Download citation
Download citation
link to html
In the title compound, C5H6N+·C2HO4·C2H2O4·2H2O, the pyridine mol­ecule exists as a cation and the oxalic acid mol­ecules as an oxalate(1−) ion and a neutral oxalic acid. The structure is stabilized by O—H...O and N—H...O hydrogen bonds in addition to carbonyl–carbonyl O...C short contacts and van der Waals interactions. The water mol­ecules are also found to mediate interactions between oxalate ions and oxalic acid mol­ecules through a number of O—H...O hydrogen bonds. Pairs of pyridinium cations related by a center of inversion are surrounded by semi-oxalate anions and oxalic acid mol­ecules, and the complex may be described as an inclusion compound.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536803009164/na6224sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536803009164/na6224Isup2.hkl
Contains datablock I

CCDC reference: 214804

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](C-C) = 0.003 Å
  • R factor = 0.037
  • wR factor = 0.113
  • Data-to-parameter ratio = 11.4

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry
Yellow Alert Alert Level C:
PLAT_369 Alert C Long C(sp2)-C(sp2) Bond C(7) - C(8) = 1.54 Ang. PLAT_369 Alert C Long C(sp2)-C(sp2) Bond C(9) - C(10) = 1.54 Ang.
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
2 Alert Level C = Please check

Comment top

The present study reports the crystal structure of pyridinium oxalate oxalic acid dihydrate, (I), as part of a series of investigations being carried out to observe conformational changes in carboxylic acid molecules and characteristic hydrogen-bonding patterns in their crystal structures.

Fig. 1 shows the molecular structure of (I) with the atom-numbering scheme. The pyridine molecule exists in the cationic form with a protonated ring N atom. One of the oxalic acid molecules exists in a mono-ionized state while the other molecule in the uncharged state. The oxalic acid molecule is more planar [the largest displacements from the plane are by 0.012 (2) Å for O1 and 0.011 (1) Å for O4, on the same side] than the hydrogen oxalate ion [the largest displacements from the plane are by 0.017 (2) Å for O6 and 0.123 (2) Å for O8, on opposite sides]. The geometric parameters of the pyridinium ion are in agreement with those of the pyridinium ions of other structures, viz. bisthiourea pyridinium bromide (Truter & Vickery, 1972) and pyridinium dichloroiodide (Tucker & Kroon, 1973). The C—C bond lengths of the oxalate ion and oxalic acid molecules [C7—C8 = 1.539 (2) Å and C9—C10 = 1.544 (2) Å] are longer than accepted values. Perhaps the abnormally long C—C distance found in the oxalic acid molecule and oxalate ion can be justified by intramolecular O···O steric hindrance, shown by the following contacts: O1···O3 = 2.682 (2), O2···O4 = 2.626 (2), O5···O7 = 2.691 (2) and O2···O4 = 2.666 (2) Å, all significantly shorter than the sum of the van der Waals radii of 3.04 Å (Bondi, 1964). This steric interaction not only causes an enlargement of about 0.04 Å of the C—C central bond in both oxalic acid residues, but also some twisting of the two carboxylic acid groups about it, twisting that is significant only in the anion, as shown by the values of the torsion angles O1—C7—C8—O3 = −0.5 (2)° and O5—C9—C10—O7 = 12.1 (2)°. However, such large deviations in bond lengths are also observed in the case of oxalic acid dihydrate, with C—C = 1.537 Å (Ahmed & Cruickshank, 1953), and in the crystal structures of anhydrous α- and β-oxalic acids, with values of 1.537 (1) and 1.537 (1) Å, respectively (Derrissen & Smith, 1974). A slight increase in the C10—O7 bond length [1.264 (2) Å] compared to C10—O8 [1.231 (2) Å] may be attributed to atom O7 participating in two hydrogen bonds and O8 in only one hydrogen bond in the structure. The other geometrical parameters of the oxalic acid molecules are found to be in agreement with those of other similar structures (oxalic acid dihydrate, anhydrous α- and β-oxalic acids, etc.).

