The crucial role of C—H...O and C=O...π inter­actions in the building of three-dimensional structures of dicarboxylic acid–biimidazole compounds

The supra­molecular architectures of three dicarboxylic acid–biimidazole compounds, namely, 2,2′-biimidazolium malonate, C₆H₈N₄²⁺·C₃H₂O₄²⁻, (I), 2,2′-bi(1H-imidazole) succinic acid, C₆H₆N₄·C₄H₆O₄, (II), and 2,2′-biimidazolium 2,2′-iminio­diacetate chloride, C₆H₈N₄²⁺·C₄H₆NO₄⁻·Cl⁻, (III), are reported. The crystal structures are assembled by the same process, namely double conventional N—H...O or O—H...N hydrogen bonds link the dicarboxyl­ates and biimidazoles to form tapes, which are stacked in parallel through lone-pair–aromatic inter­actions between carbonyl O atoms and biimidazole groups and are further linked via weak C—H...O inter­actions. The C=O...π inter­actions involved in stacking the tapes in (II) and the C—H...O inter­actions involved in linking the tapes in (II) and (III) demonstrate the crucial role of these inter­actions in the crystal packing. There is crystallographically imposed symmetry in all three structures. In (I), two independent malonate anions have their central C atoms on twofold axes and two biimidazolium dications each lie about independent inversion centres; in (II), the components lie about inversion centres, while in (III), the unique cation lies about an inversion centre and the iminiodiacetate and chloride anions lie across and on a mirror plane, respectively.

S1. Comment

Noncovalent weak interactions, such as C—H···O and C═O···π, have attracted much interest. These weak interactions have been widely discussed in realtion to the crystal packing of organic molecules and the determination of the folded structures of biological molecules (Derewenda et al., 1995; Desiraju, 1996; 2005; Khurram et al., 2006; Jain et al., 2007; Lu et al., 2007; Wan et al., 2008). However, self-assembled supramolecular architectures are often stabilized as a result of the synergy of a variety of weak interactions (Khurram et al., 2006; Shukla et al., 2007; Wan et al., 2008). It is difficult to distinguish the effect of an individual weak interaction. Desiraju (2005) suggested that weak interactions can be classified as innocuous, supportive or intrusive. We describe here the decisive role of carbonyl–π and C—H···O interactions in the assembly of the supramolecular architectures of three dicarboxylic acid–biimidazole compounds.

The asymmetric unit of (I) contains two independent malonate anions with their central C atoms on twofold axes and two biimidazolium cations each lying about independent inversion centres (Fig. 1). Strong N—H···O and hydrogen bonds (Fig. 1 and Table 1) link the malonate and biimidazolium moieties to form two distinct units, which further assemble into two different zigzag tapes designated as A and B respectively, as shown as Fig. 2. Four C—H···O interactions (Fig. 2 and Table 1) link two tapes into a three-dimensional network, and concomitantly there are three possible C═ O···π(imidazole ring) interactions, one of which takes part in the stacking of tapes A while the the other two link tapes B, as described in Table 1 (Cg1 and Cg2 are the centroids of the N1/C1/N2/C3/C2 and N3/C4/N4/C6/C5 rings, respectively) and shown as Fig. 3.

In (II), there is crystallographically imposed inversion symmetry with the succinic acid and biimidazole neutral molecules lying about inversion centres. The succinic acid and biimidazole molecules are linked by pairs of O—H···N and N—H···O hydrogen bonds (Fig. 4 and Table 2), leading to linear tapes which are further linked to form sheets in the (102) plane by a C3—H3···O2(x + 1, -y + 1/2, z + 1/2) interaction (Fig. 5 and Table 2). The sheets assemble into a three-dimensional structure by a C4═O1···π(imidazole ring)(-x + 1, -y + 1, -z + 1) interaction (Fig.6 and Table 2, where Cg3 is the centroid of the N1/C1/N2/C3/C2 ring).

