4-Meth­oxy­benzamidinium acetate

Simona Irrera; Gustavo Portalone

doi:10.1107/S1600536812044911

. 2012 Nov 3;68(Pt 12):o3277. doi: 10.1107/S1600536812044911

4-Methoxybenzamidinium acetate

Simona Irrera ^a, Gustavo Portalone ^a,^*

PMCID: PMC3588825 PMID: 23468790

Abstract

The title compound, C₈H₁₁N₂O⁺·CH₃CO₂ ⁻, was synthesized by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and acetic acid. In the cation, the amidinium group forms a dihedral angle of 11.65 (17)° with the mean plane of the benzene ring. The ionic components are associated in the crystal via N—H⁺⋯O⁻ hydrogen bonds, resulting in a one-dimensional structure consisting of dimers and catemers and orientated approximately along the c axis.

Related literature

For the biological and pharmacological relevance of benzamidine, see: Powers & Harper (1999 ▶). For structural analysis of proton-transfer adducts containing molecules of biological interest, see: Portalone, (2011a ▶); Portalone & Irrera (2011 ▶). For the supramolecular association in proton-transfer adducts containing benzamidinium cations, see; Portalone (2010 ▶, 2011b ▶, 2012 ▶); Irrera & Portalone (2012a ▶,b ▶); Irrera et al. (2012 ▶). For hydrogen-bond motifs, see Bernstein et al. (1995 ▶). For standard bond lengths, see: Allen et al. (1987 ▶).

Experimental

Crystal data

C₈H₁₁N₂O⁺·C₂H₃O₂ ⁻
M _r = 210.23
Monoclinic,
a = 8.7591 (14) Å
b = 6.5478 (8) Å
c = 19.456 (3) Å
β = 102.580 (14)°
V = 1089.0 (3) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 298 K
0.21 × 0.18 × 0.15 mm

Data collection

Oxford Diffraction Xcalibur S CCD diffractometer
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2011 ▶) T _min = 0.980, T _max = 0.986
14433 measured reflections
2365 independent reflections
1834 reflections with I > 2σ(I)
R _int = 0.040

Refinement

R[F ² > 2σ(F ²)] = 0.056
wR(F ²) = 0.141
S = 1.08
2365 reflections
156 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.21 e Å⁻³
Δρ_min = −0.15 e Å⁻³

Data collection: CrysAlis PRO (Agilent, 2011 ▶); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Click here for additional data file.^{(21.2KB, cif)}

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536812044911/tk5166sup1.cif

e-68-o3277-sup1.cif^{(21.2KB, cif)}

Click here for additional data file.^{(113.9KB, hkl)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812044911/tk5166Isup2.hkl

e-68-o3277-Isup2.hkl^{(113.9KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯O1	0.91 (3)	1.94 (3)	2.847 (2)	175 (2)
N1—H1B⋯O1ⁱ	0.91 (2)	1.98 (2)	2.832 (2)	155 (2)
N2—H2A⋯O2	0.94 (3)	1.83 (3)	2.776 (2)	176 (2)
N2—H2B⋯O2ⁱⁱ	0.88 (2)	1.95 (2)	2.817 (2)	168 (2)

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Symmetry codes: (i) Inline graphic ; (ii) .

supplementary crystallographic information

Comment

The present work is part of a general structural analysis of proton-transfer adducts containing molecules of biological interest (Portalone, 2011a; Portalone & Irrera, 2011). In this context, benzamidine derivatives, which have shown strong biological and pharmacological activity (Powers & Harper, 1999), are being used in our group as bricks for supramolecular construction (Portalone, 2010, 2011b, 2012). Indeed, the bidentate hydrogen-bonding interaction between the amidinium and the carboxylate functional groups can be a powerful organizing force in solution and in the solid-state.

We report here the single-crystal structure of the title molecular salt, 4-methoxybenzamidinium acetate, (I), which was obtained by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and acetic acid.

The asymmetric unit of (I) comprises one non-planar 4-methoxybenzamidinium cation and one acetate anion (Fig. 1).

In the cation the amidinium group forms dihedral angle of 11.65 (17)° with the mean plane of the phenyl ring, which agrees with the values observed in protonated benzamidinium ions (14.4 (1) - 32.7 (1)°, Portalone, 2010, 2012; Irrera et al., 2012). The lack of planarity in all these systems is obviously caused by steric hindrances between the H atoms of the aromatic ring and the amidine moiety. This conformation is rather common in benzamidinium-containing small-molecule crystal structures, with the only exception of benzamidinium diliturate, where the benzamidinium cation is planar (Portalone, 2010). The pattern of bond lengths and bond angles of the 4-methoxybenzamidinium cation agrees with that reported in previous structural investigations (Irrera et al., 2012; Portalone, 2010, 2012; Irrera & Portalone, 2012a, 2012b). In particular the amidinium group, true to one's expectations, features C—N bonds within experimental error [1.312 (2) and 1.306 (2) Å], evidencing the delocalization of the π electrons and double-bond character.

In the acetate moiety the C—O bond lengths indicate delocalization of the negative charge on both O atoms, since the C—O bond lengths [1.250 (2) and 1.249 (2) Å] are intermediate between single Csp²—O and double Csp²═O, and correlate well with values for carboxylate anions [1.247 - 1.262 Å, Allen et al., 1987].

Analysis of the crystal packing of (I), (Fig. 2), shows that each amidinium unit is bound to three acetate anions by four distinct N—H⁺···O^- strong intermolecular hydrogen bonds (N⁺···O^- = 2.776 (2) - 2.847 (2) Å, Table 1) into a one-dimensional structure. The ion pairs of the asymmetric unit are joined by two N⁺—H···O^- (±) hydrogen bonds to form ionic dimers with graph-set motif R²₂(8) (Bernstein et al., 1995). These subunits are then joined as catemers into linear chains approximately along the crystallographic c axis through the remaining N⁺—H···O^- hydrogen bonds to adjacent anti-parallel dimers.

Experimental

4-Methoxybenzamidine (0.1 mmol, Fluka at 96% purity) was dissolved without further purification in 8 ml of a 20% solution of acetic acid and heated under reflux for 3 h. After cooling the solution to an ambient temperature, colourless crystals suitable for single-crystal X-ray diffraction were grown by slow evaporation of the solvent after one week.