Charge-assisted hydrogen bonding in salts of 2-amino-1H-benzimidazole with 3-phenyl­propynoic acid and oct-2-ynoic acid

The 100 K structures of two salts, namely 2-amino-1H-benz­imid­azolium 3-phenyl­propynoate, C₇H₈N₃⁺·C₉H₅O₂⁻, (I), and 2-amino-1H-benzimidazolium oct-2-ynoate, C₇H₈N₃⁺·C₈H₁₁O₂⁻, (II), both have monoclinic symmetry (space group P2₁/c) and display N—H...O hydrogen bonding. Both structures show packing with corrugated sheets of hydrogen-bonded mol­ecules lying parallel to the [001] direction. Two hydrogen-bonded ring motifs can be identified and described with graph sets R²₂(8) and R⁴₄(16), respectively, in both (I) and (II). Com­putational chemistry calculations performed on both compounds show that the hydrogen-bonded ion pairs are more energetically favourable in the crystal structure than their hydrogen–bonded neutral mol­ecule counterparts.

S1. Introduction

Many naturally occurring pharmacologically active compounds contain an imidazole or imidazoline ring system, e.g. histamine [also known as 4-(2-amino)­imidazole]. It has been shown that double Michael addition reactions involving ethyl­ene or phenyl­ene di­amines and allenic or acetyl­enic nitriles, followed by the elimination of aceto­nitrile, yield 2-substituted imidazolines or benzimidazoles in good yield (>80%) (Asobo et al., 2001). Similar high-yielding reactions were observed by reacting ethano­lamines, β-amino­ethane­thiols or benzo­thiols with allenic or acetyl­enic nitriles to produce oxazolines, oxazoles, thia­zoles and thia­zolines (Fomum et al., 1975). While studying the syntheses and biological activities of these organic heterocycles, the synthesis of pyrimido[1,2-a]benzimidazoles was attempted (Fomum et al., 1989). In some cases the syntheses were successful. We report here two instances where 3-phenyl­propynoic acid and 2-octynoic acid, respectively, form salts (I) and (II), respectively, with 2-amino-1H-benzimidazole, instead of producing the envisaged benzimidazoles. A search of the Cambridge Structural Database (CSD, Version 5.35 with May 2014 updates; Allen, 2002) revealed that these structures have not been published before. The crystal structures of these two salts are therefore presented here as part of our ongoing research into synthetic routes to various nitro­gen-containing heterocycles that we have found to have excellent and varied biological applications.

S2. Experimental

S2.1. Synthesis, crystallization and characterization

Compounds (I) and (II) were synthesized using a modified literature preparation (Wahe, Asobo et al., 2003; Wahe, Mbafor et al., 2003). For (I), a mixture of 3-phenyl­propynoic acid (1.46 g, 10 mmol) and 2-amino­benzimidazole (1.33 g, 10 mmol) was refluxed in butan-1-ol (50 ml) for 72 h. For (II), a mixture of 2-octynoic acid (1.40 g, 10 mmol) and 2-amino­benzimidazole (1.33 g, 10 mmol) was refluxed in butan-1-ol (50 ml) for 72 h. Recrystallization from hexane–ethyl acetate [Solvent ratio?] gave the crystalline salts of (I) and (II) described here. Suitable single crystals of each were selected for the X-ray diffraction study. The crystal of (II) was rather weakly diffracting, as evidenced by a high fraction of unobserved reflections and an unsatisfactory R_int value. FT–IR spectra of (I) and (II) were obtained on KBr pellets using a Perkin–Elmer Spectrum 100 FT–IR spectrometer. The spectroscopic frequencies of (I) and (II) are given in Table 4.

S2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. C-bound H atoms were placed in geometrically idealized positions, with C—H = 0.93–0.98 Å, and were constrained to ride on their parent atoms, with U_iso(H) = 1.2U_eq(C) for aromatic and methyl­ene H atoms, and U_iso(H) = 1.5U_eq(C) for methyl H atoms. The methyl H atoms were initially located in a difference Fourier map, but since they are not involved in any hydrogen-bonding inter­actions they were placed in idealized positions as described above and refined as rotating groups. N-bound H atoms were also located in a difference Fourier map and, since they are involved in hydrogen bonding, these atoms were allowed to refine freely, with U_iso(H) = 1.5U_eq(N).

S2.3. Computational Chemistry

Density functional theory (DFT) calculations were carried out on both (I) and (II) using GAUSSIAN09 (Frisch et al., 2010) using the B3LYP functional (Becke, 1988, 1993; Lee et al., 1988) with the 6–311+g(d,p) basis set (Ditchfield et al., 1971). With a fine mesh for numerical integration, a spin-restricted formalism and full geometry optimization were carried out. All calculations were consistently performed on one pair of cation and anion without symmetry constraint (C₁), and all structures were calculated as singlet states. These calculations were performed on the individual imidazole molecule (as 2-amino-1H-benzimidazole), on the individual acids (as 3-phenyl­propynoic acid and 2-octynoic acid), on the respective cations and anions, and then on the salts [as (I) and (II)].