In (III) (Fig. 7), the biimidazolium cation lies about an inversion centre, the iminodiacetate ion lies across a mirror plane and the chloride ion lies on a mirror plane. Iminodiacetate anions and biimidazolium cations are linked to form wave-like tapes by pairs of N—H···O hydrogen bonds (Fig. 8 and Table 3). These tapes are linked to form sheets by C3—H3···O1(1 - x,1 - y,-z) weak interactions (Fig. 8 and Table 3). The sheets are packed to form a three-dimensional network via two N—H···Cl hydrogen bonds and two C5═O1···π interactions to imidazole rings at (-x, -y + 1, -z) and (-x + 1, -y + 1, -z +1) (Fig. 9 and Table 3, where Cg4 is the centroid of the N1/C1/N2/C2/C3 ring).

The supramolecular structures of (I), (II) and (III) reveal that they are assembled by same process, namely that pairs of N—H···O or O—H···N hydrogen bonds link the dicarboxylates and biimidazoles to form tapes, which are stacked in parallel through lone-pair–aromatic interactions between carbonyl O atoms and biimidazole groups and are further linked via weak C—H···O interaction.

Related literature

For related literature, see: Derewenda et al. (1995); Desiraju (1996, 2005); Jain et al. (2007); Khurram et al. (2006); Lu et al. (2007); Shukla et al. (2007); Wan et al. (2008).

S2. Experimental

Diimizazole (1 mmol) and malonic, succinic or iminodiacetic acid (1 mmol) were dissolved in 10 ml of water by adding 0.7–0.9 ml of 2M HCl while stirring. The solutions were left standing at room temperature, and several days later, colorless crystals (I), (II) and (III) were obtained.

S3. Refinement

For compound (III), the systematic absences permitted P2₁ or P2₁/m as possible space groups; P2₁/m was selected, and confirmed by the structure analysis. H atoms attached to C atoms of (I), (II), and (III) were placed in geometrically idealized positions and refined with U_iso(H) values of 1.2U_eq(C). H atoms attached to N and O atoms were located from difference Fourier maps and refined using a riding model, with U_iso(H) values of 1.2U_eq(N) or 1.5U_eq(O) of their parent atoms.

Computing details

For all compounds, data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL/PC (Version 6.10; Sheldrick, 2008); software used to prepare material for publication: SHELXTL/PC (Version 6.10; Sheldrick, 2008) and ORTEP-3 (Farrugia, 1997).

Figures

	Fig. 1. A view of the structure of (I), with displacement ellipsoids drawn at the 30% probability level. Dashed lines represent hydrogen bonds. [Symmetry codes: (i) -x + 1, -y, -z +1; (ii) -x, -y, -z + 1; (iv) -x, y, -z + 1/2; (ix) -x + 1, y, -z + 1/2.]
	Fig. 2. The structure built from N—H···O hydrogen bonds and C—H···O interactions in (I). Tape Ais the lower shown in the lower part of the figure and tape Bin the upper part. Dashed lines represent hydrogen bonds. [Symmetry codes: (ii) -x, -y, -z + 1; (v) x, -y + 1, z + 1/2; (vi) -x + 1, -y + 1, -z + 1; (viii) x, y + 1, z.]
	Fig. 3. The C═O···π interaction (double dashed lines) between neighbouring A tapes and B tapes in (I). Dotted lines represent hydrogen bonds. [Symmetry codes: (iv) -x, y, -z + 3/2; (v) x, -y + 1, z + 1/2; (vi) -x + 1, -y + 1, -z + 1; (viii) x, y + 1, z; (x) -x, y + 1, -z + 3/2.]
	Fig. 4. A view of the structure of (II), with displacement ellipsoids drawn at the 30% probability level. Dashed lines represent hydrogen bonds. [Symmetry codes: (i) -x + 2, -y + 1, -z + 1; (iv) -x, -y + 1, -z.]
	Fig. 5. Part of the two-dimensional sheet assembled from O—H···N, N—H···O and C—H···O interactions in (II). Dashed lines represent hydrogen bonds. [Symmetry codes: (i) -x + 2, -y + 1, -z + 1; (ii) x + 1, -y + 1/2, z + 1/2; (v) -x + 1, y - 1/2, -z + 1/2.]
	Fig. 6. The C═O···π interaction (double dashed lines) between neighbouring sheets in (II). Dotted lines represent hydrogen bonds. [Symmetry codes: (iii) -x + 1, -y + 1, -z + 1; (vi) x + 2, y, z + 1; (vii) -x + 3, -y + 1, -z + 2.]
	Fig. 7. A view of the structure of (III), with displacement ellipsoids drawn at the 30% probability level. Dashed lines represent hydrogen bonds. [Symmetry codes: (i) -x, -y + 1, -z + 1; (vii) x, -y + 3/2, z.]
	Fig. 8. The two-dimensional sheet assembled from N—H···O and C—H···O interactions in (III). Dashed lines represent hydrogen bonds. [Symmetry codes: (i) -x, -y + 1, -z + 1; (iii) -x + 1, y - 1/2, -z + 1; (iv) -x +1, -y + 1, -z; (viii) x, y, z - 1.]
	Fig. 9. The C═O···π interactions (double dashed lines) between neighbouring sheets in (III). Dotted lines represent hydrogen bonds. [Symmetry codes: (vii) x, -y + 3/2, z; (ix) -x, y + 3/2, -z +1; (x) x + 1, y, z + 1; (xi) x + 1, -y + 3/2, z + 1; (xii) -x + 1, -y, -z + 1.]

