Potassium 4-nitramino-1,2,4-triazolate

The title compound, K⁺·C₂H₂N₅O₂⁻, has an anion conformation similar to the reported conformation of 4-nitr­amino-1,2,4-triazole. Seven O and N atoms of six ligand mol­ecules coordinate the potassium cation with short values of K...O and K...N interatomic distances.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](N-C) = 0.003 Å
• R factor = 0.048
• wR factor = 0.124
• Data-to-parameter ratio = 12.4

checkCIF results

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S1. Comment

The structure of 4-nitramino-1,2,4-triazole, (II), has a zwitterionic conformation and has been solved previously (Vasiliev et al., 1999). To determine the influence of the transition from (II) to its anion on the molecular conformation and on its nitrimine fragment, the structure of the potassium salt of (II), viz. the title compound, (I), was investigated. The task arose out of a search of relationship `structure–property' in a series of energetic nitramines. This knowledge is needed for an estimation of properties of new hypothetic energetic molecules (Astachov, 1999).

The structural formula for (I) (see Scheme above) does not precisely reflect the true location of a negative charge in the anion of (I). However, as will be shown, the representation of (I) using conventional principles of chemical structural formula spelling, which takes into consideration the atom valence, and experimental geometry parameters, was a difficult task.

As a whole, the transition from (II) to its anion does not affect the molecular geomerty parameters. Like (II), the molecule of (I) is not planar, but consists of two planar fragments: 1,2,4-triazole cycle [maximum deviation 0.000 (1) Å] and nitrimide group N—N—NO₂ [r.m.s. deviation 0.012 (1) Å and maximum deviation 0.019 (1) Å]. The N4—N6—N7—O2 torsion angle is 3.0 (3)° [−2.6° for (II)]. Maximum changes of valence angles are near 5° for the triazole cycle and less than 2° for the molecular nitrimide fragment.

The bond lengths of a nitrimide fragment of (I) are practically the same as in (II) [in brackets]: N4—N6 1.408 (2) Å [1.407 (2) Å], N6—N7 1.322 (3) Å [1.319 (2) Å], N7—O1 1.261 (2) Å [1.259 (2) Å] and N7—O2 1.243 (3) Å [1.235 (2) Å]. Some interatomic distances in a triazole cycle changed rather more: N1—N2 1.393 (3) Å [1.362 (2) Å], N2—C3 1.295 (3) Å [1.300 (2) Å], C3—N4 1.351 (3) Å [1.358 (2) Å], N4—C5 1.352 (3) Å [1.341 (2) Å] and C5—N1 1.299 (3) Å [1.308 (2) Å]. The facts allow the separation of single and double bonds more definitely than in the molecule of (II). The separation is reflected in the cited above structural formula. The valence angle data is collected in Table 1.

In the crystal of (I), the seven atoms O1, O2, N1 and N2 of six anion molecules coordinate the potassium cation (Fig. 1). It is worth noting that atom O1 has a tetrahedral environment coordinated by atom N7 and three potassium ions. Close values of K···O and K···N interatomic distances [2.788–2.934 (2) Å] (Table 1) do not allow exact location of a negative charge on some of the anion atoms. Beginning with atom valency and invariability of nitrimide fragment geometry parameters, atom N6 was supplied by negative anion charge in the structural formula of (I), but the atom does not coordinate the potassium ion.

The X-ray analysis allows, in particular, the confirmation of the suggested before supposition about first step of thermolysis; namely, like (II), it is a break of the N4—N6 bond (Astachov, 1999). The established bond lengths show that the N4—N6 bond, which connects the nitrimine group and the triazole cycle is the weakest bond in the molecule of (I) and of (II) (Vasiliev et al., 1999).

S2. Experimental

Several drops of water were added to a boiling suspension of 4-nitramino-1,2,4-triazole (1 g) in caustic alcohol (0.8 g potassium hydroxide in 20 ml of 95% ethanol) for solution homogenization. To the transparent solution was added diethyl ether (20 ml) and the mixture was cooled slowly to room temperature. A fine needle-shaped precipitate was separated by filtration, washed with ethanol and dried. The yield of (I) was 1.0 g (77%).

S3. Refinement

Two H atoms were found in a difference Fourier map and were refined as riding atoms with a common isotropic displacement parameter.

Computing details

Data collection: KM-4 Software (Kuma, 1991); cell refinement: KM-4 Software; data reduction: DATARED in KM-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1995); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. The arrangement of anion molecules near the potassium ion in the crystal of (I), with the atomic numbering scheme (H atoms not shown). Dash lines are K···O and K···N contacts.

