2,2′-Dimeth­yl-4,5′-dinitro-1H,3′H-1,4′-biimidazole monohydrate

The two almost perfectly planar imidazole rings in the title compound, C₈H₈N₆O₄·H₂O, make a dihedral angle of 63.01 (10)°. The water mol­ecule acts as a double donor and double acceptor of strong and linear hydrogen bonds, including an exceptionally short C—H...O bond. These bonds create a tight three-dimensional structure and are probably responsible for the relatively high melting point of the compound.

S1. Comment

There are 28 organic and 62 organometallic crystal structures containing 2,2'-biimidazole in the Cambridge Structural Database (Allen, 2002; November 2004 version, February 2005 updates). It therefore seems strange that for 1,5'-biimidazole there is only one known crystal structure (Kubicki et al., 2001). What is more, examples of other biimidazoles are also scarce; there are only a few examples of 4,4'- (four structures) and 5,5'-biimidazoles (three examples).

Since the 4-nitroimidazole derivatives proved to be convenient subjects for studying weak intermolecular interactions in crystals (e.g. Kubicki, 2004, and references therein), it should be of interest to determine the crystal structures of their biimidazole analogues as well. Here, the crystal structure of one of the simplest members of this family, 2,2'-dimethyl-4,5'-dinitro-3'H-[1,4']-biimidazole, is reported. This compound crystallizes as a hydrate, (I).

Fig. 1 shows a perspective view of the molecule. Both imidazole rings are almost perfectly planar; the maximum deviations from the least-squares planes are 0.0032 (14) and 0.0008 (15) Å for rings A and B (hereinafter A will denote the non-primed and B the primed imidazole rings). The nitro groups are only slightly twisted with respect to the imidazole planes [the twist angles are 1.9 (3)° for A and 3.9 (4)° for B]. The dihedral angle between the imidazole rings is 63.01 (10)°; this value is large compared with the typical values for 2,2'-biimidazoles, for which angles significantly larger than a few degrees are observed only in the case of large substituents [for example, 60.5° in cis-1,1'-diacetyl-2,2'-bi-imidazole (Secondo et al., 1996)] or for charged species, i.e. biimidazolium [for example, 89.0° in 2,2'-bi(1,3-diisopropyl-4,5-dimethylimidazolyl) bis(tetrafluoroborate) monohydrate (Kuhn et al., 2001)]. The bond lengths and angles are typical.

The architecture of the crystal structure of (I) is determined mainly by hydrogen bonds involving the water molecule, which acts as a di-donor and a di-acceptor. It takes part in two OW—H···N hydrogen bonds, in which two different N atoms (i.e. N3 and N1') from two different molecules are acceptors, and also accepts one N—H···OW and one exceptionally short C—H···OW hydrogen bonds. The hydrogen-bonding geometry is given in Table 2. These four directional bonds (the D—H···A angles are larger than 156°) form a regular tetrahedral coordination of the water O atom (the H···O—H angles are in the range 98–125°). The three-dimensional hydrogen-bond network may be described using graph-set notation (Etter et al., 1990; Bernstein et al., 1995). C¹₂(7) and C²₂(8) chains of biimidazole and water molecules are interwoven to produce some relatively large rings; two examples, R⁶₆(21) and R⁶₆(23), are shown in Figs. 2(a) and 2(b). This tight network of hydrogen bonds may be responsible for relatively the high melting point of the title compound (542–543 K). Such a correlation between the hydrogen-bond network and melting points was noticed, for example, in the case of two isomeric 2-hydroxy-bornane 3-carboxylic acids (Kubicki et al., 2000).

S2. Experimental

The method of synthesis of compound (I) has been described elsewhere (Salwińska et al., 1991; Walczak et al., 2001). Crystals for data collection were grown from an aqueous solution by slow evaporation.

S3. Refinement

The H atoms of CH groups were refined freely. Those of methyl groups were allowed to ride on the appropriate C atom and rotate as a rigid group around the C—C bond (C—H = 0.98 Å); one U_iso value was refined for each methyl group. The positions of H atoms of the water molecule were freely refined; a common U_iso value was also refined for these atoms.

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2002); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2002); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: program (reference)?; software used to prepare material for publication: program (reference)?.

Figures

Fig. 1. A view of (I) (Siemens, 1989). Displacement ellipsoids are drawn at the 50% probability level, and H atoms are depicted as spheres of arbitrary radii. The hydrogen bond is drawn as a dashed line.