(I) 2,2'-biimidazol-1-ium malonate

Crystal data

C6H8N4^2+·C3H2O4^2^−	F(000) = 496
Mr = 238.21	Dx = 1.518 Mg m^−3
Monoclinic, P2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yc	Cell parameters from 2156 reflections
a = 15.663 (5) Å	θ = 2.6–26.6°
b = 4.4319 (14) Å	µ = 0.12 mm^−1
c = 18.221 (4) Å	T = 298 K
β = 124.517 (18)°	Block, colorless
V = 1042.2 (5) Å^3	0.40 × 0.40 × 0.40 mm
Z = 4

Data collection

SMART 1K CCD area detector diffractometer	1841 independent reflections
Radiation source: fine-focus sealed tube	1519 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.014
ω scans	θmax = 25.0°, θmin = 1.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 2000)	h = −18→17
Tmin = 0.845, Tmax = 0.953	k = −4→5
4027 measured reflections	l = −13→21

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)] = 0.041	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.122	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0737P)^2 + 0.1574P] where P = (Fo^2 + 2Fc^2)/3
1841 reflections	(Δ/σ)max < 0.001
155 parameters	Δρmax = 0.28 e Å^−3
0 restraints	Δρmin = −0.23 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	Occ. (<1)
N1	0.38756 (10)	−0.0994 (3)	0.50257 (10)	0.0448 (4)
H1	0.4077	−0.2324	0.5436	0.054*
N2	0.38848 (10)	0.2261 (3)	0.41376 (9)	0.0447 (4)
H2A	0.4095	0.3369	0.3882	0.054*
C1	0.44579 (11)	0.0313 (4)	0.47993 (10)	0.0376 (4)
C2	0.29033 (12)	0.0153 (5)	0.44903 (12)	0.0526 (5)
H2	0.2336	−0.0370	0.4502	0.063*
C3	0.29036 (13)	0.2176 (4)	0.39402 (13)	0.0524 (5)
H3	0.2340	0.3308	0.3506	0.063*
N3	0.11051 (10)	−0.0743 (3)	0.61516 (10)	0.0477 (4)
H3A	0.0908	−0.2065	0.6372	0.057*
N4	0.10929 (10)	0.2374 (3)	0.52270 (10)	0.0467 (4)
H4	0.0886	0.3394	0.4753	0.056*
C4	0.05320 (11)	0.0398 (4)	0.53333 (11)	0.0403 (4)
C5	0.20623 (13)	0.0560 (5)	0.65788 (13)	0.0557 (5)
H5	0.2619	0.0181	0.7161	0.067*
C6	0.20550 (13)	0.2493 (4)	0.60057 (13)	0.0547 (5)
H6	0.2605	0.3691	0.6119	0.066*
O1	−0.07742 (9)	0.4454 (3)	0.29230 (8)	0.0592 (4)
O2	0.08014 (10)	0.6000 (4)	0.39643 (9)	0.0658 (4)
C7	0.00159 (12)	0.5995 (4)	0.31838 (11)	0.0408 (4)
C8	0.0000	0.7940 (5)	0.2500	0.0447 (6)
H8A	0.0609	0.9224	0.2789	0.054*	0.50
H8B	−0.0609	0.9224	0.2211	0.054*	0.50
O3	0.58047 (9)	0.4586 (3)	0.37051 (9)	0.0566 (4)
O4	0.42010 (10)	0.5977 (4)	0.31770 (10)	0.0686 (5)
C9	0.49928 (12)	0.6059 (4)	0.31758 (11)	0.0407 (4)
C10	0.5000	0.8000 (5)	0.2500	0.0434 (6)
H10A	0.5608	0.9285	0.2800	0.052*	0.50
H10B	0.4392	0.9285	0.2200	0.052*	0.50