Potassium 4-nitramino-1,2,4-triazolate

Crystal data

K^+·C2H2N5O2^−	F(000) = 336
Mr = 167.19	Dx = 1.833 Mg m^−3
Monoclinic, P21/c	Cu Kα radiation, λ = 1.5418 Å
Hall symbol: -P 2ybc	Cell parameters from 25 reflections
a = 7.9671 (6) Å	θ = 22–28°
b = 4.8182 (4) Å	µ = 7.30 mm^−1
c = 16.812 (1) Å	T = 293 K
β = 110.165 (7)°	Transparent lump, colourless
V = 605.81 (8) Å^3	0.27 × 0.25 × 0.22 mm
Z = 4

Data collection

Kuma KM-4 diffractometer	Rint = 0.022
Radiation source: fine-focus sealed tube	θmax = 70.0°, θmin = 5.6°
Graphite monochromator	h = −9→0
θ/2θ scans	k = 0→5
1230 measured reflections	l = −18→20
1154 independent reflections	2 standard reflections every 50 reflections
1039 reflections with I > 2σ(I)	intensity decay: variation 0.4%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.048	Only H-atom displacement parameters refined
wR(F^2) = 0.124	w = 1/[σ^2(Fo^2) + (0.1004P)^2 + 0.2012P] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max = 0.003
1154 reflections	Δρmax = 0.80 e Å^−3
93 parameters	Δρmin = −0.55 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0085 (17)

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
K	−0.24012 (6)	0.08386 (11)	0.25514 (3)	0.0309 (3)
N1	0.2758 (3)	0.5141 (5)	0.62639 (13)	0.0367 (5)
N2	0.3902 (3)	0.2865 (5)	0.64968 (12)	0.0354 (5)
C3	0.4030 (3)	0.1883 (5)	0.58028 (15)	0.0334 (5)
H1	0.4716	0.0348	0.5775	0.057 (7)*
N4	0.3037 (2)	0.3378 (4)	0.51240 (12)	0.0282 (5)
C5	0.2270 (3)	0.5384 (5)	0.54458 (16)	0.0337 (6)
H2	0.1503	0.6745	0.5127	0.057 (7)*
N6	0.2994 (3)	0.3078 (5)	0.42839 (12)	0.0336 (5)
N7	0.1644 (3)	0.1445 (4)	0.38656 (11)	0.0260 (5)
O1	0.1502 (3)	0.0975 (4)	0.31070 (10)	0.0382 (5)
O2	0.0554 (2)	0.0459 (4)	0.41692 (11)	0.0394 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K	0.0307 (4)	0.0384 (4)	0.0224 (4)	0.00076 (18)	0.0076 (2)	−0.00247 (17)
N1	0.0466 (13)	0.0368 (11)	0.0257 (10)	0.0019 (10)	0.0110 (9)	−0.0042 (9)
N2	0.0355 (11)	0.0435 (12)	0.0244 (10)	−0.0006 (9)	0.0066 (8)	−0.0001 (8)
C3	0.0309 (12)	0.0390 (13)	0.0277 (12)	0.0025 (10)	0.0069 (9)	0.0014 (10)
N4	0.0270 (10)	0.0355 (10)	0.0213 (9)	−0.0011 (8)	0.0073 (7)	−0.0026 (8)
C5	0.0372 (13)	0.0343 (12)	0.0273 (11)	0.0033 (10)	0.0084 (10)	−0.0019 (10)
N6	0.0353 (10)	0.0448 (13)	0.0227 (10)	−0.0089 (9)	0.0125 (8)	−0.0043 (8)
N7	0.0289 (10)	0.0303 (9)	0.0175 (9)	0.0039 (8)	0.0062 (7)	0.0032 (7)
O1	0.0528 (11)	0.0414 (10)	0.0194 (9)	0.0014 (8)	0.0112 (8)	−0.0018 (7)
O2	0.0342 (9)	0.0548 (11)	0.0276 (9)	−0.0106 (8)	0.0088 (7)	0.0041 (8)

Geometric parameters (Å, º)

K—O1^i	2.7886 (18)	K—O2	2.9257 (18)
K—N1^ii	2.862 (2)	K—N2^v	2.934 (2)
K—O1^iii	2.9001 (18)	C3—H1	0.9300
K—N2^iv	2.914 (2)	C5—H2	0.9300
K—O1	2.923 (2)
C5—N1—N2	107.3 (2)	O2—N7—O1	121.0 (2)
C3—N2—N1	106.4 (2)	O2—N7—N6	124.3 (2)
N2—C3—N4	111.2 (2)	O1—N7—N6	114.7 (2)
C3—N4—C5	104.9 (2)	N2—C3—H1	124.4
C3—N4—N6	126.7 (2)	N4—C3—H1	124.4
C5—N4—N6	128.1 (2)	N1—C5—H2	124.8
N1—C5—N4	110.3 (2)	N4—C5—H2	124.8
N7—N6—N4	109.2 (2)
C5—N1—N2—C3	0.0 (3)	N6—N4—C5—N1	−173.2 (2)
N1—N2—C3—N4	0.0 (3)	C3—N4—N6—N7	95.2 (3)
N2—C3—N4—C5	0.0 (3)	C5—N4—N6—N7	−93.0 (3)
N2—C3—N4—N6	173.3 (2)	N4—N6—N7—O2	3.0 (3)
N2—N1—C5—N4	0.0 (3)	N4—N6—N7—O1	−178.4 (2)
C3—N4—C5—N1	0.0 (3)

Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) −x, −y+1, −z+1; (iii) −x, y+1/2, −z+1/2; (iv) −x, −y, −z+1; (v) x−1, −y+1/2, z−1/2.