Fig. 2. The elements of the three-dimensional network of hydrogen bonds. Dispalcement ellipsoids are drawn at the 50% probability level, and H atoms are depicted as spheres of arbitrary radii. Hydrogen bonds are drawn as dashed lines. (a) The R^66(21) ring and fragments of C^21(7) and C^22(8) chains. [Symmetry codes: (i) x, y, z; (ii) 1 − x, 1/2 + y, 1 − z; (iii) 2 − x, 1/2 + y, 1 − z; (iv) 1 + x, y, z.] (b) The R^66(23) ring. [Symmetry codes: (i) x, y, z; (ii) x, y, −1 + z; (iii) 1 − x, −1/2 + y, −z.]

2,2'-Dimethyl-4,5'-dinitro-1H,3'H-1,4'-biimidazole monohydrate

Crystal data

C8H8N6O4·H2O	F(000) = 280
Mr = 270.22	Dx = 1.522 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2yb	Cell parameters from 2200 reflections
a = 6.5951 (8) Å	θ = 3–20°
b = 13.4920 (13) Å	µ = 0.13 mm^−1
c = 7.2032 (9) Å	T = 100 K
β = 113.084 (12)°	Prism, colourless
V = 589.63 (13) Å^3	0.15 × 0.1 × 0.1 mm
Z = 2

Data collection

Kuma KM-4 CCD four-circle diffractometer	1595 independent reflections
Radiation source: fine-focus sealed tube	1060 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
ω scans	θmax = 29.8°, θmin = 3.9°
Absorption correction: multi-scan (SORTAV; Blessing, 1995, 1997)	h = −9→8
Tmin = 0.989, Tmax = 0.989	k = −18→18
5482 measured reflections	l = −8→9

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.035	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.049	w = 1/[σ^2(Fo^2) + (0.01P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.84	(Δ/σ)max = 0.002
1598 reflections	Δρmax = 0.21 e Å^−3
192 parameters	Δρmin = −0.22 e Å^−3
1 restraint	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.026 (2)