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0378 (7)	0.0500 (8)	0.0458 (8)	−0.0010 (6)	0.0232 (7)	0.0005 (7)
N2	0.0378 (7)	0.0511 (8)	0.0404 (8)	0.0052 (6)	0.0194 (6)	0.0035 (6)
C1	0.0323 (8)	0.0425 (9)	0.0350 (8)	−0.0004 (6)	0.0172 (7)	−0.0048 (6)
C2	0.0336 (9)	0.0674 (12)	0.0551 (11)	−0.0027 (8)	0.0241 (8)	−0.0051 (9)
C3	0.0334 (8)	0.0626 (11)	0.0480 (10)	0.0092 (8)	0.0151 (8)	0.0009 (9)
N3	0.0406 (8)	0.0572 (9)	0.0433 (8)	−0.0044 (6)	0.0226 (7)	−0.0001 (7)
N4	0.0391 (7)	0.0549 (9)	0.0469 (8)	−0.0069 (6)	0.0249 (7)	−0.0025 (7)
C4	0.0351 (8)	0.0472 (9)	0.0411 (9)	−0.0023 (7)	0.0231 (8)	−0.0062 (7)
C5	0.0365 (9)	0.0726 (13)	0.0455 (10)	−0.0029 (8)	0.0157 (8)	−0.0012 (9)
C6	0.0373 (9)	0.0652 (12)	0.0571 (12)	−0.0119 (8)	0.0240 (9)	−0.0062 (9)
O1	0.0486 (7)	0.0735 (9)	0.0468 (8)	−0.0200 (6)	0.0218 (6)	−0.0017 (6)
O2	0.0457 (7)	0.0886 (10)	0.0462 (8)	−0.0187 (7)	0.0160 (6)	0.0089 (7)
C7	0.0361 (8)	0.0439 (9)	0.0435 (10)	−0.0018 (7)	0.0232 (8)	−0.0071 (7)
C8	0.0434 (13)	0.0409 (12)	0.0472 (14)	0.000	0.0241 (11)	0.000
O3	0.0428 (7)	0.0682 (8)	0.0576 (8)	0.0090 (6)	0.0277 (6)	0.0194 (7)
O4	0.0509 (8)	0.0927 (11)	0.0728 (10)	0.0197 (7)	0.0414 (8)	0.0330 (8)
C9	0.0383 (8)	0.0430 (9)	0.0381 (9)	−0.0016 (7)	0.0200 (7)	−0.0069 (7)
C10	0.0429 (12)	0.0403 (12)	0.0457 (14)	0.000	0.0243 (11)	0.000

Geometric parameters (Å, º)

