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Acta Cryst. (2012). E68, o3334    [ doi:10.1107/S1600536812045874 ]

4-Methoxybenzamidinium nitrate

S. Irrera and G. Portalone

Abstract top

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.

Comment top

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.

Related literature top

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 top

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.

Refinement top

All H atoms were identified in difference Fourier maps, but for refinement all C-bound H atoms were placed in calculated positions, with C—H = 0.93 Å (phenyl) and 0.96 Å (methyl), and refined as riding on their carrier atoms. The Uiso values were kept equal to 1.2Ueq(C, phenyl). and to 1.5Ueq(C, methyl). Positional and thermal parameters of H atoms of the amidinium group were freely refined, giving N—H distances in the range 0.84 (3) - 0.91 (2) Å. In the absence of significant anomalous scattering in this light-atom study of the title compound, Friedel pairs were merged prior to refinement.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis CCD (Oxford Diffraction, 2006); 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).

Figures top
[Figure 1] Fig. 1. The asymmetric unit of the title compound. Displacements ellipsoids are at the 50% probability level. The asymmetric unit was selected so that the two ions are linked by N+.—H···O- hydrogen bonds. H atoms are shown as small spheres of arbitrary radii. Hydrogen bonds are indicated by dashed lines.
[Figure 2] Fig. 2. Crystal packing diagram for the title compound. All atoms are shown as small spheres of arbitrary radii. For the sake of clarity, H atoms not involved in hydrogen bonding have been omitted. Hydrogen bonding is indicated by dashed lines.
4-Methoxybenzamidinium nitrate top
Crystal data top
C8H11N2O+·NO3F(000) = 448
Mr = 213.20Dx = 1.433 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71069 Å
Hall symbol: P 2ac 2abCell parameters from 2927 reflections
a = 7.1049 (7) Åθ = 3.0–29.0°
b = 10.3558 (8) ŵ = 0.12 mm1
c = 13.4325 (9) ÅT = 298 K
V = 988.32 (14) Å3Tablets, colourless
Z = 40.20 × 0.10 × 0.08 mm
Data collection top
Oxford Diffraction Xcalibur S CCD
diffractometer
1253 independent reflections
Radiation source: Enhance (Mo) X-ray Source989 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.028
Detector resolution: 16.0696 pixels mm-1θmax = 27.0°, θmin = 3.0°
ω and φ scansh = 88
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2006)
k = 1312
Tmin = 0.977, Tmax = 0.991l = 1717
6206 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.038Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.083H atoms treated by a mixture of independent and constrained refinement
S = 0.98 w = 1/[σ2(Fo2) + (0.0527P)2 + 0.0001P]
where P = (Fo2 + 2Fc2)/3
1253 reflections(Δ/σ)max < 0.001
154 parametersΔρmax = 0.12 e Å3
0 restraintsΔρmin = 0.20 e Å3
Crystal data top
C8H11N2O+·NO3V = 988.32 (14) Å3
Mr = 213.20Z = 4
Orthorhombic, P212121Mo Kα radiation
a = 7.1049 (7) ŵ = 0.12 mm1
b = 10.3558 (8) ÅT = 298 K
c = 13.4325 (9) Å0.20 × 0.10 × 0.08 mm
Data collection top
Oxford Diffraction Xcalibur S CCD
diffractometer
1253 independent reflections
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2006)
989 reflections with I > 2σ(I)
Tmin = 0.977, Tmax = 0.991Rint = 0.028
6206 measured reflectionsθmax = 27.0°
Refinement top
R[F2 > 2σ(F2)] = 0.038H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.083Δρmax = 0.12 e Å3
S = 0.98Δρmin = 0.20 e Å3
1253 reflectionsAbsolute structure: ?
154 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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 (Å2) top
xyzUiso*/Ueq
O40.3500 (3)0.10530 (16)0.33730 (12)0.0565 (5)
N10.3218 (3)0.3966 (2)0.07851 (16)0.0441 (5)
H1A0.325 (3)0.426 (2)0.1390 (18)0.041 (6)*
H1B0.268 (3)0.448 (2)0.0308 (18)0.044 (7)*
N20.4153 (3)0.1984 (2)0.12938 (16)0.0454 (5)
H2A0.408 (3)0.222 (3)0.1914 (18)0.046 (7)*