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
C2	0.6422 (4)	0.42840 (18)	0.3674 (4)	0.0196 (6)
C2'	0.3758 (4)	0.68804 (19)	−0.0050 (4)	0.0179 (6)
C21	0.4027 (4)	0.40469 (19)	0.2704 (4)	0.0230 (7)
C21'	0.1941 (5)	0.7611 (2)	−0.0462 (4)	0.0277 (7)
C4	0.9873 (4)	0.42481 (19)	0.5458 (4)	0.0163 (6)
C4'	0.6283 (4)	0.57824 (18)	0.1624 (4)	0.0178 (6)
C5	0.9611 (4)	0.5072 (2)	0.4311 (4)	0.0187 (6)
C5'	0.6347 (4)	0.59922 (19)	−0.0196 (4)	0.0173 (6)
N1	0.7386 (3)	0.50957 (16)	0.3148 (3)	0.0168 (5)
N1'	0.4785 (3)	0.66724 (16)	−0.1256 (3)	0.0196 (5)
N3	0.7926 (3)	0.37558 (14)	0.5079 (3)	0.0193 (5)
N3'	0.4613 (4)	0.63594 (16)	0.1703 (3)	0.0183 (5)
N4	1.1900 (4)	0.38726 (18)	0.6932 (3)	0.0251 (6)
N5'	0.7775 (4)	0.55884 (16)	−0.1091 (4)	0.0225 (5)
O1W	0.2974 (3)	0.67645 (14)	0.4462 (3)	0.0204 (4)
O41	1.1832 (3)	0.30927 (14)	0.7794 (3)	0.0323 (5)
O42	1.3590 (3)	0.43515 (13)	0.7227 (3)	0.0311 (5)
O51'	0.7456 (3)	0.58377 (14)	−0.2823 (3)	0.0302 (5)
O52'	0.9230 (3)	0.50088 (13)	−0.0061 (3)	0.0283 (5)
H1W	0.235 (6)	0.744 (3)	0.426 (5)	0.068 (9)*
H21A	0.3760	0.3392	0.3153	0.051 (6)*
H21B	0.3561	0.4045	0.1234	0.051 (6)*
H21C	0.3186	0.4547	0.3087	0.051 (6)*
H21D	0.0947	0.7385	0.0166	0.062 (6)*
H21E	0.1119	0.7672	−0.1923	0.062 (6)*
H21F	0.2562	0.8257	0.0099	0.062 (6)*
H2W	0.371 (6)	0.676 (3)	0.582 (5)	0.068 (9)*
H3'	0.418 (4)	0.6461 (18)	0.264 (4)	0.019 (8)*
H5	1.058 (4)	0.5590 (19)	0.426 (4)	0.025 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C2	0.0228 (14)	0.0185 (15)	0.0181 (14)	0.0026 (12)	0.0086 (12)	0.0001 (12)
C2'	0.0185 (14)	0.0175 (15)	0.0175 (15)	0.0018 (12)	0.0070 (12)	−0.0003 (12)
C21	0.0176 (14)	0.0236 (17)	0.0261 (16)	0.0000 (12)	0.0067 (12)	0.0026 (13)
C21'	0.0259 (16)	0.0288 (17)	0.0286 (18)	0.0073 (14)	0.0107 (15)	0.0062 (14)
C4	0.0145 (13)	0.0165 (14)	0.0151 (14)	0.0009 (12)	0.0030 (11)	−0.0013 (12)
C4'	0.0159 (13)	0.0175 (15)	0.0177 (15)	0.0017 (12)	0.0042 (11)	−0.0017 (12)
C5	0.0189 (14)	0.0214 (15)	0.0157 (14)	−0.0030 (13)	0.0067 (12)	−0.0012 (13)
C5'	0.0182 (13)	0.0173 (15)	0.0178 (15)	0.0016 (11)	0.0086 (12)	−0.0010 (12)
N1	0.0177 (11)	0.0173 (12)	0.0148 (12)	0.0003 (11)	0.0056 (9)	0.0007 (10)
N1'	0.0221 (12)	0.0184 (12)	0.0182 (13)	0.0010 (10)	0.0079 (10)	−0.0004 (10)
N3	0.0195 (11)	0.0192 (13)	0.0166 (12)	0.0017 (10)	0.0044 (10)	−0.0006 (10)
N3'	0.0209 (12)	0.0203 (12)	0.0158 (13)	0.0021 (10)	0.0093 (11)	0.0009 (10)
N4	0.0269 (15)	0.0268 (14)	0.0192 (13)	0.0025 (12)	0.0064 (11)	−0.0028 (12)
N5'	0.0210 (13)	0.0254 (14)	0.0207 (13)	0.0002 (11)	0.0077 (11)	−0.0021 (11)
O1W	0.0262 (10)	0.0186 (11)	0.0160 (11)	0.0030 (10)	0.0077 (9)	−0.0007 (9)
O41	0.0306 (12)	0.0281 (12)	0.0324 (12)	0.0038 (10)	0.0061 (10)	0.0118 (10)
O42	0.0171 (10)	0.0353 (12)	0.0337 (12)	−0.0037 (9)	0.0023 (9)	0.0001 (10)
O51'	0.0384 (12)	0.0361 (12)	0.0199 (12)	0.0089 (10)	0.0156 (9)	0.0056 (10)
O52'	0.0256 (11)	0.0292 (13)	0.0283 (12)	0.0110 (10)	0.0087 (9)	0.0039 (10)

Geometric parameters (Å, º)

