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Two chiral counterparts (L- and D-cysteinium cations related by an inversion centre) are present in the structure of the title compound, C3H8NO2S+·C2HO4, with a 1:1 cation–anion ratio. The carb­oxy group of the cysteinium cation is protonated in the trans position relative to the amino group. The crystal structure is built up of double layers, in which dimers of cysteinium cations are connected to each other not directly, but via bridges of twisted semioxalate anions linked to each other via O—H...O hydrogen bonds forming infinite chains. An inter­esting feature of the crystal structure is the absence of either S—H...S or S—H...O hydrogen bonds.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010901350X/gz3159sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010901350X/gz3159Isup2.hkl
Contains datablock I

CCDC reference: 735134

Comment top

A comparison of the crystals of amino acid salts with those of individual amino acids provides valuable information on the structure–property relationships in these systems, which are widely used as biomimetics, drugs and molecular materials. Cysteine is known for its conformational lability both in pure polymorphs and in salts. The conformational changes involving the –CH2SH side chains are provoked easily by variations in temperature (Minkov, Chesalov et al., 2008; Minkov et al., 2009; Kolesov et al., 2008) and pressure (Minkov, Krylov et al., 2008), or by changing the crystalline environment in different polymorphs (Harding & Long, 1968; Görbitz & Dalhus, 1996; Minkov et al., 2009), and in different salts (Shan & Huang, 1999; Fujii et al., 2005; Drebushchak et al., 2008; Minkov & Boldyreva, 2008).

Recently, the crystal structures of the two salts formed by cysteine and oxalic acid have been described: bis-(DL-cysteinium) oxalate (Drebushchak et al., 2008), (I), and L-cysteinium semioxalate (Minkov & Boldyreva, 2008), (II). The present contribution reports the structure of a new salt from the same family, namely DL-cysteinium semioxalate, (III) (Fig. 1), in which equal amounts of L- and D- cysteinium cations are present, and the total (L + D) cation to semioxalate anion ratio is equal to 1:1.

In (III) the cysteinium cation adopts a gauche+ conformation (Fig. 1), and the values of the S—C—C—N and S—C—C—C angles are close to those in the low-temperature polymorph of DL-cysteine (Minkov et al., 2009) and in the orthorhombic L-cysteine (Kerr & Ashmore, 1973; Kerr et al., 1975), in contrast to the structures of DL-cysteine at ambient conditions (Luger & Weber, 1999), the structures of (I) (Drebushchak et al., 2008) and (II) (Minkov & Boldyreva, 2008) (Table 1).

The crystal structure of (III) is built by double layers, in which dimers of cysteinium cations linked by N1—H1N···O2 hydrogen bonds (Table 2) into a cyclic association of the R22(10) type are connected to each other not directly, but via the bridges of slightly twisted [angle between the two COO planes is 7.1 (3)°] semioxalate anions (Figs. 2, 3). For comparison, in the structure of (I) L- and D-cysteinium isomers are also linked into dimers via N—H···O hydrogen bonds and form similar R22(10) ring motifs, but in (I) the N—H-group links to another O atom of the COOH group as compared to (III): in (I) it is the protonated O atom that accepts the second hydrogen, and this results in a longer hydrogen bond [N—O distance in (I) is 3.0726 (16) Å]. In the structure of (I), the ring is more twisted than in (III), which correlates with a larger [torsion angle N—C—C—O, 37.42 (14)°] twisting of individual molecules in (I) compared with (III). In addition, in (I) there are hydrogen bonds linking the dimers with each other directly. In contrast, in the structure of (II) the cysteinium cations are not at all linked with each other. In the present structure, (III), semioxalate anions are linked with each other via O5—H5O···O3 hydrogen bonds into infinite C11(5) chains along the crystallographic a axis (Fig. 2). These chains are also present in the structure of (II), but with shorter O—H···O hydrogen bonds [the O···O distance is equal to 2.5346 (18) Å]. In contrast, in (I) there are no hydrogen bonds between anions. The shortest hydrogen bond in (III) is O1—H1O···O4 in which an oxalate anion accepts the proton of the carboxyl group, as is observed in (I). In all the three crystal structures (I), (II) and (III) there is a common ring motif of the R21(5) type formed by the N—H···O bifurcated hydrogen bond linking the ammonium group of the cysteinium cation and the anion. However, in the structure of (III) this bifurcated bond is more irregular than in (I) and (II) (the difference between bond lengths exceeds 0.2 Å, see Table 2).

