Exceeding the oxygen content of liquid oxygen: bis­(2,2,2-trinitro­ethyl) carbonate

Bis(2,2,2-trinitro­ethyl) carbonate, C₅H₄N₆O₁₅, is an oxygen-rich compound (61.83% of mol­ecular weight) of interest with respect to energetic materials. The mol­ecule adopts an s–cis–s–cis conformation of the carbonate group. Intra- as well as inter­molecular C—H...O and dipolar nitro-group inter­actions account for its exceptionally high density of 1.975 Mg m⁻³. As a consequence of the relationship between structure and crystal density, this polymorph contains available oxygen in amounts even superior to liquid oxygen.

S1. Comment

To date, many new polynitro aliphatic compounds have been discovered. These compounds, which often are derivatives of trinitromethane, contain available oxygen in amounts never before attained in solid explosive compounds. We are interested in the development and testing of energetic materials. We are determining the structures of a number of high crystal density polynitro compounds as a preliminary step in an investigation of the relationships between structure and crystal density in energetic substances. Density is a critical parameter in the prediction of explosive performance parameters, such as velocity of detonation or detonation pressure.

The structure of the valuable compound bis(2,2,2-trinitroethyl) carbonate, (I), in the solid state has not previously been investigated. We have found that (I) at 100 K has an exceptionally high density of 1.975 Mg m^-3, which is significantly higher than the reported value of 1.88 Mg m^-3 (Hill, 1956). The asymmetric unit of (I) (Fig. 1) consists of one bis(2,2,2-trinitroethyl) carbonate molecule. The geometry in both trinitroethyl moieties is very similar, with a propeller-type orientation of the nitro groups (C₃) bonded to the β-C atoms and the conformation of the substituents of the α- and β-C atoms being staggered. The bond lengths of the trinitroethyl units show unusual values in that the C—N bonds joining the three nitro groups to the β-C atom (Table 1) are significantly longer than the normal C—N bond distance of 1.47 Å (Shannon, 1976); the N—C—N bond angles are smaller (Table 1) than the tetrahedral value, whereas the corresponding N—C—C angles are greater (Table 1), as was similarily observed in the structure determinations of bis(2,2,2-trinitroethyl)urea (Lind, 1970) and 2,2,2-trinitroethanol (Göbel & Klapötke, 2007).

Early investigations into the structural properties of (I) using IR spectroscopy (Hall, 1968) could not settle the question of the molecular geometry adopted by the carbonate, with s–cis–s–cis, s–cis–s–trans or s–trans–s–trans conformations all being possible for organic carbonates. Short intramolecular C—H···O contacts are present (Table 2), associated with the s–cis–s–cis conformation. The bond lengths and angles of the carbonate moiety (Table 1) may be considered normal in comparison with the Cambridge Structural Database results (Allen, 2002). The extended structure of (I) involves intermolecular C—H···O hydrogen bonding (Table 2). The resulting bifurcated hydrogen bonding is displayed in Fig. 2.

Short intermolecular O···O distances with values substantially less than 3.04 Å, the sum of the van der Waals radii for O (1.52 Å; Bondi, 1964) are observed as a consequence of noncovalent dipolar nitro-group interactions. Dipolar nitro-group interactions were accepted for N···O contacts shorter than 3.17 Å. This value was chosen as the sum of the van der Waals radii of nitrogen and oxygen (Bondi, 1964) plus a tolerance value of 0.1 Å. Given these values, three dipolar nitro-group contacts were identified. These interactions were found for the N1/O4/O5 nitro group interacting with the N6/O14/O15 nitro group as well as with the N2/O6/O7 and the N3/O8/O9 nitro groups and finally for the N6/O14/O15 nitro group interacting with the N4/O10/O11 nitro group and the N5/O12/O13 nitro group, leading to O···O distances of 2.8317 (11) Å [O4···O7ⁱⁱ; symmetry code: (ii) -x + 3/2, y - 1/2, z], 2.8626 (12) Å [O5···O14ⁱⁱⁱ; symmetry code: (iii) -x + 3/2, -y, z - 1/2] and 2.8381 (12) Å [O14···O12ⁱⁱⁱⁱ; symmetry code: (iiii) x + 1/2, y, -z + 3/2]. The corresponding values for the N···O contacts are 3.0125 (11) Å (O4···N3ⁱⁱ), 2.9935 (12) Å (O5···N6ⁱⁱⁱ) and 3.1045 (12) Å (O14···N4ⁱⁱⁱⁱ).

