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In the title compound, 2C4H8NO4+·C2O42−, the amino acid mol­ecule exists in the cationic form and the oxalic acid mol­ecule exists as a doubly charged oxalate anion which lies across an inversion centre in the crystal. The screw-related cations are linked by N—H...O hydrogen bonds to form infinite columns parallel to the b axis. The columns are interlinked by anions through O—H...O and N—H...O hydrogen bonds, forming a three-dimensional network.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536802023334/ci6191sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S1600536802023334/ci6191Isup2.hkl
Contains datablock I

CCDC reference: 204668

Key indicators

  • Single-crystal X-ray study
  • T = 293 K
  • Mean [sigma](C-C) = 0.003 Å
  • R factor = 0.047
  • wR factor = 0.193
  • Data-to-parameter ratio = 19.6

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(5) - C(5)a = 1.54 Ang.
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check

Comment top

Aspartic acid, considered a non-essential amino acid, plays a paramount role in metabolism during construction of other amino acids and biochemicals in the citric acid cycle. The present study, which reports the crystal structure of a complex of DL-aspartic acid with oxalic acid, (I), forms part of a series of X-ray investigations being carried out in our laboratory on amino–carboxylic acid complexes. Precise X-ray investigations on these complexes have revealed interesting and useful data regarding the ionization states of individual molecules, their stoichiometry and intermolecular aggregation patterns. Recently, the crystal structures of glycinium oxalate (Subha Nandhini et al., 2001a), L-and DL-alaninium oxalate (Subha Nandhini et al., 2001b,c), DL-threoninium oxalate (Subha Nandhini et al., 2001), β-alaninium oxalate (Krishnakumar et al., 2002) and bis(serinium) oxalate dihydrate (Alagar et al., 2002) were reported from our laboratory.

Fig. 1 shows the molecular structure of (I) with the atom-numbering scheme. The amino acid molecule exists in the expected cationic form with a positively charged amino group and protonated carboxylic acid groups. Interestingly, the complexes of racemic (DL–) amino acids with oxalic acids reported so far have crystallized in monoclinic space group P21/c, with the exception of the DL-lysine complex (Venkatraman et al., 1997) in P1 and the β-alanine complex in C2/c, and the values of their shortest cell dimensions lie around 5.5 Å. The main chain torsion angle (C1—C2—C3—C4) has a value of −66.7 (3)° and is significantly different from the value of 174.2 (2)° observed in the neutron diffraction study of DL-aspartic acid (Sequeira et al., 1989). The oxalic acid molecule exists as a double negatively charged oxalate anion (uncommon in similar crystal structures) and lies across the inversion centre in the crystal and its charge contribution to the asymmetric unit is −1. Thus, one amino acid cation and half an oxalate anion are present in the asymmetric unit, leading to a 2:1 stoichiometry.

Fig. 2 shows the packing of the molecules of (I), viewed down the b axis. Each of the carboxylate O atoms of the oxalate anion participates in the hydrogen bonding as an acceptor of two hydrogen bonds. The screw-related aspartic acid cations are linked by N—H···O hydrogen bonds to form infinite column-like structures parallel to the b axis. These molecular columns are interlinked by oxalate anions through O—H···O and N—H···O hydrogen bonds, forming a three-dimensional network (Fig. 2). The aggregation of individual molecules observed in the present structure differs distinctly from other amino—carboxylic acid structures and has some resemblance to oxalic acid complex with serine.

Experimental top

Colorless needle-shaped single crystals of (I) were grown from a saturated aqueous solution containing DL-aspartic acid and oxalic acid in a 1:1 stoichiometric ratio.

Refinement top

All H atoms were generated geometrically and were allowed to ride on their respective parent atoms with SHELXL97 (Sheldrick, 1997) defaults for bond lengths and displacement parameters. Rotating-group refinement was used for the –OH groups.