An interesting feature of the crystal structure of (III) is the absence of either S—H···S, or S—H···O hydrogen bonds, which is confirmed by the Raman spectrum: only one intense and narrow band of the SH stretching vibrations at 2576 cm-1 is observed, which proves not only that the thiol group forms no hydrogen bonds, but also that the thiol groups in the structure are ordered.

The ability of the molecules of the same chirality in a racemic crystal to form domains (chains, layers) is very interesting and important. For example, serine is prone to forming homochiral clusters even in the gas phase (Yang et al., 2006), and layers of the same chirality can be found in the crystal structure of DL-serine (Kistenmacher et al., 1974). In contrast, no homochiral chains or layers can be observed in the crystal structures of pure DL-cysteine polymorphs (Minkov et al., 2009). However, the crystallization of cysteinium oxalates, unlike pure cysteine, yields homochiral domains. Infinite head-to-tail chains of the cysteinium cations linked by oxalate anions are present in (I) (Drebushchak et al., 2008); in (III) the cysteinium cations alone do not form any (either homo- or heterochiral) chains, but in each double layer formed by dimers of L- and D-cysteinium cations linked via semioxalate anions, the L-isomers are all at one side of the double layer, and the D-isomers are at another (Fig. 3), similar to what has been observed in (I).

Interestingly enough, rapid and slow crystallization from the same solution (see Experimental) give different products: respectively, (I), in which the oxalate anion is completely deprotonated and coordinates the two cysteinium isomers from its different sides by the two COO groups, and (III), with a partly deprotonated semioxalate anion and a different coordination type. A similar effect has been reported by Boldyreva & Shikina (2008) for glycinium semioxalate (Subha Nandhini et al., 2001) and bis-glycinium oxalate (Chitra & Choudhury, 2007). This phenomenon may reflect the presence of different types of `pro-crystal clusters' in the same solution and different solubility of the two compounds with a different stoichiometric ratio.

Related literature top

For related literature, see: Boldyreva & Shikina (2008); Chitra & Choudhury (2007); Drebushchak et al. (2008); Fujii et al. (2005); Görbitz & Dalhus (1996); Harding & Long (1968); Kerr & Ashmore (1973); Kerr et al. (1975); Kistenmacher et al. (1974); Kolesov et al. (2008); Luger & Weber (1999); Minkov & Boldyreva (2008); Minkov et al. (2009); Minkov, Chesalov & Boldyreva (2008); Minkov, Krylov, Boldyreva, Goryainov, Bizyaev & Vtyurin (2008); Shan & Huang (1999); Subha Nandhini, Krishnakumar & Natarajan (2001); Yang et al. (2006).

Experimental top

Crystals of (I) [(III)?] were obtained by slow evaporation of a saturated aqueous solution of DL-cysteine and oxalic acid in equimolar ratio. Colourless, thick-plate-shaped crystals were obtained.

Refinement top

All H atoms were found in a difference Fourier map and were refined freely. Subsequently, aliphatic H atoms were refined with Uiso(H) = 1.5Ueq(C)

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis CCD (Oxford Diffraction, 2008); data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: publCIF (Westrip, 2009).

