Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536801012193/ci6046sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536801012193/ci6046Isup2.hkl |
CCDC reference: 170923
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean (C-C) = 0.004 Å
- R factor = 0.053
- wR factor = 0.175
- Data-to-parameter ratio = 9.4
checkCIF results
No syntax errors found ADDSYM reports no extra symmetry
Alert Level C:
REFLT_03 From the CIF: _diffrn_reflns_theta_max 72.10 From the CIF: _reflns_number_total 1605 TEST2: Reflns within _diffrn_reflns_theta_max Count of symmetry unique reflns 1716 Completeness (_total/calc) 93.53% Alert C: < 95% complete
0 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
1 Alert Level C = Please check
Crystals of (I) were grown as fine transparent needles from a saturated aqueous solution containing DL-threonine and oxalic acid in stoichiometric ratio. The density was determined by flotation method using a liquid mixture of xylene and bromoform.
The H atoms were placed at calculated positions and were allowed to ride on their respective parent atoms with HFIX instructions using SHELXL97 (Sheldrick, 1997) defaults.
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.
Fig. 1. The molecular structure of (I) with atom-numbering scheme and 50% probability displacement ellipsoids. | |
Fig. 2. Packing diagram of the molecules of (I) viewed down the b axis. |
C4H10NO3+·C2HO4− | F(000) = 440 |
Mr = 209.16 | Dx = 1.590 Mg m−3 Dm = 1.61 (2) Mg m−3 Dm measured by flotation |
Monoclinic, P21/n | Cu Kα radiation, λ = 1.54178 Å |
a = 8.325 (5) Å | Cell parameters from 25 reflections |
b = 10.957 (4) Å | θ = 9–29° |
c = 10.363 (4) Å | µ = 1.30 mm−1 |
β = 112.39 (5)° | T = 293 K |
V = 874.0 (7) Å3 | Needle, colourless |
Z = 4 | 0.35 × 0.21 × 0.15 mm |
Enraf-Nonius CAD-4 diffractometer | 1252 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.000 |
Graphite monochromator | θmax = 72.1°, θmin = 5.8° |
ω–2θ scans | h = −10→9 |
Absorption correction: ψ scan (North et al., 1968) | k = 0→13 |
Tmin = 0.76, Tmax = 0.82 | l = 0→12 |
1605 measured reflections | 2 standard reflections every 60 min |
1605 independent reflections | intensity decay: <2% |
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)] = 0.053 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.175 | H-atom parameters constrained |
S = 1.10 | w = 1/[σ2(Fo2) + (0.1106P)2 + 0.3459P] where P = (Fo2 + 2Fc2)/3 |
1605 reflections | (Δ/σ)max < 0.001 |
171 parameters | Δρmax = 0.36 e Å−3 |
0 restraints | Δρmin = −0.30 e Å−3 |
C4H10NO3+·C2HO4− | V = 874.0 (7) Å3 |
Mr = 209.16 | Z = 4 |
Monoclinic, P21/n | Cu Kα radiation |
a = 8.325 (5) Å | µ = 1.30 mm−1 |
b = 10.957 (4) Å | T = 293 K |
c = 10.363 (4) Å | 0.35 × 0.21 × 0.15 mm |
β = 112.39 (5)° |
Enraf-Nonius CAD-4 diffractometer | 1252 reflections with I > 2σ(I) |
Absorption correction: ψ scan (North et al., 1968) | Rint = 0.000 |
Tmin = 0.76, Tmax = 0.82 | 2 standard reflections every 60 min |
1605 measured reflections | intensity decay: <2% |
1605 independent reflections |
