Glycinium maleate

In the title compound, C₂H₆NO₂⁺·C₄H₃O₄⁻, the glycine mol­ecule exists in the cationic form with a positively charged amino group and an uncharged carboxyl­ic acid group. The maleic acid mol­ecule exists in a mono-ionized state. In the semimaleate ion, an intramolecular OH...O hydrogen bond is found to be asymmetric. The glycinium and semimaleate ions aggregate into alternate columns extending along the c axis. A C—H...O hydrogen bond is also observed.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.029
• wR factor = 0.082
• Data-to-parameter ratio = 9.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level B:



THETM_01  Alert B The value of sine(theta_max)/wavelength is less than 0.575
          Calculated sin(theta_max)/wavelength =    0.5568


 Alert Level C:



REFNR_01  Alert C Ratio of reflections to parameters is < 10 for a
          centrosymmetric structure
          sine(theta)/lambda                0.5568
          Proportion of unique data used    1.0000
          Ratio reflections to parameters   9.5950


 0 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 1 Alert Level C = Please check

---

S1. Comment

Glycine remains one of the most extensively studied amino acids as it is known to form innumerable complexes with metals, inorganic salts and inorganic acids. However, structural data on complexes of organic acids with amino acids in general, particularly glycine, seem to be very limited. A series of investigations are being carried out in our laboratory to obtain structural information on biomolecular interactions and characteristic aggregation patterns of amino acid carboxylic acids, at atomic resolution. The present study reports the crystal structure of (I), a complex of glycine with maleic acid. Recently, the crystal structure of a complex of glycine with oxalic acid (Subha Nandhini et al., 2001) has been reported.

Fig. 1 shows the molecular strcuture with the atom-numbering scheme. The glycine molecule exists in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The maleic acid molecule exists in a mono-ionized state. The semimaleate ion is essentially planar as observed in the crystal structures of similar complexes. In the semimeleate ion, an intramolecular hydrogen bond between atoms O3 and O5 is found to be asymmetric, as in the crystal structure of maleic acid (James & Williams, 1974). However, in the crystal structures of complexes of maleic acid with DL– and L– arginine (Ravishankar et al., 1998), and L-histidine and L-lysine (Pratap et al., 2000), this intramolecular hydrogen bond between the carboxylic acid and carboxylate groups is symmetric with a H atom shared between the respective O atoms.

The packing of molecules of (I) within the unit cell viewed down the b axis is shown in Fig. 2. The glycinium and semimaleate ions aggregate into alternate columns extending along the c axis. In these columns, the molecules related by centre of inversion form hydrogen-bonded double layers parallel to the diagonal of the ac plane. No hydrogen bond is observed between these double layers and are held together by van der Waals interactions. A head-to-tail hydrogen bond between the glide related glycinium ions is present. The mode of aggregation of molecules in the crystal structure is similar to that observed in glycinium oxalate (Subha Nandhini et al., 2001).

S2. Experimental

Colorless prismatic single crystals of (I) were grown from a saturated aqueous solution containing glycine and maleic acid in a stoichiometric ratio.

S3. Refinement

All the H atoms were generated geometrically and were allowed to ride on their respective parent atoms with SHELXL97 (Sheldrick, 1997) defaults for bond lengths. The torsion angles about the C—O bonds of the hydroxyl groups were allowed to refine.

Computing details

Data collection: SMART-NT (Bruker, 1999); cell refinement: SMART-NT; data reduction: SAINT-NT (Bruker, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2000); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure of (I) with the atom-numbering scheme and 50% probability displacement ellipsoids.
	Fig. 2. Packing of the molecules of (I) viewed down the b axis.

Glycinium maleate

Crystal data

CH6NO2^+·C5H3O4^−	Dx = 1.582 Mg m^−3 Dm = 1.58 (3) Mg m^−3 Dm measured by flotation in a mixture of bromoform and xylene
Mr = 191.14	Melting point: not measured K
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 17.689 (4) Å	Cell parameters from 1024 reflections
b = 5.6610 (11) Å	θ = 2.5–23.0°
c = 17.328 (4) Å	µ = 0.14 mm^−1
β = 112.30 (3)°	T = 293 K
V = 1605.4 (6) Å^3	Prismatic, colorles
Z = 8	0.5 × 0.3 × 0.3 mm
F(000) = 752

Data collection

Bruker SMART CCD diffractometer	1161 independent reflections
Radiation source: fine-focus sealed tube	1091 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
Detector resolution: 8 pixels mm^-1	θmax = 23.3°, θmin = 2.5°
ω scans	h = −19→19
Absorption correction: empirical (using intensity measurements) (SADABS; Bruker, 1998)	k = −6→6
Tmin = 0.933, Tmax = 0.959	l = −19→19
6136 measured reflections

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)] = 0.029	H-atom parameters constrained
wR(F^2) = 0.082	w = 1/[σ^2(Fo^2) + (0.0422P)^2 + 1.7034P] where P = (Fo^2 + 2Fc^2)/3
S = 1.11	(Δ/σ)max < 0.001
1161 reflections	Δρmax = 0.18 e Å^−3
121 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: 0.0020 (6)