Figures top
[Figure 1] Fig. 1. The asymmetric unit of (III), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. Hydrogen bonding (dashed lines) between the semioxalate anions and cysteine cations of (III). [Symmetry code: (v) – 1 + x, y, z; (vi) 1 + x, y, 1 + z; for other codes, see Table 2.]. The H atoms of the CH2 group are not shown.
[Figure 3] Fig. 3. A fragment of the crystal arrangement of (III) projected on the bc plane. Hydrogen bonds are shown as dashed lines. The H atoms of the CH2 group are not shown.
DL-Cysteinium semioxalate top
Crystal data top
C3H8NO2S+·C2HO4Z = 2
Mr = 211.20F(000) = 220
Triclinic, P1Dx = 1.581 Mg m3
Hall symbol: -P 1Mo Kα radiation, λ = 0.71073 Å
a = 5.6664 (2) ÅCell parameters from 6974 reflections
b = 9.0149 (4) Åθ = 3.8–37.4°
c = 9.7749 (5) ŵ = 0.37 mm1
α = 109.349 (4)°T = 295 K
β = 102.282 (3)°Plate, colorless
γ = 100.119 (3)°0.55 × 0.46 × 0.15 mm
V = 443.62 (4) Å3
Data collection top
Oxford Diffraction KM4 CCD
diffractometer
2695 independent reflections
Radiation source: Enhance (Mo) X-ray Source2240 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.028
Detector resolution: 10.3457 pixels mm-1θmax = 30.5°, θmin = 3.8°
rotation method scansh = 88
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2008)
k = 1212
Tmin = 0.814, Tmax = 0.940l = 1313
13760 measured reflections
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)] = 0.035Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.101H atoms treated by a mixture of independent and constrained refinement
S = 1.09 w = 1/[σ2(Fo2) + (0.0621P)2 + 0.0266P]
where P = (Fo2 + 2Fc2)/3
2695 reflections(Δ/σ)max < 0.001
151 parametersΔρmax = 0.42 e Å3
0 restraintsΔρmin = 0.36 e Å3
Crystal data top
C3H8NO2S+·C2HO4γ = 100.119 (3)°
Mr = 211.20V = 443.62 (4) Å3
Triclinic, P1Z = 2
a = 5.6664 (2) ÅMo Kα radiation
b = 9.0149 (4) ŵ = 0.37 mm1
c = 9.7749 (5) ÅT = 295 K
α = 109.349 (4)°0.55 × 0.46 × 0.15 mm
β = 102.282 (3)°
Data collection top
Oxford Diffraction KM4 CCD
diffractometer
2695 independent reflections
Absorption correction: multi-scan
(CrysAlis RED; Oxford Diffraction, 2008)
2240 reflections with I > 2σ(I)
Tmin = 0.814, Tmax = 0.940Rint = 0.028
13760 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0350 restraints
wR(F2) = 0.101H atoms treated by a mixture of independent and constrained refinement
S = 1.09Δρmax = 0.42 e Å3
2695 reflectionsΔρmin = 0.36 e Å3
151 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
C10.28468 (19)0.16858 (15)0.06629 (12)0.0271 (2)
C20.40259 (19)0.21604 (14)0.23449 (12)0.0264 (2)
H20.274 (3)0.2211 (18)0.2793 (17)0.032 (3)*
C30.5927 (2)0.38238 (15)0.31221 (14)0.0336 (2)
H310.655 (3)0.403 (2)0.416 (2)0.040*
H320.511 (3)0.464 (2)0.3027 (19)0.040*
C40.84731 (18)0.19623 (13)0.65949 (12)0.0238 (2)
C51.07475 (18)0.19774 (13)0.59557 (12)0.0244 (2)
N10.5172 (2)0.08572 (13)0.25509 (12)0.0285 (2)
H2N0.396 (3)0.006 (2)0.2281 (19)0.041 (4)*
H1N0.624 (3)0.070 (2)0.2034 (19)0.040 (4)*