S3. Results and discussion

The crystal structures of (I) and (II) are new and they both crystallize in the monoclinic crystal system in space group P2₁/c. The asymmetric unit of (I) contains one 2-amino-1H-benzimidazolium cation and one 3-phenyl­propynoate anion as a salt, and the asymmetric unit of (II) contains 2-amino-1H-benzimidazolium cation and one 2-octynoate anion also as a salt. The molecular structures of (I) and (II) are shown in Figs. 1 and 2, respectively. A geometric analysis of all bond distances and angles was performed by carrying out a Mogul geometry check implemented in the program Mercury (Macrae et al., 2008).

There are two aspects of structures (I) and (II) that merit comparison and discussion: (a) the classical hydrogen-bonding scheme and the resulting motifs that are evident for these amine–acid salts; and (b) computational chemistry calculations proving that the hydrogen-bonded salts are more stable than the two individual molecules and the hydrogen-bonded neutral molecules, and that these inter­actions are charge-assisted. It is important to note at this stage that neither (I) nor (II) has been published before, and so a comprehensive comparison with similar molecules was challenging but was achieved.

Both salt structures exhibit classical charge-assisted hydrogen bonding between the amine and acid group. In both (I) and (II), the two independent ions are linked by four N–H···O hydrogen bonds (Tables 2 and 3, respectively) into a two-dimensional structure with some complexity. For simplicity and for the description of the supra­molecular aggregation, the asymmetric units of both compounds have been arranged to show neutral ion-pair aggregates (Figs. 1 and 2, respectively) in which each cation is linked to an anion by means of two N—H···O hydrogen bonds (all of which are nearly linear). There are then two more N—H···O hydrogen bonds which link subsequent cations and anions into sheets and their formation is described as follows. For (I), amino atom N1 at (x, y, z) acts as a hydrogen-bond donor, via atom H1A, to carboxyl­ate atom O2 also at (x, y, z) and, via atom H1B, to carboxyl­ate atom O1 at (x, -y + 3/2, z + 1/2). Propagation of these hydrogen bonds then generates by translation (from the 2₁ screw axis) a level-2 C²₄(12)[R²₂(8)][R²₂(8)] corrugated chain of rings (Bernstein et al., 1995) running along the [001] direction (Fig. 3). For (II), a similar propagation pattern is also generated by translation (from the 2₁ screw axis) of the level-2 C²₄(12)[R²₂(8)][R²₂(8)] chain of rings, also running along the [001] direction (Fig. 4). There is also evidence of a further larger level-2 hydrogen-bonded ring motif with the graph-set notation R⁴₄(16) in both compounds (see Figs. 5 and 6).

A motif search was conducted in Mercury within the CSD as follows. Firstly, a search was conducted for the `R<sup>2</sup><sub>2</sub>(8)COONHNH<sub>2</sub>' motif. Since this is a very common motif, the search criteria have been built into the motif search option in Mercury. This search yielded 592 hits and the search was then manually refined to motifs that involved the imidazolium cation and the general carboxyl­ate acid anion only. This refined search yielded only three hits where the hydrogen-bonding inter­actions take place through the positively charged NH<sup>+</sup> and the NH<sub>2</sub> groups of the five-membered benzimidazolium cation and the acid anion. These structures (listed with their respective CSD codes) are 2-amino­benzimidazolium O-ethyl malonate (EMIHAJ; Low et al., 2003), bis­(2-amino­benzimidazolium) phthalate (JEJMUH; Tan et al., 2006) and 2-amino-1H-benzimidazolium nicotinate (XIHMAE; Zu et al., 2011); this last structure had no three-dimensional coordinates available and was therefore excluded from all comparative discussions. Secondly, a search was conducted for the R<sup>4</sup><sub>4</sub>(16) motif using Conquest within the CSD by drawing the groups involved in the hydrogen-bonding inter­actions and then manually setting up the contacts using the `Contact' option in the search query. Again, refining the search results to include only the imidazolium cation and the general carboxyl­ate anion yielded one result, EMIHAJ. Compounds (I) and (II) are then only the third and fourth compounds that match the refined search criteria. The hydrogen-bonding inter­actions of (I) and (II) are similar to those of both EMIHAJ and JEJMUH, although there are marked differences in the graph-set motifs identified. For (I) and (II), both the R²₂(8) and R⁴₄(16) motifs are level-2 motifs. For EMIHAJ, the R²₂(8) motif is level 2 while the R⁴₄(16) motif is level 4. For JEJMUH, the R²₂(8) motif is level 2 while the R⁴₄(16) motif is not present in the crystal structure at all. Details of the geometry of the hydrogen-bonding inter­actions in (I) and (II) can be found in Tables 2 and 3, respectively.

