Redetermination of ammonium oxalate oxalic acid dihydrate

The crystal structure of the triclinic form of the title compound, NH₄⁺·C₂HO₄⁻·C₂H₂O₄·2H₂O, has been redetermined, providing a significant increase in the precision of the derived geometric parameters. The asymmetric unit comprises an ammonium cation, an oxalate anion, half each of two oxalic acid mol­ecules, each disposed about a centre of inversion, and two water mol­ecules of crystallization.

Key indicators

• Single-crystal X-ray study
• T = 298 K
• Mean [sigma](C-C) = 0.001 Å
• R factor = 0.043
• wR factor = 0.132
• Data-to-parameter ratio = 34.9

checkCIF/PLATON results

No syntax errors found



Alert level A
PLAT772_ALERT_2_A Suspect O-H Bond in CIF:      O9     -H6      ..       1.46 Ang.

Author Response: See text's comment on this point

Alert level B
PLAT029_ALERT_3_B _diffrn_measured_fraction_theta_full Low .......       0.96
PLAT417_ALERT_2_B Short Inter D-H..H-D       H1     ..  H6      ..       1.97 Ang.
PLAT417_ALERT_2_B Short Inter D-H..H-D       H2     ..  H6      ..       1.94 Ang.
PLAT417_ALERT_2_B Short Inter D-H..H-D       H4     ..  H5      ..       2.05 Ang.
PLAT432_ALERT_2_B Short Inter X...Y Contact  O1     ..  C2      ..       2.91 Ang.

Alert level C
PLAT042_ALERT_1_C Calc. and Rep. MoietyFormula Strings Differ ....          ?
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       3.11
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O3     -   H7     ...       1.04 Ang.
PLAT355_ALERT_3_C Long    O-H Bond (0.82A)   O2     -   H6     ...       1.01 Ang.
PLAT369_ALERT_2_C Long   C(sp2)-C(sp2) Bond  C1     -   C1_a   ...       1.55 Ang.
PLAT369_ALERT_2_C Long   C(sp2)-C(sp2) Bond  C2     -   C2_b   ...       1.54 Ang.
PLAT369_ALERT_2_C Long   C(sp2)-C(sp2) Bond  C3     -   C4     ...       1.55 Ang.
PLAT432_ALERT_2_C Short Inter X...Y Contact  O1     ..  C2      ..       2.98 Ang.

   1 ALERT level A = In general: serious problem
   5 ALERT level B = Potentially serious problem
   8 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   1 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
  10 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

---

Computing details

Data collection: XCS (Colapietro et al., 1992); cell refinement: XCS; data reduction: XCS; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

ammonium oxalate oxalic acid dihydrate

Crystal data

NH4^+·C2HO4^−·C2H2O4·2H2O	Z = 2
Mr = 233.14	F(000) = 244
Triclinic, P1	Dx = 1.652 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.710689 Å
a = 6.3387 (8) Å	Cell parameters from 121 reflections
b = 7.2227 (9) Å	θ = 20–24°
c = 10.5527 (11) Å	µ = 0.17 mm^−1
α = 94.172 (10)°	T = 298 K
β = 100.274 (10)°	Block, colourless
γ = 97.704 (10)°	0.30 × 0.20 × 0.20 mm
V = 468.77 (10) Å^3

Data collection

Huber CS four-circle diffractometer	Rint = 0.021
Radiation source: X-ray tube	θmax = 42.0°, θmin = 2.9°
Graphite monochromator	h = 0→11
ω scans	k = −13→13
6934 measured reflections	l = −19→19
6283 independent reflections	3 standard reflections every 97 reflections
5265 reflections with I > 2σ(I)	intensity decay: 1%

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.043	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.132	All H-atom parameters refined
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0705P)^2 + 0.0474P] where P = (Fo^2 + 2Fc^2)/3
6283 reflections	(Δ/σ)max < 0.001
180 parameters	Δρmax = 0.44 e Å^−3
0 restraints	Δρmin = −0.31 e Å^−3

