Benzamidinium 2-meth­oxy­benzoate

Gustavo Portalone

doi:10.1107/S1600536813016395

. 2013 Jun 19;69(Pt 7):o1114–o1115. doi: 10.1107/S1600536813016395

Benzamidinium 2-methoxybenzoate

Gustavo Portalone ^a,^*

PMCID: PMC3770387 PMID: 24046672

Abstract

The title molecular salt, C₇H₉N₂ ^+.C₈H₇O₃ ⁻, was synthesized by reaction between benzamidine (benzenecarboximidamide) and 2-methoxybenzoic acid. In the cation, the amidinium group has two similar C—N bonds [1.3070 (17) and 1.3145 (16) Å] and is almost coplanar with the benzene ring, making a dihedral angle of 5.34 (12)°. In the anion, the methoxy substituent forces the carboxylate group to be twisted by 69.45 (6)° with respect to the plane of the aromatic fragment. In the crystal, the components are connected by two N⁺—H⋯O⁻ (±)CAHB (charge-assisted hydrogen bonds), forming centrosymmetric ionic dimers with graph-set motif R ₂ ²(8). These ionic dimers are then joined in ribbons running along the b-axis direction by another R ₄ ²(8) motif involving the remaining N⁺—H⋯O⁻ hydrogen bonds. Remarkably, at variance with the well known carboxylic dimer R ₂ ²(8) motif, the carboxylate–amidinium pair is not planar, the dihedral angle between the planes defined by the CN₂ ⁺ and CO₂ ⁻ atoms being 18.57 (12)°.

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 (2010 ▶, 2013 ▶). For the supramolecular association in proton-transfer adducts containing benzamidinium cations, see: Portalone (2010 ▶, 2012 ▶, 2013 ▶); Irrera & Portalone (2012 ▶, 2013 ▶); Irrera et al. (2012 ▶). For 2-methoxybenzoic acid derivatives, see: Portalone (2011 ▶). For hydrogen-bond motifs, see: Bernstein et al. (1995 ▶). graphic file with name e-69-o1114-scheme1.jpg

Experimental

Crystal data

C₇H₉N₂ ⁺·C₈H₇O₃ ⁻
M _r = 272.30
Triclinic,
a = 7.5154 (3) Å
b = 9.1393 (4) Å
c = 11.6498 (5) Å
α = 69.612 (3)°
β = 80.500 (5)°
γ = 72.482 (4)°
V = 713.63 (6) Å³
Z = 2
Mo Kα radiation
μ = 0.09 mm⁻¹
T = 298 K
0.12 × 0.09 × 0.05 mm

Data collection

Agilent Xcalibur Sapphire3 diffractometer
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2011 ▶) T _min = 0.989, T _max = 0.996
20559 measured reflections
4332 independent reflections
3188 reflections with I > 2σ(I)
R _int = 0.025

Refinement

R[F ² > 2σ(F ²)] = 0.062
wR(F ²) = 0.161
S = 1.05
4332 reflections
199 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.38 e Å⁻³
Δρ_min = −0.18 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 for Windows (Farrugia, 2012 ▶); software used to prepare material for publication: WinGX (Farrugia, 2012 ▶).

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536813016395/nk2209sup1.cif

e-69-o1114-sup1.cif^{(24.3KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536813016395/nk2209Isup2.hkl

e-69-o1114-Isup2.hkl^{(208KB, 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	0.913 (19)	1.87 (2)	2.7777 (16)	172.4 (17)
N1—H1B⋯O1ⁱ	0.87 (2)	1.97 (2)	2.7926 (15)	155.7 (17)
N2—H2A⋯O2	0.959 (19)	1.93 (2)	2.8863 (17)	175.4 (16)
N2—H2B⋯O2ⁱⁱ	0.86 (2)	2.00 (2)	2.8230 (16)	160.3 (18)

Open in a new tab

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

supplementary crystallographic information

Comment

The present study is a continuation of the work carried out in this Laboratory on proton-transfer adducts containing molecules of biological interest (Portalone, 2010, 2013), and deals with the single-crystal structure of the molecular salt, benzamidinium 2-methoxybenzoate, (I), obtained by a reaction between benzamidine (benzenecarboximidamide) and 2-methoxybenzoic acid in water solution. Benzamidine derivatives, which have shown strong biological and pharmacological activity (Powers & Harper, 1999), are being used in this Laboratory as bricks for supramolecular construction (Portalone, 2010). Indeed, these molecules are strong Lewis base and their cations can be easily anchored onto numerous inorganic and organic anions and polyanions, largely because of the presence of four potential donor sites for hydrogen-bonding.

The asymmetric unit of (I) comprises one planar benzamidinium cation and one 2-methoxybenzoate anion (Fig. 1).

In the cation the amidinium group forms a dihedral angle of 5.34 (12)° with the mean plane of the phenyl ring, at variance with the values observed in protonated benzamidinium ions (23.2 - 31.1°, Portalone, 2010; Portalone, 2013; Irrera et al., 2012; Irrera & Portalone, 2012, 2013). The pattern of bond lengths and bond angles of the benzamidinium cation agrees with that reported in previous structural investigations. In particular the amidinium group, true to one's expectations, features similar C—N bonds [1.3070 (17) and 1.3145 (16) Å], evidencing the delocalization of the π electrons and double-bond character.

In the 2-methoxybenzoate anion the benzene ring is essentially planar and the methoxy substituent forces the carboxylate group to be twisted with respect to the plane of the aromatic fragment by 69.45 (6)°. In the anion bond lengths and bond angles of the benzene ring are in accord with corresponding values obtained for both the orthorhombic and tetragonal forms of 2,6-dimethoxybenzoic acid (Portalone, 2011 and reference therein) and 4-methoxybenzamidinium 2,6-dimethoxybenzoate (Portalone, 2012). The C—O distances of the carboxylate group, 1.2441 (16) and 1.2488 (15) Å, indicate the delocalization of the negative charge.

The molecular components of the molecular salt are connected by two N⁺—H···O^- (±)CAHB hydrogen bonds to form ionic dimers with graph-set motif R²₂(8) (Bernstein et al., 1995). Furthermore, centrosymmetric ionic dimers are joined in ribbons running along the b axis by another R²₄(8) motif involving the remaining N⁺—H···O^- hydrogen bonds (Fig. 2). Remarkably, at variance with the well known carboxylic dimer R²₂ (8) motif, the carboxylate-amidinium pair is not planar, as the dihedral angle for the planes defined by the CN₂⁺ and CO₂^- atoms is equal to 18.57 (12)°.

Experimental

Equimolar amounts (0.1 mmol) of benzamidine (Fluka at 96% purity) and 2-methoxybenzoic acid (Aldrich at 99% purity) were dissolved without further purification in 6 ml of hot water and heated under reflux for 6 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 two weeks.