Initial FT–IR analysis showed a broad peak in the 3200 nm [Units - cm^-1?] area which alluded to the fact that the carb­oxy­lic acid group was still intact, and the shift indicated possible hydrogen bonding. The expected peaks for amines were overshadowed by the broad hydroxyl peak and were thus not visible. Consequently, the crystal structures were determined by X-ray diffraction and the hydrogen bonding thus identified for both structures confirms what is seen in the FT–IR spectra. The IR frequencies for (I) and (II) can be found in Table 4.

Inter­estingly, the inter­molecular potentials for the two structures are significantly different. This is confirmed by the approximate energies calculated from the imidazolium cation with the respective acid anions and other van der Waals forces, using UNI force-field calculations (Filippini & Gavezotti, 1993; Gavezzotti & Filippini, 1994) implemented in the program Mercury. The results indicate that the inter­molecular potentials are -37.8 kJ mol^-1 for (I) and -30.6 kJ mol^-1 for (II). This implies that the inter­action between the imidazolium cation and the octynoate anion in (II) is slightly weaker than that between the imidazolium cation and the 3-phenyl­propynoate anion in (I).

The DFT calculations show that, for both (I) and (II), the formation of hydrogen-bonded salts is more favourable than if the two individual molecules were to form as a hydrogen-bonded neutral molecule. This is evident from the fact that the calculated energy of the hydrogen-bonded neutral molecules is less negative than the calculated energy of the hydrogen-bonded salts in both (I) and (II). An energy difference of -13.84 kJ mol^-1 was calculated for (I) and -13.66 kJ mol^-1 was calculated for (II) (see Table 5). These negative values indicate strong charge-assisted hydrogen-bonding inter­actions and the energy calculations corroborate the stronger inter­actions evident between the ion pairs in (I) than in (II) and concur with the trend seen in the calculation of the inter­molecular potentials.

The crystal structures presented here assist in our understanding of the mechanisms of formation of synthetic materials that we are currently investigating as potentially potent biologically active medicinal compounds. These inter­actions between cation and anion help us to visualize, using synthetic mimics, how medicinal compounds extracted from plant material are formed naturally.

Related literature

For related literature, see: Allen (2002); Becke (1988, 1993).

Computing details

For both compounds, data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS2014/7 (Sheldrick, 2014); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2014); molecular graphics: OLEX2 (Dolomanov et al., 2009) and Mercury (Macrae et al., 2008); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

Figures

	Fig. 1. The molecular structure of (I), showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Selected hydrogen bonds are indicated by dashed lines. The R^22(8) hydrogen-bonding motif can be clearly seen.
	Fig. 2. The molecular structure of (II), showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. Selected hydrogen bonds are indicated by dashed lines. The R^22(8) hydrogen-bonding motif can be clearly seen.
	Fig. 3. A view of part of the crystal structure of (I), showing the formation of the chain of rings along [001]. Dashed lines indicate hydrogen bonds. H atoms bonded to C atoms have been omitted for clarity. Selected atoms are labelled with their symmetry codes to demonstrate the propagation of the corrugated sheets down the c axis.
	Fig. 4. A view of part of the crystal structure of (II), showing the formation of the chain of rings along [001]. Dashed lines indicate hydrogen bonds. H atoms bonded to C atoms have been omitted for clarity. Selected atoms are labelled with their symmetry codes to demonstrate the propagation of the corrugated sheets down the c axis.
	Fig. 5. The molecular structure of (I), showing the R^44(16) hydrogen-bonded ring motif. Dashed lines indicate hydrogen bonds. Selected atoms are labelled with their symmetry codes and H atoms bonded to C atoms have been omitted for clarity.
	Fig. 6. The molecular structure of (II), showing the R^44(16) hydrogen-bonding ring motif. Dashed lines indicate hydrogen bonds. Selected atoms are labelled with their symmetry codes and H atoms bonded to C atoms have been omitted for clarity.

(I) 2-amino-1H-benzimidazolium 3-phenylpropynoate

Crystal data

C7H8N3^+·C9H5O2^−	F(000) = 584
Mr = 279.29	Dx = 1.327 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.9391 (11) Å	Cell parameters from 1404 reflections
b = 11.3093 (10) Å	θ = 2.2–19.8°
c = 11.7865 (11) Å	µ = 0.09 mm^−1
β = 118.531 (2)°	T = 100 K
V = 1398.2 (2) Å^3	Block, colourless
Z = 4	0.25 × 0.1 × 0.05 mm

Data collection

Bruker APEXII CCD area-detector diffractometer	2858 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.034
ϕ and ω scans	θmax = 28.3°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −15→15
Tmin = 0.665, Tmax = 0.746	k = −15→15
26493 measured reflections	l = −15→15
3461 independent reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F^2 > 2σ(F^2)] = 0.036	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.094	w = 1/[σ^2(Fo^2) + (0.0429P)^2 + 0.4559P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max = 0.001
3461 reflections	Δρmax = 0.25 e Å^−3
206 parameters	Δρmin = −0.26 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.

