DL-Aspartic acid

A form of DL-aspartic acid, C₄H₇NO₄ is presented, which crystallizes in the same space group as the previously reported form but with a slightly different a axis. Its structure exhibits a three-dimensional supra­molecular network of N—H...O and O—H...O bonds, which stabilizes the crystal packing.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.038
• wR factor = 0.103
• Data-to-parameter ratio = 10.0

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT222_ALERT_3_B Large Non-Solvent    H     Ueq(max)/Ueq(min) ...       4.62 Ratio
PLAT430_ALERT_2_B Short Inter D...A Contact  O1     ..  O1      ..       2.84 Ang.

Alert level C
PLAT066_ALERT_1_C Predicted and Reported Transmissions Identical .          ?
PLAT088_ALERT_3_C Poor Data / Parameter Ratio ....................       9.95
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.19

Alert level G
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        293 K
PLAT200_ALERT_1_G Check the Reported _diffrn_ambient_temperature .        293 K
PLAT793_ALERT_1_G Check the Absolute Configuration of C3     = ...          S

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

   4 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 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

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S1. Comment

Interest in D,L-aspartic acid has spanned several decades, from the first structural determination by Rao (1973), due to its acting as important ligand in the preparation of transition metal complexes (Ciunik, 1987; Casellato et al., 1991; Barfod et al., 1999). In exploring the possibility of introducing D,L-aspartic acid into a phosphite system, we unexpectedly obtained the title compound. To the best of our knowledge, there are only four reports on the structure of D,L-aspartic acid (Rao et al., 1968; Rao, 1973; Sequeira et al., 1989; Flaig et al., 1998). The present structure of D,L-aspartic acid differs slightly from these previously reported ones, since it presents the same space group and a similar molecular disposition, but with an a parameter some 7–8% shorter.

The molecules (Fig. 1) are interconnected with each other by hydrogen bonds to form a 3-D supramolecular network (Table 1 and Fig. 2).

Related literature

For related literature, see: Barfod et al. (1999); Casellato et al. (1991); Ciunik (1987); Flaig et al. (1998); Rao (1973); Rao et al. (1968); Sequeira et al. (1989).

S2. Experimental

The title compound was obtained by hydrothermal methods. A mixture of Zn(CH₃COO)₂·2H₂O (0.16 g), H₃PO₃ (0.19 g), D,L-aspartic acid (0.25 g) and H₂O (8 ml), was sealed in a 25 ml Teflon-lined steel autoclave and heated under autogenous pressure at 363 K for 3 days. Then, the filtrate was kept at room temperature and colorless prism-like crystals were obtained after three weeks.

S3. Refinement

All the H atoms were located from difference-density maps in a difference Fourier map and their positions and isotropic displacement parameters were refined.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SAINT (Bruker, 1999); data reduction: SAINT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Bruker, 1999); software used to prepare material for publication: SHELXTL (Bruker, 1999).

Figures

	Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids.
	Fig. 2. Packing diagram of the title compound.

D,L-aspartic acid

Crystal data

C4H7NO4	F(000) = 560
Mr = 133.11	Dx = 1.645 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 4179 reflections
a = 17.5813 (2) Å	θ = 2.6–26.5°
b = 7.4369 (5) Å	µ = 0.15 mm^−1
c = 9.1807 (3) Å	T = 293 K
β = 116.436 (3)°	Prism, colorless
V = 1074.86 (9) Å^3	0.18 × 0.14 × 0.06 mm
Z = 8

Data collection

Siemems SMART CCD diffractometer	1105 independent reflections
Radiation source: fine-focus sealed tube	986 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
φ and ω scans	θmax = 26.5°, θmin = 2.6°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −22→22
Tmin = 0.974, Tmax = 0.991	k = −9→9
4179 measured reflections	l = −11→11

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.039	All H-atom parameters refined
wR(F^2) = 0.103	w = 1/[σ^2(Fo^2) + (0.0514P)^2 + 0.5964P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
1105 reflections	Δρmax = 0.23 e Å^−3
111 parameters	Δρmin = −0.18 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.017 (2)

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
C1	0.00684 (9)	0.2497 (2)	0.49490 (19)	0.0227 (4)
C2	0.09882 (9)	0.2473 (2)	0.52666 (19)	0.0238 (4)
H2	0.1006 (12)	0.204 (3)	0.431 (3)	0.035 (5)*
H3	0.1188 (13)	0.374 (3)	0.544 (3)	0.042 (6)*
C3	0.15383 (9)	0.1315 (2)	0.67210 (19)	0.0199 (4)
H4	0.1312 (10)	0.014 (2)	0.6575 (18)	0.016 (4)*
C4	0.24516 (9)	0.1148 (2)	0.69224 (19)	0.0205 (4)
O1	−0.01739 (7)	0.17330 (17)	0.58347 (15)	0.0342 (4)
O2	−0.04289 (8)	0.33822 (18)	0.36471 (15)	0.0348 (4)
H1	−0.1002 (18)	0.338 (4)	0.349 (3)	0.074 (8)*
O3	0.30295 (7)	0.17660 (17)	0.82024 (14)	0.0319 (4)
O4	0.25457 (7)	0.03708 (15)	0.58062 (13)	0.0270 (3)
N1	0.15498 (9)	0.2014 (2)	0.82518 (17)	0.0232 (4)
H7	0.1800 (14)	0.318 (3)	0.855 (3)	0.040 (6)*
H6	0.1879 (14)	0.126 (3)	0.911 (3)	0.041 (6)*
H5	0.1023 (14)	0.203 (3)	0.818 (3)	0.040 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0161 (8)	0.0309 (9)	0.0199 (7)	0.0015 (6)	0.0069 (6)	−0.0019 (6)
C2	0.0165 (8)	0.0321 (9)	0.0227 (8)	0.0018 (6)	0.0085 (7)	0.0036 (7)
C3	0.0153 (7)	0.0219 (8)	0.0218 (8)	−0.0023 (6)	0.0075 (6)	−0.0020 (6)
C4	0.0158 (7)	0.0196 (8)	0.0253 (8)	0.0012 (6)	0.0084 (6)	0.0024 (6)
O1	0.0183 (6)	0.0553 (8)	0.0298 (7)	0.0011 (5)	0.0116 (5)	0.0096 (6)
O2	0.0165 (6)	0.0565 (8)	0.0287 (7)	0.0073 (5)	0.0077 (5)	0.0144 (6)
O3	0.0150 (6)	0.0461 (8)	0.0311 (7)	−0.0033 (5)	0.0071 (5)	−0.0111 (5)
O4	0.0217 (6)	0.0301 (6)	0.0302 (6)	0.0014 (5)	0.0125 (5)	−0.0050 (5)
N1	0.0155 (7)	0.0322 (8)	0.0219 (7)	−0.0006 (6)	0.0083 (6)	0.0003 (6)

Geometric parameters (Å, º)

C1—O1	1.2140 (19)	C3—H4	0.945 (17)
C1—O2	1.3023 (19)	C4—O3	1.2494 (19)
C1—C2	1.510 (2)	C4—O4	1.2501 (18)
C2—C3	1.520 (2)	O2—H1	0.95 (3)
C2—H2	0.95 (2)	N1—H7	0.95 (2)
C2—H3	0.99 (2)	N1—H6	0.93 (2)
C3—N1	1.490 (2)	N1—H5	0.90 (2)
C3—C4	1.537 (2)
O1—C1—O2	123.98 (14)	C2—C3—H4	109.7 (10)
O1—C1—C2	122.01 (14)	C4—C3—H4	107.0 (10)
O2—C1—C2	114.01 (13)	O3—C4—O4	126.31 (14)
C1—C2—C3	112.60 (13)	O3—C4—C3	116.86 (13)
C1—C2—H2	107.4 (12)	O4—C4—C3	116.81 (13)
C3—C2—H2	110.4 (12)	C1—O2—H1	112.0 (16)
C1—C2—H3	107.0 (12)	C3—N1—H7	113.5 (13)
C3—C2—H3	110.8 (12)	C3—N1—H6	109.4 (13)
H2—C2—H3	108.5 (17)	H7—N1—H6	105.5 (18)
N1—C3—C2	111.55 (13)	C3—N1—H5	110.9 (14)
N1—C3—C4	109.87 (12)	H7—N1—H5	109.6 (18)
C2—C3—C4	111.94 (13)	H6—N1—H5	107.6 (18)
N1—C3—H4	106.5 (9)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H1···O3^i	0.95 (3)	1.61 (3)	2.5574 (16)	176 (3)
N1—H7···O4^ii	0.95 (2)	1.93 (2)	2.8782 (19)	171.8 (18)
N1—H6···O4^iii	0.93 (2)	1.91 (2)	2.8381 (18)	177.4 (19)
N1—H5···O1^iv	0.90 (2)	2.07 (2)	2.8992 (18)	152.5 (19)
N1—H5···O1	0.90 (2)	2.26 (2)	2.8572 (18)	124.0 (17)

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