organic compounds
Bis(L-serinium) oxalate dihydrate: polymorph II
aChemistry Department, University of Warsaw, Pasteura 1, 02-093 Warszawa, Poland, and, Centre of New Technologies, University of Warsaw, Zwirki i Wigury 93, 02-089 Warszawa, Poland, and bChemistry Department, University of Warsaw, Pasteura 1, 02-093 Warszawa, Poland
*Correspondence e-mail: kwozniak@chem.uw.edu.pl
A corrected and improved structure of the polymorph II of 2C3H8NO3+·C2O42−·2H2O, based on single-crystal data, is presented. The structure is refined with anisotropic displacement parameters for all non-H atoms and all H atoms are located. Due to the charged moieties, the structure is classified as a molecular salt. Intermolecular O—H⋯O−, O—H⋯O and N+—H⋯O−hydrogen bonds link the components of the structure. The L-serinium cations and oxalate anions form a network of channels in [100] direction, filled with the water molecules of crystallization. The dihedral angle between the CO2 units of the oxalate dianion is 10.2 (3)°
CCDC reference: 964780
Related literature
Crystallization of serine with oxalic acid leads to diverse molecular salts, with some of them exhibiting 3H7NO3+·C2O42−·2H2O have already been described, see: Braga et al. (2013). Form II was determined by powder X-ray diffraction methods and therefore the lacks properly located H atoms and anisotropic displacement parameters of all heavy atoms in the structure.
The polymorphs I and II of 2CExperimental
Crystal data
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Data collection: CrysAlis PRO (Agilent, 2012); cell CrysAlis PRO; data reduction: CrysAlis PRO and SORTAV (Blessing, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 1999); software used to prepare material for publication: SHELXL97.
Supporting information
CCDC reference: 964780
10.1107/S160053681302727X/gk2581sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: 10.1107/S160053681302727X/gk2581Isup2.hkl
Supporting information file. DOI: 10.1107/S160053681302727X/gk2581Isup3.cdx
Supporting information file. DOI: 10.1107/S160053681302727X/gk2581Isup4.cml
A mixture of L-serine (0.158 mg) with oxalic acid (0.068 mg) was dissolved in water (15 mL) in the 2:1 stoichiometric ratio and set aside to crystallize by slow evaporation at 309 K. Little needle-shaped crystals of bis(L-serinium) oxalate dihydrate form II (m.p. 357 K) have grown on bigger needle-shaped crystals of oxalic acid.
All H-atoms bound to C were placed at the calculated positions and were treated as riding on the parent atom with Uiso(H) = 1.2Ueq(C) and C–H distances of 0.98 Å for methine and 0.97 Å for methylene groups. N+-bound H atoms were placed in locations indicated by a difference Fourier synthesis and were refined using a riding model, with Uiso(H) = 1.5Ueq(C) and N– H distance of 0.89 Å. H atoms attached to O were placed in locations indicated by a difference Fourier synthesis and were refined using a riding model with Uiso(H) values set at 1.5 Ueq(O) and with a distance restraint of O–H = 0.82 Å, except for the water molecules for which O-H distances were constrained to 0.840 (5) Å. An