N1—C1	1.328 (2)	C4—C4^ii	1.443 (3)
N1—C2	1.359 (2)	C5—C6	1.346 (3)
N1—H1	0.8600	C5—H5	0.9300
N2—C1	1.333 (2)	C6—H6	0.9300
N2—C3	1.366 (2)	O1—C7	1.248 (2)
N2—H2A	0.8600	O2—C7	1.246 (2)
C1—C1^i	1.445 (3)	C7—C8	1.504 (2)
C2—C3	1.345 (3)	C8—C7^iii	1.504 (2)
C2—H2	0.9300	C8—H8A	0.9700
C3—H3	0.9300	C8—H8B	0.9700
N3—C4	1.330 (2)	O3—C9	1.258 (2)
N3—C5	1.366 (2)	O4—C9	1.242 (2)
N3—H3A	0.8600	C9—C10	1.508 (2)
N4—C4	1.330 (2)	C10—C9^iv	1.508 (2)
N4—C6	1.365 (2)	C10—H10A	0.9700
N4—H4	0.8600	C10—H10B	0.9700
C1—N1—C2	107.55 (15)	C6—C5—N3	107.65 (16)
C1—N1—H1	126.2	C6—C5—H5	126.2
C2—N1—H1	126.2	N3—C5—H5	126.2
C1—N2—C3	107.50 (15)	C5—C6—N4	107.51 (15)
C1—N2—H2A	126.3	C5—C6—H6	126.2
C3—N2—H2A	126.3	N4—C6—H6	126.2
N1—C1—N2	109.53 (14)	O2—C7—O1	124.07 (17)
N1—C1—C1^i	125.16 (19)	O2—C7—C8	119.12 (14)
N2—C1—C1^i	125.31 (19)	O1—C7—C8	116.81 (14)
C3—C2—N1	108.11 (16)	C7—C8—C7^iii	110.04 (19)
C3—C2—H2	125.9	C7—C8—H8A	109.7
N1—C2—H2	125.9	C7^iii—C8—H8A	109.7
C2—C3—N2	107.31 (15)	C7—C8—H8B	109.7
C2—C3—H3	126.3	C7^iii—C8—H8B	109.7
N2—C3—H3	126.3	H8A—C8—H8B	108.2
C4—N3—C5	107.68 (16)	O4—C9—O3	124.07 (16)
C4—N3—H3A	126.2	O4—C9—C10	119.19 (14)
C5—N3—H3A	126.2	O3—C9—C10	116.74 (13)
C4—N4—C6	107.78 (15)	C9—C10—C9^iv	110.39 (19)
C4—N4—H4	126.1	C9—C10—H10A	109.6
C6—N4—H4	126.1	C9^iv—C10—H10A	109.6
N3—C4—N4	109.38 (14)	C9—C10—H10B	109.6
N3—C4—C4^ii	125.1 (2)	C9^iv—C10—H10B	109.6
N4—C4—C4^ii	125.5 (2)	H10A—C10—H10B	108.1
C2—N1—C1—N2	0.15 (19)	C6—N4—C4—N3	−0.1 (2)
C2—N1—C1—C1^i	−179.1 (2)	C6—N4—C4—C4^ii	−180.0 (2)
C3—N2—C1—N1	0.01 (19)	C4—N3—C5—C6	−0.1 (2)
C3—N2—C1—C1^i	179.2 (2)	N3—C5—C6—N4	0.0 (2)
C1—N1—C2—C3	−0.3 (2)	C4—N4—C6—C5	0.0 (2)
N1—C2—C3—N2	0.3 (2)	O2—C7—C8—C7^iii	113.09 (17)
C1—N2—C3—C2	−0.2 (2)	O1—C7—C8—C7^iii	−66.74 (13)
C5—N3—C4—N4	0.1 (2)	O4—C9—C10—C9^iv	−110.35 (17)
C5—N3—C4—C4^ii	180.0 (2)	O3—C9—C10—C9^iv	69.08 (14)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O3^i	0.86	1.78	2.612 (2)	163
N2—H2A···O4	0.86	1.80	2.646 (2)	166
N3—H3A···O1^ii	0.86	1.77	2.609 (2)	166
N4—H4···O2	0.86	1.79	2.626 (2)	164
C2—H2···O2^v	0.93	2.58	3.401 (2)	148
C3—H3···O1^iii	0.93	2.41	3.292 (2)	158
C5—H5···O4^vi	0.93	2.70	3.317 (2)	125
C6—H6···O3^vii	0.93	2.45	3.345 (2)	162
C7—O1···Cg2^viii	1.25 (1)	3.49 (1)	3.714 (3)	90
C9—O3···Cg1^vii	1.26 (1)	3.54 (1)	3.796 (2)	92
C9—O4···Cg1^ix	1.24 (1)	3.68 (1)	4.538 (3)	127

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

(II) 2,2'-bi(1H-imidazole) succinic acid

Crystal data

C6H6N4·C4H6O4	F(000) = 264
Mr = 252.24	Dx = 1.457 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 903 reflections
a = 4.906 (3) Å	θ = 2.8–23.3°
b = 13.887 (8) Å	µ = 0.12 mm^−1
c = 8.468 (5) Å	T = 298 K
β = 94.839 (8)°	Block, colorless
V = 574.9 (6) Å^3	0.30 × 0.30 × 0.27 mm
Z = 2