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

	x	y	z	Uiso*/Ueq
O1	0.43475 (7)	0.85709 (7)	0.41840 (7)	0.02078 (18)
O2	0.36467 (8)	0.91433 (7)	0.55484 (7)	0.02016 (18)
C1	0.10503 (10)	1.27170 (11)	0.27195 (12)	0.0255 (3)
H1	0.1423	1.2721	0.3634	0.031*
C2	0.02565 (11)	1.36399 (11)	0.20088 (14)	0.0323 (3)
H2A	0.0097	1.4275	0.2439	0.039*
C3	−0.03018 (12)	1.36341 (13)	0.06742 (15)	0.0362 (3)
H3A	−0.0847	1.4263	0.0187	0.043*
C4	−0.00614 (13)	1.27070 (15)	0.00515 (14)	0.0424 (4)
H4	−0.0446	1.2704	−0.0864	0.051*
C5	0.07350 (12)	1.17826 (13)	0.07508 (12)	0.0339 (3)
H5	0.0893	1.1151	0.0315	0.041*
C6	0.13047 (10)	1.17835 (10)	0.21010 (11)	0.0215 (2)
C7	0.21449 (10)	1.08479 (10)	0.28664 (10)	0.0209 (2)
C8	0.28506 (10)	1.01043 (10)	0.35731 (10)	0.0194 (2)
C9	0.36808 (10)	0.92079 (9)	0.45002 (10)	0.0161 (2)
N1	0.49450 (10)	0.73019 (9)	0.73155 (9)	0.0213 (2)
H1A	0.4495 (14)	0.7893 (14)	0.6758 (15)	0.033 (4)*
H1B	0.4696 (14)	0.7010 (13)	0.7848 (15)	0.031 (4)*
N2	0.56532 (8)	0.67316 (8)	0.58324 (8)	0.01666 (19)
H2	0.5249 (15)	0.7372 (14)	0.5267 (15)	0.039 (4)*
N3	0.61582 (9)	0.55714 (8)	0.75066 (9)	0.0189 (2)
H3	0.6210 (15)	0.5252 (15)	0.8239 (16)	0.043 (4)*
C10	0.66516 (10)	0.50429 (10)	0.67705 (10)	0.0176 (2)
C11	0.73280 (10)	0.40034 (10)	0.69448 (11)	0.0217 (2)
H11	0.7534	0.3502	0.7665	0.026*
C12	0.76921 (10)	0.37271 (11)	0.60164 (11)	0.0237 (2)
H12	0.8163	0.3024	0.6106	0.028*
C13	0.73787 (10)	0.44648 (11)	0.49547 (11)	0.0221 (2)
H13	0.7645	0.4252	0.4340	0.027*
C14	0.66848 (10)	0.55066 (10)	0.47735 (10)	0.0189 (2)
H14	0.6467	0.6004	0.4048	0.023*
C15	0.63301 (9)	0.57794 (9)	0.57039 (10)	0.0165 (2)
C16	0.55458 (10)	0.65706 (9)	0.69080 (10)	0.0175 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0282 (4)	0.0193 (4)	0.0186 (4)	0.0055 (3)	0.0143 (3)	0.0025 (3)
O2	0.0288 (4)	0.0183 (4)	0.0165 (4)	0.0001 (3)	0.0133 (3)	−0.0009 (3)
C1	0.0186 (5)	0.0229 (6)	0.0309 (6)	−0.0038 (5)	0.0086 (5)	−0.0023 (5)
C2	0.0211 (5)	0.0198 (6)	0.0525 (8)	−0.0025 (5)	0.0148 (5)	−0.0018 (6)
C3	0.0222 (6)	0.0341 (7)	0.0532 (8)	0.0096 (5)	0.0187 (6)	0.0229 (6)
C4	0.0328 (7)	0.0661 (11)	0.0323 (7)	0.0235 (7)	0.0189 (6)	0.0241 (7)
C5	0.0314 (6)	0.0480 (8)	0.0261 (6)	0.0184 (6)	0.0167 (5)	0.0099 (6)
C6	0.0165 (5)	0.0242 (6)	0.0246 (5)	0.0018 (4)	0.0105 (4)	0.0058 (4)
C7	0.0194 (5)	0.0234 (6)	0.0202 (5)	−0.0009 (4)	0.0098 (4)	−0.0001 (4)
C8	0.0209 (5)	0.0211 (5)	0.0178 (5)	−0.0005 (4)	0.0106 (4)	−0.0009 (4)
C9	0.0183 (5)	0.0143 (5)	0.0151 (4)	−0.0031 (4)	0.0073 (4)	−0.0015 (4)
N1	0.0288 (5)	0.0204 (5)	0.0182 (4)	0.0015 (4)	0.0142 (4)	0.0019 (4)
N2	0.0193 (4)	0.0162 (4)	0.0151 (4)	0.0008 (4)	0.0087 (3)	0.0025 (3)
N3	0.0219 (4)	0.0187 (5)	0.0147 (4)	−0.0004 (4)	0.0076 (4)	0.0034 (3)
C10	0.0154 (4)	0.0187 (5)	0.0156 (5)	−0.0026 (4)	0.0049 (4)	0.0010 (4)
C11	0.0174 (5)	0.0195 (6)	0.0225 (5)	−0.0002 (4)	0.0049 (4)	0.0048 (4)
C12	0.0171 (5)	0.0197 (6)	0.0304 (6)	0.0018 (4)	0.0081 (4)	0.0000 (5)
C13	0.0184 (5)	0.0231 (6)	0.0258 (5)	−0.0011 (4)	0.0114 (4)	−0.0031 (4)
C14	0.0174 (5)	0.0204 (5)	0.0182 (5)	−0.0010 (4)	0.0080 (4)	0.0013 (4)
C15	0.0144 (4)	0.0148 (5)	0.0174 (5)	−0.0013 (4)	0.0054 (4)	0.0011 (4)
C16	0.0189 (5)	0.0169 (5)	0.0148 (4)	−0.0036 (4)	0.0067 (4)	0.0003 (4)