H3N0.592 (3)0.109 (2)0.349 (2)0.042 (4)*
O10.22721 (19)0.29039 (12)0.03569 (11)0.0402 (2)
H1O0.147 (4)0.260 (2)0.049 (2)0.050 (5)*
O20.24641 (17)0.03154 (12)0.02465 (10)0.0358 (2)
O30.64841 (14)0.19237 (12)0.57170 (9)0.0338 (2)
O40.87180 (15)0.19387 (12)0.78779 (9)0.0346 (2)
O51.28301 (15)0.21306 (12)0.69425 (10)0.0336 (2)
H5O1.395 (4)0.206 (2)0.646 (2)0.055 (5)*
O61.05197 (17)0.18219 (14)0.46616 (10)0.0422 (2)
S10.86160 (6)0.39771 (4)0.24091 (5)0.04595 (13)
H1S0.769 (4)0.404 (2)0.137 (2)0.051 (5)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0185 (4)0.0403 (6)0.0233 (5)0.0072 (4)0.0063 (4)0.0137 (4)
C20.0226 (5)0.0360 (6)0.0216 (5)0.0087 (4)0.0070 (4)0.0116 (4)
C30.0343 (6)0.0327 (6)0.0279 (5)0.0092 (5)0.0059 (5)0.0059 (5)
C40.0178 (4)0.0302 (5)0.0235 (5)0.0044 (4)0.0059 (4)0.0116 (4)
C50.0196 (4)0.0298 (5)0.0257 (5)0.0069 (4)0.0073 (4)0.0125 (4)
O10.0438 (5)0.0437 (5)0.0296 (4)0.0120 (4)0.0009 (4)0.0166 (4)
O20.0323 (4)0.0428 (5)0.0265 (4)0.0104 (4)0.0053 (3)0.0081 (4)
O30.0180 (3)0.0590 (6)0.0271 (4)0.0115 (3)0.0060 (3)0.0195 (4)
O40.0232 (4)0.0584 (6)0.0284 (4)0.0093 (4)0.0084 (3)0.0244 (4)
O50.0194 (4)0.0553 (5)0.0329 (4)0.0137 (3)0.0092 (3)0.0224 (4)
O60.0285 (4)0.0749 (7)0.0283 (4)0.0154 (4)0.0114 (3)0.0234 (4)
N10.0281 (4)0.0349 (5)0.0235 (4)0.0067 (4)0.0060 (4)0.0143 (4)
S10.03309 (18)0.03741 (19)0.0639 (3)0.00329 (13)0.01617 (16)0.01699 (17)
Geometric parameters (Å, º) top
S1—C31.8079 (13)C1—O11.3050 (15)
S1—H1S1.06 (2)O1—H1O0.78 (2)
N1—C21.4872 (15)C3—H310.938 (19)
N1—H2N0.898 (18)C3—H320.954 (16)
N1—H1N0.870 (18)O3—C41.2501 (12)
N1—H3N0.860 (18)O5—C51.3085 (12)
C2—C11.5161 (15)O5—H5O0.87 (2)
C2—C31.5218 (17)C4—O41.2399 (13)
C2—H20.927 (16)C4—C51.5471 (14)
O2—C11.2082 (15)C5—O61.2013 (13)
C3—S1—H1S96.8 (10)O1—C1—C2112.07 (10)
C2—N1—H2N109.4 (11)C1—O1—H1O110.2 (14)
C2—N1—H1N110.8 (11)C2—C3—S1113.94 (8)
H2N—N1—H1N111.5 (15)C2—C3—H31109.0 (12)
C2—N1—H3N111.8 (11)S1—C3—H31106.4 (12)
H2N—N1—H3N104.4 (15)C2—C3—H32109.1 (10)
H1N—N1—H3N108.8 (16)S1—C3—H32109.9 (10)
N1—C2—C1108.28 (9)H31—C3—H32108.3 (15)
N1—C2—C3111.06 (9)C5—O5—H5O106.1 (12)
C1—C2—C3114.15 (10)O4—C4—O3125.54 (10)
N1—C2—H2109.4 (9)O4—C4—C5119.20 (9)
C1—C2—H2106.8 (9)O3—C4—C5115.22 (9)
C3—C2—H2106.9 (9)O6—C5—O5125.51 (10)
O2—C1—O1125.85 (10)O6—C5—C4121.11 (9)
O2—C1—C2122.06 (10)O5—C5—C4113.36 (9)
N1—C2—C1—O215.17 (14)C1—C2—C3—S162.22 (12)
C3—C2—C1—O2139.43 (12)O4—C4—C5—O6171.83 (12)
N1—C2—C1—O1166.39 (9)O3—C4—C5—O66.01 (17)
C3—C2—C1—O142.14 (13)O4—C4—C5—O56.57 (15)
N1—C2—C3—S160.53 (12)O3—C4—C5—O5175.59 (10)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H3N···O30.860 (18)1.986 (18)2.8023 (13)157.9 (16)
N1—H3N···O60.860 (18)2.484 (17)3.0694 (14)126.0 (14)
N1—H2N···O4i0.897 (18)2.004 (18)2.8882 (14)168.4 (15)
N1—H1N···O2ii0.870 (18)2.036 (18)2.8618 (14)158.1 (16)
O1—H1O···O4iii0.78 (2)1.82 (2)2.5682 (12)159 (2)
O5—H5O···O3iv0.87 (2)1.74 (2)2.6076 (12)172.2 (18)
Symmetry codes: (i) x+1, y, z+1; (ii) x+1, y, z; (iii) x1, y, z1; (iv) x+1, y, z.

