organic compounds
4-Methoxybenzamidinium hydrogen oxalate monohydrate
aChemistry Department, "Sapienza" University of Rome, P.le A. Moro, 5, I-00185 Rome, Italy
*Correspondence e-mail: g.portalone@caspur.it
The title hydrated salt, C8H11N2O+·C2HO4−·H2O, was synthesized by a reaction of 4-methoxybenzamidine (4-amidinoanisole) and oxalic acid in water solution. In the cation, the amidinium group forms a dihedral angle of 15.60 (6)° with the mean plane of the benzene ring. In the crystal, each amidinium unit is bound to three acetate anions and one water molecule by six distinct N—H⋯O hydrogen bonds. The ion pairs of the are joined by two N—H⋯O hydrogen bonds into ionic dimers in which the carbonyl O atom of the semi-oxalate anion acts as a bifurcated acceptor, thus generating an R12(6) motif. These subunits are then joined through the remaining N—H⋯O hydrogen bonds to adjacent semi-oxalate anions into linear tetrameric chains running approximately along the b axis. The structure is stabilized by N—H⋯O and O—H⋯O intermolecular hydrogen bonds. The water molecule plays an important role in the cohesion and the stability of the being involved in three hydrogen bonds connecting two semi-oxalate anions as donor and a benzamidinium cation as acceptor.
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, (2011a); Portalone & Irrera (2011). For supramolecular association in proton-transfer adducts containing benzamidinium cations, see; Portalone (2010, 2011b, 2012); Irrera et al. (2012); Irrera & Portalone (2012a,b,c). For hydrogen-bond motifs, see Bernstein et al. (1995).
Experimental
Crystal data
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Refinement
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Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell 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).
Supporting information
10.1107/S1600536812046351/kp2440sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S1600536812046351/kp2440Isup2.hkl
4-Methoxybenzamidine (0.01 mmol, Fluka at 96% purity) was dissolved without further purification in 6 mL of a hot aqueous solution of oxalic acid (0.01 mmol, Aldrich at 99.99% purity) and heated under reflux for 3 h. After cooling the solution to an ambient temperature, colourless crystals suitable for single-crystal X-ray diffraction separated from the solution after a week.
All H atoms were identified in difference Fourier maps, but for