Special details

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 (Ų)

	x	y	z	Uiso*/Ueq
O1	0.66148 (9)	0.66530 (8)	0.43215 (5)	0.03350 (10)
O2	0.49852 (9)	0.07707 (9)	0.34789 (5)	0.03568 (11)
O3	0.34181 (10)	0.49021 (8)	0.34594 (5)	0.03643 (12)
O4	0.23800 (9)	−0.09787 (8)	0.42365 (5)	0.03535 (11)
O5	0.81598 (13)	0.43035 (7)	0.18644 (5)	0.04050 (14)
O6	0.72643 (11)	0.15335 (7)	0.06757 (5)	0.03674 (12)
O7	0.66656 (11)	0.33721 (7)	−0.14887 (5)	0.03692 (12)
O8	0.76210 (11)	0.60954 (7)	−0.02241 (5)	0.03831 (13)
O9	0.23164 (10)	0.07154 (8)	0.14523 (5)	0.03311 (10)
O10	0.94415 (10)	0.25231 (11)	0.37405 (6)	0.04401 (15)
N1	0.84141 (11)	0.84410 (8)	0.22442 (6)	0.03114 (10)
C1	0.50660 (10)	0.54737 (7)	0.43714 (5)	0.02526 (9)
C2	0.41858 (10)	−0.00905 (8)	0.43560 (5)	0.02634 (9)
C3	0.75572 (10)	0.32392 (8)	0.07806 (5)	0.02591 (9)
C4	0.72488 (10)	0.43596 (8)	−0.04184 (5)	0.02586 (9)
H1	0.239 (3)	0.186 (3)	0.1174 (18)	0.074 (5)*
H2	0.255 (2)	0.003 (2)	0.0830 (15)	0.053 (4)*
H3	0.862 (4)	0.218 (3)	0.437 (2)	0.093 (6)*
H4	1.070 (3)	0.304 (2)	0.4216 (19)	0.070 (5)*
H5	0.866 (3)	0.357 (2)	0.2592 (15)	0.055 (4)*
H6	0.393 (3)	0.071 (2)	0.2627 (17)	0.069 (5)*
H7	0.347 (3)	0.554 (3)	0.2609 (19)	0.075 (5)*
H8	0.760 (3)	0.800 (3)	0.2804 (18)	0.073 (5)*
H9	0.973 (3)	0.867 (2)	0.2685 (16)	0.058 (4)*
H10	0.795 (4)	0.943 (3)	0.188 (2)	0.095 (6)*
H11	0.815 (2)	0.750 (2)	0.1599 (15)	0.052 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0368 (2)	0.0350 (2)	0.02636 (18)	−0.00582 (17)	0.00462 (16)	0.01145 (16)
O2	0.0339 (2)	0.0455 (3)	0.02599 (19)	−0.00090 (19)	0.00202 (16)	0.01405 (18)
O3	0.0426 (3)	0.0356 (2)	0.02447 (18)	−0.00835 (19)	−0.00450 (17)	0.01198 (16)
O4	0.0306 (2)	0.0423 (3)	0.0290 (2)	−0.00429 (17)	−0.00101 (16)	0.01066 (18)
O5	0.0714 (4)	0.0268 (2)	0.02048 (17)	0.0063 (2)	0.0011 (2)	0.00472 (14)
O6	0.0594 (3)	0.02220 (17)	0.02691 (19)	0.00290 (18)	0.0036 (2)	0.00826 (14)
O7	0.0583 (3)	0.0279 (2)	0.02035 (16)	0.00007 (19)	−0.00063 (18)	0.00594 (14)
O8	0.0653 (4)	0.02177 (17)	0.0267 (2)	0.0053 (2)	0.0044 (2)	0.00816 (15)
O9	0.0437 (3)	0.0316 (2)	0.02445 (18)	0.00745 (18)	0.00410 (17)	0.00880 (15)
O10	0.0366 (3)	0.0581 (4)	0.0332 (2)	−0.0065 (2)	−0.00142 (19)	0.0222 (2)
N1	0.0374 (3)	0.0266 (2)	0.0281 (2)	−0.00018 (17)	0.00499 (18)	0.00645 (16)
C1	0.0323 (2)	0.02228 (18)	0.02043 (18)	0.00096 (16)	0.00349 (15)	0.00656 (14)
C2	0.0286 (2)	0.0266 (2)	0.02299 (19)	0.00306 (16)	0.00198 (16)	0.00588 (15)
C3	0.0342 (2)	0.02283 (19)	0.02089 (18)	0.00418 (16)	0.00387 (16)	0.00705 (14)
C4	0.0335 (2)	0.02303 (19)	0.02084 (18)	0.00365 (16)	0.00293 (16)	0.00756 (14)