Computing details top

Data collection: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1996); cell refinement: MSC/AFC Diffractometer Control Software; data reduction: TEXSAN for Windows (Molecular Structure Corporation, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003); 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 50% probability displacement ellipsoids.
[Figure 2] Fig. 2. The packing of the molecules of (I), viewed down the b axis.
(I) top
Crystal data top
C4H8NO4+·0.5C2O42F(000) = 372
Mr = 178.12Dx = 1.600 Mg m3
Dm = 1.61 Mg m3
Dm measured by flotation in a mixture of xylene and bromoform
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ynCell parameters from 25 reflections
a = 7.387 (1) Åθ = 39.3–39.8°
b = 5.477 (1) ŵ = 0.15 mm1
c = 18.522 (3) ÅT = 293 K
β = 99.36 (1)°Needle, colourless
V = 739.4 (2) Å30.24 × 0.22 × 0.12 mm
Z = 4
Data collection top
Rigaku AFC-5R
diffractometer
1191 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.050
Graphite monochromatorθmax = 30.1°, θmin = 2.8°
ω–2θ scansh = 010
Absorption correction: ψ scan
(North et al., 1968)
k = 07
Tmin = 0.89, Tmax = 0.99l = 2625
2321 measured reflections3 standard reflections every 150 reflections
2171 independent reflections intensity decay: none
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)] = 0.047Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.193H-atom parameters constrained
S = 1.04 w = 1/[σ2(Fo2) + (0.0959P)2 + 0.3684P]
where P = (Fo2 + 2Fc2)/3
2171 reflections(Δ/σ)max < 0.001
111 parametersΔρmax = 0.38 e Å3
0 restraintsΔρmin = 0.36 e Å3
Crystal data top
C4H8NO4+·0.5C2O42V = 739.4 (2) Å3
Mr = 178.12Z = 4
Monoclinic, P21/nMo Kα radiation
a = 7.387 (1) ŵ = 0.15 mm1
b = 5.477 (1) ÅT = 293 K
c = 18.522 (3) Å0.24 × 0.22 × 0.12 mm
β = 99.36 (1)°
Data collection top
Rigaku AFC-5R
diffractometer
1191 reflections with I > 2σ(I)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.050
Tmin = 0.89, Tmax = 0.993 standard reflections every 150 reflections
2321 measured reflections intensity decay: none
2171 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0470 restraints
wR(F2) = 0.193H-atom parameters constrained
S = 1.04Δρmax = 0.38 e Å3
2171 reflectionsΔρmin = 0.36 e Å3
111 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
O10.2183 (3)0.8831 (4)0.93073 (11)0.0458 (5)
H10.25701.00790.95230.069*
O20.0508 (3)1.0786 (3)0.91478 (11)0.0442 (5)
O30.0634 (4)0.5955 (4)0.69742 (10)0.0547 (6)
H30.04210.68430.66140.082*
O40.0869 (3)0.8853 (4)0.74711 (10)0.0480 (5)
O50.4943 (3)0.6218 (4)0.08590 (9)0.0431 (5)
O60.6566 (3)0.7363 (4)0.00140 (10)0.0489 (6)
N10.2429 (3)0.6923 (5)0.86635 (11)0.0426 (6)
H1A0.29610.55250.85020.064*
H1B0.26760.80620.83190.064*
H1C0.28590.73970.90630.064*
C10.0416 (3)0.8988 (4)0.91156 (12)0.0313 (5)
C20.0412 (4)0.6565 (4)0.88420 (12)0.0314 (5)
H20.01800.54030.92490.038*
C30.0402 (4)0.5495 (4)0.82089 (12)0.0344 (5)
H3A0.17220.53800.83510.041*
H3B0.00690.38530.81140.041*
C40.0010 (3)0.6954 (4)0.75167 (12)0.0324 (5)
C50.5432 (3)0.6033 (4)0.02542 (12)0.0301 (5)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0421 (10)0.0444 (11)0.0502 (11)0.0088 (8)0.0051 (9)0.0195 (9)
O20.0526 (11)0.0283 (9)0.0518 (11)0.0028 (8)0.0087 (9)0.0013 (8)
O30.0939 (17)0.0446 (11)0.0312 (10)0.0182 (11)0.0269 (10)0.0083 (8)
O40.0622 (13)0.0525 (12)0.0327 (10)0.0206 (10)0.0173 (9)0.0153 (8)
O50.0590 (12)0.0467 (11)0.0282 (8)0.0185 (9)0.0206 (8)0.0161 (8)
O60.0573 (12)0.0558 (13)0.0393 (10)0.0347 (10)0.0246 (9)0.0213 (9)
N10.0475 (13)0.0549 (14)0.0278 (10)0.0213 (11)0.0135 (9)0.0079 (9)
C10.0426 (13)0.0273 (11)0.0250 (10)0.0091 (10)0.0083 (9)0.0008 (8)
C20.0457 (13)0.0274 (11)0.0207 (9)0.0107 (10)0.0047 (9)0.0011 (8)
C30.0548 (14)0.0260 (11)0.0219 (10)0.0016 (10)0.0051 (9)0.0023 (8)
C40.0401 (13)0.0331 (12)0.0253 (10)0.0040 (10)0.0089 (9)0.0035 (9)
C50.0299 (11)0.0346 (12)0.0267 (10)0.0072 (9)0.0077 (8)0.0080 (9)
Geometric parameters (Å, º) top
O1—C11.299 (3)N1—H1B0.89
O1—H10.82N1—H1C0.89
O2—C11.205 (3)C1—C21.514 (3)
O3—C41.300 (3)C2—C31.520 (3)
O3—H30.82C2—H20.98
O4—C41.214 (3)C3—C41.499 (3)
O5—C51.236 (3)C3—H3A0.97
O6—C51.246 (3)C3—H3B0.97
N1—C21.486 (3)C5—C5i1.542 (4)
N1—H1A0.89
C1—O1—H1109.5C1—C2—H2107.5
C4—O3—H3109.5C3—C2—H2107.5
C2—N1—H1A109.5C4—C3—C2113.8 (2)
C2—N1—H1B109.5C4—C3—H3A108.8
H1A—N1—H1B109.5C2—C3—H3A108.8
C2—N1—H1C109.5C4—C3—H3B108.8
H1A—N1—H1C109.5C2—C3—H3B108.8
H1B—N1—H1C109.5H3A—C3—H3B107.7
O2—C1—O1126.4 (2)O4—C4—O3124.0 (2)
O2—C1—C2122.1 (2)O4—C4—C3123.2 (2)
O1—C1—C2111.5 (2)O3—C4—C3112.8 (2)
N1—C2—C1107.1 (2)O5—C5—O6126.0 (2)
N1—C2—C3112.81 (19)O5—C5—C5i117.4 (2)
C1—C2—C3114.0 (2)O6—C5—C5i116.5 (2)
N1—C2—H2107.5
O2—C1—C2—N11.3 (3)N1—C2—C3—C455.8 (3)
O1—C1—C2—N1178.05 (19)C1—C2—C3—C466.7 (3)
O2—C1—C2—C3124.2 (3)C2—C3—C4—O42.0 (4)
O1—C1—C2—C356.4 (3)C2—C3—C4—O3177.3 (2)
Symmetry code: (i) x+1, y+1, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O6ii0.821.712.530 (3)178
O3—H3···O5iii0.821.752.565 (2)179
N1—H1A···O4iv0.892.082.822 (3)140
N1—H1B···O40.892.262.855 (3)124
N1—H1C···O6v0.891.882.733 (3)160
Symmetry codes: (ii) x+1, y+2, z+1; (iii) x1/2, y+3/2, z+1/2; (iv) x1/2, y1/2, z+3/2; (v) x1, y, z+1.