R[F2 > 2σ(F2)] = 0.053 | 0 restraints |
wR(F2) = 0.175 | H-atom parameters constrained |
S = 1.10 | Δρmax = 0.36 e Å−3 |
1605 reflections | Δρmin = −0.30 e Å−3 |
171 parameters |
Experimental. The low completeness of data is due to very poor diffraction by the crystal at high angles. |
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. |
x | y | z | Uiso*/Ueq | ||
O1 | 0.1063 (3) | 0.88436 (19) | 0.5225 (2) | 0.0431 (6) | |
O2 | 0.2280 (3) | 1.0062 (2) | 0.4105 (2) | 0.0458 (6) | |
H2 | 0.1416 | 0.9881 | 0.3419 | 0.069* | |
O3 | 0.2232 (3) | 1.18732 (18) | 0.6792 (2) | 0.0425 (6) | |
H3 | 0.1379 | 1.1663 | 0.6113 | 0.064* | |
O4 | 0.3107 (3) | 0.72656 (19) | 0.4016 (2) | 0.0432 (6) | |
H4 | 0.2165 | 0.7324 | 0.3362 | 0.065* | |
O5 | 0.1712 (3) | 0.5840 (2) | 0.4736 (2) | 0.0449 (6) | |
O6 | 0.5377 (3) | 0.73866 (19) | 0.6711 (2) | 0.0452 (6) | |
O7 | 0.4884 (3) | 0.53842 (18) | 0.6839 (2) | 0.0452 (6) | |
N1 | 0.3322 (3) | 0.9414 (2) | 0.7730 (3) | 0.0371 (6) | |
H1A | 0.4164 | 0.9653 | 0.8520 | 0.056* | |
H1B | 0.3342 | 0.8605 | 0.7662 | 0.056* | |
H1C | 0.2299 | 0.9648 | 0.7730 | 0.056* | |
C1 | 0.2180 (4) | 0.9568 (2) | 0.5210 (3) | 0.0364 (7) | |
C2 | 0.3595 (4) | 0.9977 (2) | 0.6520 (3) | 0.0343 (7) | |
H2A | 0.4693 | 0.9662 | 0.6512 | 0.041* | |
C3 | 0.3769 (4) | 1.1372 (2) | 0.6686 (3) | 0.0346 (7) | |
H3A | 0.3912 | 1.1719 | 0.5865 | 0.041* | |
C4 | 0.5268 (4) | 1.1768 (3) | 0.7975 (3) | 0.0434 (8) | |
H4A | 0.5310 | 1.2643 | 0.8020 | 0.065* | |
H4B | 0.6333 | 1.1463 | 0.7942 | 0.065* | |
H4C | 0.5120 | 1.1451 | 0.8786 | 0.065* | |
C5 | 0.2987 (4) | 0.6477 (2) | 0.4915 (3) | 0.0355 (7) | |
C6 | 0.4580 (4) | 0.6422 (2) | 0.6273 (3) | 0.0361 (7) |
U11 | U22 | U33 | U12 | U13 | U23 | |
O1 | 0.0492 (13) | 0.0320 (11) | 0.0506 (13) | −0.0079 (9) | 0.0219 (11) | −0.0050 (9) |
O2 | 0.0612 (15) | 0.0328 (11) | 0.0433 (13) | −0.0107 (9) | 0.0197 (11) | −0.0012 (9) |
O3 | 0.0505 (13) | 0.0236 (10) | 0.0548 (14) | 0.0018 (8) | 0.0215 (11) | −0.0051 (9) |
O4 | 0.0505 (13) | 0.0381 (11) | 0.0424 (12) | −0.0014 (9) | 0.0191 (11) | 0.0100 (9) |
O5 | 0.0485 (13) | 0.0394 (12) | 0.0429 (13) | −0.0120 (9) | 0.0132 (10) | 0.0015 (9) |
O6 | 0.0524 (13) | 0.0329 (11) | 0.0472 (13) | −0.0083 (9) | 0.0156 (11) | −0.0039 (9) |
O7 | 0.0599 (14) | 0.0294 (10) | 0.0370 (13) | 0.0035 (9) | 0.0081 (11) | 0.0040 (8) |
N1 | 0.0504 (15) | 0.0194 (10) | 0.0425 (14) | −0.0005 (9) | 0.0189 (12) | −0.0003 (9) |
C1 | 0.0449 (16) | 0.0213 (12) | 0.0464 (17) | 0.0026 (11) | 0.0211 (14) | −0.0039 (11) |
C2 | 0.0424 (15) | 0.0210 (12) | 0.0432 (17) | −0.0013 (10) | 0.0205 (14) | −0.0031 (10) |
C3 | 0.0413 (15) | 0.0234 (13) | 0.0410 (16) | −0.0049 (10) | 0.0179 (14) | −0.0027 (10) |
C4 | 0.0541 (19) | 0.0305 (14) | 0.0495 (19) | −0.0095 (13) | 0.0242 (16) | −0.0053 (13) |
C5 | 0.0495 (16) | 0.0229 (12) | 0.0386 (16) | 0.0021 (11) | 0.0219 (14) | 0.0004 (10) |
C6 | 0.0460 (16) | 0.0275 (13) | 0.0403 (17) | 0.0007 (11) | 0.0228 (14) | −0.0015 (11) |
O1—C1 | 1.227 (4) | N1—H1B | 0.8900 |
