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The title compound, C
4H
10N
3O
2+·C
2H
2NO
3-·C
2H
3NO
3, contains at least 11 distinct hydrogen-bond interactions showing a great variety of bond strengths. The shortest and strongest hydrogen bond [O
O = 2.5004 (12) Å] is found between the uncharged oxamic acid molecule and the oxamate monoanion. The grouping formed by such a strong hydrogen bond can thus be considered as a hydrogen bis(oxamate) monoanion. It lacks crystallographic symmetry and the two oxamate groups have different conformations, showing an asymmetric hydrogen-bond interaction. Significantly, the asymmetry allows us to draw a direct comparison of site basicity for the two inequivalent carboxylate O atoms in the planar oxamate anion. The constituent molecular ions of (I) form ribbons, where all amide and carboxylate groups are coplanar. Graph-set analysis of the hydrogen-bonded networks reveals the
R22(10) and
R22(9) homodromic nets as important structure-directing motifs, which appear to be a common feature of many oxamate-containing compounds.
Supporting information
CCDC reference: 774094
Crystals of (I) were obtained as a by-product from a synthesis of 1,2-ethylene
bis(oxamide). 1,2-Ethylenediamine (1.70 ml, 25.4 mmol) was slowly added to a
stirred solution of O-ethyloxamate (10.7 g, 89.7 mmol) in a mixture of
water (20 ml) and ethanol (40 ml). The reaction was heated to reflux for 2 h
and then allowed to cool to room temperature, whereupon the precipitate of
1,2-ethylene bis(oxamide) was recovered by filtration. After a few days,
crystals of (I) started to grow in the filtrate. Spectroscopic analysis: IR
(Medium?, ν, cm-1): 3499, 3418,3263, 3210, 2991, 2938, 1715, 1627,
1508.
The ethylene H atoms were placed in idealized geometries with C—H = 0.97 Å
and refined in riding mode, with Uiso(H) = 1.2Ueq(C). All
other H atoms are involved in hydrogen bonding. While all of these H atoms
were located in the difference Fourier map and all had their coordinates
refined freely, the amide N-bound H atoms had Uiso(H) =
1.2Ueq(N). For the H atom in the hydrogen bis(carboxylate) unit (H7),
Uiso(H) was refined freely (geometric parameters given in Table 2).
Data collection: SAINT (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SMART (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008) and WinGX (Farrugia, 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) and WinGX (Farrugia, 1999); molecular graphics: DIAMOND (Brandenburg, 1999).
2-(oxamoylamino)ethylammonium oxamate–oxamic acid (1/1)
top
Crystal data top
C4H10N3O2+·C2H2NO3−·C2H3NO3 | Z = 2 |
Mr = 309.25 | F(000) = 324 |
Triclinic, P1 | Dx = 1.647 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 5.1723 (2) Å | Cell parameters from 768 reflections |
b = 10.3560 (4) Å | θ = 1.7–28.2° |
c = 12.1866 (5) Å | µ = 0.15 mm−1 |
α = 97.765 (2)° | T = 100 K |