has been assigned by reference to an unchanging chiral centre in the crystallization procedure. For the 1367 Friedel pairs were not merged.Data collection: CrysAlis PRO (Agilent, 2012); cell
CrysAlis PRO (Agilent, 2012); data reduction: CrysAlis PRO (Agilent, 2012) and SORTAV (Blessing, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 1999).Fig. 1. Atomic displacement parameters at the 50% probability level and atom labeling scheme of the asymmetric part of the unit cell in polymorph II | |
Fig. 2. The crystal packing in polymorph II viewed along the a axis. Dashed lines indicate hydrogen bonds. |
2C3H8NO3+·C2O42−·2H2O | F(000) = 356 |
Mr = 336.26 | Dx = 1.586 Mg m−3 |
Monoclinic, P21 | Melting point: 357 K |
Hall symbol: P 2yb | Mo Kα radiation, λ = 0.71073 Å |
a = 5.1524 (2) Å | Cell parameters from 8206 reflections |
b = 11.1467 (4) Å | θ = 1.7–26.4° |
c = 12.4478 (5) Å | µ = 0.15 mm−1 |
β = 99.967 (4)° | T = 90 K |
V = 704.12 (5) Å3 | Needle, colourless |
Z = 2 | 0.28 × 0.10 × 0.08 mm |
Agilent Xcalibur Opal diffractometer | 2876 independent reflections |
Radiation source: Enhance (Mo) X-ray Source | 2430 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.030 |
Detector resolution: 8.4441 pixels mm-1 | θmax = 26.4°, θmin = 1.7° |
ω scans | h = −6→6 |
Absorption correction: multi-scan [SCALE3 ABSPACK (Blessing, 1995) and CrysAlis PRO (Agilent, 2012)] | k = −13→13 |
Tmin = 0.980, Tmax = 1.000 | l = −15→15 |
17202 measured reflections |
Refinement on F2 | 0 constraints |
Least-squares matrix: full | H atoms treated by a mixture of independent and constrained refinement |
R[F2 > 2σ(F2)] = 0.032 | w = 1/[σ2(Fo2) + (0.0288P)2] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.065 | (Δ/σ)max < 0.001 |
S = 1.01 | Δρmax = 0.17 e Å−3 |
2876 reflections | Δρmin = −0.17 e Å−3 |
217 parameters | Absolute structure: Flack (1983), 1367 Friedel pairs |
5 restraints | Absolute structure parameter: −0.4 (9) |
2C3H8NO3+·C2O42−·2H2O | V = 704.12 (5) Å3 |
Mr = 336.26 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 5.1524 (2) Å | µ = 0.15 mm−1 |
b = 11.1467 (4) Å | T = 90 K |
c = 12.4478 (5) Å | 0.28 × 0.10 × 0.08 mm |
β = 99.967 (4)° |
Agilent Xcalibur Opal diffractometer | 2876 independent reflections |
Absorption correction: multi-scan [SCALE3 ABSPACK (Blessing, 1995) and CrysAlis PRO (Agilent, 2012)] | 2430 reflections with I > 2σ(I) |
Tmin = 0.980, Tmax = 1.000 | Rint = 0.030 |
17202 measured reflections |
R[F2 > 2σ(F2)] = 0.032 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.065 | Δρmax = 0.17 e Å−3 |
S = 1.01 | Δρmin = −0.17 e Å−3 |
2876 reflections | Absolute structure: Flack (1983), 1367 Friedel pairs |
217 parameters | Absolute structure parameter: −0.4 (9) |
5 restraints |
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 | ||