Data collection

SMART 1K CCD area detector diffractometer	1055 independent reflections
Radiation source: fine-focus sealed tube	868 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.026
ω scans	θmax = 25.5°, θmin = 2.8°
Absorption correction: multi-scan (SADABS; Sheldrick, 2000)	h = −5→3
Tmin = 0.845, Tmax = 0.970	k = −15→16
2390 measured reflections	l = −9→10

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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.117	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.054P)^2 + 0.1478P] where P = (Fo^2 + 2Fc^2)/3
1055 reflections	(Δ/σ)max < 0.001
82 parameters	Δρmax = 0.19 e Å^−3
0 restraints	Δρmin = −0.15 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
N1	0.7906 (3)	0.39353 (12)	0.44355 (19)	0.0466 (5)
N2	1.1535 (3)	0.39751 (11)	0.61309 (19)	0.0447 (5)
H2B	1.2933	0.4191	0.6704	0.054*
C1	0.9846 (3)	0.44912 (13)	0.5131 (2)	0.0390 (5)
C2	0.8420 (4)	0.30310 (15)	0.5024 (3)	0.0569 (6)
H2A	0.7393	0.2486	0.4740	0.068*
C3	1.0633 (4)	0.30485 (15)	0.6073 (3)	0.0557 (6)
H3	1.1398	0.2529	0.6646	0.067*
O1	0.4082 (3)	0.54988 (10)	0.17524 (16)	0.0513 (4)
O2	0.3784 (3)	0.39482 (10)	0.23405 (17)	0.0573 (5)
H2	0.5124	0.4025	0.3028	0.086*
C4	0.2966 (4)	0.47178 (14)	0.1573 (2)	0.0401 (5)
C5	0.0499 (4)	0.45539 (14)	0.0442 (2)	0.0425 (5)
H5A	−0.0967	0.4305	0.1026	0.051*
H5B	0.0929	0.4067	−0.0321	0.051*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0446 (10)	0.0426 (10)	0.0494 (10)	−0.0011 (7)	−0.0151 (8)	0.0019 (7)
N2	0.0421 (9)	0.0427 (10)	0.0460 (9)	0.0028 (7)	−0.0160 (7)	0.0019 (7)
C1	0.0364 (10)	0.0419 (10)	0.0371 (10)	0.0029 (8)	−0.0068 (8)	0.0017 (8)
C2	0.0585 (13)	0.0397 (12)	0.0678 (14)	−0.0041 (9)	−0.0214 (11)	0.0030 (10)
C3	0.0614 (13)	0.0385 (11)	0.0630 (13)	0.0026 (9)	−0.0202 (10)	0.0072 (10)
O1	0.0479 (9)	0.0457 (9)	0.0559 (9)	−0.0044 (6)	−0.0222 (7)	−0.0007 (7)
O2	0.0549 (9)	0.0490 (9)	0.0620 (9)	−0.0050 (6)	−0.0301 (7)	0.0089 (7)
C4	0.0361 (10)	0.0440 (11)	0.0388 (10)	0.0009 (8)	−0.0047 (8)	−0.0006 (8)
C5	0.0389 (10)	0.0453 (11)	0.0412 (10)	−0.0030 (8)	−0.0097 (8)	0.0009 (8)

Geometric parameters (Å, º)

N1—C1	1.324 (2)	C3—H3	0.9300
N1—C2	1.366 (3)	O1—C4	1.219 (2)
N2—C1	1.341 (2)	O2—C4	1.297 (2)
N2—C3	1.360 (3)	O2—H2	0.8475
N2—H2B	0.8603	C4—C5	1.497 (3)
C1—C1^i	1.440 (4)	C5—C5^ii	1.507 (4)
C2—C3	1.344 (3)	C5—H5A	0.9700
C2—H2A	0.9300	C5—H5B	0.9700
C1—N1—C2	105.66 (15)	N2—C3—H3	126.8
C1—N2—C3	107.51 (16)	C4—O2—H2	115.5
C1—N2—H2B	126.2	O1—C4—O2	123.67 (17)
C3—N2—H2B	126.3	O1—C4—C5	123.09 (17)
N1—C1—N2	110.60 (17)	O2—C4—C5	113.24 (16)
N1—C1—C1^i	125.76 (19)	C4—C5—C5^ii	113.81 (19)
N2—C1—C1^i	123.6 (2)	C4—C5—H5A	108.8
C3—C2—N1	109.78 (18)	C5^ii—C5—H5A	108.8
C3—C2—H2A	125.1	C4—C5—H5B	108.8
N1—C2—H2A	125.1	C5^ii—C5—H5B	108.8
C2—C3—N2	106.44 (17)	H5A—C5—H5B	107.7
C2—C3—H3	126.8
C2—N1—C1—N2	−0.4 (2)	N1—C2—C3—N2	−0.6 (3)
C2—N1—C1—C1^i	179.5 (2)	C1—N2—C3—C2	0.4 (2)
C3—N2—C1—N1	0.0 (2)	O1—C4—C5—C5^ii	−0.6 (3)
C3—N2—C1—C1^i	−179.9 (2)	O2—C4—C5—C5^ii	179.2 (2)
C1—N1—C2—C3	0.6 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···N1	0.85	1.74	2.575 (2)	169
N2—H2B···O1^i	0.86	1.93	2.779 (2)	170
C3—H3···O2^iii	0.93	2.41	3.309 (3)	162
C4—O1···Cg1^iv	1.22 (1)	3.37 (1)	3.720 (3)	97