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 and the carboxylic groups were refined, giving N—H distances in the range 0.86 (2) - 0.92 (3) Å, and O—H distance equal to 1.02 (3) Å. The water molecule is disordered over two sites, O2W and O21W. Their occupancies were refined to to 0.85 (2) and 0.15 (2), respectively, by imposing that their values must add up to precisely one. The O—H distances of the H atoms attached to O2W were restrained to 0.85 (2) - 0.88 (2) Å.Data collection: CrysAlis CCD (Oxford Diffraction, 2006); cell
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).Fig. 1. The asymmetric unit of (I), showing the atom-labelling scheme. Displacements ellipsoids are at the 50% probability level. The major occupied site of the disordered water molecule is shown, only. H atoms are shown as small spheres of arbitrary radii. Hydrogen bonding is indicated by dashed lines. | |
Fig. 2. Crystal packing diagram for (I), viewed approximately down a. All atoms are shown as small spheres of arbitrary radii. For the sake of clarity, only the major occupied site of the disordered water molecule and H atoms involved in hydrogen bonding are shown. Hydrogen bonding is indicated by dashed lines. |
C8H11N2O+·C2HO4−·H2O | F(000) = 544 |
Mr = 258.23 | Dx = 1.468 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71069 Å |
Hall symbol: -P 2ybc | Cell parameters from 4235 reflections |
a = 7.1444 (8) Å | θ = 3.0–29.1° |
b = 9.0428 (7) Å | µ = 0.12 mm−1 |
c = 18.115 (2) Å | T = 298 K |
β = 93.156 (10)° | Tablets, colourless |
V = 1168.5 (2) Å3 | 0.18 × 0.12 × 0.09 mm |
Z = 4 |
Oxford Diffraction Xcalibur S CCD diffractometer | 2135 independent reflections |
Radiation source: Enhance (Mo) X-ray Source | 1693 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.046 |
Detector resolution: 16.0696 pixels mm-1 | θmax = 25.4°, θmin = 3.2° |
ω and ϕ scans | h = −8→8 |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2011) | k = −10→10 |
Tmin = 0.978, Tmax = 0.989 | l = −21→21 |
15203 measured reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.047 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.110 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.09 | w = 1/[σ2(Fo2) + (0.0502P)2 + 0.2028P] where P = (Fo2 + 2Fc2)/3 |
2135 reflections | (Δ/σ)max < 0.001 |
201 parameters | Δρmax = 0.16 e Å−3 |
2 restraints | Δρmin = −0.15 e Å−3 |
C8H11N2O+·C2HO4−·H2O | V = 1168.5 (2) Å3 |
Mr = 258.23 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 7.1444 (8) Å | µ = 0.12 mm−1 |
b = 9.0428 (7) Å | T = 298 K |
c = 18.115 (2) Å | 0.18 × 0.12 × 0.09 mm |
β = 93.156 (10)° |
Oxford Diffraction Xcalibur S CCD diffractometer | 2135 independent reflections |
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2011) | 1693 reflections with I > 2σ(I) |
Tmin = 0.978, Tmax = 0.989 | Rint = 0.046 |
15203 measured reflections |
R[F2 > 2σ(F2)] = 0.047 | 2 restraints |