Experimental details

Crystal data
Chemical formulaC4H8NO4+·0.5C2O42
Mr178.12
Crystal system, space groupMonoclinic, P21/n
Temperature (K)293
a, b, c (Å)7.387 (1), 5.477 (1), 18.522 (3)
β (°) 99.36 (1)
V3)739.4 (2)
Z4
Radiation typeMo Kα
µ (mm1)0.15
Crystal size (mm)0.24 × 0.22 × 0.12
Data collection
DiffractometerRigaku AFC-5R
diffractometer
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.89, 0.99
No. of measured, independent and
observed [I > 2σ(I)] reflections
2321, 2171, 1191
Rint0.050
(sin θ/λ)max1)0.705
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.047, 0.193, 1.04
No. of reflections2171
No. of parameters111
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.38, 0.36

Computer programs: MSC/AFC Diffractometer Control Software (Molecular Structure Corporation, 1996), MSC/AFC Diffractometer Control Software, TEXSAN for Windows (Molecular Structure Corporation, 1997), SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 2003), SHELXL97.

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O6i0.821.712.530 (3)178
O3—H3···O5ii0.821.752.565 (2)179
N1—H1A···O4iii0.892.082.822 (3)140
N1—H1B···O40.892.262.855 (3)124
N1—H1C···O6iv0.891.882.733 (3)160
Symmetry codes: (i) x+1, y+2, z+1; (ii) x1/2, y+3/2, z+1/2; (iii) x1/2, y1/2, z+3/2; (iv) x1, y, z+1.
 

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