Fig. 2 shows the packing pattern of (I), viewed down the a axis. The oxalate and oxalic acid residues related by a center of inversion are alternately linked along the diagonal of the ac plane. Pyridinium ions link the oxalate ion layers through bifurcated N—H···O hydrogen bonds, leading to a characteristic three-dimensional aggregation pattern. One of the water molecules (O10) as donor, mediates O—H···O interactions with the oxalic acid residue. The other water molecule (O9) links the uncharged oxalic acid molecules and the oxalate ions through O—H···O hydrogen bonds. Short carbonyl contacts [C7···O5 = 3.004 (4) Å, C8···O5 = 2.995 (3) Å and C8···O10(-x, −y, −z + 1) = 3.002 (3) Å] are also observed (Allen et al., 1998). Thus the structure is stabilized by O—H···O and N—H···O hydrogen bonds in addition to short contacts and van der Waals interactions. The complex can be described as an inclusion compound with the oxalate ion and oxalic acid molecule as hosts and the pyridinium ion as the guest.

Experimental top

Colorless prismatic single crystals of (I) were obtained during an attempt to grow the complex of L-proline with oxalic acid, in the presence of a few drops of pyridine, from a saturated aqueous solution containing proline and oxalic acid in a stoichiometric ratio. Unexpectedly, instead of L-prolinium oxalate, only the title compound, (I), was obtained.

Refinement top

All the H atoms except those of the water molecules were generated geometrically and were allowed to ride on their respective parent atoms. The water H atoms were located from the difference Fourier map and allowed to refine isotropically.

