organic compounds
4-Methoxybenzamidinium bromide
aChemistry Department, "Sapienza" University of Rome, P.le A. Moro, 5, I-00185 Rome, Italy
*Correspondence e-mail: g.portalone@caspur.it
The title salt, C8H11N2O+·Br−, was synthesized by the reaction between 4-methoxybenzamidine (4-amidinoanisole) and hydrobromic acid. In the cation, the amidinium group has two similar C—N bonds [1.304 (2) and 1.316 (2) Å], and its plane forms a dihedral angle of 31.08 (5)° with the benzene ring. The ions are associated in the crystal into a three-dimension hydrogen-bonded supramolecular network featuring N—H+⋯Br− interactions.
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 (2011); Portalone & Irrera (2011). For the supramolecular association in proton-transfer adducts containing benzamidinium cations, see: Portalone (2010, 2012); Irrera et al. (2012); Irrera & Portalone (2012a,b,c,d,e). For hydrogen-bond motifs, see: Bernstein et al. (1995).
Experimental
Crystal data
|
Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell CrysAlis RED (Oxford Diffraction, 2006); data reduction: CrysAlis RED; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: WinGX (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).
Supporting information
https://doi.org/10.1107/S1600536812049872/rz5032sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536812049872/rz5032Isup2.hkl
4-Methoxybenzamidine (1 mmol, Fluka at 96% purity) was dissolved without further purification in 6 ml of hot water and heated under reflux for 6 h. While stirring, HBr (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 four weeks.
All H atoms were identified in a difference Fourier map, but for
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) or 1.5Ueq(C) for methyl H atoms. The hydrogen atoms of the methyl group were allowed to rotate with a fixed angle around the C–C bond to best fit the experimental electron density [HFIX 137 in the SHELX program suite]. Positional and isotropic thermal parameters of H atoms of the amidinium group were freely refined, giving N—H distances in the range 0.78 (2)-0.95 (3) Å.As part of our ongoing interest in systematic structural analysis of proton-transfer adducts containing molecules of biological interest (Portalone, 2011; Portalone & Irrera, 2011) this study reports the single-crystal structure of the title molecular salt, 4-methoxybenzamidinium bromide, (I), which was obtained by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and hydrobromic acid in water solution. 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; Portalone, 2012). Indeed, these molecules are strong
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
of (I) comprises one non-planar 4-methoxybenzamidinium cation and one bromide anion (Fig. 1).In the cation the amidinium group forms a dihedral angle of 31.08 (5)° with the benzene ring, which is close to the values observed in protonated benzamidinium ions (23.2-30.4°; Portalone, 2010; Portalone, 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 (Portalone, 2010; Portalone, 2012; Irrera et al., 2012; Irrera & Portalone, 2012a, 2012b, 2012c, 2012d, 2012e). In particular the amidinium group, true to one's expectations, features similar C—N bonds [1.304 (2) and 1.316 (2) Å], evidencing the delocalization of the π electrons and partial double-bond character.
Analysis of the crystal packing of (I), (Fig. 2), shows that each amidinium unit is bound to three bromide anions by four distinct weak N—H+···Br- hydrogen bonds (N+···Br- = 3.3163 (19)-3.4765 (17) Å; Table 1). The ion pairs of the
are joined by two N—H+···Br- hydrogen bonds in ionic dimers, where Br- anion acts as a bifurcated acceptor, thus generating an R12(6) motif (Bernstein et al., 1995). These subunits are then joined through the remaining N—H+···Br- hydrogen bonds to adjacent Br- anions leading to the formation of three-dimension hydrogen-bonded network.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 (2011); Portalone & Irrera (2011). For the supramolecular association in proton-transfer adducts containing benzamidinium cations, see: Portalone (2010, 2012); Irrera et al. (2012); Irrera & Portalone (2012a,b,c,d,e). For hydrogen-bond motifs, see: Bernstein et al. (1995).
Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell
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: WinGX (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).C8H11N2O+·Br− | F(000) = 464 |
Mr = 231.10 | Dx = 1.617 Mg m−3 |
Orthorhombic, P212121 | Mo Kα radiation, λ = 0.71069 Å |
Hall symbol: P 2ac 2ab | Cell parameters from 10829 reflections |
a = 7.5657 (6) Å | θ = 3.2–32.5° |
b = 10.8711 (7) Å | µ = 4.29 mm−1 |
c = 11.5419 (7) Å | T = 298 K |
V = 949.29 (11) Å3 | Tablets, colourless |
Z = 4 | 0.18 × 0.12 × 0.10 mm |
Agilent Xcalibur Sapphire3 diffractometer | 3278 independent reflections |
Radiation source: Enhance (Mo) X-ray Source | 2903 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.043 |
Detector resolution: 16.0696 pixels mm-1 | θmax = 32.0°, θmin = 3.2° |
ω and φ scans | h = −11→11 |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2011) | k = −16→16 |
Tmin = 0.513, Tmax = 0.674 | l = −17→17 |
34724 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.027 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.055 | w = 1/[σ2(Fo2) + (0.0236P)2 + 0.1235P] where P = (Fo2 + 2Fc2)/3 |
S = 1.09 | (Δ/σ)max < 0.001 |
3278 reflections | Δρmax = 0.22 e Å−3 |
126 parameters | Δρmin = −0.31 e Å−3 |
0 restraints | Absolute structure: Flack (1983), 1387 Friedel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: −0.002 (9) |
C8H11N2O+·Br− | V = 949.29 (11) Å3 |
Mr = 231.10 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 7.5657 (6) Å | µ = 4.29 mm−1 |
b = 10.8711 (7) Å | T = 298 K |
c = 11.5419 (7) Å | 0.18 × 0.12 × 0.10 mm |
Agilent Xcalibur Sapphire3 diffractometer | 3278 independent reflections |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2011) | 2903 reflections with I > 2σ(I) |
Tmin = 0.513, Tmax = 0.674 | Rint = 0.043 |
34724 measured reflections |
R[F2 > 2σ(F2)] = 0.027 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.055 | Δρmax = 0.22 e Å−3 |
S = 1.09 | Δρmin = −0.31 e Å−3 |
3278 reflections | Absolute structure: Flack (1983), 1387 Friedel pairs |
126 parameters | Absolute structure parameter: −0.002 (9) |
0 restraints |
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. |
x | y | z | Uiso*/Ueq | ||
Br1 | 0.35106 (3) | 0.611694 (17) | −0.195955 (16) | 0.04325 (6) | |
O1 | 0.3480 (2) | −0.16213 (12) | 0.17351 (11) | 0.0435 (3) | |
N1 | 0.4313 (3) | 0.31784 (17) | −0.13950 (15) | 0.0431 (4) | |
H1A | 0.431 (3) | 0.392 (3) | −0.169 (2) | 0.056 (7)* | |
H1B | 0.484 (3) | 0.261 (3) | −0.181 (2) | 0.062 (8)* | |
N2 | 0.3375 (3) | 0.40022 (16) | 0.02982 (15) | 0.0440 (4) | |
H2A | 0.329 (3) | 0.480 (2) | −0.003 (2) | 0.060 (7)* | |
H2B | 0.300 (3) | 0.394 (3) | 0.092 (2) | 0.054 (7)* | |
C1 | 0.3765 (2) | 0.18004 (16) | 0.01954 (14) | 0.0312 (3) | |
C2 | 0.3378 (3) | 0.07914 (17) | −0.04827 (15) | 0.0387 (4) | |
H2 | 0.3177 | 0.0898 | −0.1271 | 0.046* | |
C3 | 0.3284 (3) | −0.03770 (17) | −0.00107 (16) | 0.0407 (4) | |
H3 | 0.3034 | −0.1052 | −0.0477 | 0.049* | |
C4 | 0.3568 (3) | −0.05267 (15) | 0.11722 (15) | 0.0347 (3) | |
C5 | 0.3987 (2) | 0.04789 (17) | 0.18527 (16) | 0.0383 (4) | |
H5 | 0.4210 | 0.0370 | 0.2638 | 0.046* | |
C6 | 0.4076 (2) | 0.16333 (18) | 0.13810 (16) | 0.0364 (4) | |
H6 | 0.4344 | 0.2306 | 0.1848 | 0.044* | |
C7 | 0.3823 (2) | 0.30343 (17) | −0.03201 (15) | 0.0319 (4) | |
