supplementary materials


rz5020 scheme

Acta Cryst. (2012). E68, o3244    [ doi:10.1107/S1600536812044327 ]

4-Methoxybenzamidinium hydrogen sulfate

S. Irrera and G. Portalone

Abstract top

The title salt, C8H11N2O+·HSO4-, has been synthesized by the reaction between 4-methoxybenzamidine and sulfuric acid. The asymmetric unit comprises a nonplanar 4-methoxybenzamidinium cation and one hydrogen sulfate anion. In the cation, the amidinium group has two identical C-N bonds [1.306 (2) and 1.308 (2) Å], and its plane forms a dihedral angle of 6.49 (8)° with the mean plane of the benzene ring. The ionic components are associated in the crystal via N-H+...O-, resulting in chains running approximately along the b-axis direction whicg are interconnected by O-H...O- hydrogen bonds.

Comment top

In our search for new salt compounds as part of investigation of the functionality of biological systems (Portalone, 2011a; Portalone & Irrera, 2011), we have prepared 4-methoxybenzamidinium hydrogen sulfate, (I), which was obtained by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and sulfuric acid.

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.

The asymmetric unit of (I) comprises one non-planar 4-methoxybenzamidinium cation and one hydrogen sulfate anion (Fig. 1). In the cation the amidinium group forms dihedral angle of 6.49 (8)° with the mean plane of the phenyl ring, which is close to the 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, 2012). In particular the amidinium group, true to one's expectations, features identical C—N bonds within experimental error [1.306 (2) and 1.308 (2) Å], evidencing the delocalization of the π electrons and double-bond character.

Bond lengths in the slightly distorted tetrahedral hydrogen sulfate anion indicate the position of the H atom. There are three short S—O bonds of 1.4504 (13), 1.4442 (13) and 1.4464 (13) Å to terminal atoms O2, O4 and O5, respectively, and one longer bond of 1.5470 (15) Å to atom O3, which is bound to atom H3A.

The ionic components of compound (I) are joined by two N+—H···O- (±) hydrogen bonds (Table 1) to form ionic dimers with graph-set motif R22(8) (Bernstein et al., 1995). Analysis of the crystal packing of (I), (Fig. 2), shows that four N+—H···O- hydrogen bonds link the molecular components into a mono-dimensional structure. As previously mentioned, each subunit, built from the ion pairs of the asymmetric unit, forms R22(8) dimers via the bidentate interaction of the N—H and S—O groups. Adjacent ion pairs are then linked together by way of the remaining two N+—H···O- hydrogen bonds to form R24(8), resulting in chains running approximately along crystallographic b axis. These chains are then interconnected by means of the only O—H···O hydrogen bond present in the structure.

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, H2SO4 (2 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 0.97 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 and of the hydrogen sulfate ion were freely refined, giving N—H distances in the range 0.84 (2)–0.86 (2) Å and an O—H distance equal to 0.78 (3) Å.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell refinement: CrysAlis RED (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, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top
[Figure 1] Fig. 1. The asymmetric unit of (I), showing displacements ellipsoids drawn 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 bonding is indicated by dashed lines.
[Figure 2] Fig. 2. Crystal packing diagram for (I), viewed approximately down the c axis. Displacements ellipsoids are at the 50% probability level. H atoms are shown as small spheres of arbitrary radii. For the sake of clarity, H atoms not involved in hydrogen bonding (dashed lines) have been omitted.
4-Methoxybenzamidinium hydrogen sulfate top
Crystal data top
C8H11N2O+·HSO4F(000) = 520
Mr = 248.26Dx = 1.503 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71069 Å
Hall symbol: -P 2ybcCell parameters from 4647 reflections
a = 14.2608 (14) Åθ = 2.9–29.7°
b = 10.1844 (9) ŵ = 0.30 mm1
c = 7.5723 (9) ÅT = 298 K
β = 94.206 (10)°Tablets, colourless
V = 1096.83 (19) Å30.31 × 0.25 × 0.15 mm
Z = 4
Data collection top
Oxford Diffraction Xcalibur S CCD
diffractometer
2626 independent reflections
Radiation source: Enhance (Mo) X-ray Source2133 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.036
Detector resolution: 16.0696 pixels mm-1θmax = 28.0°, θmin = 2.9°
ω and φ scansh = 1818
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2006)
k = 1313
Tmin = 0.912, Tmax = 0.956l = 99
16529 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)] = 0.039Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.114H atoms treated by a mixture of independent and constrained refinement
S = 1.04 w = 1/[σ2(Fo2) + (0.0582P)2 + 0.2957P]
where P = (Fo2 + 2Fc2)/3
2626 reflections(Δ/σ)max < 0.001
167 parametersΔρmax = 0.26 e Å3
0 restraintsΔρmin = 0.34 e Å3
Crystal data top
C8H11N2O+·HSO4V = 1096.83 (19) Å3
Mr = 248.26Z = 4
Monoclinic, P21/cMo Kα radiation
a = 14.2608 (14) ŵ = 0.30 mm1
b = 10.1844 (9) ÅT = 298 K
c = 7.5723 (9) Å0.31 × 0.25 × 0.15 mm
β = 94.206 (10)°
Data collection top
Oxford Diffraction Xcalibur S CCD
diffractometer
2626 independent reflections
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2006)
2133 reflections with I > 2σ(I)
Tmin = 0.912, Tmax = 0.956Rint = 0.036
16529 measured reflectionsθmax = 28.0°
Refinement top
R[F2 > 2σ(F2)] = 0.039H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.114Δρmax = 0.26 e Å3
S = 1.04Δρmin = 0.34 e Å3
2626 reflectionsAbsolute structure: ?
167 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