Computing details top

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: CAD-4 Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The molecular structure of (I) with the atom-numbering scheme and ellipsoids at the 50% probability level.
[Figure 2] Fig. 2. The packing of the molecules of (I), viewed down the a axis.
Pyridinium oxalate oxalic acid dihydrate top
Crystal data top
C5H6N+·C2H2O4·C2HO4·2H2OZ = 2
Mr = 295.20F(000) = 308
Triclinic, P1Dx = 1.537 Mg m3
Dm = 1.55 Mg m3
Dm measured by flotation in a mixture of xylene and bromoform
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 6.992 (7) ÅCell parameters from 25 reflections
b = 9.539 (2) Åθ = 2.0–25.0°
c = 10.098 (2) ŵ = 0.14 mm1
α = 84.36 (2)°T = 293 K
β = 79.54 (4)°Prismatic, colourless
γ = 74.71 (6)°0.40 × 0.35 × 0.17 mm
V = 638.0 (7) Å3
Data collection top
Enraf-Nonius CAD-4
diffractometer
1946 reflections with I > 2s(I)
Radiation source: fine-focus sealed tubeRint = 0.006
Graphite monochromatorθmax = 25.0°, θmin = 2.1°
ω–2θ scansh = 08
Absorption correction: ψ scan
(North et al., 1968)
k = 1011
Tmin = 0.948, Tmax = 0.971l = 1111
2451 measured reflections2 standard reflections every 200 reflections
2250 independent reflections intensity decay: <1%
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.037H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.113 w = 1/[σ2(Fo2) + (0.0645P)2 + 0.1652P]
where P = (Fo2 + 2Fc2)/3
S = 1.09(Δ/σ)max < 0.001
2250 reflectionsΔρmax = 0.26 e Å3
198 parametersΔρmin = 0.21 e Å3
0 restraintsExtinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.017 (5)
Crystal data top
C5H6N+·C2H2O4·C2HO4·2H2Oγ = 74.71 (6)°
Mr = 295.20V = 638.0 (7) Å3
Triclinic, P1Z = 2
a = 6.992 (7) ÅMo Kα radiation
b = 9.539 (2) ŵ = 0.14 mm1
c = 10.098 (2) ÅT = 293 K
α = 84.36 (2)°0.40 × 0.35 × 0.17 mm
β = 79.54 (4)°
Data collection top
Enraf-Nonius CAD-4
diffractometer
1946 reflections with I > 2s(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.006
Tmin = 0.948, Tmax = 0.9712 standard reflections every 200 reflections
2451 measured reflections intensity decay: <1%
2250 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0370 restraints
wR(F2) = 0.113H atoms treated by a mixture of independent and constrained refinement
S = 1.09Δρmax = 0.26 e Å3
2250 reflectionsΔρmin = 0.21 e Å3
198 parameters
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(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
O10.2512 (2)0.37241 (12)0.15703 (13)0.0503 (4)
O20.30716 (18)0.18041 (12)0.02663 (12)0.0425 (3)
H2A0.39410.24170.01710.064*
O30.02042 (17)0.19127 (11)0.32664 (11)0.0367 (3)
H3A0.09390.12800.37520.055*
O40.04479 (18)0.00249 (11)0.19387 (12)0.0397 (3)
O50.45749 (18)0.16978 (11)0.32184 (11)0.0388 (3)
O60.55016 (18)0.01715 (11)0.20116 (11)0.0390 (3)
H6A0.61400.04560.14880.058*
O70.24706 (17)0.01413 (12)0.51304 (11)0.0377 (3)
O80.28745 (19)0.20154 (12)0.36944 (12)0.0433 (3)
O90.62884 (18)0.32827 (13)0.11797 (12)0.0400 (3)
H70.653 (3)0.290 (2)0.201 (2)0.049 (5)*
H80.663 (4)0.415 (3)0.129 (2)0.067 (7)*
O100.19735 (19)0.15999 (14)0.97140 (12)0.0391 (3)
H90.156 (3)0.099 (2)1.038 (2)0.055 (6)*
H100.238 (4)0.214 (3)1.014 (2)0.066 (7)*
N10.2595 (2)0.70956 (15)0.57175 (16)0.0450 (4)
H10.28130.78500.52360.054*
C20.2537 (3)0.5940 (2)0.50914 (18)0.0459 (4)
H20.27370.59550.41550.055*
C30.2181 (3)0.47385 (18)0.58428 (19)0.0445 (4)
H30.21250.39290.54210.053*
C40.1909 (3)0.47313 (19)0.72162 (19)0.0463 (4)
H40.16820.39130.77350.056*