Geometric parameters (Å, º)

O1—C1	1.2219 (7)	O9—H2	0.838 (16)
O2—C2	1.2912 (8)	O9—H6	1.459 (18)
O2—H6	1.016 (18)	O10—H3	0.94 (2)
O3—C1	1.2867 (8)	O10—H4	0.879 (19)
O3—H7	1.042 (19)	N1—H8	0.90 (2)
O4—C2	1.2155 (8)	N1—H9	0.866 (18)
O5—C3	1.2970 (8)	N1—H10	0.89 (2)
O5—H5	0.995 (16)	N1—H11	0.903 (16)
O6—C3	1.2150 (7)	C1—C1^i	1.5464 (10)
O7—C4	1.2586 (8)	C2—C2^ii	1.5386 (11)
O8—C4	1.2392 (7)	C3—C4	1.5483 (7)
O9—H1	0.89 (2)
C2—O2—H6	113.9 (9)	O1—C1—O3	126.54 (5)
C1—O3—H7	114.2 (10)	O1—C1—C1^i	120.29 (7)
C3—O5—H5	111.3 (9)	O3—C1—C1^i	113.16 (6)
H1—O9—H2	103.7 (15)	O4—C2—O2	126.72 (6)
H1—O9—H6	110.8 (14)	O4—C2—C2^ii	120.98 (7)
H2—O9—H6	112.2 (12)	O2—C2—C2^ii	112.30 (6)
H3—O10—H4	102.3 (17)	O6—C3—O5	125.20 (5)
H8—N1—H9	104.9 (15)	O6—C3—C4	121.59 (5)
H8—N1—H10	112.7 (18)	O5—C3—C4	113.21 (5)
H9—N1—H10	114.3 (16)	O8—C4—O7	127.69 (5)
H8—N1—H11	103.1 (14)	O8—C4—C3	117.30 (5)
H9—N1—H11	115.9 (14)	O7—C4—C3	115.00 (5)
H10—N1—H11	105.6 (17)
O6—C3—C4—O8	−178.70 (7)	O6—C3—C4—O7	0.48 (10)
O5—C3—C4—O8	0.76 (9)	O5—C3—C4—O7	179.94 (7)

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) −x+1, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H6···O9	1.016 (18)	1.459 (18)	2.4731 (8)	175.7 (17)
O3—H7···O7^iii	1.042 (19)	1.463 (19)	2.4974 (7)	171.3 (18)
O5—H5···O10	0.995 (16)	1.517 (16)	2.5120 (8)	177.4 (14)
O9—H2···O6^iv	0.838 (16)	1.913 (17)	2.7476 (9)	173.4 (15)
O9—H1···O8^iii	0.89 (2)	1.85 (2)	2.7231 (8)	166.7 (18)
O10—H4···O1^v	0.879 (19)	2.06 (2)	2.8959 (9)	158.3 (16)
O10—H3···O4^ii	0.94 (2)	1.92 (2)	2.8311 (8)	162 (2)
N1—H8···O1	0.90 (2)	2.079 (19)	2.9466 (8)	162.0 (17)
N1—H9···O4^vi	0.866 (18)	2.101 (18)	2.9359 (9)	161.6 (15)
N1—H10···O6^vii	0.89 (2)	2.09 (2)	2.9671 (8)	166 (2)
N1—H11···O8	0.903 (16)	2.058 (16)	2.9275 (9)	161.2 (14)

Symmetry codes: (ii) −x+1, −y, −z+1; (iii) −x+1, −y+1, −z; (iv) −x+1, −y, −z; (v) −x+2, −y+1, −z+1; (vi) x+1, y+1, z; (vii) x, y+1, z.