The high oxygen content of (I), together with the intermolecular contacts (dipolar nitro-group interactions and hydrogen bonding) yield a high-crystal-density polymorph that displays an oxygen content of 1.221 Mg m^-3, higher than the value 1.140 Mg m^-3 (Holleman, 1995) in liquid oxygen at 90 K.

Related literature

For related literature, see: Allen (2002); Bondi (1964); Göbel & Klapötke (2007); Hall (1968); Hill (1956); Holleman (1995); Lind (1970); Shannon (1976).

S2. Experimental

Caution: bis(2,2,2-trinitroethyl) carbonate is an energetic material. Proper protective measures [safety glasses, face shields, leather coat, earthing (equipment and person), Kevlar gloves and ear protectors] should be used when handling this material. Bis(2,2,2-trinitroethyl) carbonate (Hill, 1956) was prepared from the reaction of trinitroethanol with phosgene (Hall, 1968). The crystal growth was accomplished by concentration of a saturated CHCl₃ solution at ambient temperature, yielding colourless single crystals.

S3. Refinement

H atoms were directly located in difference maps and then refined freely, giving a range of C—H distances of 0.923 (13)–0.966 (13) Å.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED (Oxford Diffraction, 2006); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: PLATON (Spek, 2003), SHELXL97 (Sheldrick, 1997), ORTEP-3 (Farrugia, 1997), DIAMOND (Brandenburg & Putz, 2005) and publCIF (Westrip, 2008).

Figures

	Fig. 1. The asymmetric unit of (I), together with the atomic numbering scheme. Displacement ellipsoids are shown at the 50% probability level. N2 O atoms are labelled incorrectly
	Fig. 2. A centrosymemtric dimer containing two bis(2,2,2-trinitroethyl) carbonate molecules. The bifurcated hydrogen bonding is indicated by dashed lines. [Symmetry code: (i) -x + 1, -y, -z + 1].]

bis(2,2,2-trinitroethyl) carbonate

Crystal data

C5H4N6O15	F(000) = 1568
Mr = 388.14	Dx = 1.975 Mg m^−3
Orthorhombic, Pbca	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2ab	Cell parameters from 5759 reflections
a = 10.8828 (2) Å	θ = 3.7–32.3°
b = 11.4746 (2) Å	µ = 0.20 mm^−1
c = 20.9073 (4) Å	T = 100 K
V = 2610.81 (8) Å^3	Triangular plate, colourless
Z = 8	0.18 × 0.17 × 0.03 mm

Data collection

Oxford Diffraction Xcalibur3 CCD diffractometer	2765 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.025
Graphite monochromator	θmax = 30.0°, θmin = 3.7°
ω scans	h = −15→13
12846 measured reflections	k = −16→11
3795 independent reflections	l = −21→29

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.027	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.068	All H-atom parameters refined
S = 0.99	w = 1/[σ^2(Fo^2) + (0.0368P)^2] where P = (Fo^2 + 2Fc^2)/3
3795 reflections	(Δ/σ)max = 0.001
251 parameters	Δρmax = 0.38 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