C1 | 0.4625 (4) | 0.52285 (19) | 0.52693 (16) | 0.0118 (4) | |
C2 | 0.2932 (4) | 0.63226 (18) | 0.49184 (14) | 0.0116 (4) | |
H2 | 0.3931 | 0.7053 | 0.5150 | 0.014* | |
C3 | 0.0458 (4) | 0.62912 (19) | 0.54164 (15) | 0.0130 (4) | |
H3A | −0.0591 | 0.5602 | 0.5133 | 0.016* | |
H3B | 0.0944 | 0.6192 | 0.6200 | 0.016* | |
C4 | 0.0979 (4) | 0.39834 (17) | 0.75125 (15) | 0.0090 (4) | |
C5 | 0.3329 (4) | 0.30988 (18) | 0.76828 (15) | 0.0091 (4) | |
C11 | 0.9862 (4) | 0.69260 (18) | 1.00499 (16) | 0.0110 (4) | |
C12 | 0.7188 (4) | 0.63044 (18) | 0.98188 (14) | 0.0099 (4) | |
H12 | 0.5875 | 0.6845 | 1.0039 | 0.012* | |
C13 | 0.7174 (4) | 0.51374 (18) | 1.04585 (16) | 0.0127 (4) | |
H13A | 0.8354 | 0.4565 | 1.0207 | 0.015* | |
H13B | 0.7810 | 0.5290 | 1.1226 | 0.015* | |
N1 | 0.2229 (3) | 0.62971 (16) | 0.37022 (12) | 0.0123 (4) | |
H1A | 0.1372 | 0.5620 | 0.3493 | 0.015* | |
H1B | 0.3692 | 0.6334 | 0.3414 | 0.015* | |
H1C | 0.1204 | 0.6922 | 0.3475 | 0.015* | |
N2 | 0.6468 (3) | 0.60909 (15) | 0.86212 (12) | 0.0111 (4) | |
H2A | 0.4974 | 0.5674 | 0.8483 | 0.013* | |
H2B | 0.7747 | 0.5679 | 0.8391 | 0.013* | |
H2C | 0.6253 | 0.6792 | 0.8274 | 0.013* | |
O1 | 0.5153 (3) | 0.44889 (13) | 0.46302 (11) | 0.0160 (3) | |
O2 | 0.5432 (3) | 0.51993 (13) | 0.63342 (10) | 0.0136 (3) | |
H2D | 0.6541 | 0.4670 | 0.6485 | 0.020* | |
O3 | −0.1098 (3) | 0.73504 (12) | 0.51957 (10) | 0.0145 (3) | |
H3 | −0.1608 | 0.7412 | 0.4537 | 0.022* | |
O4 | 0.3329 (3) | 0.22639 (12) | 0.70100 (10) | 0.0127 (3) | |
O5 | 0.5089 (3) | 0.32894 (12) | 0.85114 (10) | 0.0118 (3) | |
O6 | −0.0945 (3) | 0.36793 (12) | 0.67897 (10) | 0.0113 (3) | |
O7 | 0.1134 (3) | 0.49023 (12) | 0.80848 (11) | 0.0131 (3) | |
O9 | 0.9872 (3) | 0.40357 (13) | 0.31699 (11) | 0.0172 (3) | |
O8 | 0.4472 (3) | 0.34223 (13) | 0.22167 (11) | 0.0154 (3) | |
O11 | 1.0996 (3) | 0.72817 (12) | 0.93378 (11) | 0.0139 (3) | |
O12 | 1.0685 (3) | 0.70526 (12) | 1.11088 (10) | 0.0134 (3) | |
H12A | 1.2031 | 0.7460 | 1.1213 | 0.020* | |
O13 | 0.4594 (3) | 0.46436 (13) | 1.03248 (11) | 0.0151 (3) | |
H13 | 0.4326 | 0.4231 | 0.9771 | 0.023* | |
H9A | 0.8281 (17) | 0.388 (2) | 0.2924 (17) | 0.023* | |
H9B | 1.028 (4) | 0.3640 (18) | 0.3750 (11) | 0.023* | |
H8A | 0.316 (3) | 0.365 (2) | 0.2477 (18) | 0.023* | |
H8B | 0.428 (5) | 0.3845 (18) | 0.1648 (12) | 0.023* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0076 (10) | 0.0142 (11) | 0.0139 (11) | −0.0019 (9) | 0.0027 (8) | 0.0010 (9) |
C2 | 0.0106 (11) | 0.0128 (10) | 0.0109 (10) | 0.0007 (9) | 0.0004 (8) | 0.0002 (9) |
C3 | 0.0132 (11) | 0.0128 (10) | 0.0129 (10) | 0.0019 (9) | 0.0021 (9) | 0.0006 (9) |
C4 | 0.0111 (11) | 0.0082 (10) | 0.0078 (10) | −0.0013 (9) | 0.0025 (8) | 0.0036 (8) |
C5 | 0.0070 (10) | 0.0105 (10) | 0.0105 (10) | −0.0028 (8) | 0.0036 (8) | 0.0029 (8) |
C11 | 0.0113 (10) | 0.0064 (10) | 0.0148 (10) | 0.0020 (8) | 0.0004 (8) | −0.0018 (8) |