wR(F2) = 0.110 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.09 | Δρmax = 0.16 e Å−3 |
2135 reflections | Δρmin = −0.15 e Å−3 |
201 parameters |
Experimental. Absorption correction: CrysAlisPro, Agilent Technologies, Version 1.171.35.19 (release 27-10-2011 CrysAlis171 .NET) (compiled Oct 27 2011,15:02:11) 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. |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
O1 | 0.8980 (2) | 0.07501 (16) | 0.24710 (8) | 0.0511 (4) | |
N1 | 0.7104 (3) | −0.2554 (2) | −0.06019 (12) | 0.0484 (5) | |
H1A | 0.671 (4) | −0.287 (3) | −0.1070 (16) | 0.084 (9)* | |
H1B | 0.728 (3) | −0.326 (3) | −0.0238 (13) | 0.060 (7)* | |
N2 | 0.6975 (3) | −0.0163 (2) | −0.09613 (11) | 0.0439 (5) | |
H2A | 0.668 (3) | −0.043 (2) | −0.1409 (14) | 0.055 (7)* | |
H2B | 0.702 (3) | 0.080 (3) | −0.0883 (12) | 0.053 (7)* | |
C1 | 0.7801 (2) | −0.0672 (2) | 0.03205 (10) | 0.0327 (4) | |
C2 | 0.8530 (3) | −0.1659 (2) | 0.08440 (11) | 0.0420 (5) | |
H2 | 0.8730 | −0.2635 | 0.0707 | 0.050* | |
C3 | 0.8970 (3) | −0.1231 (2) | 0.15668 (11) | 0.0414 (5) | |
H3 | 0.9472 | −0.1908 | 0.1910 | 0.050* | |
C4 | 0.8654 (3) | 0.0217 (2) | 0.17730 (11) | 0.0371 (5) | |
C5 | 0.7954 (3) | 0.1222 (2) | 0.12537 (11) | 0.0440 (5) | |
H5 | 0.7761 | 0.2199 | 0.1390 | 0.053* | |
C6 | 0.7543 (3) | 0.0788 (2) | 0.05387 (11) | 0.0395 (5) | |
H6 | 0.7085 | 0.1478 | 0.0194 | 0.047* | |
C7 | 0.7288 (2) | −0.1139 (2) | −0.04408 (10) | 0.0346 (5) | |
C8 | 0.9800 (3) | −0.0223 (3) | 0.30183 (12) | 0.0542 (6) | |
H8A | 0.9075 (15) | −0.1129 (14) | 0.3028 (6) | 0.081* | |
H8B | 0.981 (2) | 0.0250 (9) | 0.3499 (7) | 0.081* | |
H8C | 1.1076 (19) | −0.0452 (14) | 0.2900 (5) | 0.081* | |
O3 | 0.6035 (2) | −0.17989 (15) | −0.22870 (8) | 0.0506 (4) | |
O4 | 0.4130 (2) | −0.35402 (14) | −0.27537 (8) | 0.0448 (4) | |
H4 | 0.454 (4) | −0.412 (3) | −0.2291 (15) | 0.086 (8)* | |
O5 | 0.4872 (2) | 0.00180 (14) | −0.34351 (8) | 0.0478 (4) | |
O6 | 0.3608 (2) | −0.19541 (15) | −0.39997 (8) | 0.0517 (4) | |
C9 | 0.4936 (3) | −0.22516 (19) | −0.27658 (11) | 0.0354 (5) | |
C10 | 0.4403 (3) | −0.1325 (2) | −0.34652 (11) | 0.0383 (5) | |
O2W | 0.7296 (9) | −0.5215 (3) | 0.02842 (17) | 0.0531 (13) | 0.85 (2) |
H21W | 0.646 (3) | −0.530 (3) | 0.0600 (14) | 0.080* | |
H22W | 0.699 (4) | −0.578 (3) | −0.0102 (12) | 0.080* | |
O21W | 0.845 (10) | −0.520 (2) | 0.008 (2) | 0.101 (17) | 0.15 (2) |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0703 (10) | 0.0445 (8) | 0.0369 (8) | 0.0073 (7) | −0.0118 (7) | −0.0061 (7) |
N1 | 0.0728 (13) | 0.0325 (10) | 0.0385 (11) | −0.0018 (9) | −0.0083 (10) | −0.0023 (9) |
N2 | 0.0607 (12) | 0.0371 (11) | 0.0328 (11) | −0.0035 (8) | −0.0074 (9) | 0.0024 (8) |