C50.1972 (3)0.5944 (2)0.78308 (19)0.0516 (5)
H50.17740.59580.87660.062*
C60.2332 (3)0.71304 (18)0.7038 (2)0.0477 (5)
H60.23900.79560.74330.057*
C70.2200 (2)0.24363 (15)0.13065 (15)0.0303 (3)
C80.0676 (2)0.13161 (15)0.22227 (14)0.0279 (3)
C90.4514 (2)0.04164 (15)0.30302 (14)0.0278 (3)
C100.3170 (2)0.07087 (15)0.40268 (14)0.0292 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0652 (8)0.0209 (6)0.0537 (8)0.0061 (5)0.0134 (6)0.0043 (5)
O20.0475 (7)0.0294 (6)0.0386 (7)0.0038 (5)0.0145 (5)0.0011 (5)
O30.0438 (6)0.0246 (6)0.0352 (6)0.0071 (5)0.0088 (5)0.0023 (4)
O40.0452 (7)0.0209 (6)0.0448 (7)0.0047 (5)0.0080 (5)0.0009 (5)
O50.0478 (7)0.0222 (6)0.0420 (6)0.0079 (5)0.0026 (5)0.0018 (4)
O60.0501 (7)0.0262 (6)0.0338 (6)0.0093 (5)0.0117 (5)0.0041 (4)
O70.0468 (7)0.0282 (6)0.0321 (6)0.0091 (5)0.0079 (5)0.0006 (4)
O80.0620 (8)0.0222 (6)0.0376 (6)0.0077 (5)0.0087 (5)0.0027 (4)
O90.0520 (7)0.0238 (6)0.0367 (7)0.0045 (5)0.0059 (5)0.0036 (5)
O100.0486 (7)0.0346 (7)0.0337 (6)0.0142 (5)0.0001 (5)0.0022 (5)
N10.0466 (8)0.0280 (7)0.0604 (10)0.0131 (6)0.0123 (7)0.0146 (6)
C20.0516 (10)0.0442 (10)0.0412 (10)0.0108 (8)0.0110 (8)0.0038 (7)
C30.0506 (10)0.0288 (9)0.0571 (11)0.0116 (7)0.0126 (8)0.0050 (7)
C40.0538 (10)0.0319 (9)0.0539 (11)0.0187 (8)0.0048 (8)0.0091 (7)
C50.0647 (12)0.0486 (11)0.0412 (10)0.0180 (9)0.0009 (8)0.0048 (8)
C60.0513 (10)0.0256 (9)0.0668 (13)0.0085 (7)0.0093 (9)0.0093 (8)
C70.0341 (8)0.0240 (8)0.0318 (8)0.0073 (6)0.0022 (6)0.0024 (6)
C80.0300 (7)0.0246 (7)0.0288 (7)0.0088 (6)0.0017 (6)0.0002 (6)
C90.0314 (7)0.0244 (7)0.0277 (7)0.0086 (6)0.0036 (6)0.0003 (6)
C100.0330 (8)0.0254 (8)0.0287 (7)0.0090 (6)0.0009 (6)0.0021 (6)
Geometric parameters (Å, º) top
O1—C71.201 (2)N1—C61.315 (2)
O2—C71.294 (2)N1—C21.336 (2)
O2—H2A0.8200N1—H10.8600
O3—C81.283 (2)C2—C31.365 (3)
O3—H3A0.8200C2—H20.9300
O4—C81.212 (2)C3—C41.365 (3)
O5—C91.209 (2)C3—H30.9300
O6—C91.297 (2)C4—C51.380 (3)
O6—H6A0.8200C4—H40.9300
O7—C101.264 (2)C5—C61.373 (3)
O8—C101.231 (2)C5—H50.9300
O9—H70.88 (2)C6—H60.9300
O9—H80.81 (3)C7—C81.539 (2)
O10—H90.90 (2)C9—C101.544 (2)
O10—H100.83 (3)
C7—O2—H2A109.5C6—C5—H5120.6
C8—O3—H3A109.5C4—C5—H5120.6
C9—O6—H6A109.5N1—C6—C5119.76 (16)
H7—O9—H8103 (2)N1—C6—H6120.1
H9—O10—H10102 (2)C5—C6—H6120.1
C6—N1—C2122.9 (2)O1—C7—O2126.3 (1)
C6—N1—H1118.6O1—C7—C8122.4 (1)
C2—N1—H1118.6O2—C7—C8111.3 (1)
N1—C2—C3119.2 (2)O4—C8—O3127.0 (1)
N1—C2—H2120.4O4—C8—C7120.3 (1)
C3—C2—H2120.4O3—C8—C7112.7 (1)
C2—C3—C4119.60 (16)O5—C9—O6125.8 (1)
C2—C3—H3120.2O5—C9—C10121.3 (1)
C4—C3—H3120.2O6—C9—C10112.8 (1)
C3—C4—C5119.70 (16)O8—C10—O7127.0 (1)
C3—C4—H4120.1O8—C10—C9119.4 (1)
C5—C4—H4120.1O7—C10—C9113.6 (1)
C6—C5—C4118.82 (18)
C6—N1—C2—C30.3 (3)O2—C7—C8—O41.3 (2)
N1—C2—C3—C40.6 (3)O1—C7—C8—O30.5 (2)
C2—C3—C4—C50.8 (3)O2—C7—C8—O3179.7 (1)
C3—C4—C5—C60.7 (3)O5—C9—C10—O8167.5 (2)
C2—N1—C6—C50.3 (3)O6—C9—C10—O811.9 (2)
C4—C5—C6—N10.5 (3)O5—C9—C10—O712.1 (2)
O1—C7—C8—O4178.0 (2)O6—C9—C10—O7168.5 (1)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2A···O90.821.802.592 (3)161
O3—H3A···O7i0.821.672.486 (2)174
O6—H6A···O10ii0.821.822.626 (2)166
O9—H7···O8iii0.88 (2)1.85 (2)2.735 (2)176 (2)
O9—H8···O1iv0.81 (3)1.99 (3)2.802 (2)179 (3)
O10—H9···O4v0.90 (2)1.92 (2)2.811 (2)171 (2)
O10—H10···O9ii0.83 (3)2.07 (3)2.897 (2)173 (2)
N1—H1···O7vi0.862.132.889 (2)147
N1—H1···O5vi0.862.252.934 (2)137
Symmetry codes: (i) x, y, z+1; (ii) x+1, y, z+1; (iii) x+1, y, z; (iv) x+1, y1, z; (v) x, y, z+1; (vi) x, y+1, z.