H2B0.463 (3)0.127 (3)0.1138 (17)0.045 (8)*
C10.3682 (3)0.2331 (2)0.04594 (15)0.0359 (5)
C20.4110 (3)0.3182 (2)0.12224 (14)0.0377 (5)
H20.44260.40320.10720.045*
C30.4073 (3)0.2785 (2)0.22025 (16)0.0419 (5)
H30.43720.33630.27080.050*
C40.3588 (3)0.1520 (2)0.24330 (16)0.0397 (5)
C50.3158 (3)0.0660 (2)0.16755 (17)0.0432 (5)
H50.28320.01880.18270.052*
C60.3215 (3)0.1061 (2)0.07021 (17)0.0401 (5)
H60.29370.04780.01970.048*
C70.3686 (3)0.2769 (2)0.05791 (15)0.0347 (5)
C80.3767 (4)0.1947 (3)0.41712 (18)0.0639 (8)
H8A0.498 (3)0.2338 (16)0.4114 (9)0.096*
H8B0.368 (3)0.1501 (8)0.4793 (11)0.096*
H8C0.282 (2)0.2602 (17)0.4141 (9)0.096*
N30.3829 (3)0.3901 (2)0.35182 (15)0.0471 (5)
O10.3880 (3)0.46641 (18)0.28077 (14)0.0669 (5)
O20.3696 (3)0.27255 (18)0.33771 (13)0.0735 (6)
O30.3962 (3)0.43439 (17)0.43752 (12)0.0611 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O40.0789 (12)0.0439 (10)0.0466 (9)0.0041 (10)0.0002 (8)0.0075 (9)
N10.0525 (12)0.0399 (12)0.0401 (11)0.0049 (10)0.0049 (9)0.0023 (10)
N20.0481 (12)0.0456 (14)0.0425 (12)0.0050 (11)0.0003 (9)0.0013 (10)
C10.0272 (10)0.0357 (12)0.0448 (11)0.0026 (9)0.0010 (9)0.0008 (10)
C20.0386 (12)0.0279 (12)0.0466 (12)0.0024 (9)0.0005 (9)0.0001 (10)
C30.0477 (13)0.0346 (11)0.0433 (11)0.0016 (11)0.0055 (10)0.0071 (11)
C40.0403 (12)0.0363 (12)0.0426 (11)0.0034 (10)0.0002 (9)0.0048 (11)
C50.0460 (13)0.0297 (12)0.0537 (13)0.0028 (11)0.0043 (11)0.0007 (11)
C60.0370 (11)0.0345 (12)0.0488 (12)0.0006 (10)0.0001 (10)0.0055 (11)
C70.0264 (10)0.0359 (12)0.0416 (11)0.0001 (9)0.0020 (9)0.0032 (11)
C80.0867 (19)0.0635 (18)0.0415 (12)0.0123 (17)0.0007 (13)0.0001 (13)
N30.0480 (11)0.0489 (12)0.0446 (10)0.0027 (10)0.0002 (10)0.0090 (11)
O10.0978 (14)0.0531 (11)0.0498 (9)0.0019 (11)0.0058 (10)0.0028 (9)
O20.1182 (17)0.0438 (11)0.0586 (10)0.0156 (12)0.0060 (12)0.0124 (9)
O30.0836 (12)0.0565 (11)0.0434 (9)0.0070 (10)0.0062 (9)0.0164 (9)
Geometric parameters (Å, º) top
O4—C41.354 (3)C3—C41.390 (3)
O4—C81.429 (3)C3—H30.9300
N1—C71.313 (3)C4—C51.387 (3)
N1—H1A0.87 (2)C5—C61.373 (3)
N1—H1B0.91 (2)C5—H50.9300
N2—C71.302 (3)C6—H60.9300
N2—H2A0.87 (2)C8—H8A0.9572
N2—H2B0.84 (3)C8—H8B0.9572
C1—C21.386 (3)C8—H8C0.9572
C1—C61.395 (3)N3—O21.235 (3)
C1—C71.467 (3)N3—O11.240 (3)
C2—C31.379 (3)N3—O31.243 (2)
C2—H20.9300
C4—O4—C8117.53 (18)C6—C5—C4119.9 (2)
C7—N1—H1A121.4 (16)C6—C5—H5120.1
C7—N1—H1B120.3 (14)C4—C5—H5120.1
H1A—N1—H1B118 (2)C5—C6—C1121.0 (2)
C7—N2—H2A120.8 (17)C5—C6—H6119.5
C7—N2—H2B118.0 (16)C1—C6—H6119.5
H2A—N2—H2B121 (2)N2—C7—N1120.0 (2)
C2—C1—C6118.62 (19)N2—C7—C1120.6 (2)
C2—C1—C7120.41 (18)N1—C7—C1119.49 (19)
C6—C1—C7120.95 (19)O4—C8—H8A109.5
C3—C2—C1120.8 (2)O4—C8—H8B109.5
C3—C2—H2119.6H8A—C8—H8B109.5
C1—C2—H2119.6O4—C8—H8C109.5
C2—C3—C4119.9 (2)H8A—C8—H8C109.5
C2—C3—H3120.1H8B—C8—H8C109.5
C4—C3—H3120.1O2—N3—O1120.82 (19)
O4—C4—C5116.40 (19)O2—N3—O3120.8 (2)
O4—C4—C3123.8 (2)O1—N3—O3118.4 (2)
C5—C4—C3119.8 (2)
C6—C1—C2—C30.1 (3)C3—C4—C5—C60.1 (3)
C7—C1—C2—C3178.67 (18)C4—C5—C6—C10.6 (3)
C1—C2—C3—C40.5 (3)C2—C1—C6—C50.6 (3)
C8—O4—C4—C5174.4 (2)C7—C1—C6—C5178.10 (19)
C8—O4—C4—C35.5 (3)C2—C1—C7—N2148.0 (2)
C2—C3—C4—O4179.38 (19)C6—C1—C7—N233.3 (3)
C2—C3—C4—C50.5 (3)C2—C1—C7—N131.7 (3)
O4—C4—C5—C6179.9 (2)C6—C1—C7—N1147.0 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O10.87 (2)2.00 (2)2.850 (3)166 (2)
N1—H1B···O3i0.91 (2)2.10 (2)3.008 (3)170 (2)
N2—H2A···O20.87 (2)2.05 (2)2.920 (3)175 (2)
N2—H2B···O1ii0.84 (3)2.43 (3)3.030 (3)129 (2)
N2—H2B···O3ii0.84 (3)2.33 (3)3.174 (3)177 (2)
Symmetry codes: (i) x+1/2, y+1, z+1/2; (ii) x+1, y1/2, z1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1A···O10.87 (2)2.00 (2)2.850 (3)166 (2)
N1—H1B···O3i0.91 (2)2.10 (2)3.008 (3)170 (2)
N2—H2A···O20.87 (2)2.05 (2)2.920 (3)175 (2)
N2—H2B···O1ii0.84 (3)2.43 (3)3.030 (3)129 (2)
N2—H2B···O3ii0.84 (3)2.33 (3)3.174 (3)177 (2)
Symmetry codes: (i) x+1/2, y+1, z+1/2; (ii) x+1, y1/2, z1/2.
references
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