β = 97.304 (2)° | Block, colourless |
γ = 102.394 (2)° | 0.6 × 0.1 × 0.1 mm |
V = 623.43 (4) Å3 | |
Data collection top
Bruker APEXII CCD area-detector diffractometer | 2895 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.035 |
Graphite monochromator | θmax = 30.6°, θmin = 1.7° |
ϕ and ω scans | h = −7→7 |
13083 measured reflections | k = −13→14 |
3812 independent reflections | l = −17→17 |
Refinement top
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)] = 0.040 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.106 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | w = 1/[σ2(Fo2) + (0.0561P)2 + 0.0433P] where P = (Fo2 + 2Fc2)/3 |
3812 reflections | (Δ/σ)max < 0.001 |
224 parameters | Δρmax = 0.54 e Å−3 |
0 restraints | Δρmin = −0.24 e Å−3 |
Crystal data top
C4H10N3O2+·C2H2NO3−·C2H3NO3 | γ = 102.394 (2)° |
Mr = 309.25 | V = 623.43 (4) Å3 |
Triclinic, P1 | Z = 2 |
a = 5.1723 (2) Å | Mo Kα radiation |
b = 10.3560 (4) Å | µ = 0.15 mm−1 |
c = 12.1866 (5) Å | T = 100 K |
α = 97.765 (2)° | 0.6 × 0.1 × 0.1 mm |
β = 97.304 (2)° | |
Data collection top
Bruker APEXII CCD area-detector diffractometer | 2895 reflections with I > 2σ(I) |
13083 measured reflections | Rint = 0.035 |
3812 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.040 | 0 restraints |
wR(F2) = 0.106 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.04 | Δρmax = 0.54 e Å−3 |
3812 reflections | Δρmin = −0.24 e Å−3 |
224 parameters | |
Special details top
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 >
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. All
hydrogen atoms had their isotropic thermal parameters constrained to 1.2
× that of the parent atom, except H7, involved in the strong hydrogen
bond, which was refined freely. The ethylene hydrogen atoms were placed in
idealised geometries (C—H = 0.97 Å) and refined in riding mode. While all
other hydrogen atoms had their coordinates refined freely. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | |
N1 | 0.2608 (2) | 0.72976 (12) | 0.45733 (10) | 0.0209 (3) | |
H1A | 0.313 (3) | 0.7663 (16) | 0.5326 (15) | 0.025* | |
H1B | 0.121 (4) | 0.6674 (17) | 0.4383 (15) | 0.025* | |
C1 | 0.4053 (2) | 0.77512 (12) | 0.38268 (10) | 0.0136 (2) | |
O1 | 0.61092 (19) | 0.86607 (9) | 0.40618 (8) | 0.0200 (2) | |
C2 | 0.2994 (2) | 0.70454 (12) | 0.26115 (10) | 0.0124 (2) | |
O2 | 0.09733 (18) | 0.61105 (9) | 0.23891 (8) | 0.01561 (19) | |
N2 | 0.4447 (2) | 0.75179 (11) | 0.18648 (9) | 0.0135 (2) | |
H2 | 0.582 (3) | 0.8130 (15) | 0.2119 (13) | 0.016* | |
C3 | 0.3995 (2) | 0.68371 (13) | 0.06999 (10) | 0.0148 (2) | |
H3D | 0.4098 | 0.5913 | 0.0699 | 0.018* | |
H3E | 0.5433 | 0.7257 | 0.0333 | 0.018* | |
C4 | 0.1346 (2) | 0.68464 (12) | 0.00155 (10) | 0.0147 (2) | |
H4C | 0.1078 | 0.6234 | −0.0687 | 0.018* | |
H4D | −0.0094 | 0.6523 | 0.0420 | 0.018* | |
N3 | 0.1192 (2) | 0.82033 (11) | −0.02295 (9) | 0.0153 (2) | |