Geometric parameters (Å, º)

O1—C9	1.2550 (13)	N1—C16	1.3259 (14)
O2—C9	1.2576 (12)	N2—H2	0.945 (16)
C1—H1	0.9500	N2—C15	1.3974 (14)
C1—C2	1.3896 (17)	N2—C16	1.3462 (13)
C1—C6	1.3962 (17)	N3—H3	0.910 (17)
C2—H2A	0.9500	N3—C10	1.3948 (14)
C2—C3	1.385 (2)	N3—C16	1.3479 (14)
C3—H3A	0.9500	C10—C11	1.3849 (16)
C3—C4	1.386 (2)	C10—C15	1.4002 (14)
C4—H4	0.9500	C11—H11	0.9500
C4—C5	1.3884 (18)	C11—C12	1.3922 (17)
C5—H5	0.9500	C12—H12	0.9500
C5—C6	1.4005 (17)	C12—C13	1.3981 (17)
C6—C7	1.4406 (15)	C13—H13	0.9500
C7—C8	1.2002 (16)	C13—C14	1.3968 (16)
C8—C9	1.4729 (15)	C14—H14	0.9500
N1—H1A	0.911 (16)	C14—C15	1.3859 (15)
N1—H1B	0.878 (16)
C2—C1—H1	119.7	C16—N2—H2	121.4 (9)
C2—C1—C6	120.59 (12)	C16—N2—C15	108.54 (9)
C6—C1—H1	119.7	C10—N3—H3	124.2 (11)
C1—C2—H2A	120.0	C16—N3—H3	127.1 (11)
C3—C2—C1	120.06 (13)	C16—N3—C10	108.56 (9)
C3—C2—H2A	120.0	N3—C10—C15	106.71 (9)
C2—C3—H3A	120.1	C11—C10—N3	131.38 (10)
C2—C3—C4	119.74 (12)	C11—C10—C15	121.91 (10)
C4—C3—H3A	120.1	C10—C11—H11	121.5
C3—C4—H4	119.6	C10—C11—C12	116.92 (10)
C3—C4—C5	120.76 (13)	C12—C11—H11	121.5
C5—C4—H4	119.6	C11—C12—H12	119.4
C4—C5—H5	120.1	C11—C12—C13	121.26 (11)
C4—C5—C6	119.82 (13)	C13—C12—H12	119.4
C6—C5—H5	120.1	C12—C13—H13	119.1
C1—C6—C5	119.03 (11)	C14—C13—C12	121.73 (11)
C1—C6—C7	119.24 (10)	C14—C13—H13	119.1
C5—C6—C7	121.74 (11)	C13—C14—H14	121.6
C8—C7—C6	175.78 (12)	C15—C14—C13	116.73 (10)
C7—C8—C9	176.11 (11)	C15—C14—H14	121.6
O1—C9—O2	125.53 (10)	N2—C15—C10	106.61 (9)
O1—C9—C8	118.19 (9)	C14—C15—N2	131.95 (10)
O2—C9—C8	116.28 (9)	C14—C15—C10	121.44 (10)
H1A—N1—H1B	120.5 (13)	N1—C16—N2	124.62 (10)
C16—N1—H1A	115.5 (10)	N1—C16—N3	125.83 (10)
C16—N1—H1B	116.9 (10)	N2—C16—N3	109.54 (9)
C15—N2—H2	129.8 (9)
C1—C2—C3—C4	−0.26 (19)	C11—C10—C15—N2	179.68 (10)
C2—C1—C6—C5	−0.79 (17)	C11—C10—C15—C14	−0.56 (16)
C2—C1—C6—C7	179.20 (10)	C11—C12—C13—C14	−0.24 (17)
C2—C3—C4—C5	−0.1 (2)	C12—C13—C14—C15	0.51 (16)
C3—C4—C5—C6	0.0 (2)	C13—C14—C15—N2	179.57 (11)
C4—C5—C6—C1	0.47 (19)	C13—C14—C15—C10	−0.12 (15)
C4—C5—C6—C7	−179.52 (12)	C15—N2—C16—N1	−179.21 (10)
C6—C1—C2—C3	0.70 (18)	C15—N2—C16—N3	1.86 (12)
N3—C10—C11—C12	−179.71 (11)	C15—C10—C11—C12	0.82 (16)
N3—C10—C15—N2	0.09 (11)	C16—N2—C15—C10	−1.18 (11)
N3—C10—C15—C14	179.85 (9)	C16—N2—C15—C14	179.09 (11)
C10—N3—C16—N1	179.28 (10)	C16—N3—C10—C11	−178.50 (11)
C10—N3—C16—N2	−1.80 (12)	C16—N3—C10—C15	1.03 (11)
C10—C11—C12—C13	−0.43 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O2	0.911 (16)	1.918 (17)	2.8273 (13)	175.7 (14)
N1—H1B···O1^i	0.878 (16)	1.925 (16)	2.7989 (12)	173.0 (14)
N2—H2···O1	0.945 (16)	1.821 (17)	2.7637 (12)	175.1 (14)
N3—H3···O2^ii	0.910 (17)	1.847 (17)	2.7217 (12)	160.5 (15)