Experimental. Absorption correction: [CrysAlis RED (Oxford Diffraction, 2006); empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm]

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
S10.16129 (3)0.16203 (4)0.84884 (6)0.03448 (15)
O20.20315 (10)0.11649 (13)1.00664 (17)0.0514 (4)
O30.24735 (9)0.20809 (15)0.7284 (2)0.0498 (4)
H3A0.2287 (18)0.259 (3)0.662 (4)0.064 (8)*
O40.09972 (9)0.27365 (12)0.87891 (18)0.0467 (3)
O50.11706 (9)0.05608 (12)0.75864 (19)0.0485 (3)
O10.49301 (10)0.19362 (16)0.4667 (3)0.0684 (5)
N10.07593 (12)0.28008 (15)0.6992 (3)0.0452 (4)
H1A0.0189 (18)0.280 (2)0.730 (3)0.053 (6)*
H1B0.1027 (17)0.354 (2)0.693 (3)0.061 (7)*
N20.07598 (14)0.06125 (17)0.6593 (3)0.0595 (5)
H2A0.0212 (18)0.058 (2)0.692 (3)0.057 (7)*
H2B0.107 (2)0.009 (3)0.647 (4)0.087 (9)*
C10.21780 (12)0.18063 (15)0.6067 (2)0.0346 (4)
C20.26115 (13)0.30028 (17)0.5855 (3)0.0465 (5)
H20.22750.37700.60200.056*
C30.35275 (14)0.30917 (18)0.5407 (3)0.0497 (5)
H30.38060.39100.52880.060*
C40.40279 (13)0.19663 (19)0.5136 (3)0.0465 (5)
C50.36028 (15)0.0754 (2)0.5315 (3)0.0595 (6)
H50.39370.00100.51230.071*
C60.26906 (14)0.06751 (18)0.5775 (3)0.0493 (5)
H60.24130.01430.58920.059*
C70.12029 (12)0.17365 (15)0.6575 (2)0.0365 (4)
C80.54205 (16)0.3152 (3)0.4575 (4)0.0749 (8)
H8A0.5094 (10)0.3716 (13)0.369 (2)0.112*
H8B0.6058 (12)0.2988 (4)0.425 (3)0.112*
H8C0.5445 (13)0.3583 (13)0.573 (2)0.112*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0360 (3)0.0244 (2)0.0440 (3)0.00176 (15)0.00969 (18)0.00018 (16)
O20.0718 (9)0.0368 (7)0.0477 (8)0.0093 (6)0.0198 (7)0.0026 (6)
O30.0352 (7)0.0531 (8)0.0616 (9)0.0021 (6)0.0082 (6)0.0112 (7)
O40.0456 (7)0.0321 (7)0.0627 (9)0.0101 (5)0.0068 (6)0.0029 (6)
O50.0488 (7)0.0302 (6)0.0688 (9)0.0022 (5)0.0193 (6)0.0041 (6)
O10.0351 (8)0.0586 (9)0.1145 (14)0.0038 (7)0.0259 (8)0.0054 (9)
N10.0333 (8)0.0306 (8)0.0735 (12)0.0025 (6)0.0154 (8)0.0090 (7)
N20.0389 (10)0.0285 (8)0.1137 (17)0.0032 (7)0.0232 (10)0.0039 (9)
C10.0304 (8)0.0282 (8)0.0454 (9)0.0011 (6)0.0031 (7)0.0015 (7)
C20.0367 (9)0.0277 (8)0.0763 (14)0.0020 (7)0.0133 (9)0.0030 (8)
C30.0395 (10)0.0335 (9)0.0775 (14)0.0050 (8)0.0137 (9)0.0031 (9)
C40.0309 (9)0.0457 (10)0.0639 (12)0.0020 (8)0.0097 (8)0.0032 (9)
C50.0448 (11)0.0352 (10)0.1007 (17)0.0089 (8)0.0210 (11)0.0056 (10)
C60.0423 (10)0.0277 (8)0.0793 (14)0.0008 (7)0.0132 (9)0.0048 (9)