H3C | 0.253 (3) | 0.8556 (15) | −0.0567 (14) | 0.018* | |
H3A | 0.122 (3) | 0.8772 (15) | 0.0409 (14) | 0.018* | |
H3B | −0.032 (3) | 0.8127 (15) | −0.0727 (14) | 0.018* | |
N4 | 0.8935 (2) | 0.98516 (11) | 0.63823 (9) | 0.0164 (2) | |
H4A | 0.762 (3) | 0.9358 (16) | 0.5854 (14) | 0.020* | |
H4B | 1.043 (3) | 1.0304 (15) | 0.6198 (13) | 0.020* | |
C5 | 0.8681 (2) | 0.99644 (12) | 0.74536 (10) | 0.0123 (2) | |
O3 | 1.04099 (18) | 1.06597 (9) | 0.82274 (8) | 0.01670 (19) | |
C6 | 0.6007 (2) | 0.91625 (12) | 0.77285 (10) | 0.0125 (2) | |
O4 | 0.57424 (18) | 0.92886 (9) | 0.87283 (8) | 0.0169 (2) | |
O5 | 0.43537 (17) | 0.84384 (9) | 0.68968 (7) | 0.01457 (19) | |
N5 | −0.6253 (2) | 0.50466 (11) | 0.66850 (9) | 0.0146 (2) | |
H5A | −0.765 (3) | 0.4711 (15) | 0.6960 (14) | 0.017* | |
H5B | −0.632 (3) | 0.4842 (15) | 0.5946 (14) | 0.017* | |
C7 | −0.4199 (2) | 0.59075 (12) | 0.73629 (10) | 0.0120 (2) | |
O6 | −0.40840 (18) | 0.62595 (9) | 0.83769 (7) | 0.01561 (19) | |
C8 | −0.1838 (2) | 0.64464 (12) | 0.67667 (10) | 0.0117 (2) | |
O7 | 0.00814 (18) | 0.72967 (9) | 0.74660 (8) | 0.01465 (19) | |
H7 | 0.160 (4) | 0.7713 (19) | 0.7159 (17) | 0.048 (6)* | |
O8 | −0.18686 (18) | 0.60920 (9) | 0.57703 (7) | 0.0167 (2) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
N1 | 0.0200 (6) | 0.0261 (6) | 0.0107 (5) | −0.0071 (5) | 0.0036 (4) | 0.0015 (5) |
C1 | 0.0139 (6) | 0.0157 (6) | 0.0112 (6) | 0.0023 (4) | 0.0024 (4) | 0.0034 (5) |
O1 | 0.0174 (5) | 0.0242 (5) | 0.0137 (5) | −0.0052 (4) | 0.0034 (4) | 0.0018 (4) |
C2 | 0.0124 (5) | 0.0144 (5) | 0.0110 (5) | 0.0034 (4) | 0.0015 (4) | 0.0040 (4) |
O2 | 0.0135 (4) | 0.0170 (4) | 0.0143 (4) | −0.0015 (3) | 0.0024 (3) | 0.0037 (3) |
N2 | 0.0123 (5) | 0.0166 (5) | 0.0103 (5) | 0.0001 (4) | 0.0020 (4) | 0.0025 (4) |
C3 | 0.0150 (6) | 0.0185 (6) | 0.0108 (6) | 0.0029 (5) | 0.0032 (5) | 0.0027 (5) |
C4 | 0.0156 (6) | 0.0153 (6) | 0.0115 (6) | 0.0000 (4) | 0.0013 (5) | 0.0030 (5) |
N3 | 0.0173 (5) | 0.0174 (5) | 0.0101 (5) | 0.0026 (4) | 0.0012 (4) | 0.0017 (4) |
N4 | 0.0124 (5) | 0.0208 (5) | 0.0127 (5) | −0.0037 (4) | 0.0025 (4) | 0.0032 (4) |
C5 | 0.0117 (5) | 0.0114 (5) | 0.0142 (6) | 0.0024 (4) | 0.0028 (4) | 0.0030 (4) |
O3 | 0.0136 (4) | 0.0187 (4) | 0.0141 (4) | −0.0019 (3) | 0.0019 (3) | −0.0007 (4) |
C6 | 0.0123 (5) | 0.0108 (5) | 0.0144 (6) | 0.0015 (4) | 0.0030 (4) | 0.0028 (4) |
O4 | 0.0183 (5) | 0.0177 (4) | 0.0127 (4) | −0.0012 (4) | 0.0055 (4) | 0.0016 (3) |
O5 | 0.0124 (4) | 0.0167 (4) | 0.0118 (4) | −0.0021 (3) | 0.0009 (3) | 0.0025 (3) |
N5 | 0.0108 (5) | 0.0179 (5) | 0.0127 (5) | −0.0015 (4) | 0.0027 (4) | 0.0022 (4) |
C7 | 0.0122 (5) | 0.0121 (5) | 0.0129 (6) | 0.0033 (4) | 0.0037 (4) | 0.0042 (4) |
O6 | 0.0158 (4) | 0.0195 (4) | 0.0112 (4) | 0.0023 (3) | 0.0037 (3) | 0.0026 (4) |
C8 | 0.0116 (5) | 0.0123 (5) | 0.0116 (5) | 0.0026 (4) | 0.0021 (4) | 0.0035 (4) |