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

(II) 2-amino-1H-benzimidazolium 2-octynoate

Crystal data

C7H8N3^+·C8H11O2^−	F(000) = 584
Mr = 273.33	Dx = 1.231 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 9.295 (3) Å	Cell parameters from 1404 reflections
b = 13.713 (5) Å	θ = 2.2–19.8°
c = 11.810 (4) Å	µ = 0.08 mm^−1
β = 101.638 (5)°	T = 100 K
V = 1474.5 (8) Å^3	Block, colourless
Z = 4	0.26 × 0.18 × 0.15 mm

Data collection

Bruker APEXII CCD area-detector diffractometer	1827 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.155
ϕ and ω scans	θmax = 28.4°, θmin = 2.2°
Absorption correction: multi-scan (SADABS; Bruker, 2008)	h = −12→7
Tmin = 0.981, Tmax = 0.985	k = −18→18
26096 measured reflections	l = −15→15
3693 independent reflections

Refinement

Refinement on F^2	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.060	w = 1/[σ^2(Fo^2) + (0.069P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.158	(Δ/σ)max < 0.001
S = 0.97	Δρmax = 0.28 e Å^−3
3693 reflections	Δρmin = −0.27 e Å^−3
199 parameters	Extinction correction: SHELXL2014/7 (Sheldrick, 2014), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.015 (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.