O2—C1 | 1.298 (4) | N1—H1C | 0.8900 |
O2—H2 | 0.8200 | C1—C2 | 1.488 (4) |
O3—C3 | 1.434 (3) | C2—C3 | 1.539 (4) |
O3—H3 | 0.8200 | C2—H2A | 0.9800 |
O4—C5 | 1.302 (3) | C3—C4 | 1.504 (5) |
O4—H4 | 0.8200 | C3—H3A | 0.9800 |
O5—C5 | 1.224 (4) | C4—H4A | 0.9600 |
O6—C6 | 1.239 (4) | C4—H4B | 0.9600 |
O7—C6 | 1.260 (3) | C4—H4C | 0.9600 |
N1—C2 | 1.490 (4) | C5—C6 | 1.523 (5) |
N1—H1A | 0.8900 | ||
C1—O2—H2 | 109.5 | O3—C3—C4 | 106.5 (2) |
C3—O3—H3 | 109.5 | O3—C3—C2 | 109.9 (2) |
C5—O4—H4 | 109.5 | C4—C3—C2 | 113.4 (3) |
C2—N1—H1A | 109.5 | O3—C3—H3A | 109.0 |
C2—N1—H1B | 109.5 | C4—C3—H3A | 109.0 |
H1A—N1—H1B | 109.5 | C2—C3—H3A | 109.0 |
C2—N1—H1C | 109.5 | C3—C4—H4A | 109.5 |
H1A—N1—H1C | 109.5 | C3—C4—H4B | 109.5 |
H1B—N1—H1C | 109.5 | H4A—C4—H4B | 109.5 |
O1—C1—O2 | 125.8 (3) | C3—C4—H4C | 109.5 |
O1—C1—C2 | 121.6 (3) | H4A—C4—H4C | 109.5 |
O2—C1—C2 | 112.6 (2) | H4B—C4—H4C | 109.5 |
C1—C2—N1 | 108.8 (2) | O5—C5—O4 | 124.6 (3) |
C1—C2—C3 | 114.2 (2) | O5—C5—C6 | 121.1 (3) |
N1—C2—C3 | 110.8 (2) | O4—C5—C6 | 114.2 (2) |
C1—C2—H2A | 107.6 | O6—C6—O7 | 127.9 (3) |
N1—C2—H2A | 107.6 | O6—C6—C5 | 117.4 (3) |
C3—C2—H2A | 107.6 | O7—C6—C5 | 114.6 (3) |
O1—C1—C2—N1 | −2.5 (4) | C1—C2—C3—C4 | −176.7 (2) |
O2—C1—C2—N1 | 177.2 (2) | N1—C2—C3—C4 | 60.1 (3) |
O1—C1—C2—C3 | −126.8 (3) | O5—C5—C6—O6 | −144.2 (3) |
O2—C1—C2—C3 | 52.9 (3) | O4—C5—C6—O6 | 34.3 (4) |
C1—C2—C3—O3 | 64.2 (3) | O5—C5—C6—O7 | 33.4 (4) |
N1—C2—C3—O3 | −59.0 (3) | O4—C5—C6—O7 | −148.2 (3) |
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H2···O7i | 0.82 | 1.67 | 2.483 (4) | 168 |
O3—H3···O1ii | 0.82 | 2.05 | 2.854 (4) | 165 |
O4—H4···O6i | 0.82 | 1.82 | 2.623 (4) | 167 |
N1—H1A···O5iii | 0.89 | 2.08 | 2.810 (4) | 138 |
N1—H1A···O5iv | 0.89 | 2.55 | 3.065 (3) | 118 |
N1—H1B···O6 | 0.89 | 2.63 | 3.217 (3) | 125 |
N1—H1B···O3v | 0.89 | 2.09 | 2.895 (3) | 151 |
N1—H1C···O7iv | 0.89 | 2.18 | 3.060 (4) | 168 |
C2—H2A···O6 | 0.98 | 2.55 | 3.174 (4) | 122 |
Symmetry codes: (i) x−1/2, −y+3/2, z−1/2; (ii) −x, −y+2, −z+1; (iii) x+1/2, −y+3/2, z+1/2; (iv) −x+1/2, y+1/2, −z+3/2; (v) −x+1/2, y−1/2, −z+3/2. |
Experimental details
Crystal data | |
Chemical formula | C4H10NO3+·C2HO4− |
Mr | 209.16 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 293 |
a, b, c (Å) | 8.325 (5), 10.957 (4), 10.363 (4) |
β (°) | 112.39 (5) |
V (Å3) | 874.0 (7) |
Z | 4 |
Radiation type | Cu Kα |
µ (mm−1) | 1.30 |
Crystal size (mm) | 0.35 × 0.21 × 0.15 |
Data collection | |
Diffractometer | Enraf-Nonius CAD-4 diffractometer |
Absorption correction | ψ scan (North et al., 1968) |
Tmin, Tmax | 0.76, 0.82 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1605, 1605, 1252 |
Rint | 0.000 |
(sin θ/λ)max (Å−1) | 0.617 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.053, 0.175, 1.10 |
No. of reflections | 1605 |
No. of parameters | 171 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 0.36, −0.30 |
Computer programs: CAD-4 Software (Enraf-Nonius, 1989), CAD-4 Software, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), PLATON (Spek, 1999), SHELXL97.