O7 | 0.0120 (4) | 0.0169 (4) | 0.0124 (4) | −0.0020 (3) | 0.0021 (3) | 0.0015 (3) |
O8 | 0.0164 (4) | 0.0202 (5) | 0.0112 (4) | −0.0003 (4) | 0.0031 (3) | 0.0012 (4) |
Geometric parameters (Å, º) top
N1—C1 | 1.3208 (15) | N3—H3B | 0.908 (17) |
N1—H1A | 0.926 (18) | N4—C5 | 1.3207 (16) |
N1—H1B | 0.841 (19) | N4—H4A | 0.888 (17) |
C1—O1 | 1.2330 (15) | N4—H4B | 0.888 (17) |
C1—C2 | 1.5353 (17) | C5—O3 | 1.2381 (15) |
C2—O2 | 1.2353 (15) | C5—C6 | 1.5542 (17) |
C2—N2 | 1.3297 (15) | C6—O4 | 1.2358 (15) |
N2—C3 | 1.4634 (16) | C6—O5 | 1.2726 (15) |
N2—H2 | 0.838 (16) | N5—C7 | 1.3331 (16) |
C3—C4 | 1.5135 (17) | N5—H5A | 0.860 (17) |
C3—H3D | 0.9700 | N5—H5B | 0.891 (16) |
C3—H3E | 0.9700 | C7—O6 | 1.2303 (15) |
C4—N3 | 1.4918 (16) | C7—C8 | 1.5406 (16) |
C4—H4C | 0.9700 | C8—O8 | 1.2172 (15) |
C4—H4D | 0.9700 | C8—O7 | 1.3015 (15) |
N3—H3C | 0.887 (16) | O7—H7 | 0.96 (2) |
N3—H3A | 0.907 (17) | | |
| | | |
C1—N1—H1A | 119.9 (11) | C4—N3—H3A | 111.0 (9) |
C1—N1—H1B | 121.5 (12) | H3C—N3—H3A | 108.7 (14) |
H1A—N1—H1B | 118.6 (16) | C4—N3—H3B | 109.1 (9) |
O1—C1—N1 | 124.06 (12) | H3C—N3—H3B | 105.0 (14) |
O1—C1—C2 | 121.19 (11) | H3A—N3—H3B | 110.9 (14) |
N1—C1—C2 | 114.75 (11) | C5—N4—H4A | 121.1 (11) |
O2—C2—N2 | 125.02 (12) | C5—N4—H4B | 118.4 (11) |
O2—C2—C1 | 120.66 (10) | H4A—N4—H4B | 120.4 (15) |
N2—C2—C1 | 114.31 (11) | O3—C5—N4 | 124.30 (11) |
C2—N2—C3 | 121.79 (11) | O3—C5—C6 | 119.40 (11) |
C2—N2—H2 | 116.5 (11) | N4—C5—C6 | 116.30 (11) |
C3—N2—H2 | 120.6 (11) | O4—C6—O5 | 127.52 (11) |
N2—C3—C4 | 115.14 (10) | O4—C6—C5 | 116.40 (11) |
N2—C3—H3D | 108.5 | O5—C6—C5 | 116.07 (10) |
C4—C3—H3D | 108.5 | C7—N5—H5A | 118.9 (11) |
N2—C3—H3E | 108.5 | C7—N5—H5B | 123.6 (10) |
C4—C3—H3E | 108.5 | H5A—N5—H5B | 117.3 (15) |
H3D—C3—H3E | 107.5 | O6—C7—N5 | 125.47 (11) |
N3—C4—C3 | 113.03 (10) | O6—C7—C8 | 120.73 (11) |
N3—C4—H4C | 109.0 | N5—C7—C8 | 113.80 (11) |
C3—C4—H4C | 109.0 | O8—C8—O7 | 126.90 (11) |
N3—C4—H4D | 109.0 | O8—C8—C7 | 122.18 (11) |
C3—C4—H4D | 109.0 | O7—C8—C7 | 110.93 (10) |
H4C—C4—H4D | 107.8 | C8—O7—H7 | 116.6 (12) |
C4—N3—H3C | 112.0 (10) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O7—H7···O5 | 0.96 (2) | 1.55 (2) | 2.5004 (12) | 169.0 (19) |
N1—H1A···O5 | 0.926 (18) | 1.941 (18) | 2.8665 (15) | 178.0 (16) |
N1—H1B···O8 | 0.841 (19) | 2.513 (17) | 3.0261 (14) | 120.3 (15) |
N2—H2···O3i | 0.838 (16) | 2.202 (16) | 2.9377 (14) | 146.6 (14) |
N3—H3C···O4ii | 0.887 (16) | 2.018 (17) | 2.9027 (14) | 175.8 (15) |
N3—H3A···O3iii | 0.907 (17) | 2.029 (17) | 2.8606 (14) | 151.7 (14) |
N3—H3A···O4iii | 0.907 (17) | 2.295 (16) | 2.9695 (15) | 130.9 (13) |
N3—H3B···O7ii | 0.908 (17) | 2.305 (16) | 2.7828 (14) | 112.6 (12) |
N3—H3B···O6ii | 0.908 (17) | 2.449 (17) | 3.1502 (15) | 134.2 (12) |
N3—H3B···O4iv | 0.908 (17) | 2.639 (16) | 3.4143 (15) | 143.9 (13) |
N4—H4A···O1 | 0.888 (17) | 2.191 (17) | 2.9811 (15) | 148.0 (14) |
N4—H4B···O1i | 0.888 (17) | 1.964 (17) | 2.8497 (14) | 174.7 (15) |