C12 | 0.0104 (10) | 0.0133 (10) | 0.0057 (9) | 0.0009 (8) | 0.0011 (8) | −0.0010 (8) |
C13 | 0.0118 (11) | 0.0136 (11) | 0.0117 (10) | −0.0039 (9) | −0.0008 (8) | 0.0014 (8) |
N1 | 0.0112 (9) | 0.0135 (9) | 0.0121 (8) | 0.0019 (7) | 0.0018 (7) | 0.0036 (7) |
N2 | 0.0125 (9) | 0.0099 (9) | 0.0100 (8) | −0.0020 (7) | −0.0001 (7) | −0.0008 (7) |
O1 | 0.0159 (8) | 0.0155 (8) | 0.0149 (8) | 0.0046 (7) | −0.0022 (6) | −0.0025 (6) |
O2 | 0.0128 (8) | 0.0165 (8) | 0.0107 (8) | 0.0072 (6) | 0.0002 (6) | 0.0024 (6) |
O3 | 0.0160 (8) | 0.0160 (8) | 0.0108 (7) | 0.0071 (6) | 0.0003 (6) | 0.0004 (6) |
O4 | 0.0137 (7) | 0.0114 (7) | 0.0126 (7) | 0.0015 (6) | 0.0013 (6) | −0.0042 (6) |
O5 | 0.0094 (7) | 0.0144 (8) | 0.0107 (7) | 0.0015 (6) | −0.0009 (6) | −0.0009 (6) |
O6 | 0.0114 (7) | 0.0102 (7) | 0.0107 (7) | 0.0012 (6) | −0.0023 (6) | −0.0009 (5) |
O7 | 0.0119 (7) | 0.0123 (8) | 0.0143 (7) | 0.0014 (6) | 0.0004 (6) | −0.0034 (6) |
O9 | 0.0154 (8) | 0.0188 (9) | 0.0160 (8) | −0.0037 (7) | −0.0017 (7) | 0.0029 (7) |
O8 | 0.0183 (8) | 0.0149 (8) | 0.0137 (8) | 0.0000 (7) | 0.0051 (7) | 0.0014 (6) |
O11 | 0.0138 (7) | 0.0161 (7) | 0.0124 (7) | −0.0030 (6) | 0.0036 (6) | −0.0001 (6) |
O12 | 0.0092 (7) | 0.0192 (8) | 0.0117 (7) | −0.0074 (6) | 0.0013 (5) | −0.0038 (6) |
O13 | 0.0171 (8) | 0.0161 (8) | 0.0113 (7) | −0.0083 (6) | 0.0004 (6) | −0.0023 (6) |
C1—O1 | 1.209 (2) | C12—H12 | 0.9800 |
C1—O2 | 1.319 (2) | C13—O13 | 1.422 (2) |
C1—C2 | 1.519 (3) | C13—H13A | 0.9700 |
C2—N1 | 1.495 (2) | C13—H13B | 0.9700 |
C2—C3 | 1.511 (3) | N1—H1A | 0.8900 |
C2—H2 | 0.9800 | N1—H1B | 0.8900 |
C3—O3 | 1.427 (2) | N1—H1C | 0.8900 |
C3—H3A | 0.9700 | N2—H2A | 0.8900 |
C3—H3B | 0.9700 | N2—H2B | 0.8900 |
C4—O7 | 1.242 (2) | N2—H2C | 0.8900 |
C4—O6 | 1.264 (2) | O2—H2D | 0.8200 |
C4—C5 | 1.547 (3) | O3—H3 | 0.8200 |
C5—O4 | 1.252 (2) | O9—H9A | 0.843 (5) |
C5—O5 | 1.268 (2) | O9—H9B | 0.841 (5) |
C11—O11 | 1.210 (2) | O8—H8A | 0.838 (5) |
C11—O12 | 1.321 (2) | O8—H8B | 0.842 (5) |
C11—C12 | 1.524 (3) | O12—H12A | 0.8200 |
C12—N2 | 1.492 (2) | O13—H13 | 0.8200 |
C12—C13 | 1.526 (3) | ||
O1—C1—O2 | 125.23 (19) | N2—C12—H12 | 108.2 |
O1—C1—C2 | 122.80 (17) | C11—C12—H12 | 108.2 |
O2—C1—C2 | 111.96 (17) | C13—C12—H12 | 108.2 |
N1—C2—C3 | 109.96 (16) | O13—C13—C12 | 110.96 (16) |
N1—C2—C1 | 107.60 (15) | O13—C13—H13A | 109.4 |
C3—C2—C1 | 110.29 (17) | C12—C13—H13A | 109.4 |
N1—C2—H2 | 109.7 | O13—C13—H13B | 109.4 |
C3—C2—H2 | 109.7 | C12—C13—H13B | 109.4 |
C1—C2—H2 | 109.7 | H13A—C13—H13B | 108.0 |
O3—C3—C2 | 112.81 (17) | C2—N1—H1A | 109.5 |
O3—C3—H3A | 109.0 | C2—N1—H1B | 109.5 |
C2—C3—H3A | 109.0 | H1A—N1—H1B | 109.5 |
O3—C3—H3B | 109.0 | C2—N1—H1C | 109.5 |
C2—C3—H3B | 109.0 | H1A—N1—H1C | 109.5 |
H3A—C3—H3B | 107.8 | H1B—N1—H1C | 109.5 |
O7—C4—O6 | 126.43 (19) | C12—N2—H2A | 109.5 |
O7—C4—C5 | 118.41 (16) | C12—N2—H2B | 109.5 |
O6—C4—C5 | 115.16 (16) | H2A—N2—H2B | 109.5 |
O4—C5—O5 | 125.86 (18) | C12—N2—H2C | 109.5 |
O4—C5—C4 | 118.22 (16) | H2A—N2—H2C | 109.5 |