Experimental details

Crystal data
Chemical formulaC3H8NO2S+·C2HO4
Mr211.20
Crystal system, space groupTriclinic, P1
Temperature (K)295
a, b, c (Å)5.6664 (2), 9.0149 (4), 9.7749 (5)
α, β, γ (°)109.349 (4), 102.282 (3), 100.119 (3)
V3)443.62 (4)
Z2
Radiation typeMo Kα
µ (mm1)0.37
Crystal size (mm)0.55 × 0.46 × 0.15
Data collection
DiffractometerOxford Diffraction KM4 CCD
diffractometer
Absorption correctionMulti-scan
(CrysAlis RED; Oxford Diffraction, 2008)
Tmin, Tmax0.814, 0.940
No. of measured, independent and
observed [I > 2σ(I)] reflections
13760, 2695, 2240
Rint0.028
(sin θ/λ)max1)0.714
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.101, 1.09
No. of reflections2695
No. of parameters151
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.42, 0.36

Computer programs: CrysAlis CCD (Oxford Diffraction, 2008), CrysAlis RED (Oxford Diffraction, 2008), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), Mercury (Macrae et al., 2006), publCIF (Westrip, 2009).

Selected torsion angles (º) top
N1—C2—C1—O215.17 (14)C1—C2—C3—S162.22 (12)
C3—C2—C1—O2139.43 (12)O4—C4—C5—O6171.83 (12)
N1—C2—C1—O1166.39 (9)O3—C4—C5—O66.01 (17)
C3—C2—C1—O142.14 (13)O4—C4—C5—O56.57 (15)
N1—C2—C3—S160.53 (12)O3—C4—C5—O5175.59 (10)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H3N···O30.860 (18)1.986 (18)2.8023 (13)157.9 (16)
N1—H3N···O60.860 (18)2.484 (17)3.0694 (14)126.0 (14)
N1—H2N···O4i0.897 (18)2.004 (18)2.8882 (14)168.4 (15)
N1—H1N···O2ii0.870 (18)2.036 (18)2.8618 (14)158.1 (16)
O1—H1O···O4iii0.78 (2)1.82 (2)2.5682 (12)159 (2)
O5—H5O···O3iv0.87 (2)1.74 (2)2.6076 (12)172.2 (18)
Symmetry codes: (i) x+1, y, z+1; (ii) x+1, y, z; (iii) x1, y, z1; (iv) x+1, y, z.
 

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