N5—H5A···O2v | 0.860 (17) | 2.052 (17) | 2.9122 (14) | 179.4 (16) |
N5—H5B···O8v | 0.891 (16) | 2.181 (17) | 3.0172 (15) | 156.2 (14) |
Symmetry codes: (i) −x+2, −y+2, −z+1; (ii) x, y, z−1; (iii) −x+1, −y+2, −z+1; (iv) x−1, y, z−1; (v) −x−1, −y+1, −z+1. |
Experimental details
Crystal data |
Chemical formula | C4H10N3O2+·C2H2NO3−·C2H3NO3 |
Mr | 309.25 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 100 |
a, b, c (Å) | 5.1723 (2), 10.3560 (4), 12.1866 (5) |
α, β, γ (°) | 97.765 (2), 97.304 (2), 102.394 (2) |
V (Å3) | 623.43 (4) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 0.15 |
Crystal size (mm) | 0.6 × 0.1 × 0.1 |
|
Data collection |
Diffractometer | Bruker APEXII CCD area-detector diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 13083, 3812, 2895 |
Rint | 0.035 |
(sin θ/λ)max (Å−1) | 0.715 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.040, 0.106, 1.04 |
No. of reflections | 3812 |
No. of parameters | 224 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.54, −0.24 |
Selected geometric parameters (Å, º) topN1—C1 | 1.3208 (15) | C5—O3 | 1.2381 (15) |
C1—O1 | 1.2330 (15) | C5—C6 | 1.5542 (17) |
C1—C2 | 1.5353 (17) | C6—O4 | 1.2358 (15) |
C2—O2 | 1.2353 (15) | C6—O5 | 1.2726 (15) |
C2—N2 | 1.3297 (15) | N5—C7 | 1.3331 (16) |
N2—C3 | 1.4634 (16) | C7—O6 | 1.2303 (15) |
C3—C4 | 1.5135 (17) | C7—C8 | 1.5406 (16) |
C4—N3 | 1.4918 (16) | C8—O8 | 1.2172 (15) |
N4—C5 | 1.3207 (16) | C8—O7 | 1.3015 (15) |
| | | |
O1—C1—N1 | 124.06 (12) | N4—C5—C6 | 116.30 (11) |
O1—C1—C2 | 121.19 (11) | O4—C6—O5 | 127.52 (11) |
N1—C1—C2 | 114.75 (11) | O4—C6—C5 | 116.40 (11) |
O2—C2—N2 | 125.02 (12) | O5—C6—C5 | 116.07 (10) |
O2—C2—C1 | 120.66 (10) | O6—C7—N5 | 125.47 (11) |
N2—C2—C1 | 114.31 (11) | O6—C7—C8 | 120.73 (11) |
C2—N2—C3 | 121.79 (11) | N5—C7—C8 | 113.80 (11) |
N2—C3—C4 | 115.14 (10) | O8—C8—O7 | 126.90 (11) |
N3—C4—C3 | 113.03 (10) | O8—C8—C7 | 122.18 (11) |
O3—C5—N4 | 124.30 (11) | O7—C8—C7 | 110.93 (10) |
O3—C5—C6 | 119.40 (11) | | |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
O7—H7···O5 | 0.96 (2) | 1.55 (2) | 2.5004 (12) | 169.0 (19) |
N1—H1A···O5 | 0.926 (18) | 1.941 (18) | 2.8665 (15) | 178.0 (16) |
N1—H1B···O8 | 0.841 (19) | 2.513 (17) | 3.0261 (14) | 120.3 (15) |
N2—H2···O3i | 0.838 (16) | 2.202 (16) | 2.9377 (14) | 146.6 (14) |
N3—H3C···O4ii | 0.887 (16) | 2.018 (17) | 2.9027 (14) | 175.8 (15) |
N3—H3A···O3iii | 0.907 (17) | 2.029 (17) | 2.8606 (14) | 151.7 (14) |
N3—H3A···O4iii | 0.907 (17) | 2.295 (16) | 2.9695 (15) | 130.9 (13) |
N3—H3B···O7ii | 0.908 (17) | 2.305 (16) | 2.7828 (14) | 112.6 (12) |
N3—H3B···O6ii | 0.908 (17) | 2.449 (17) | 3.1502 (15) | 134.2 (12) |
N3—H3B···O4iv | 0.908 (17) | 2.639 (16) | 3.4143 (15) | 143.9 (13) |
N4—H4A···O1 | 0.888 (17) | 2.191 (17) | 2.9811 (15) | 148.0 (14) |
N4—H4B···O1i | 0.888 (17) | 1.964 (17) | 2.8497 (14) | 174.7 (15) |
