and showed a consistently good fit over all such classes.
Fig. 1 shows our labeling scheme for molecule A; that for molecule B is identical. In this regard, even the displacement ellipsoids of the nitro groups of the two molecules appear very similar; in fact, the absolute structures of the two independent molecules are inverted with respect to one another. The shorter intermolecular contacts include, but are not limited to, possible hydrogen-bond interactions with H···O distances of 2.462, 2.491 and 2.516 Å, C···O contacts of 2.954, 2.969 and 2.979 Å, and N···O contacts of 2.919, 2.935 and 2.969 Å.
Fig. 2(a) shows the packing of the molecules as viewed along the b axis. The a axis and c axis are interchanged relative to those given above, and the cell contents are shifted from the normal placement of the 21 axes by a/4, so that the remarkable similarity (noted earlier) with the corresponding projection for HNS can be shown (Fig. 2b; Gerard & Hardy, 1988). Note that HNS belongs to P21/c and each of its molecules resides on an inversion center. Examination of the dihedral angles for the HNAB molecules shows significant differences between not only those molecules in HNS but also that for HNAB-I. In HNAB-III, the phenyl planes form smaller angles with respect to the linkage (C—N—N—C) planes [ϕl = 27.7 (3), 32.0 (3), 50.8 (3) and 57.4 (3)°] and the phenyl planes are twisted with respect to one another [ϕp = 82.7 (3) and 84.9 (3)° for A and B], while in HNS, the phenyl planes form larger angles with respect to the linkage (C—C—C—C) planes [ϕl = 67.1 (4) and 72.0 (4)°] and the phenyl planes are in parallel alignment as required by the inversion center (ϕp = 0°). Interestingly, HNAB-I also shows this parallel disposition for the phenyl planes (ϕp = 0°, with a phenyl-linkage angle of ϕl = 43.2 (4)°], while in HNAB-II, the phenyl planes are twisted, but to a smaller degree than in HNAB-III [ϕp = 81.1 (5)°, with phenyl-linkage angles of ϕl = 48.0 (5) and 51.3 (5)°]. Table 1 summarizes the angles between the appropriate planes formed by various entities of the molecules in these crystal structures.
HNS shows pseudosymmetry (Fig. 2b), and imposing a mirror at y = 1/4 creates a 1:1 disordered structure of approximate Pnma symmetry in the cell a' = a + c/2, b' = b, c' = c/2 but with β' = 90.87°. Upon ordering this structure to create the B-centered cell 2a', b', 2c' equivalent to the real structure, the symmetry elements associated with the a' and c' directions must be destroyed. However, they suggest a mechanism for stacking faults and twinning if β' had been 90°. The structure of HNAB-III has β' = 90.00° within the estimated error for the cell a' = a/2 + c, b' = −b, c' = a/2, but although the structure looks similar to that of HNS in projection, the centers of non-equivalent molecules now differ in y by about 1/4. However a twofold screw operation parallel to the a axis is the likely twin operation, as it leaves NO2 groups adjacent to the twin plane at z = 1/4 unchanged to a first approximation.
The most striking differences between the three HNAB forms are in the Cring—Nazo bond lengths, which increase with the corresponding decrease in the crystal densities (1.795, 1.744 and 1.703 Mg/m−3 for I, II and III). These differences are not considered significant by the usual statistical criteria (Hamilton, 1964); however, the increasing values of 1.426 (5) Å for HNAB-I, 1.430 (5) and 1.438 (5) Å for HNAB-II, and 1.441 (7), 1.442 (6), 1.447 (6) and 1.457 (7) Å for HNAB-III, together with the increasing phenyl ring twisting from the parallel configuration, must contribute toward the packing contributions responsible for the density differences.
The examination of various specific bond lengths led to a further comparison with other nitro-containing and other aromatic energetic materials, considering how the electron-withdrawing characteristics of various substituting groups might impose on the ring bond lengths. The variation of the C—Cring bond lengths in other related nitro-containing and aromatic explosive materials, particularly the long values, were initially attributed to steric effects of the crowded substituents; other reports since relate this variation to electronic effects associated with resonance structures, as well as the quinonoid contribution involving the ring. This led Holden et al. (1972) to demonstrate an inverse correlation between the lengths of the ring bonds and the length of the C—N bond in various aromatic amine compounds. Fig. 3 shows this relationship and includes the values for the different HNAB forms, as well as some other recent structure determinations. The C—N values range from 1.310 to 1.466 Å. [The C—N value of 1.497 Å for an average ring bond of 1.391 Å found in tetryl (Cady, 1967) is an exception to this linear relationship and is probably due to steric intramolecular interactions.] In decreasing order the values are 1.457, 1.447, 1.442 and 1.441 Å (HNAB-III), 1.438 Å (HNAB-II), 1.433 Å (azotoluene; Brown, 1966a), 1.434 Å (azobenzene; Brown, 1966b), 1.430 Å (HNAB-II), 1.426 Å (HNAB-I), 1.426 Å (2,4,6-tribromoaniline; Christensen & Stromme, 1969), 1.412 Å (1,3,5-triaminobenzene 1,3,5-trinitrobenzene or TAB-TNB; Iwasaki & Saito, 1970), 1.407 Å (2,5-dichloroaniline; Sakurai et al., 1963), 1.40 Å (4-chloroaniline; Palm, 1966), 1.392 and 1.391 Å for TAB-TNB, 1.386 Å (2-chloro-4-nitroaniline; McPhail & Sim, 1965), 1.371 Å (4-nitroanaline; Trueblood et al., 1961), 1.367 Å (2-amino-3-methylbenzoic acid; Brown & Marsh, 1963), 1.358 Å (2,6-dichloro-4-nitroaniline; Hughes & Trotter, 1971), 1.340 Å (2,4,6-trinitroanaline or TNA; Holden et al., 1972), 1.32 Å (1,3-diamino-2,4,6-trinitrobenzene or DATB; Holden, 1967), 1.320 Å (1,3,5-triamino-2,4,6-trinitrobenzene or TATB; Cady & Larson, 1965), 1.312 Å (2,3,4,6-tetranitroanaline; Dickinson et al., 1966), and 1.311 and 1.310 Å (TATB). The interesting result of this plot is the relative position of the values for the nitro-containing HNAB molecules. The C—N lengths are longer than those for aromatic amines containing no nitro groups; a possible reason for the shortened values is the electron-withdrawing properties of the nitro group. It had previously been noted from the position of 2-amino-3-methyl benzoic acid that the acid group also functions in such a capacity. This suggests that the azo linkage must be an even greater electron-withdrawing group in order to neutralize the affect of the nitro groups.
The benzene ring is also distorted by the increase in the C—C lengths given in the above inverse correlation. This is achieved in part by the C—C—C ring angles increasing at the location of the corresponding nitro groups. Other uncorrelated and minor contributions to the distortion of the ring are the quinonoid and resonance shortening of the other C—C lengths (details available from authors).