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

	x	y	z	Uiso*/Ueq
O1	0.5531 (2)	0.81078 (11)	1.01678 (12)	0.0309 (5)
O2	0.5818 (2)	0.86996 (11)	0.84613 (12)	0.0331 (5)
N1	0.5110 (3)	0.67822 (15)	0.74365 (17)	0.0321 (6)
H1A	0.517 (3)	0.6634 (19)	0.664 (2)	0.049 (8)*
H1B	0.548 (3)	0.739 (2)	0.776 (2)	0.051 (8)*
N2	0.4201 (2)	0.65104 (14)	0.91189 (15)	0.0279 (5)
H2	0.462 (3)	0.715 (2)	0.950 (2)	0.067 (9)*
N3	0.3802 (2)	0.53532 (13)	0.78071 (16)	0.0304 (5)
H3	0.390 (3)	0.498 (2)	0.720 (2)	0.054 (9)*
C1	0.3052 (3)	0.56671 (17)	1.0621 (2)	0.0329 (6)
H1	0.3234	0.6167	1.1188	0.039*
C2	0.2351 (3)	0.48051 (18)	1.0811 (2)	0.0383 (7)
H2A	0.2042	0.4713	1.1523	0.046*
C3	0.2094 (3)	0.40767 (18)	0.9977 (2)	0.0408 (7)
H3A	0.1615	0.3495	1.0136	0.049*
C4	0.2513 (3)	0.41718 (17)	0.8920 (2)	0.0365 (7)
H4	0.2330	0.3673	0.8351	0.044*
C5	0.3212 (3)	0.50296 (16)	0.87405 (19)	0.0288 (6)
C6	0.3474 (3)	0.57639 (15)	0.95705 (18)	0.0265 (6)
C7	0.4413 (3)	0.62342 (16)	0.80769 (19)	0.0283 (6)
C8	0.5965 (3)	0.87404 (15)	0.95380 (18)	0.0248 (6)
C9	0.6701 (3)	0.96001 (16)	1.01197 (18)	0.0275 (6)
C10	0.7324 (3)	1.03030 (16)	1.05801 (19)	0.0293 (6)
C11	0.8045 (3)	1.11981 (16)	1.1065 (2)	0.0334 (7)
H11A	0.9000	1.1035	1.1570	0.040*
H11B	0.7429	1.1524	1.1546	0.040*
C12	0.8298 (3)	1.18948 (16)	1.01142 (19)	0.0308 (6)
H12A	0.7349	1.2014	0.9578	0.037*
H12B	0.8652	1.2527	1.0469	0.037*
C13	0.9400 (3)	1.15149 (17)	0.9425 (2)	0.0323 (6)
H13A	1.0387	1.1496	0.9933	0.039*
H13B	0.9131	1.0840	0.9170	0.039*
C14	0.9459 (3)	1.21419 (17)	0.83729 (19)	0.0318 (6)
H14A	0.8478	1.2144	0.7855	0.038*
H14B	0.9695	1.2821	0.8628	0.038*
C15	1.0589 (3)	1.1788 (2)	0.7699 (2)	0.0431 (7)
H15A	1.0602	1.2228	0.7048	0.065*
H15B	1.0332	1.1128	0.7408	0.065*
H15C	1.1563	1.1779	0.8208	0.065*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0439 (13)	0.0258 (8)	0.0247 (8)	−0.0035 (8)	0.0109 (8)	0.0007 (6)
O2	0.0496 (14)	0.0287 (9)	0.0211 (8)	−0.0025 (8)	0.0072 (8)	0.0005 (6)
N1	0.0455 (17)	0.0300 (11)	0.0226 (10)	−0.0024 (10)	0.0112 (10)	−0.0019 (8)
N2	0.0383 (15)	0.0266 (10)	0.0192 (9)	−0.0028 (10)	0.0067 (9)	−0.0007 (7)
N3	0.0401 (16)	0.0264 (10)	0.0243 (10)	−0.0015 (10)	0.0058 (10)	−0.0061 (8)
C1	0.041 (2)	0.0311 (13)	0.0263 (12)	0.0021 (12)	0.0074 (12)	0.0003 (10)
C2	0.043 (2)	0.0390 (14)	0.0355 (13)	0.0013 (13)	0.0133 (14)	0.0054 (11)
C3	0.044 (2)	0.0340 (14)	0.0443 (15)	−0.0059 (13)	0.0080 (15)	0.0044 (11)
C4	0.039 (2)	0.0315 (13)	0.0366 (14)	−0.0043 (13)	0.0019 (13)	−0.0027 (10)
C5	0.0312 (18)	0.0278 (12)	0.0261 (11)	0.0004 (11)	0.0027 (12)	0.0004 (9)
C6	0.0285 (17)	0.0252 (11)	0.0249 (11)	0.0022 (11)	0.0032 (11)	0.0006 (9)
C7	0.0333 (18)	0.0285 (12)	0.0226 (11)	0.0040 (11)	0.0045 (12)	0.0004 (9)
C8	0.0294 (17)	0.0224 (11)	0.0238 (11)	0.0034 (10)	0.0081 (11)	0.0019 (8)
C9	0.0304 (17)	0.0290 (12)	0.0239 (11)	0.0025 (11)	0.0073 (11)	0.0042 (9)
C10	0.0347 (18)	0.0301 (12)	0.0238 (11)	0.0013 (12)	0.0076 (12)	0.0027 (10)
C11	0.041 (2)	0.0292 (12)	0.0298 (13)	−0.0032 (12)	0.0069 (13)	−0.0034 (9)
C12	0.0352 (18)	0.0258 (12)	0.0308 (12)	−0.0029 (11)	0.0052 (12)	−0.0016 (9)
C13	0.0341 (18)	0.0310 (12)	0.0318 (12)	0.0025 (12)	0.0068 (12)	0.0037 (10)
C14	0.0323 (18)	0.0318 (12)	0.0303 (12)	0.0021 (12)	0.0044 (12)	0.0032 (10)
C15	0.045 (2)	0.0475 (16)	0.0389 (14)	0.0056 (14)	0.0132 (14)	0.0089 (12)

Geometric parameters (Å, º)