C1 | 0.0334 (10) | 0.0303 (10) | 0.0341 (11) | −0.0011 (8) | 0.0007 (8) | −0.0002 (8) |
C2 | 0.0576 (13) | 0.0273 (10) | 0.0406 (12) | 0.0026 (9) | −0.0034 (10) | −0.0015 (9) |
C3 | 0.0513 (13) | 0.0332 (10) | 0.0386 (12) | 0.0015 (9) | −0.0080 (10) | 0.0052 (9) |
C4 | 0.0373 (11) | 0.0383 (11) | 0.0353 (11) | −0.0010 (8) | −0.0021 (8) | −0.0038 (9) |
C5 | 0.0572 (13) | 0.0292 (10) | 0.0449 (13) | 0.0061 (9) | −0.0045 (10) | −0.0041 (9) |
C6 | 0.0494 (12) | 0.0315 (10) | 0.0370 (11) | 0.0048 (9) | −0.0043 (9) | 0.0042 (9) |
C7 | 0.0354 (11) | 0.0333 (10) | 0.0348 (11) | −0.0016 (8) | −0.0007 (8) | 0.0009 (9) |
C8 | 0.0646 (15) | 0.0563 (14) | 0.0402 (13) | 0.0030 (11) | −0.0105 (11) | 0.0007 (11) |
O3 | 0.0705 (10) | 0.0363 (8) | 0.0427 (9) | −0.0050 (7) | −0.0184 (8) | −0.0008 (6) |
O4 | 0.0650 (10) | 0.0293 (7) | 0.0386 (9) | −0.0066 (6) | −0.0096 (7) | 0.0046 (6) |
O5 | 0.0765 (11) | 0.0278 (7) | 0.0379 (8) | −0.0054 (7) | −0.0081 (7) | 0.0019 (6) |
O6 | 0.0857 (11) | 0.0329 (8) | 0.0343 (9) | −0.0044 (7) | −0.0164 (8) | −0.0001 (6) |
C9 | 0.0458 (12) | 0.0257 (9) | 0.0345 (11) | 0.0045 (8) | −0.0006 (9) | −0.0040 (8) |
C10 | 0.0511 (12) | 0.0289 (10) | 0.0346 (11) | 0.0007 (9) | −0.0014 (9) | −0.0016 (8) |
O2W | 0.074 (3) | 0.0401 (12) | 0.0453 (15) | −0.0055 (13) | 0.0009 (14) | −0.0065 (9) |
O21W | 0.15 (4) | 0.067 (10) | 0.078 (16) | 0.022 (14) | −0.04 (2) | −0.021 (9) |
O1—C4 | 1.361 (2) | C5—C6 | 1.370 (3) |
O1—C8 | 1.427 (2) | C5—H5 | 0.9300 |
N1—C7 | 1.317 (3) | C6—H6 | 0.9300 |
N1—H1A | 0.92 (3) | C8—H8A | 0.9696 |
N1—H1B | 0.92 (2) | C8—H8B | 0.9697 |
N2—C7 | 1.302 (2) | C8—H8C | 0.9696 |
N2—H2A | 0.86 (2) | O3—C9 | 1.209 (2) |
N2—H2B | 0.88 (2) | O4—C9 | 1.300 (2) |
C1—C2 | 1.383 (3) | O4—H4 | 1.02 (3) |
C1—C6 | 1.393 (3) | O5—C10 | 1.260 (2) |
C1—C7 | 1.470 (3) | O6—C10 | 1.234 (2) |
C2—C3 | 1.385 (3) | C9—C10 | 1.549 (3) |
C2—H2 | 0.9300 | O2W—O21W | 0.92 (8) |
C3—C4 | 1.383 (3) | O2W—H21W | 0.854 (17) |
C3—H3 | 0.9300 | O2W—H22W | 0.883 (17) |
C4—C5 | 1.382 (3) | O21W—H22W | 1.20 (6) |
C4—O1—C8 | 118.00 (16) | C5—C6—H6 | 119.5 |
C7—N1—H1A | 121.5 (18) | C1—C6—H6 | 119.5 |
C7—N1—H1B | 120.6 (14) | N2—C7—N1 | 119.1 (2) |
H1A—N1—H1B | 118 (2) | N2—C7—C1 | 120.56 (18) |
C7—N2—H2A | 121.0 (15) | N1—C7—C1 | 120.28 (18) |
C7—N2—H2B | 123.3 (14) | O1—C8—H8A | 109.5 |
H2A—N2—H2B | 116 (2) | O1—C8—H8B | 109.5 |
C2—C1—C6 | 117.90 (17) | H8A—C8—H8B | 109.5 |
C2—C1—C7 | 121.50 (17) | O1—C8—H8C | 109.5 |
C6—C1—C7 | 120.59 (17) | H8A—C8—H8C | 109.5 |
C1—C2—C3 | 121.65 (18) | H8B—C8—H8C | 109.5 |
C1—C2—H2 | 119.2 | C9—O4—H4 | 111.6 (15) |
C3—C2—H2 | 119.2 | O3—C9—O4 | 124.20 (18) |
C4—C3—C2 | 119.22 (18) | O3—C9—C10 | 121.61 (17) |