Special details

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.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
H2A	0.3686 (10)	0.2456 (11)	0.5439 (6)	0.014 (3)*
H2B	0.4240 (12)	0.1334 (10)	0.5126 (6)	0.011 (3)*
H4A	0.4584 (11)	−0.1715 (11)	0.7031 (6)	0.017 (3)*
H4B	0.5670 (12)	−0.1028 (10)	0.6729 (6)	0.015 (3)*
C1	0.43634 (9)	0.02260 (9)	0.60920 (5)	0.0123 (2)
C2	0.36168 (10)	0.16376 (9)	0.53759 (5)	0.0122 (2)
C3	0.24022 (9)	0.14251 (8)	0.50397 (5)	0.01087 (19)
C4	0.49053 (11)	−0.09783 (9)	0.69622 (5)	0.0142 (2)
C5	0.51345 (9)	−0.04047 (9)	0.76071 (5)	0.0129 (2)
N1	0.22602 (8)	0.01774 (7)	0.48014 (4)	0.01249 (18)
N2	0.12991 (8)	0.16707 (8)	0.54660 (4)	0.01453 (18)
N3	0.22827 (8)	0.22014 (7)	0.44539 (4)	0.01318 (18)
N4	0.59469 (8)	0.06766 (8)	0.75644 (4)	0.01551 (18)
N5	0.57242 (9)	−0.12303 (8)	0.80806 (4)	0.01640 (19)
N6	0.39188 (8)	0.00038 (8)	0.78950 (4)	0.01512 (19)
O1	0.52104 (7)	−0.00527 (6)	0.57650 (4)	0.01538 (16)
O2	0.40148 (7)	−0.02641 (6)	0.66476 (3)	0.01448 (16)
O3	0.35593 (7)	0.10894 (6)	0.59871 (3)	0.01366 (15)
O4	0.24523 (8)	−0.05702 (6)	0.52031 (4)	0.02044 (18)
O5	0.19703 (7)	0.00315 (7)	0.42498 (4)	0.01894 (17)
O6	0.04168 (7)	0.10346 (7)	0.54118 (4)	0.0274 (2)
O7	0.14032 (7)	0.25140 (6)	0.58146 (4)	0.01880 (17)
O8	0.12754 (7)	0.26055 (7)	0.43389 (4)	0.02010 (18)
O9	0.32251 (7)	0.23232 (6)	0.41497 (4)	0.01766 (17)
O10	0.58438 (8)	0.12474 (7)	0.70779 (4)	0.02207 (18)
O11	0.65962 (8)	0.08911 (7)	0.80214 (4)	0.0253 (2)
O12	0.64279 (8)	−0.19342 (7)	0.78468 (4)	0.02372 (19)
O13	0.54623 (8)	−0.11084 (7)	0.86410 (4)	0.0250 (2)
O14	0.31547 (7)	−0.07659 (7)	0.79429 (4)	0.02226 (18)
O15	0.38146 (8)	0.10227 (7)	0.80339 (4)	0.02193 (18)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0133 (5)	0.0132 (5)	0.0105 (5)	−0.0010 (4)	−0.0029 (4)	−0.0021 (4)