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

(III) 2,2'-biimidazol-1-ium 2,2'-iminiodiacetate chloride

Crystal data

C6H8N4^2+·C4H6NO4^−·Cl^−	F(000) = 316
Mr = 303.71	Dx = 1.526 Mg m^−3
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yb	Cell parameters from 1551 reflections
a = 5.3095 (13) Å	θ = 3.6–26.6°
b = 22.941 (6) Å	µ = 0.31 mm^−1
c = 5.7023 (14) Å	T = 298 K
β = 107.930 (3)°	Block, yellow
V = 660.8 (3) Å^3	0.40 × 0.40 × 0.40 mm
Z = 2

Data collection

SMART 1K CCD area detector diffractometer	1158 independent reflections
Radiation source: fine-focus sealed tube	1027 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.017
ω scans	θmax = 25.0°, θmin = 3.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 2000)	h = −6→5
Tmin = 0.747, Tmax = 0.886	k = −20→26
3079 measured reflections	l = −6→6

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)] = 0.064	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.180	H-atom parameters constrained
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0925P)^2 + 0.8396P] where P = (Fo^2 + 2Fc^2)/3
1158 reflections	(Δ/σ)max < 0.001
94 parameters	Δρmax = 0.69 e Å^−3
0 restraints	Δρmin = −0.32 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
N1	0.2023 (5)	0.49819 (11)	0.2887 (5)	0.0385 (7)
H1	0.2387	0.5310	0.2527	0.046*
N2	0.0893 (5)	0.42347 (11)	0.4647 (5)	0.0416 (7)
H2A	0.0247	0.4029	0.5492	0.050*
C1	0.0703 (5)	0.48133 (12)	0.4398 (5)	0.0346 (7)
C2	0.2378 (7)	0.40320 (14)	0.3255 (6)	0.0469 (8)
H2	0.2823	0.3645	0.3091	0.056*
C3	0.3078 (6)	0.44979 (14)	0.2159 (6)	0.0445 (8)
H3	0.4100	0.4491	0.1096	0.053*
O1	0.3315 (5)	0.59463 (9)	0.1183 (5)	0.0482 (7)
O2	0.1026 (6)	0.65277 (10)	0.2873 (6)	0.0662 (9)
N3	0.2625 (12)	0.7500	0.1448 (11)	0.0686 (15)
H3A	0.3034	0.7500	0.3101	0.082*
H3B	0.0848	0.7500	0.0820	0.082*
C4	0.3658 (8)	0.69548 (13)	0.0673 (8)	0.0532 (10)
H4A	0.5576	0.6952	0.1294	0.064*
H4B	0.3131	0.6934	−0.1111	0.064*
C5	0.2559 (7)	0.64376 (13)	0.1683 (6)	0.0442 (8)
Cl1	0.7269 (4)	0.7500	0.6775 (3)	0.0716 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0461 (14)	0.0283 (13)	0.0448 (14)	−0.0015 (10)	0.0197 (11)	−0.0002 (10)
N2	0.0540 (16)	0.0257 (13)	0.0506 (15)	0.0004 (11)	0.0241 (12)	0.0024 (11)
C1	0.0385 (15)	0.0265 (14)	0.0396 (15)	−0.0005 (11)	0.0132 (12)	−0.0016 (11)
C2	0.0575 (19)	0.0282 (16)	0.059 (2)	0.0077 (14)	0.0236 (16)	−0.0040 (14)
C3	0.0507 (18)	0.0394 (18)	0.0483 (18)	0.0012 (14)	0.0226 (15)	−0.0063 (14)
O1	0.0655 (15)	0.0243 (11)	0.0662 (15)	0.0022 (10)	0.0370 (12)	0.0005 (9)
O2	0.097 (2)	0.0305 (12)	0.101 (2)	0.0020 (12)	0.0743 (18)	0.0044 (12)
N3	0.108 (4)	0.0205 (19)	0.115 (4)	0.000	0.088 (3)	0.000
C4	0.077 (2)	0.0213 (17)	0.081 (2)	0.0016 (14)	0.053 (2)	−0.0007 (14)
C5	0.0587 (19)	0.0276 (16)	0.0560 (19)	−0.0009 (14)	0.0318 (16)	0.0001 (13)
Cl1	0.1025 (12)	0.0356 (7)	0.0912 (11)	0.000	0.0512 (9)	0.000