C4—C3—H3 | 120.4 | O4—C9—C10 | 114.18 (17) |
C2—C3—H3 | 120.4 | O6—C10—O5 | 126.03 (18) |
O1—C4—C5 | 115.88 (17) | O6—C10—C9 | 118.28 (16) |
O1—C4—C3 | 124.32 (18) | O5—C10—C9 | 115.68 (17) |
C5—C4—C3 | 119.80 (18) | O21W—O2W—H21W | 161 (2) |
C6—C5—C4 | 120.39 (18) | O21W—O2W—H22W | 83 (2) |
C6—C5—H5 | 119.8 | H21W—O2W—H22W | 109 (3) |
C4—C5—H5 | 119.8 | O2W—O21W—H22W | 47 (3) |
C5—C6—C1 | 121.01 (18) | ||
C6—C1—C2—C3 | 0.9 (3) | C2—C1—C6—C5 | −1.6 (3) |
C7—C1—C2—C3 | −178.30 (18) | C7—C1—C6—C5 | 177.63 (18) |
C1—C2—C3—C4 | 0.7 (3) | C2—C1—C7—N2 | −165.77 (19) |
C8—O1—C4—C5 | −176.59 (18) | C6—C1—C7—N2 | 15.0 (3) |
C8—O1—C4—C3 | 3.7 (3) | C2—C1—C7—N1 | 15.5 (3) |
C2—C3—C4—O1 | 177.98 (18) | C6—C1—C7—N1 | −163.68 (19) |
C2—C3—C4—C5 | −1.7 (3) | O3—C9—C10—O6 | 164.7 (2) |
O1—C4—C5—C6 | −178.67 (17) | O4—C9—C10—O6 | −14.1 (3) |
C3—C4—C5—C6 | 1.1 (3) | O3—C9—C10—O5 | −13.9 (3) |
C4—C5—C6—C1 | 0.6 (3) | O4—C9—C10—O5 | 167.33 (17) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O3 | 0.92 (3) | 2.43 (3) | 3.180 (3) | 138 (2) |
N1—H1B···O2W | 0.92 (2) | 2.00 (2) | 2.891 (3) | 161 (2) |
N1—H1A···O5i | 0.92 (3) | 2.37 (3) | 3.096 (2) | 135 (2) |
N2—H2A···O3 | 0.86 (2) | 2.05 (2) | 2.869 (2) | 159 (2) |
N2—H2A···O4ii | 0.86 (2) | 2.34 (2) | 2.827 (2) | 116.4 (18) |
N2—H2B···O6ii | 0.88 (2) | 2.09 (3) | 2.932 (2) | 159.5 (19) |
O4—H4···O5i | 1.02 (3) | 1.56 (3) | 2.5840 (19) | 178 (2) |
O2W—H21W···O5iii | 0.85 (2) | 2.15 (2) | 2.976 (6) | 163 (3) |
O2W—H22W···O6i | 0.88 (2) | 1.97 (2) | 2.853 (3) | 177 (3) |
Symmetry codes: (i) −x+1, y−1/2, −z−1/2; (ii) −x+1, y+1/2, −z−1/2; (iii) x, −y−1/2, z+1/2. |
Experimental details
Crystal data | |
Chemical formula | C8H11N2O+·C2HO4−·H2O |
Mr | 258.23 |
Crystal system, space group | Monoclinic, P21/c |
Temperature (K) | 298 |
a, b, c (Å) | 7.1444 (8), 9.0428 (7), 18.115 (2) |
β (°) | 93.156 (10) |
V (Å3) | 1168.5 (2) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.12 |
Crystal size (mm) | 0.18 × 0.12 × 0.09 |
Data collection | |
Diffractometer | Oxford Diffraction Xcalibur S CCD diffractometer |
Absorption correction | Multi-scan (CrysAlis PRO; Agilent, 2011) |
Tmin, Tmax | 0.978, 0.989 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 15203, 2135, 1693 |
Rint | 0.046 |
(sin θ/λ)max (Å−1) | 0.602 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.047, 0.110, 1.09 |
No. of reflections | 2135 |
No. of parameters | 201 |
No. of restraints | 2 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.16, −0.15 |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2006), CrysAlis RED (Oxford Diffraction, 2006), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 2008), ORTEP-3 (Farrugia, 2012), WinGX (Farrugia, 2012).