O5—C5—C4 | 115.92 (16) | H2B—N2—H2C | 109.5 |
O11—C11—O12 | 125.74 (19) | C1—O2—H2D | 109.5 |
O11—C11—C12 | 123.09 (18) | C3—O3—H3 | 109.5 |
O12—C11—C12 | 111.14 (16) | H9A—O9—H9B | 107 (2) |
N2—C12—C11 | 108.76 (15) | H8A—O8—H8B | 100 (2) |
N2—C12—C13 | 111.26 (16) | C11—O12—H12A | 109.5 |
C11—C12—C13 | 112.01 (16) | C13—O13—H13 | 109.5 |
O1—C1—C2—N1 | −2.1 (3) | O7—C4—C5—O5 | 10.2 (2) |
O2—C1—C2—N1 | 177.53 (16) | O6—C4—C5—O5 | −169.46 (16) |
O1—C1—C2—C3 | 117.8 (2) | O11—C11—C12—N2 | 7.0 (3) |
O2—C1—C2—C3 | −62.5 (2) | O12—C11—C12—N2 | −175.16 (15) |
N1—C2—C3—O3 | −66.8 (2) | O11—C11—C12—C13 | 130.4 (2) |
C1—C2—C3—O3 | 174.68 (15) | O12—C11—C12—C13 | −51.8 (2) |
O7—C4—C5—O4 | −170.34 (17) | N2—C12—C13—O13 | −64.5 (2) |
O6—C4—C5—O4 | 10.0 (2) | C11—C12—C13—O13 | 173.51 (15) |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O9i | 0.89 | 1.94 | 2.826 (2) | 172 |
N1—H1B···O4ii | 0.89 | 2.00 | 2.809 (2) | 151 |
N1—H1C···O6iii | 0.89 | 1.99 | 2.779 (2) | 148 |
N1—H1C···O4iii | 0.89 | 2.34 | 3.044 (2) | 136 |
N2—H2A···O7 | 0.89 | 2.14 | 3.020 (2) | 172 |
N2—H2A···O5 | 0.89 | 2.66 | 3.200 (2) | 120 |
N2—H2B···O7iv | 0.89 | 2.04 | 2.922 (2) | 169 |
N2—H2C···O8ii | 0.89 | 1.93 | 2.811 (2) | 168 |
O2—H2D···O6iv | 0.82 | 1.69 | 2.5122 (19) | 175 |
O3—H3···O4iii | 0.82 | 1.98 | 2.7887 (18) | 168 |
O8—H8A···O9i | 0.84 (1) | 2.08 (1) | 2.910 (2) | 174 (2) |
O8—H8B···O13v | 0.84 (1) | 1.90 (1) | 2.730 (2) | 167 (2) |
O9—H9A···O8 | 0.84 (1) | 2.07 (1) | 2.911 (2) | 175 (2) |
O9—H9B···O3vi | 0.84 (1) | 1.94 (1) | 2.7607 (19) | 164 (2) |
O12—H12A···O5vii | 0.82 | 1.73 | 2.5513 (19) | 177 |
O13—H13···O5 | 0.82 | 1.98 | 2.7637 (19) | 159 |
O13—H13···O7 | 0.82 | 2.55 | 3.0521 (19) | 121 |
Symmetry codes: (i) x−1, y, z; (ii) −x+1, y+1/2, −z+1; (iii) −x, y+1/2, −z+1; (iv) x+1, y, z; (v) x, y, z−1; (vi) −x+1, y−1/2, −z+1; (vii) −x+2, y+1/2, −z+2. |
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1A···O9i | 0.89 | 1.94 | 2.826 (2) | 172.3 |
N1—H1B···O4ii | 0.89 | 2.00 | 2.809 (2) | 150.9 |
N1—H1C···O6iii | 0.89 | 1.99 | 2.779 (2) | 147.5 |
N1—H1C···O4iii | 0.89 | 2.34 | 3.044 (2) | 136.1 |
N2—H2A···O7 | 0.89 | 2.14 | 3.020 (2) | 172.2 |
N2—H2A···O5 | 0.89 | 2.66 | 3.200 (2) | 120.2 |
N2—H2B···O7iv | 0.89 | 2.04 | 2.922 (2) | 169.4 |
N2—H2C···O8ii | 0.89 | 1.93 | 2.811 (2) | 168.4 |
O2—H2D···O6iv | 0.82 | 1.69 | 2.5122 (19) | 174.5 |
O3—H3···O4iii | 0.82 | 1.98 | 2.7887 (18) | 167.7 |
O8—H8A···O9i | 0.838 (5) | 2.075 (6) | 2.910 (2) | 174 (2) |
O8—H8B···O13v | 0.842 (5) | 1.903 (8) | 2.730 (2) | 167 (2) |
O9—H9A···O8 | 0.843 (5) | 2.070 (6) | 2.911 (2) | 175 (2) |
O9—H9B···O3vi | 0.841 (5) | 1.943 (8) | 2.7607 (19) | 164 (2) |
O12—H12A···O5vii | 0.82 | 1.73 | 2.5513 (19) | 177.4 |
O13—H13···O5 | 0.82 | 1.98 | 2.7637 (19) | 159.1 |
O13—H13···O7 | 0.82 | 2.55 | 3.0521 (19) | 121.2 |
Symmetry codes: (i) x−1, y, z; (ii) −x+1, y+1/2, −z+1; (iii) −x, y+1/2, −z+1; (iv) x+1, y, z; (v) x, y, z−1; (vi) −x+1, y−1/2, −z+1; (vii) −x+2, y+1/2, −z+2. |