C2	0.0135 (5)	0.0132 (5)	0.0099 (5)	0.0003 (4)	−0.0006 (4)	0.0009 (4)
C3	0.0125 (5)	0.0094 (4)	0.0107 (4)	0.0006 (4)	0.0016 (4)	−0.0003 (4)
C4	0.0175 (5)	0.0142 (5)	0.0109 (5)	0.0031 (4)	−0.0020 (4)	0.0003 (4)
C5	0.0130 (5)	0.0144 (5)	0.0112 (5)	0.0013 (4)	0.0007 (4)	0.0020 (4)
N1	0.0117 (4)	0.0118 (4)	0.0140 (4)	−0.0004 (3)	0.0005 (3)	−0.0012 (3)
N2	0.0133 (4)	0.0149 (4)	0.0154 (4)	0.0015 (4)	0.0025 (4)	0.0015 (3)
N3	0.0162 (4)	0.0106 (4)	0.0128 (4)	0.0011 (3)	−0.0025 (3)	0.0002 (3)
N4	0.0153 (4)	0.0161 (4)	0.0152 (4)	0.0006 (4)	−0.0002 (4)	−0.0009 (3)
N5	0.0180 (4)	0.0175 (4)	0.0137 (5)	−0.0004 (4)	−0.0020 (4)	0.0035 (3)
N6	0.0154 (4)	0.0210 (4)	0.0089 (4)	0.0015 (4)	−0.0007 (3)	0.0009 (3)
O1	0.0165 (4)	0.0178 (4)	0.0118 (4)	0.0034 (3)	0.0014 (3)	−0.0004 (3)
O2	0.0148 (3)	0.0189 (4)	0.0098 (3)	0.0025 (3)	−0.0005 (3)	0.0024 (3)
O3	0.0154 (4)	0.0165 (3)	0.0090 (3)	0.0042 (3)	−0.0001 (3)	0.0005 (3)
O4	0.0303 (4)	0.0118 (4)	0.0192 (4)	−0.0005 (3)	−0.0043 (4)	0.0032 (3)
O5	0.0251 (4)	0.0182 (4)	0.0135 (4)	−0.0024 (3)	−0.0043 (3)	−0.0034 (3)
O6	0.0159 (4)	0.0273 (5)	0.0392 (5)	−0.0078 (4)	0.0079 (4)	−0.0079 (4)
O7	0.0226 (4)	0.0149 (4)	0.0189 (4)	0.0022 (3)	0.0053 (3)	−0.0038 (3)
O8	0.0173 (4)	0.0206 (4)	0.0224 (4)	0.0061 (3)	−0.0058 (3)	0.0025 (3)
O9	0.0197 (4)	0.0175 (4)	0.0158 (4)	0.0004 (3)	0.0048 (3)	0.0030 (3)
O10	0.0261 (4)	0.0202 (4)	0.0200 (4)	−0.0035 (3)	−0.0017 (3)	0.0072 (3)
O11	0.0249 (4)	0.0282 (4)	0.0228 (4)	−0.0063 (4)	−0.0095 (4)	−0.0014 (4)
O12	0.0257 (4)	0.0220 (4)	0.0235 (5)	0.0100 (3)	0.0012 (4)	0.0029 (3)
O13	0.0291 (5)	0.0347 (5)	0.0113 (4)	0.0045 (4)	−0.0005 (3)	0.0045 (3)
O14	0.0170 (4)	0.0305 (4)	0.0193 (4)	−0.0059 (3)	0.0020 (3)	0.0001 (3)
O15	0.0260 (4)	0.0205 (4)	0.0194 (4)	0.0067 (3)	0.0042 (3)	−0.0017 (3)