N1—C5	1.376 (3)	N1'—C5'	1.367 (3)
N1—C2	1.391 (3)	C2'—N3'	1.359 (3)
N1—C4'	1.402 (3)	C2'—C21'	1.489 (4)
C2—N3	1.315 (3)	C21'—H21D	0.9800
C2—C21	1.490 (3)	C21'—H21E	0.9800
C21—H21A	0.9800	C21'—H21F	0.9800
C21—H21B	0.9800	N3'—C4'	1.368 (3)
C21—H21C	0.9800	N3'—H3'	0.84 (2)
N3—C4	1.375 (3)	C5'—C4'	1.358 (3)
C4—C5	1.354 (4)	C5'—N5'	1.440 (3)
C4—N4	1.434 (3)	N5'—O51'	1.228 (2)
N4—O41	1.231 (3)	N5'—O52'	1.235 (3)
N4—O42	1.233 (3)	O1W—H1W	0.99 (4)
C5—H5	0.96 (2)	O1W—H2W	0.91 (4)
N1'—C2'	1.325 (3)
C5—N1—C2	107.9 (2)	N1'—C2'—N3'	111.5 (2)
C5—N1—C4'	126.5 (2)	N1'—C2'—C21'	126.0 (2)
C2—N1—C4'	125.5 (2)	N3'—C2'—C21'	122.4 (2)
N3—C2—N1	110.4 (2)	C2'—C21'—H21D	109.5
N3—C2—C21	125.9 (2)	C2'—C21'—H21E	109.5
N1—C2—C21	123.7 (2)	H21D—C21'—H21E	109.5
C2—C21—H21A	109.5	C2'—C21'—H21F	109.5
C2—C21—H21B	109.5	H21D—C21'—H21F	109.5
H21A—C21—H21B	109.5	H21E—C21'—H21F	109.5
C2—C21—H21C	109.5	C2'—N3'—C4'	107.7 (2)
H21A—C21—H21C	109.5	C2'—N3'—H3'	121.0 (17)
H21B—C21—H21C	109.5	C4'—N3'—H3'	131.1 (17)
C2—N3—C4	104.8 (2)	C4'—C5'—N1'	112.2 (2)
C5—C4—N3	112.9 (2)	C4'—C5'—N5'	128.8 (2)
C5—C4—N4	126.9 (2)	N1'—C5'—N5'	119.1 (2)
N3—C4—N4	120.2 (2)	C5'—C4'—N3'	104.6 (2)
O41—N4—O42	124.7 (2)	C5'—C4'—N1	133.7 (2)
O41—N4—C4	117.9 (2)	N3'—C4'—N1	121.5 (2)
O42—N4—C4	117.4 (2)	O51'—N5'—O52'	124.5 (2)
C4—C5—N1	104.0 (2)	O51'—N5'—C5'	118.0 (2)
C4—C5—H5	134.0 (15)	O52'—N5'—C5'	117.5 (2)
N1—C5—H5	121.9 (15)	H1W—O1W—H2W	100 (3)
C2'—N1'—C5'	104.1 (2)
C5—N1—C2—N3	−0.6 (3)	N1'—C2'—N3'—C4'	−0.1 (3)
C4'—N1—C2—N3	176.3 (2)	C21'—C2'—N3'—C4'	−178.2 (2)
C5—N1—C2—C21	−178.7 (2)	C2'—N1'—C5'—C4'	0.1 (3)
C4'—N1—C2—C21	−1.8 (3)	C2'—N1'—C5'—N5'	179.3 (2)
N1—C2—N3—C4	0.5 (3)	N1'—C5'—C4'—N3'	−0.2 (3)
C21—C2—N3—C4	178.5 (2)	N5'—C5'—C4'—N3'	−179.2 (2)
C2—N3—C4—C5	−0.2 (3)	N1'—C5'—C4'—N1	173.9 (3)
C2—N3—C4—N4	−179.8 (2)	N5'—C5'—C4'—N1	−5.1 (5)
C5—C4—N4—O41	−177.9 (2)	C2'—N3'—C4'—C5'	0.1 (3)
N3—C4—N4—O41	1.7 (3)	C2'—N3'—C4'—N1	−174.9 (2)
C5—C4—N4—O42	1.3 (3)	C5—N1—C4'—C5'	64.9 (4)
N3—C4—N4—O42	−179.1 (2)	C2—N1—C4'—C5'	−111.5 (3)
N3—C4—C5—N1	−0.2 (3)	C5—N1—C4'—N3'	−121.8 (3)
N4—C4—C5—N1	179.4 (2)	C2—N1—C4'—N3'	61.8 (3)
C2—N1—C5—C4	0.5 (3)	C4'—C5'—N5'—O51'	175.4 (3)
C4'—N1—C5—C4	−176.4 (2)	N1'—C5'—N5'—O51'	−3.5 (3)
C5'—N1'—C2'—N3'	0.0 (3)	C4'—C5'—N5'—O52'	−4.1 (4)
C5'—N1'—C2'—C21'	178.0 (2)	N1'—C5'—N5'—O52'	176.9 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C21—H21B···O41^i	0.98	2.62	3.499 (3)	149
C5—H5···O1W^ii	0.96 (2)	2.20 (3)	3.155 (3)	175 (2)
N3′—H3′···O1W	0.84 (2)	1.83 (2)	2.665 (3)	173 (2)
C21′—H21F···O52′^iii	0.98	2.64	3.381 (3)	133
O1W—H1W···N3^iv	0.99 (4)	1.86 (3)	2.799 (3)	157 (3)
O1W—H2W···N1′^v	0.91 (4)	1.94 (4)	2.840 (3)	170 (3)

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