Acknowledgements
The authors acknowledge support from Foundation for Polish Science Team project (TEAM/2009–3/8) co-financed by European Regional Development Fund operated within Innovative Economy Operational Programme.
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Divers crystal forms of molecular salts of L-serine with oxalic acid can be obtained by grinding or kneading powders of both compounds, as decribed earlier (Braga et al., 2013). However, previously reported structure of form II of 2C3H7NO3+.C2O42-.2H2O was based on powder diffraction X-ray data and therefore hydrogen atoms were positioned geometrically (including –NH3+ and –COOH groups) and the structure refined with isotropic displacement parameters for for L-serinium cations. Moreover, the H atoms of water molecules were not located. Crystallization of the polymorph II of 2C3H7NO3+.C2O42-.2H2O is also possible by slow evaporation from water solution and it results in crystals of the size sufficient to perform single-crystal X-ray diffraction experiment. Hence, the proper H-atom positions can be found. Both hydrate polymorphs have different unit-cell dimensions, whereas crystal packing remains virtually very similar, with a characteristic motif of the zigzag chains formed by hydrogen bonds between the water molecules along the [100] direction. The location of hydrogen bond network surrounding the oxalate anion allows for discrimination between the polymorphic forms. The form I contains 8 hydrogen bonds between the oxalate anion and 6 neighbouring serine cations. In the polymorph II, obtained from powder data, due to the lack of proper positions of H-atoms, one can suspect the presence of 11 hydrogen bonds around the oxalate anion, located within the donor-acceptor distance in the range from 2.4 to 3.0 Å. In the polymorph II structure derived from single-crystal X-ray diffraction data, 9 hydrogen bonds are formed between the oxalate anion to the 6 neighbouring serine cations. This difference results from a wrong assignment of the carboxylic H-atom in one of the serinium cations in the structure obtained from powder data (see Fig.1, atoms O2 and O12).Both structures of the form II have different distances between the oxalate anions. The structure of Braga et al. (2013) presents a denser arrangement between the oxalate anions. The distances between oxygen atoms from neighbouring anions for the structure obtained by single crystal X-ray measurement range from 3.237 (2) to 4.975 (2) Å. The corresponding values in the structure derived from the powder data are between 2.63 (1) to 4.97 (1) Å.
To compare the unit cell parameters obtained by powder methods at room temperature [a= 12.5711 (6), b= 11.2144 (5), c= 5.2079 (2) Å, β= 100.529 (3)°] these parameters were also determined at room temperature from a single crystal [a= 5.1869 (2), b= 11.1906 (5), c= 12.5305 (5) Å, β= 100.485 (4)°].