Geometric parameters (Å, º)

N1—C1	1.324 (4)	O1—C5	1.258 (4)
N1—C3	1.365 (4)	O2—C5	1.227 (4)
N1—H1	0.8192	N3—C4	1.486 (4)
N2—C1	1.335 (4)	N3—C4^ii	1.486 (4)
N2—C2	1.361 (4)	N3—H3A	0.9000
N2—H2A	0.8209	N3—H3B	0.9000
C1—C1^i	1.442 (6)	C4—C5	1.512 (4)
C2—C3	1.347 (5)	C4—H4A	0.9700
C2—H2	0.9300	C4—H4B	0.9700
C3—H3	0.9300
C1—N1—C3	108.0 (2)	C4—N3—C4^ii	114.6 (4)
C1—N1—H1	130.1	C4—N3—H3A	108.6
C3—N1—H1	121.4	C4^ii—N3—H3A	108.6
C1—N2—C2	108.4 (3)	C4—N3—H3B	108.6
C1—N2—H2A	127.0	C4^ii—N3—H3B	108.6
C2—N2—H2A	124.6	H3A—N3—H3B	107.6
N1—C1—N2	108.8 (3)	N3—C4—C5	109.0 (3)
N1—C1—C1^i	126.3 (3)	N3—C4—H4A	109.9
N2—C1—C1^i	124.9 (3)	C5—C4—H4A	109.9
C3—C2—N2	106.9 (3)	N3—C4—H4B	109.9
C3—C2—H2	126.5	C5—C4—H4B	109.9
N2—C2—H2	126.5	H4A—C4—H4B	108.3
C2—C3—N1	107.9 (3)	O2—C5—O1	126.1 (3)
C2—C3—H3	126.1	O2—C5—C4	118.5 (3)
N1—C3—H3	126.1	O1—C5—C4	115.4 (3)
C3—N1—C1—N2	0.0 (3)	N2—C2—C3—N1	0.0 (4)
C3—N1—C1—C1^i	179.6 (4)	C1—N1—C3—C2	0.0 (3)
C2—N2—C1—N1	0.0 (4)	C4^ii—N3—C4—C5	177.2 (3)
C2—N2—C1—C1^i	−179.6 (4)	N3—C4—C5—O2	1.5 (5)
C1—N2—C2—C3	0.0 (4)	N3—C4—C5—O1	−179.1 (4)

Symmetry codes: (i) −x, −y+1, −z+1; (ii) x, −y+3/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O1	0.82	1.79	2.592 (3)	167
N2—H2A···O2^i	0.82	1.83	2.643 (3)	171
N3—H3A···Cl1	0.90	2.56	3.271 (7)	137
N3—H3B···Cl1^iii	0.90	2.50	3.244 (7)	141
C2—H2···Cl1^iv	0.93	2.63	3.520 (3)	161
C3—H3···O1^v	0.93	2.38	3.253 (4)	156
C5—O1···Cg1^vi	1.26 (1)	3.33 (1)	3.816 (4)	103
C5—O1···Cg1^vii	1.26 (1)	3.50 (1)	4.029 (4)	106

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