N5—H5A···O2v | 0.860 (17) | 2.052 (17) | 2.9122 (14) | 179.4 (16) |
N5—H5B···O8v | 0.891 (16) | 2.181 (17) | 3.0172 (15) | 156.2 (14) |
Symmetry codes: (i) −x+2, −y+2, −z+1; (ii) x, y, z−1; (iii) −x+1, −y+2, −z+1; (iv) x−1, y, z−1; (v) −x−1, −y+1, −z+1. |
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Hydrogen bonding is a topic that receives much attention, as it pervades a great many aspects of the world of condensed matter. Hydrogen-bond interactions are crucial in directing structure and subsequent function, from the nature and properties of DNA (Watson & Crick, 1953) to the bizarre polyamorphization of water (Mishima & Stanley, 1998). Taking a materials perspective, there are many ways in which the control of aggregation through hydrogen bonding can be used to advance some specific physical property. Structural assembly can be achieved by using molecules where a particular hydrogen-bond motif is much lower in energy than alternative geometric arrangements (Desiraju, 1995). Such molecules, often dubbed tectons, give a level of predictability to the structures of aggregates. Thus Yang et al. (1994) and Keizer et al. (2005) described molecules which self-assemble in solution to form hexameric supramolecular entities. In the solid state, hydrogen-bond interactions that result in discrete adducts can be used to induce mesomorphic behaviour (Bruce & Price, 1994; Willis et al., 1995; Price et al., 1996; Kato et al., 2006), while more extensive interactions can result in predictable extended network structures (Subramanian & Zaworotko, 1994; Coles et al., 2002). Understanding the nature of strong hydrogen bonds is both fundamental to our theoretical understanding of these interactions and useful as a practical tool to engineer specific structural features.
The title compound, (I), consists of three distinct molecular components, a 2-(N-oxamido)ethylammonium cation, C4H10N3O2+, an oxamide anion, C2H2NO3-, and a neutral molecule of oxamic acid, C2H3NO3 (Fig. 1, Table 1). Out of the 11 potential hydrogen-bond donors (N—H and O—H), there are at least 11 distinct hydrogen bonds distributed over eight potential acceptor atoms. Hydrogen-bond parameters are given in Table 2. The shortest and strongest interaction is the O—H···O ionic hydrogen bond between atoms O7 of the carboxylic acid and O5 of the carboxylate ion, with O···O = 2.5004 (12) Å. Strong O—H···O hydrogen bonds are defined with O···O separations in the range 2.50–2.65 Å, and very strong hydrogen bonds with O···O < 2.50 Å (Pimentel & McClellan, 1971; Gilli et al., 1994). Thus, in the present case the hydrogen bond is a strong interaction, and such carboxylate/carboxylic acid adducts are often considered as distinct structural fragments. Thus, (I) can be considered as 2-(N-oxamido)ethylammonium hydrogen bis(oxamate), and is best formulated as C4H10N3O2+.C4H5N2O6- or (H3NCH2CH2NHCOCONH2)+.[(H2NCOCO2)2H]-.