C8 | 0.3064 (3) | −0.26858 (18) | 0.1078 (2) | 0.0521 (6) | |
H8A | 0.1936 | −0.2578 | 0.0711 | 0.078* | |
H8B | 0.3021 | −0.3388 | 0.1581 | 0.078* | |
H8C | 0.3955 | −0.2811 | 0.0498 | 0.078* |
U11 | U22 | U33 | U12 | U13 | U23 | |
Br1 | 0.05673 (11) | 0.03755 (9) | 0.03548 (8) | −0.00280 (10) | −0.00105 (9) | 0.01017 (8) |
O1 | 0.0614 (8) | 0.0328 (6) | 0.0364 (7) | 0.0010 (7) | −0.0039 (7) | 0.0042 (5) |
N1 | 0.0643 (11) | 0.0313 (8) | 0.0338 (8) | 0.0052 (8) | 0.0086 (8) | 0.0021 (7) |
N2 | 0.0634 (10) | 0.0317 (8) | 0.0368 (8) | 0.0032 (10) | 0.0107 (8) | −0.0013 (7) |
C1 | 0.0340 (9) | 0.0304 (8) | 0.0291 (7) | 0.0011 (7) | 0.0007 (7) | 0.0000 (6) |
C2 | 0.0536 (11) | 0.0369 (9) | 0.0255 (7) | −0.0042 (9) | −0.0032 (8) | −0.0002 (6) |
C3 | 0.0581 (13) | 0.0329 (8) | 0.0311 (8) | −0.0050 (9) | −0.0029 (9) | −0.0035 (7) |
C4 | 0.0385 (8) | 0.0324 (8) | 0.0332 (8) | 0.0036 (9) | 0.0004 (9) | 0.0038 (6) |
C5 | 0.0489 (10) | 0.0387 (9) | 0.0272 (8) | 0.0020 (7) | −0.0061 (8) | 0.0017 (7) |
C6 | 0.0459 (10) | 0.0335 (9) | 0.0298 (8) | 0.0018 (8) | −0.0040 (7) | −0.0055 (7) |
C7 | 0.0331 (9) | 0.0312 (8) | 0.0313 (8) | −0.0008 (7) | −0.0005 (7) | −0.0012 (6) |
C8 | 0.0759 (17) | 0.0332 (10) | 0.0474 (11) | 0.0008 (10) | 0.0045 (11) | 0.0001 (8) |
O1—C4 | 1.357 (2) | C2—C3 | 1.384 (3) |
O1—C8 | 1.419 (2) | C2—H2 | 0.9300 |
N1—C7 | 1.304 (2) | C3—C4 | 1.392 (2) |
N1—H1A | 0.87 (3) | C3—H3 | 0.9300 |
N1—H1B | 0.88 (3) | C4—C5 | 1.383 (3) |
N2—C7 | 1.316 (2) | C5—C6 | 1.370 (3) |
N2—H2A | 0.95 (3) | C5—H5 | 0.9300 |
N2—H2B | 0.78 (2) | C6—H6 | 0.9300 |
C1—C2 | 1.379 (2) | C8—H8A | 0.9600 |
C1—C6 | 1.400 (2) | C8—H8B | 0.9600 |
C1—C7 | 1.468 (2) | C8—H8C | 0.9600 |
C4—O1—C8 | 118.05 (14) | O1—C4—C3 | 124.37 (16) |
C7—N1—H1A | 118.6 (16) | C5—C4—C3 | 120.01 (16) |
C7—N1—H1B | 124.6 (17) | C6—C5—C4 | 120.66 (16) |
H1A—N1—H1B | 116 (2) | C6—C5—H5 | 119.7 |
C7—N2—H2A | 122.2 (16) | C4—C5—H5 | 119.7 |
C7—N2—H2B | 122 (2) | C5—C6—C1 | 119.93 (17) |
H2A—N2—H2B | 115 (3) | C5—C6—H6 | 120.0 |
C2—C1—C6 | 119.15 (17) | C1—C6—H6 | 120.0 |
C2—C1—C7 | 120.22 (15) | N1—C7—N2 | 119.54 (18) |
C6—C1—C7 | 120.62 (16) | N1—C7—C1 | 120.25 (16) |
C1—C2—C3 | 121.18 (16) | N2—C7—C1 | 120.21 (16) |
C1—C2—H2 | 119.4 | O1—C8—H8A | 109.5 |
C3—C2—H2 | 119.4 | O1—C8—H8B | 109.5 |
C2—C3—C4 | 119.05 (16) | H8A—C8—H8B | 109.5 |
C2—C3—H3 | 120.5 | O1—C8—H8C | 109.5 |
C4—C3—H3 | 120.5 | H8A—C8—H8C | 109.5 |
O1—C4—C5 | 115.62 (15) | H8B—C8—H8C | 109.5 |
C6—C1—C2—C3 | 0.4 (3) | C3—C4—C5—C6 | 1.9 (3) |
C7—C1—C2—C3 | −178.8 (2) | C4—C5—C6—C1 | −0.8 (3) |
C1—C2—C3—C4 | 0.7 (3) | C2—C1—C6—C5 | −0.3 (3) |
C8—O1—C4—C5 | −179.67 (18) | C7—C1—C6—C5 | 178.87 (17) |
C8—O1—C4—C3 | −0.2 (3) | C2—C1—C7—N1 | −31.3 (3) |
C2—C3—C4—O1 | 178.8 (2) | C6—C1—C7—N1 | 149.52 (19) |
C2—C3—C4—C5 | −1.8 (3) | C2—C1—C7—N2 | 148.4 (2) |
O1—C4—C5—C6 | −178.63 (18) | C6—C1—C7—N2 | −30.7 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···Br1 | 0.87 (3) | 2.48 (3) | 3.3163 (19) | 159 (2) |
N1—H1B···Br1i | 0.88 (3) | 2.49 (3) | 3.3676 (19) | 176 (2) |
N2—H2A···Br1 | 0.95 (3) | 2.65 (3) | 3.4765 (17) | 145 (2) |
N2—H2B···Br1ii | 0.78 (2) | 2.70 (3) | 3.4742 (17) | 175 (2) |
Symmetry codes: (i) −x+1, y−1/2, −z−1/2; (ii) −x+1/2, −y+1, z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C8H11N2O+·Br− |