D—H···A | D—H | H···A | D···A | D—H···A |
O2—H2···O7i | 0.82 | 1.67 | 2.483 (4) | 168 |
O3—H3···O1ii | 0.82 | 2.05 | 2.854 (4) | 165 |
O4—H4···O6i | 0.82 | 1.82 | 2.623 (4) | 167 |
N1—H1A···O5iii | 0.89 | 2.08 | 2.810 (4) | 138 |
N1—H1A···O5iv | 0.89 | 2.55 | 3.065 (3) | 118 |
N1—H1B···O6 | 0.89 | 2.63 | 3.217 (3) | 125 |
N1—H1B···O3v | 0.89 | 2.09 | 2.895 (3) | 151 |
N1—H1C···O7iv | 0.89 | 2.18 | 3.060 (4) | 168 |
C2—H2A···O6 | 0.98 | 2.55 | 3.174 (4) | 122 |
Symmetry codes: (i) x−1/2, −y+3/2, z−1/2; (ii) −x, −y+2, −z+1; (iii) x+1/2, −y+3/2, z+1/2; (iv) −x+1/2, y+1/2, −z+3/2; (v) −x+1/2, y−1/2, −z+3/2. |
Threonine, an essential amino acid necessary to maintain nitrogen equilibrium in the adult human, is a significant constituent of many common plant and milk proteins. It does not undergo transamination and is also potentially glucogenic. X-ray (Shoemaker et al., 1950) and neutron (Ramanadham et al., 1973) diffraction investigations on the crystals of the L-isomer have already been carried out. Recently, a precise determination of the crystal structure of L-threonine at 12 K (Janczak et al., 1997) was reported. However, the crystal structure of its racemate is not yet known since, on crystallization, DL-threonine produces a racemic mixture of the crystals of D– and L– forms (Shoemaker et al., 1950). A similar phenomenon has been observed in the case of L-allothreonine (Swaminathan & Srinivasan, 1975). The present study reports the crystal structure of a complex of DL-threonine with oxalic acid.
Fig. 1 shows the molecular structure of the title compound (I) with atom numbering scheme. The amino acid exists in the cationic form with a positively charged amino group and a protonated carboxylic acid group. The torsion angles Ψ1 (N1—C2—C1—O1) and Ψ2 (N1—C2—C1—O2) describing the torsions of the two C—O bonds around C1—C2 are -2.5 (4) and 177.2 (2)°, indicating that the carboxylic acid and the amino group lie in the same plane. Interestingly, L-threoninium cations exhibit a significant deviation from this planarity in the crystal structures of bis(L-threoninium) sulfate monohydrate (Sridhar et al., 2001), O-phospho-L-threonine and O-phospho-DL-threonine (Maniukiewicz et al., 1996). The conformation of the molecule about the Cα–Cβ bond corresponds to the staggered ethane type. The sidechain conformation is described by the torsion angles Ξ11, Ξ12 and Ξ13 of -59.0 (3), 60.1 (3) and -178°, respectively.
The oxalic acid molecule exists as a semi-oxalate anion. Unlike in the crystal structures of other similar complexes, in the present case the semi-oxalate ion deviates far from planarity as the carboxyl groups are rotated by 33.9 (3)° with respect to the C5—C6 bond. The C—O distances in the carboxylate group of the semi-oxalate anion are unequal, presumably due to the participation of one atom (O6) in one hydrogen bond (O–H···O) and the other (O7) in two hydrogen bonds (O–H···O and N–H···O). Usually, the semi-oxalate ion has a tendency to be planar and the observed departure from planarity seems to be necessitated by requirements for optimum packing within the lattice.
Fig. 2 shows the packing of molecules of (I) viewed down the b axis. The semi-oxalate ions form hydrogen-bonded strings generated by the glide plane as in DL-arginine semi-oxalate complex (Chandra et al., 1998). The threoninium and semi-oxalate ions are tied together by an infinite network of hydrogen bonds between them. The O3 (Oγ) atom participates in the hydrogen-bonding network both as an acceptor and as a donor mediating the amino acid–amino acid interactions. No classic head-to-tail hydrogen bonds are observed in the crystal structure. The molecules aggregate into infinite parallel layers which extend along diagonal of the ac plane. These layers have no hydrogen-bonded interactions among them apart from van der Waals interactions.