It is well known that as hydrogen bonds become shorter and stronger, the potential will change from an asymmetric shape to a symmetric double-well shape and ultimately to a single symmetric flat-bottomed potential (Emsley, 1980; Perrin & Nielson, 1997). However, environmental factors can have a very significant effect on the nature of the hydrogen-bond potential. Such effects can be seen in all condensed matter states. Perrin (1994) has shown the effect on molecules in different solvents, while Price et al. (1995, 1997) have shown changes in the potential as mesomorphic hydrogen-bonded adducts pass through different liquid crystal phases. The solid state is replete with examples where small environmental perturbations affect the hydrogen bond. For example, in the mineral schultonite (PbHAsO4), the H atom experiences a double-well potential, and at high temperatures the H atom is positionally disordered over the two sites. On cooling, a broken symmetry and a localization of the H atom to one side are observed, resulting in a ferroelectric phase (Wilson, 1997).
Anionic hydrogen bis(carboxylates) are well known to form strong hydrogen bonds (Price et al., 2005), and in many of these the hydrogen-bond potential is symmetric. However, it is particularly difficult, using X-ray diffraction data, to discriminate single-well from double-well potentials based upon the H-atom position. There is one reported structure that contains the hydrogen bis(oxamate) monoanion (Kovalchukkova et al., 2002), where crystallographic symmetry imposes a symmetric potential and, in the reported model, the H atom is located centrally. In (I), the hydrogen bis(oxamate) anion not only lacks any crystallographic symmetry, but is additionally comprised of two oxamate groups with very different conformations (Fig. 2a). Labelled oxamates A and B, these molecules have planar geometries in which the carboxylate carbonyl group is clearly localized. In oxamate A, the C═O/C—O distances are 1.236 (2)/1.273 (2) Å (Δ = 0.037 Å) and in this fragment the carbonyl O atoms are related by a cis geometry. In oxamate B, the C═ O/C—O distances are 1.217 (2)/1.302 (3) Å (Δ = 0.085 Å) and the carbonyl O atoms in a trans geometry. The H atom in this hydrogen bis(oxamate) anion is clearly visible in the Fourier difference map and is located on oxamate B.
The fact that we observe the structure depicted in Fig. 2(a) and not the alternative geometry shown in Fig. 2(b) has interesting implications for the relative basicities of the two distinct carboxylate O atoms in the oxamate anion A. Clearly, the O atom trans to the NH2 group of oxamate A is more basic than the O atom in cis geometry (Fig. 2c). Under solution conditions, where free rotation of the C—C bond occurs, it does not normally make sense to distinguish between these sites, but in rigid solids, and where molecular conformations may be restrained, such a geometric comparison is very useful.
While the anionic hydrogen bis(oxamate) entity contains the shortest and strongest hydrogen bond, we note that in general the interactions of the amide H atoms are generally shorter and more linear than those of the cationic ammonium group (Table 2), in which atom H3B may even form a trifurcated interaction. The stronger amide hydrogen-bond interactions result in a tape-like structure, where all of the oxamide and oxamate groups are approximately coplanar and the peripheral ethyleneammonium group adopts a gauche conformation (Fig. 3). These ribbons run parallel to the (310) direction, and adjacent ribbons are held together in a three-dimensional net through weaker hydrogen bonds to the ethyleneammonium group. Within the ribbon there are seven distinct hydrogen bonds, which together form a number of different motifs. We note the dominance of a first-order R22(10) homodromic motif and two second-order R22(9) homodromic nets (Etter et al., 1990) as significant components of the structure (Fig. 3a). These interactions, along with the related R22(8) motif, have been highlighted by Aakeröy et al. (1996) as key hydrogen-bonded patterns in the architecture of oxamide and oxamate salts. A search of latest version of the Cambridge Structural Database (Version 5.30; Allen, 2002) using CONQUEST (Version 1.11; Bruno et al., 2002) reveals the repeated occurrence of these motifs and confirms their importance in determining the network structures of oxamide-containing compounds.