Experimental details

Crystal data
Chemical formulaC5H6N+·C2H2O4·C2HO4·2H2O
Mr295.20
Crystal system, space groupTriclinic, P1
Temperature (K)293
a, b, c (Å)6.992 (7), 9.539 (2), 10.098 (2)
α, β, γ (°)84.36 (2), 79.54 (4), 74.71 (6)
V3)638.0 (7)
Z2
Radiation typeMo Kα
µ (mm1)0.14
Crystal size (mm)0.40 × 0.35 × 0.17
Data collection
DiffractometerEnraf-Nonius CAD-4
diffractometer
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.948, 0.971
No. of measured, independent and
observed [I > 2s(I)] reflections
2451, 2250, 1946
Rint0.006
(sin θ/λ)max1)0.594
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.037, 0.113, 1.09
No. of reflections2250
No. of parameters198
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.26, 0.21

Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1999), SHELXL97.

Selected geometric parameters (Å, º) top
O1—C71.201 (2)O8—C101.231 (2)
O2—C71.294 (2)N1—C61.315 (2)
O3—C81.283 (2)N1—C21.336 (2)
O4—C81.212 (2)C2—C31.365 (3)
O5—C91.209 (2)C3—C41.365 (3)
O6—C91.297 (2)C4—C51.380 (3)
O7—C101.264 (2)
C6—N1—C2122.9 (2)O3—C8—C7112.7 (1)
N1—C2—C3119.2 (2)O5—C9—O6125.8 (1)
O1—C7—O2126.3 (1)O5—C9—C10121.3 (1)
O1—C7—C8122.4 (1)O6—C9—C10112.8 (1)
O2—C7—C8111.3 (1)O8—C10—O7127.0 (1)
O4—C8—O3127.0 (1)O8—C10—C9119.4 (1)
O4—C8—C7120.3 (1)O7—C10—C9113.6 (1)
C6—N1—C2—C30.3 (3)O2—C7—C8—O3179.7 (1)
N1—C2—C3—C40.6 (3)O5—C9—C10—O8167.5 (2)
O1—C7—C8—O4178.0 (2)O6—C9—C10—O811.9 (2)
O2—C7—C8—O41.3 (2)O5—C9—C10—O712.1 (2)
O1—C7—C8—O30.5 (2)O6—C9—C10—O7168.5 (1)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O2—H2A···O90.821.802.592 (3)161
O3—H3A···O7i0.821.672.486 (2)174
O6—H6A···O10ii0.821.822.626 (2)166
O9—H7···O8iii0.88 (2)1.85 (2)2.735 (2)176 (2)
O9—H8···O1iv0.81 (3)1.99 (3)2.802 (2)179 (3)
O10—H9···O4v0.90 (2)1.92 (2)2.811 (2)171 (2)
O10—H10···O9ii0.83 (3)2.07 (3)2.897 (2)173 (2)
N1—H1···O7vi0.862.132.889 (2)147
N1—H1···O5vi0.862.252.934 (2)137
Symmetry codes: (i) x, y, z+1; (ii) x+1, y, z+1; (iii) x+1, y, z; (iv) x+1, y1, z; (v) x, y, z+1; (vi) x, y+1, z.
 

Follow Acta Cryst. E
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds