L-Alaninium oxalate

In the title compound, C₃H₈NO₂⁺·C₂HO₄⁻, the alanine mol­ecule exists in the cationic form and the oxalic acid mol­ecule in the mono-ionized state. The alaninium and semi-oxalate ions form alternate columns leading to a layered arrangement parallel to the ac plane and each such layer is interconnected to the other through N—H...O hydrogen bonds. The overall aggregation pattern is distinctly different from that observed in the glycine–oxalic acid complex.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.030
• wR factor = 0.083
• Data-to-parameter ratio = 7.8

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



PLAT_369  Alert C Long   C(sp2)-C(sp2) Bond  C(4)   -   C(5)   =       1.55 Ang.

General Notes



REFLT_03
         From the CIF: _diffrn_reflns_theta_max           67.91
         From the CIF: _reflns_number_total                879
         Count of symmetry unique reflns          879
         Completeness (_total/calc)            100.00%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured         0
         Fraction of Friedel pairs measured     0.000
         Are heavy atom types Z>Si present           no
          Please check that the estimate of the number of Friedel pairs is
          correct. If it is not, please give the correct count in the
          _publ_section_exptl_refinement section of the submitted CIF.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

X-ray studies on crystalline complexes of amino acids with carboxylic acids have provided a wealth of information regarding intermolecular interactions and biomolecular aggregation patterns (Vijayan, 1988; Prasad & Vijayan, 1993). The crystal structures of glycinium oxalate (Subha Nandhini et al., 2001) and sarcosinium oxalate monohydrate (Krishnakumar et al., 1999) were elucidated in our laboratory. The present study reports the crystal structure of L-alaninium oxalate, (I), as part of a series of investigations being carried out to observe conformational changes in amino acid molecules and characteristic hydrogen-bonding patterns in their crystal structures.

Fig. 1 shows the molecular structure with the numering scheme. The alanine molecule exists in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The oxalic acid molecule exists in a mono-ionized state. The conformation of the L-alaninum cation about the N—C^α bond corresponds to the staggered ethane-type. A common feature among the crystal structures of glycinium oxalate and (I) is that the shortest cell dimensions are similar, 5.650 (2) and 5.6304 (15) Å, respectively. The semi-oxalate ions form hydrogen-bonded strings along the shortest cell axis, generated by translation, as in the structures of oxalic acid complexes of glycine (Subha Nandhini et al., 2001) and lysine (Venkatraman et al., 1997).

In the asymmetric unit, the L-alaninium cation and the semi-oxalate anion are linked to each other through a N—H···O hydrogen bond (Fig. 1). The head-to-tail hydrogen bond, with O2 of the carboxyl group as acceptor, observed among the amino acid molecules in the crystal structure may be described as a zigzag sequence along the 2₁ screw axis along the direction of the a axis. The alaninium and semi-oxalate ions form alternate columns leading to a layered arrangement parallel to the ac plane and each such layer is interconnected to the other through N—H···O hydrogen bonds. Two short C···O contacts involving the carboxyl oxygen of the alaninium ion [C1···O2(-1/2 + x, 3/2 - y, -z) = 2.931 (3) Å and C2···O2(-1/2 + x, 3/2 - y, -z) = 2.977 (3) Å] is also observed among these layers. The slight difference observed in the bond lengths of C5—O5 and C5—O6 in the carboxylate group of the semi-oxalate ion may be attributed to the difference in the strengths of the N—H···O hydrogen bonds in which both O5 and O6 are involved (Table 2). The overall aggregation pattern is distinctly different from that observed in the glycine–oxalic acid complex.

S2. Experimental

Crystals of (I) were grown from a saturated aqueous solution containing L-alanine and oxalic acid in a stoichiometric ratio.

S3. Refinement

The absolute structure of (I) was not established by the analysis but is known from the configuration of the starting reagents. 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.

Computing details

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.

Figures

Fig. 1. The molecular structure of with the atom-numbering scheme and 50% probability displacement ellipsoids.

L-alaninium oxalate

Crystal data

C3H8NO2^+·C2HO4^−	Dx = 1.490 Mg m^−3 Dm = 1.49 Mg m^−3 Dm measured by flotation in a mixture of carbon tetrachloride and bromoform
Mr = 179.13	Cu Kα radiation, λ = 1.54180 Å
Orthorhombic, P212121	Cell parameters from 25 reflections
a = 5.6304 (15) Å	θ = 4–68°
b = 7.2353 (15) Å	µ = 1.23 mm^−1
c = 19.597 (3) Å	T = 293 K
V = 798.3 (2) Å^3	Needle, colourless
Z = 4	0.2 × 0.15 × 0.11 mm
F(000) = 376

Data collection

Enraf-Nonius sealed tube diffractometer	853 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 67.9°, θmin = 4.5°
ω–2θ scans	h = 0→6
Absorption correction: ψ scan (North et al., 1968)	k = 0→8
Tmin = 0.79, Tmax = 0.87	l = 0→23
879 measured reflections	2 standard reflections every 25 reflections
879 independent reflections	intensity decay: 0.1%

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.030	w = 1/[σ^2(Fo^2) + (0.0481P)^2 + 0.1739P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.083	(Δ/σ)max < 0.001
S = 1.09	Δρmax = 0.14 e Å^−3
879 reflections	Δρmin = −0.14 e Å^−3
112 parameters	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
0 restraints	Extinction coefficient: 0.040 (3)
Primary atom site location: structure-invariant direct methods	Absolute structure: see text
Secondary atom site location: difference Fourier map

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
N1	0.2644 (3)	0.8562 (2)	0.10946 (7)	0.0359 (4)
H1A	0.1867	0.8789	0.1481	0.054*
H1B	0.4196	0.8708	0.1163	0.054*
H1C	0.2356	0.7408	0.0962	0.054*
O1	0.1991 (3)	0.9924 (3)	−0.06326 (7)	0.0511 (5)
H1	0.2798	0.9719	−0.0973	0.077*
O2	0.5153 (3)	0.8816 (2)	−0.00816 (7)	0.0411 (4)
O3	0.4157 (3)	0.5324 (4)	0.21396 (8)	0.0623 (7)
H3	0.5443	0.5063	0.2311	0.093*
O4	0.2719 (3)	0.4667 (3)	0.31722 (7)	0.0489 (5)
O5	−0.0096 (3)	0.5505 (2)	0.16329 (6)	0.0410 (4)
O6	−0.1695 (3)	0.4814 (4)	0.26207 (8)	0.0760 (8)
C1	0.3174 (3)	0.9450 (3)	−0.00888 (9)	0.0322 (5)
C2	0.1832 (4)	0.9866 (3)	0.05590 (9)	0.0342 (5)
H2	0.0125	0.9702	0.0481	0.041*
C3	0.2320 (7)	1.1841 (3)	0.07866 (13)	0.0664 (9)
H3A	0.1459	1.2093	0.1199	0.100*
H3B	0.1820	1.2683	0.0436	0.100*
H3C	0.3990	1.1993	0.0868	0.100*
C4	0.2478 (4)	0.5021 (4)	0.25784 (10)	0.0344 (4)
C5	0.0000 (3)	0.5137 (3)	0.22394 (9)	0.0314 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0392 (10)	0.0462 (9)	0.0223 (7)	−0.0056 (9)	0.0030 (7)	−0.0009 (7)
O1	0.0435 (9)	0.0828 (12)	0.0269 (7)	0.0179 (11)	0.0048 (6)	0.0122 (8)
O2	0.0390 (8)	0.0535 (8)	0.0308 (7)	0.0133 (7)	0.0067 (6)	0.0025 (7)
O3	0.0209 (7)	0.1291 (19)	0.0369 (8)	0.0020 (11)	0.0013 (6)	0.0228 (11)
O4	0.0315 (7)	0.0865 (12)	0.0286 (7)	0.0002 (9)	−0.0048 (6)	0.0114 (7)
O5	0.0320 (7)	0.0665 (10)	0.0246 (6)	−0.0041 (8)	−0.0033 (6)	0.0080 (6)
O6	0.0203 (7)	0.172 (2)	0.0361 (8)	−0.0033 (13)	0.0015 (6)	0.0402 (12)
C1	0.0353 (10)	0.0340 (9)	0.0271 (9)	0.0027 (8)	0.0044 (8)	0.0029 (8)
C2	0.0350 (10)	0.0404 (10)	0.0273 (9)	0.0051 (11)	0.0042 (8)	−0.0018 (8)
C3	0.105 (3)	0.0392 (11)	0.0552 (14)	0.0083 (17)	0.0140 (18)	−0.0081 (11)
C4	0.0212 (8)	0.0548 (11)	0.0273 (9)	−0.0004 (9)	−0.0006 (8)	0.0063 (9)
C5	0.0222 (9)	0.0469 (11)	0.0252 (8)	−0.0011 (10)	−0.0007 (7)	0.0060 (8)

Geometric parameters (Å, º)

N1—C2	1.483 (3)	O5—C5	1.219 (2)
N1—H1A	0.8900	O6—C5	1.235 (2)
N1—H1B	0.8900	C1—C2	1.508 (3)
N1—H1C	0.8900	C2—C3	1.522 (3)
O1—C1	1.303 (2)	C2—H2	0.9800
O1—H1	0.8200	C3—H3A	0.9600
O2—C1	1.205 (2)	C3—H3B	0.9600
O3—C4	1.297 (2)	C3—H3C	0.9600
O3—H3	0.8200	C4—C5	1.548 (3)
O4—C4	1.199 (2)
C2—N1—H1A	109.5	C1—C2—H2	109.6
C2—N1—H1B	109.5	C3—C2—H2	109.6
H1A—N1—H1B	109.5	C2—C3—H3A	109.5
C2—N1—H1C	109.5	C2—C3—H3B	109.5
H1A—N1—H1C	109.5	H3A—C3—H3B	109.5
H1B—N1—H1C	109.5	C2—C3—H3C	109.5
C1—O1—H1	109.5	H3A—C3—H3C	109.5
C4—O3—H3	109.5	H3B—C3—H3C	109.5
O2—C1—O1	125.65 (18)	O4—C4—O3	126.7 (2)
O2—C1—C2	121.97 (18)	O4—C4—C5	122.01 (18)
O1—C1—C2	112.32 (17)	O3—C4—C5	111.32 (15)
N1—C2—C1	108.33 (16)	O5—C5—O6	126.65 (19)
N1—C2—C3	109.50 (18)	O5—C5—C4	118.05 (17)
C1—C2—C3	110.07 (19)	O6—C5—C4	115.29 (15)
N1—C2—H2	109.6
O2—C1—C2—N1	−29.3 (3)	O4—C4—C5—O5	180.0 (2)
O1—C1—C2—N1	153.29 (18)	O3—C4—C5—O5	−1.0 (3)
O2—C1—C2—C3	90.4 (3)	O4—C4—C5—O6	−1.0 (4)
O1—C1—C2—C3	−87.0 (2)	O3—C4—C5—O6	178.1 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O6^i	0.89	1.91	2.728 (2)	152
N1—H1B···O4^ii	0.89	2.28	3.085 (2)	150
N1—H1C···O2^iii	0.89	2.30	2.978 (2)	133
N1—H1C···O5	0.89	2.35	2.896 (2)	120
O1—H1···O5^iv	0.82	1.76	2.575 (2)	170
O3—H3···O6^v	0.82	1.73	2.545 (2)	172

Symmetry codes: (i) −x, y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1/2; (iii) x−1/2, −y+3/2, −z; (iv) x+1/2, −y+3/2, −z; (v) x+1, y, z.