4-Meth­oxy­benzamidinium nitrate

Simona Irrera; Gustavo Portalone

doi:10.1107/S1600536812045874

. 2012 Nov 10;68(Pt 12):o3334. doi: 10.1107/S1600536812045874

4-Methoxybenzamidinium nitrate

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

PMCID: PMC3588936 PMID: 23476172

Abstract

The title salt, C₈H₁₁N₂O⁺·NO₃ ⁻, was synthesized by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and nitric acid. The asymmetric unit comprises a non-planar 4-methoxybenzamidinium cation and a nitrate anion. In the cation, the amidinium group has two similar C—N bond lengths [1.302 (3) and 1.313 (3) Å] and its plane forms a dihedral angle of 32.66 (5)° with the mean plane of the benzene ring. The nitrate–amidinium ion pair is not planar, as the dihedral angle between the planes defined by the CN₂ ⁺ and NO₃ ⁻ units is 19.28 (6)°. The ionic components are associated in the crystal via N—H⋯O hydrogen bonds, resulting in a three-dimensional network.

Related literature

For the biological and pharmacological relevance of benzamidine, see: Powers & Harper (1999 ▶); Grzesiak et al. (2000 ▶). 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 (2012 ▶); Irrera et al. (2012 ▶). For hydrogen-bond motifs, see: Bernstein et al. (1995 ▶).

Experimental

Crystal data

C₈H₁₁N₂O⁺·NO₃ ⁻
M _r = 213.20
Orthorhombic,
a = 7.1049 (7) Å
b = 10.3558 (8) Å
c = 13.4325 (9) Å
V = 988.32 (14) Å³
Z = 4
Mo Kα radiation
μ = 0.12 mm⁻¹
T = 298 K
0.20 × 0.10 × 0.08 mm

Data collection

Oxford Diffraction Xcalibur S CCD diffractometer
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2006 ▶) T _min = 0.977, T _max = 0.991
6206 measured reflections
1253 independent reflections
989 reflections with I > 2σ(I)
R _int = 0.028

Refinement

R[F ² > 2σ(F ²)] = 0.038
wR(F ²) = 0.083
S = 0.98
1253 reflections
154 parameters
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.12 e Å⁻³
Δρ_min = −0.20 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2006 ▶); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2006 ▶); 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, 2012 ▶); software used to prepare material for publication: WinGX (Farrugia, 2012 ▶).

Supplementary Material

Click here for additional data file.^{(20.8KB, cif)}

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536812045874/fi2127sup1.cif

e-68-o3334-sup1.cif^{(20.8KB, cif)}

Click here for additional data file.^{(60.7KB, hkl)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812045874/fi2127Isup2.hkl

e-68-o3334-Isup2.hkl^{(60.7KB, 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	0.87 (2)	2.00 (2)	2.850 (3)	166 (2)
N1—H1B⋯O3ⁱ	0.91 (2)	2.10 (2)	3.008 (3)	170 (2)
N2—H2A⋯O2	0.87 (2)	2.05 (2)	2.920 (3)	175 (2)
N2—H2B⋯O1ⁱⁱ	0.84 (3)	2.43 (3)	3.030 (3)	129 (2)
N2—H2B⋯O3ⁱⁱ	0.84 (3)	2.33 (3)	3.174 (3)	177 (2)

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

supplementary crystallographic information

Comment

Following our on-going interest on systematic structural analysis of proton-transfer adducts containing molecules of biological interest (Portalone, 2011a; Portalone & Irrera, 2011), benzamidine derivatives, which have shown strong biological and pharmacological activity (Powers & Harper, 1999; Grzesiak et al., 2000), are being used in our group as bricks for supramolecular construction (Portalone, 2010, 2011b, 2012). Indeed, these molecules are strong Lewis bases 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.

We report here the crystal structure of the title compound, 4-methoxybenzamidinium nitrate, which was obtained by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and nitric acid.

The asymmetric unit of the title compound comprises one non-planar 4-methoxybenzamidinium cation and one nitrate anion (Fig. 1).

In the cation, the amidinium group forms dihedral angle of 32.66 (5)° with the mean plane of the phenyl ring, which is close to the the values observed in protonated benzamidinium ions (14.4 (1) - 30.4 (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 group. 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, 2012). In particular the amidinium group, true to one's expectations, features similar C—N bonds [1.302 (3) and 1.313 (3) Å], evidencing the delocalization of the π electrons and double-bond character. The molecular parameters for the nitrate ion are in the expected range.

The ionic components of compound (I) are joined by two N⁺—H···O^- (±) hydrogen bonds to form ionic dimers with graph-set motif R²₂(8) (Bernstein et al., 1995). Remarkably, at variance with the well known carboxylic dimer R²₂ (8) motif, the nitrate-amidinium pair is not planar, as the dihedral angles for the planes defined by the CN₂⁺ and NO₃^- atoms is 19.28 (6)°. Similar deviation from planarity has been previously observed in the carboxylate-amidinium pair of benzamidinium 2,6-dimethoxybenzoate (Irrera et al., 2012).

Analysis of the crystal packing of the title compound (Fig. 2) shows that each amidinium unit is bound to three nitrate anions by five distinct N—H⁺···O^- intermolecular hydrogen bonds (N⁺···O^- = 2.850 (3) - 3.174 (3) Å, Table 1). Four cation-to-anion N⁺···O^- interactions form two types of hydrogen-bonded rings: the R²₁(4), which indicates a bifurcated hydrogen bond from N2—H2b to the two acceptors (O1, O3), and the already mentioned R²₂(8) supramolecular synthon. Both these ring motifs lead to the formation of ribbons approximately along crystallographic b axis. These ribbons are then interconnected by means of the remaining N⁺···O^- intermolecular hydrogen bond.

Experimental

4-methoxybenzamidine (0.1 mmol, Fluka at 96% purity) was dissolved without further purification in 6 ml of hot water and heated under reflux for 3 h. While stirring, HNO₃ (4 mol L^-1) was added dropwise until pH reached 2. 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.