Mr | 231.10 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 298 |
a, b, c (Å) | 7.5657 (6), 10.8711 (7), 11.5419 (7) |
V (Å3) | 949.29 (11) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 4.29 |
Crystal size (mm) | 0.18 × 0.12 × 0.10 |
Data collection | |
Diffractometer | Agilent Xcalibur Sapphire3 |
Absorption correction | Multi-scan (CrysAlis PRO; Agilent, 2011) |
Tmin, Tmax | 0.513, 0.674 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 34724, 3278, 2903 |
Rint | 0.043 |
(sin θ/λ)max (Å−1) | 0.745 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.027, 0.055, 1.09 |
No. of reflections | 3278 |
No. of parameters | 126 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.22, −0.31 |
Absolute structure | Flack (1983), 1387 Friedel pairs |
Absolute structure parameter | −0.002 (9) |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2006), CrysAlis RED (Oxford Diffraction, 2006), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 2008), WinGX (Farrugia, 2012).
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···Br1 | 0.87 (3) | 2.48 (3) | 3.3163 (19) | 159 (2) |
N1—H1B···Br1i | 0.88 (3) | 2.49 (3) | 3.3676 (19) | 176 (2) |
N2—H2A···Br1 | 0.95 (3) | 2.65 (3) | 3.4765 (17) | 145 (2) |
N2—H2B···Br1ii | 0.78 (2) | 2.70 (3) | 3.4742 (17) | 175 (2) |
Symmetry codes: (i) −x+1, y−1/2, −z−1/2; (ii) −x+1/2, −y+1, z+1/2. |
References
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This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
As part of our ongoing interest in systematic structural analysis of proton-transfer adducts containing molecules of biological interest (Portalone, 2011; Portalone & Irrera, 2011) this study reports the single-crystal structure of the title molecular salt, 4-methoxybenzamidinium bromide, (I), which was obtained by a reaction between 4-methoxybenzamidine (4-amidinoanisole) and hydrobromic acid in water solution. 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; Portalone, 2012). 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 non-planar 4-methoxybenzamidinium cation and one bromide anion (Fig. 1).
In the cation the amidinium group forms a dihedral angle of 31.08 (5)° with the benzene ring, which is close to the values observed in protonated benzamidinium ions (23.2-30.4°; Portalone, 2010; Portalone, 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 (Portalone, 2010; Portalone, 2012; Irrera et al., 2012; Irrera & Portalone, 2012a, 2012b, 2012c, 2012d, 2012e). In particular the amidinium group, true to one's expectations, features similar C—N bonds [1.304 (2) and 1.316 (2) Å], evidencing the delocalization of the π electrons and partial double-bond character.
Analysis of the crystal packing of (I), (Fig. 2), shows that each amidinium unit is bound to three bromide anions by four distinct weak N—H+···Br- hydrogen bonds (N+···Br- = 3.3163 (19)-3.4765 (17) Å; Table 1). The ion pairs of the asymmetric unit are joined by two N—H+···Br- hydrogen bonds in ionic dimers, where Br- anion acts as a bifurcated acceptor, thus generating an R12(6) motif (Bernstein et al., 1995). These subunits are then joined through the remaining N—H+···Br- hydrogen bonds to adjacent Br- anions leading to the formation of three-dimension hydrogen-bonded network.