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	0.68057 (7)	0.8766 (2)	0.88058 (7)	0.0272 (3)
H1	0.6637	0.9898	0.8492	0.041*
O2	0.75707 (7)	0.8163 (2)	0.80487 (7)	0.0284 (3)
O3	0.54759 (7)	0.1698 (2)	0.95560 (7)	0.0301 (3)
H3	0.5076	0.1371	0.9137	0.045*
O4	0.62551 (7)	0.4757 (2)	1.00944 (7)	0.0289 (3)
O5	0.43179 (7)	0.0812 (2)	0.82628 (7)	0.0263 (3)
O6	0.37059 (7)	0.2607 (2)	0.70397 (7)	0.0246 (3)
N1	0.80447 (8)	0.3823 (2)	0.87312 (8)	0.0214 (3)
H1A	0.8248	0.2582	0.9060	0.032*
H1B	0.8441	0.4529	0.8619	0.032*
H1C	0.7656	0.3344	0.8258	0.032*
C1	0.73478 (10)	0.7614 (3)	0.86060 (10)	0.0206 (4)
C2	0.76939 (10)	0.5510 (3)	0.91588 (10)	0.0221 (4)
H2A	0.8115	0.6023	0.9678	0.026*
H2B	0.7266	0.4741	0.9288	0.026*
C3	0.56540 (9)	0.3911 (3)	0.95380 (10)	0.0214 (4)
C4	0.51330 (10)	0.5490 (3)	0.88593 (10)	0.0223 (4)
H4	0.5260	0.7088	0.8943	0.027*
C5	0.45103 (9)	0.4980 (3)	0.81475 (10)	0.0219 (4)
H5	0.4261	0.6277	0.7821	0.026*
C6	0.41564 (9)	0.2637 (3)	0.77995 (10)	0.0205 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0287 (7)	0.0294 (7)	0.0231 (6)	0.0075 (5)	0.0094 (5)	0.0055 (5)
O2	0.0333 (7)	0.0325 (7)	0.0201 (6)	0.0069 (5)	0.0107 (6)	0.0067 (5)
O3	0.0258 (7)	0.0240 (7)	0.0265 (7)	−0.0038 (5)	−0.0057 (5)	0.0051 (5)
O4	0.0275 (7)	0.0276 (7)	0.0208 (6)	−0.0042 (5)	−0.0030 (5)	0.0023 (5)
O5	0.0231 (6)	0.0209 (6)	0.0263 (7)	−0.0018 (5)	−0.0001 (5)	0.0042 (5)
O6	0.0229 (6)	0.0262 (7)	0.0193 (6)	−0.0031 (5)	0.0020 (5)	−0.0002 (5)
N1	0.0210 (7)	0.0227 (7)	0.0160 (7)	−0.0001 (6)	0.0019 (6)	0.0025 (6)
C1	0.0185 (8)	0.0243 (9)	0.0142 (8)	−0.0029 (7)	0.0010 (7)	−0.0036 (7)
C2	0.0237 (8)	0.0254 (9)	0.0144 (8)	−0.0015 (7)	0.0041 (7)	−0.0005 (7)
C3	0.0204 (9)	0.0229 (9)	0.0193 (9)	−0.0003 (7)	0.0058 (7)	0.0005 (7)
C4	0.0252 (9)	0.0175 (9)	0.0223 (9)	0.0000 (7)	0.0069 (8)	0.0004 (7)
C5	0.0217 (8)	0.0211 (9)	0.0203 (8)	0.0040 (7)	0.0049 (7)	0.0037 (7)
C6	0.0150 (8)	0.0226 (9)	0.0228 (9)	0.0013 (6)	0.0060 (7)	0.0013 (7)

Geometric parameters (Å, º)

O1—C1	1.310 (2)	N1—H1B	0.8900
O1—H1	0.8200	N1—H1C	0.8900
O2—C1	1.214 (2)	C1—C2	1.505 (2)
O3—C3	1.295 (2)	C2—H2A	0.9700
O3—H3	0.8200	C2—H2B	0.9700
O4—C3	1.229 (2)	C3—C4	1.486 (2)
O5—C6	1.273 (2)	C4—C5	1.337 (2)
O6—C6	1.254 (2)	C4—H4	0.9300
N1—C2	1.482 (2)	C5—C6	1.493 (2)
N1—H1A	0.8900	C5—H5	0.9300
C1—O1—H1	109.5	C1—C2—H2B	109.7
C3—O3—H3	109.5	H2A—C2—H2B	108.2
C2—N1—H1A	109.5	O4—C3—O3	120.25 (15)
C2—N1—H1B	109.5	O4—C3—C4	118.59 (15)
H1A—N1—H1B	109.5	O3—C3—C4	121.15 (14)
C2—N1—H1C	109.5	C5—C4—C3	130.29 (16)
H1A—N1—H1C	109.5	C5—C4—H4	114.9
H1B—N1—H1C	109.5	C3—C4—H4	114.9
O2—C1—O1	125.03 (15)	C4—C5—C6	129.58 (15)
O2—C1—C2	122.16 (15)	C4—C5—H5	115.2
O1—C1—C2	112.79 (14)	C6—C5—H5	115.2
N1—C2—C1	109.78 (13)	O6—C6—O5	123.53 (15)
N1—C2—H2A	109.7	O6—C6—C5	115.99 (14)
C1—C2—H2A	109.7	O5—C6—C5	120.48 (14)
N1—C2—H2B	109.7
O2—C1—C2—N1	−22.3 (2)	C3—C4—C5—C6	−1.9 (3)
O1—C1—C2—N1	158.89 (13)	C4—C5—C6—O6	−163.82 (16)
O4—C3—C4—C5	171.82 (17)	C4—C5—C6—O5	15.9 (3)
O3—C3—C4—C5	−9.3 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O6^i	0.82	1.77	2.5861 (17)	171
O3—H3···O5	0.82	1.63	2.4465 (19)	176
N1—H1A···O4^ii	0.89	1.92	2.8051 (18)	171
N1—H1B···O5^iii	0.89	2.01	2.8960 (19)	173
N1—H1C···O2^iv	0.89	2.15	2.8791 (19)	139
N1—H1C···O6^v	0.89	2.30	2.951 (2)	130
C2—H2A···O1^vi	0.97	2.58	3.320 (2)	133

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