O1—C8	1.261 (2)	C5—C6	1.392 (3)
O2—C8	1.252 (3)	C8—C9	1.463 (3)
N1—H1A	0.98 (3)	C9—C10	1.197 (3)
N1—H1B	0.95 (3)	C10—C11	1.459 (3)
N1—C7	1.324 (3)	C11—H11A	0.9900
N2—H2	1.02 (3)	C11—H11B	0.9900
N2—C6	1.391 (3)	C11—C12	1.528 (3)
N2—C7	1.340 (3)	C12—H12A	0.9900
N3—H3	0.90 (3)	C12—H12B	0.9900
N3—C5	1.399 (3)	C12—C13	1.523 (3)
N3—C7	1.346 (3)	C13—H13A	0.9900
C1—H1	0.9500	C13—H13B	0.9900
C1—C2	1.390 (3)	C13—C14	1.522 (3)
C1—C6	1.381 (3)	C14—H14A	0.9900
C2—H2A	0.9500	C14—H14B	0.9900
C2—C3	1.389 (3)	C14—C15	1.520 (3)
C3—H3A	0.9500	C15—H15A	0.9800
C3—C4	1.387 (4)	C15—H15B	0.9800
C4—H4	0.9500	C15—H15C	0.9800
C4—C5	1.380 (3)
H1A—N1—H1B	119 (2)	C10—C9—C8	178.6 (3)
C7—N1—H1A	124.3 (16)	C9—C10—C11	175.9 (2)
C7—N1—H1B	116.5 (16)	C10—C11—H11A	109.4
C6—N2—H2	129.2 (16)	C10—C11—H11B	109.4
C7—N2—H2	122.1 (17)	C10—C11—C12	111.33 (19)
C7—N2—C6	108.49 (19)	H11A—C11—H11B	108.0
C5—N3—H3	124.1 (18)	C12—C11—H11A	109.4
C7—N3—H3	126.7 (19)	C12—C11—H11B	109.4
C7—N3—C5	108.19 (18)	C11—C12—H12A	108.9
C2—C1—H1	121.5	C11—C12—H12B	108.9
C6—C1—H1	121.5	H12A—C12—H12B	107.7
C6—C1—C2	117.0 (2)	C13—C12—C11	113.5 (2)
C1—C2—H2A	119.5	C13—C12—H12A	108.9
C3—C2—C1	121.1 (2)	C13—C12—H12B	108.9
C3—C2—H2A	119.5	C12—C13—H13A	109.1
C2—C3—H3A	119.0	C12—C13—H13B	109.1
C4—C3—C2	122.1 (2)	H13A—C13—H13B	107.8
C4—C3—H3A	119.0	C14—C13—C12	112.5 (2)
C3—C4—H4	121.8	C14—C13—H13A	109.1
C5—C4—C3	116.4 (2)	C14—C13—H13B	109.1
C5—C4—H4	121.8	C13—C14—H14A	109.0
C4—C5—N3	131.5 (2)	C13—C14—H14B	109.0
C4—C5—C6	121.9 (2)	H14A—C14—H14B	107.8
C6—C5—N3	106.5 (2)	C15—C14—C13	112.9 (2)
N2—C6—C5	106.97 (19)	C15—C14—H14A	109.0
C1—C6—N2	131.6 (2)	C15—C14—H14B	109.0
C1—C6—C5	121.5 (2)	C14—C15—H15A	109.5
N1—C7—N2	122.9 (2)	C14—C15—H15B	109.5
N1—C7—N3	127.3 (2)	C14—C15—H15C	109.5
N2—C7—N3	109.8 (2)	H15A—C15—H15B	109.5
O1—C8—C9	116.90 (19)	H15A—C15—H15C	109.5
O2—C8—O1	125.9 (2)	H15B—C15—H15C	109.5
O2—C8—C9	117.23 (19)
N3—C5—C6—N2	0.4 (3)	C5—N3—C7—N2	−2.2 (3)
N3—C5—C6—C1	−178.6 (2)	C6—N2—C7—N1	−178.4 (2)
C1—C2—C3—C4	−0.3 (4)	C6—N2—C7—N3	2.5 (3)
C2—C1—C6—N2	−179.0 (3)	C6—C1—C2—C3	0.2 (4)
C2—C1—C6—C5	−0.2 (4)	C7—N2—C6—C1	177.2 (3)
C2—C3—C4—C5	0.4 (4)	C7—N2—C6—C5	−1.8 (3)
C3—C4—C5—N3	178.3 (3)	C7—N3—C5—C4	−177.8 (3)
C3—C4—C5—C6	−0.4 (4)	C7—N3—C5—C6	1.0 (3)
C4—C5—C6—N2	179.4 (2)	C10—C11—C12—C13	−66.8 (3)
C4—C5—C6—C1	0.3 (4)	C11—C12—C13—C14	171.2 (2)
C5—N3—C7—N1	178.8 (2)	C12—C13—C14—C15	178.2 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1^i	0.98 (3)	1.86 (3)	2.789 (2)	156 (2)
N1—H1B···O2	0.95 (3)	1.98 (3)	2.914 (3)	168 (3)
N2—H2···O1	1.02 (3)	1.68 (3)	2.691 (3)	172 (3)
N3—H3···O2^ii	0.90 (3)	1.96 (3)	2.779 (2)	151 (2)

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