C70.0328 (9)0.0283 (8)0.0483 (10)0.0003 (6)0.0023 (7)0.0020 (7)
C80.0381 (12)0.0773 (17)0.112 (2)0.0104 (11)0.0238 (13)0.0012 (15)
Geometric parameters (Å, º) top
S1—O41.4442 (13)C1—C61.391 (2)
S1—O51.4464 (13)C1—C71.471 (2)
S1—O21.4504 (13)C2—C31.377 (3)
S1—O31.5470 (15)C2—H20.9300
O3—H3A0.78 (3)C3—C41.374 (3)
O1—C41.360 (2)C3—H30.9300
O1—C81.427 (3)C4—C51.386 (3)
N1—C71.306 (2)C5—C61.374 (3)
N1—H1A0.86 (2)C5—H50.9300
N1—H1B0.84 (2)C6—H60.9300
N2—C71.308 (2)C8—H8A0.9739
N2—H2A0.84 (2)C8—H8B0.9739
N2—H2B0.86 (3)C8—H8C0.9739
C1—C21.381 (2)
O4—S1—O5112.37 (8)C4—C3—H3120.2
O4—S1—O2113.83 (8)C2—C3—H3120.2
O5—S1—O2111.75 (8)O1—C4—C3124.73 (18)
O4—S1—O3107.52 (8)O1—C4—C5115.75 (17)
O5—S1—O3107.60 (8)C3—C4—C5119.52 (17)
O2—S1—O3103.05 (9)C6—C5—C4120.42 (17)
S1—O3—H3A106.6 (19)C6—C5—H5119.8
C4—O1—C8118.01 (17)C4—C5—H5119.8
C7—N1—H1A123.0 (15)C5—C6—C1120.68 (17)
C7—N1—H1B119.6 (16)C5—C6—H6119.7
H1A—N1—H1B117 (2)C1—C6—H6119.7
C7—N2—H2A120.2 (16)N1—C7—N2118.74 (18)
C7—N2—H2B118.6 (19)N1—C7—C1120.48 (15)
H2A—N2—H2B120 (2)N2—C7—C1120.77 (16)
C2—C1—C6117.86 (16)O1—C8—H8A109.5
C2—C1—C7120.84 (15)O1—C8—H8B109.5
C6—C1—C7121.29 (15)H8A—C8—H8B109.5
C3—C2—C1121.85 (16)O1—C8—H8C109.5
C3—C2—H2119.1H8A—C8—H8C109.5
C1—C2—H2119.1H8B—C8—H8C109.5
C4—C3—C2119.65 (17)
C6—C1—C2—C31.4 (3)C3—C4—C5—C60.5 (4)
C7—C1—C2—C3179.01 (19)C4—C5—C6—C10.0 (4)
C1—C2—C3—C40.9 (3)C2—C1—C6—C50.9 (3)
C8—O1—C4—C34.9 (3)C7—C1—C6—C5179.5 (2)
C8—O1—C4—C5176.0 (2)C2—C1—C7—N16.3 (3)
C2—C3—C4—O1179.1 (2)C6—C1—C7—N1174.06 (19)
C2—C3—C4—C50.1 (3)C2—C1—C7—N2172.7 (2)
O1—C4—C5—C6179.6 (2)C6—C1—C7—N26.9 (3)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3A···O2i0.78 (3)1.79 (3)2.562 (2)172 (3)
N1—H1A···O40.86 (2)2.10 (2)2.938 (2)163 (2)
N1—H1B···O5ii0.84 (2)2.10 (2)2.884 (2)154 (2)
N2—H2A···O50.84 (2)2.07 (3)2.907 (2)177 (2)
N2—H2B···O4iii0.86 (3)2.22 (3)2.965 (2)145 (3)
Symmetry codes: (i) x, y+1/2, z1/2; (ii) x, y+1/2, z+3/2; (iii) x, y1/2, z+3/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3A···O2i0.78 (3)1.79 (3)2.562 (2)172 (3)
N1—H1A···O40.86 (2)2.10 (2)2.938 (2)163 (2)
N1—H1B···O5ii0.84 (2)2.10 (2)2.884 (2)154 (2)
N2—H2A···O50.84 (2)2.07 (3)2.907 (2)177 (2)
N2—H2B···O4iii0.86 (3)2.22 (3)2.965 (2)145 (3)
Symmetry codes: (i) x, y+1/2, z1/2; (ii) x, y+1/2, z+3/2; (iii) x, y1/2, z+3/2.
references
References top

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