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O3 | 0.92 (3) | 2.43 (3) | 3.180 (3) | 138 (2) |
N1—H1B···O2W | 0.92 (2) | 2.00 (2) | 2.891 (3) | 161 (2) |
N1—H1A···O5i | 0.92 (3) | 2.37 (3) | 3.096 (2) | 135 (2) |
N2—H2A···O3 | 0.86 (2) | 2.05 (2) | 2.869 (2) | 159 (2) |
N2—H2A···O4ii | 0.86 (2) | 2.34 (2) | 2.827 (2) | 116.4 (18) |
N2—H2B···O6ii | 0.88 (2) | 2.09 (3) | 2.932 (2) | 159.5 (19) |
O4—H4···O5i | 1.02 (3) | 1.56 (3) | 2.5840 (19) | 178 (2) |
O2W—H21W···O5iii | 0.854 (17) | 2.150 (19) | 2.976 (6) | 163 (3) |
O2W—H22W···O6i | 0.883 (17) | 1.972 (18) | 2.853 (3) | 177 (3) |
Symmetry codes: (i) −x+1, y−1/2, −z−1/2; (ii) −x+1, y+1/2, −z−1/2; (iii) x, −y−1/2, z+1/2. |
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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.
For some time now, we have studied proton-transfer adducts containing molecules of biological interest (Portalone, 2011a; Portalone & Irrera, 2011). In this context, benzamidine derivatives, which have shown strong biological and pharmacological activity (Powers & Harper, 1999), have been used in our group as bricks for supramolecular construction (Portalone, 2010, 2011b, 2012). Indeed, the bidentate hydrogen-bonding interaction between the amidinium and the carboxylate functional groups can be a powerful organizing force in solution and in the solid state.
The present study reports the single-crystal structure of the title molecular salt, 4-methoxybenzamidinium hydrogen oxalate monohydrate, (I), which was obtained by a reaction of 4-methoxybenzamidine (4-amidinoanisole) and oxalic acid in a water solution.
The asymmetric unit of the title compound comprises a non-planar 4-methoxybenzamidinium cation, a hydrogen oxalate anion and water molecule of crystallization (Fig. 1).
In the cation the amidinium group forms dihedral angle of 15.60 (6)° with the mean plane of the phenyl ring, which agrees with 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). Geometrical parameters of the 4-methoxybenzamidinium cation agree with those reported in previous investigations of other similar structures (Irrera et al., 2012; Portalone, 2010, 2012; Irrera & Portalone, 2012a, 2012b, 2012c). In particular the amidinium group, true to one's expectations, features similar C—N bonds [1.317 (3) and 1.302 (2) Å], evidencing the delocalization of the π electrons and double-bond character.
The semi-oxalate anion is not planar, as the dihedral angle for the planes defined by the CO2H and CO2- non-H atoms is 14.1 (3)°. Bond distances around atom C10 indicate a carboxylate group with delocalization of the negative charge between atoms O5 and O6. Bond distances around atom C9 are consistent with a carboxylic acid group.
In the crystal structure of (I), (Fig. 2), the hydrogen-bonding scheme is rather complex. Each amidinium unit is bound to three acetate anions and one water molecule by six distinct N—H···O intermolecular hydrogen bonds (N···O = 2.827 (2) - 3.180 (3) Å, Table 1) into a one-dimensional structure. The ion pairs of the asymmetric unit are joined by two N—H···O hydrogen bonds in ionic dimers, where the carbonyl atom O3 of the semi-oxalate 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···O hydrogen bonds to adjacent semi-oxalate anions into linear tetrameric chains running approximately along crystallographic b axis.
Water molecule plays an important role in the cohesion and the stability of the crystal structure: they are involved in three hydrogen bonds connecting two semi-oxalate anions as donor (O2W—H21W···O5 and O2W—H22W···O6) and a benzamidinium cation as acceptor O2W···H1B—N1 (Table 1).