Geometric parameters (Å, º)

C1—O1	1.1915 (12)	C5—N4	1.5262 (14)
C1—O3	1.3399 (12)	C5—N6	1.5271 (13)
C1—O2	1.3451 (12)	N1—O5	1.2073 (12)
C2—O3	1.4255 (12)	N1—O4	1.2185 (11)
C2—C3	1.5168 (14)	N2—O6	1.2115 (11)
C2—H2A	0.951 (12)	N2—O7	1.2167 (11)
C2—H2B	0.923 (13)	N3—O8	1.2142 (11)
C3—N3	1.5201 (13)	N3—O9	1.2148 (11)
C3—N2	1.5214 (13)	N4—O11	1.2136 (12)
C3—N1	1.5238 (13)	N4—O10	1.2150 (11)
C4—O2	1.4294 (13)	N5—O13	1.2138 (12)
C4—C5	1.5211 (15)	N5—O12	1.2158 (12)
C4—H4A	0.926 (13)	N6—O15	1.2101 (12)
C4—H4B	0.966 (13)	N6—O14	1.2172 (12)
C5—N5	1.5131 (13)
O1—C1—O3	127.57 (10)	N5—C5—N6	107.57 (8)
O1—C1—O2	126.98 (9)	C4—C5—N6	109.88 (8)
O3—C1—O2	105.46 (8)	N4—C5—N6	105.99 (8)
O3—C2—C3	107.83 (8)	O5—N1—O4	127.27 (9)
O3—C2—H2A	108.3 (8)	O5—N1—C3	117.98 (8)
C3—C2—H2A	107.0 (7)	O4—N1—C3	114.75 (8)
O3—C2—H2B	111.8 (7)	O6—N2—O7	127.52 (9)
C3—C2—H2B	108.5 (7)	O6—N2—C3	117.32 (9)
H2A—C2—H2B	113.1 (10)	O7—N2—C3	115.14 (8)
C2—C3—N3	110.72 (8)	O8—N3—O9	127.93 (9)
C2—C3—N2	112.73 (8)	O8—N3—C3	117.42 (8)
N3—C3—N2	107.22 (8)	O9—N3—C3	114.64 (8)
C2—C3—N1	113.01 (8)	O11—N4—O10	127.13 (10)
N3—C3—N1	106.17 (8)	O11—N4—C5	117.13 (9)
N2—C3—N1	106.59 (8)	O10—N4—C5	115.71 (8)
O2—C4—C5	105.72 (8)	O13—N5—O12	127.78 (9)
O2—C4—H4A	109.8 (8)	O13—N5—C5	117.37 (9)
C5—C4—H4A	108.6 (8)	O12—N5—C5	114.84 (8)
O2—C4—H4B	112.7 (7)	O15—N6—O14	128.12 (9)
C5—C4—H4B	109.4 (7)	O15—N6—C5	118.19 (9)
H4A—C4—H4B	110.4 (10)	O14—N6—C5	113.68 (8)
N5—C5—C4	112.25 (8)	C1—O2—C4	116.48 (8)
N5—C5—N4	107.55 (8)	C1—O3—C2	116.39 (8)
C4—C5—N4	113.26 (8)
O3—C2—C3—N3	167.33 (8)	N5—C5—N4—O11	−24.40 (12)
O3—C2—C3—N2	47.23 (11)	C4—C5—N4—O11	−149.03 (10)
O3—C2—C3—N1	−73.72 (10)	N6—C5—N4—O11	90.42 (11)
O2—C4—C5—N5	161.52 (8)	N5—C5—N4—O10	157.49 (9)
O2—C4—C5—N4	−76.44 (10)	C4—C5—N4—O10	32.86 (12)
O2—C4—C5—N6	41.87 (11)	N6—C5—N4—O10	−87.68 (10)
C2—C3—N1—O5	−128.80 (10)	C4—C5—N5—O13	−147.46 (9)
N3—C3—N1—O5	−7.25 (11)	N4—C5—N5—O13	87.31 (11)
N2—C3—N1—O5	106.83 (10)	N6—C5—N5—O13	−26.47 (12)
C2—C3—N1—O4	51.58 (11)	C4—C5—N5—O12	33.58 (13)
N3—C3—N1—O4	173.13 (8)	N4—C5—N5—O12	−91.65 (10)
N2—C3—N1—O4	−72.79 (10)	N6—C5—N5—O12	154.57 (9)
C2—C3—N2—O6	−142.90 (9)	N5—C5—N6—O15	114.25 (10)
N3—C3—N2—O6	95.01 (10)	C4—C5—N6—O15	−123.29 (10)
N1—C3—N2—O6	−18.35 (12)	N4—C5—N6—O15	−0.57 (12)
C2—C3—N2—O7	38.81 (12)	N5—C5—N6—O14	−67.11 (11)
N3—C3—N2—O7	−83.29 (10)	C4—C5—N6—O14	55.36 (11)
N1—C3—N2—O7	163.35 (8)	N4—C5—N6—O14	178.07 (8)
C2—C3—N3—O8	−141.99 (9)	O1—C1—O2—C4	17.35 (15)
N2—C3—N3—O8	−18.65 (11)	O3—C1—O2—C4	−162.59 (8)
N1—C3—N3—O8	95.00 (10)	C5—C4—O2—C1	118.99 (9)
C2—C3—N3—O9	39.17 (11)	O1—C1—O3—C2	9.22 (15)
N2—C3—N3—O9	162.51 (8)	O2—C1—O3—C2	−170.84 (8)
N1—C3—N3—O9	−83.84 (10)	C3—C2—O3—C1	117.22 (9)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2B···O1^i	0.923 (13)	2.448 (12)	3.2598 (13)	146.7 (10)
C4—H4B···O9^i	0.966 (13)	2.651 (13)	3.4532 (13)	140.7 (9)
C4—H4B···O1	0.966 (13)	2.359 (12)	2.7392 (13)	102.8 (8)
C2—H2B···O1	0.923 (13)	2.330 (12)	2.7261 (13)	105.5 (8)

Symmetry code: (i) −x+1, −y, −z+1.