DL-Valinium maleate at 150 K

In the title compound, C₅H₁₂NO₂⁺·C₄H₃O₄⁻, the amino acid exists in the cationic form and the maleic acid mol­ecule in the mono-ionized state. The intramolecular hydrogen bond observed between atoms O3 and O5 in the semimaleate anion is found to be asymmetric. The non-polar side chains of the DL-valinium cations form alternating hydro­phobic columns down the a axis. The crystal structure is stabilized by O—H...O and N—H...O hydrogen bonds.

Key indicators

• Single-crystal X-ray study
• T = 150 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.045
• wR factor = 0.134
• Data-to-parameter ratio = 14.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Valine [(CH₃)₂CH—CH(NH₂)-COOH, 2-amino-3-methylbutanoic acid] is one of the amino acids, required in the human and animal diet for the maintenance of nitrogen equilibrium. It is also glucogenic. Being hydrophobic with a non-polar hydrocarbon chain, it plays a vital role in the stabilization of the structures of protein molecules. Though crystal structures of complexes of valine with a few inorganic acids are known, structural data on the crystalline complexes of valine with organic acids are scarce. The present study on a complex of DL-valine with maleic acid forms a part of a series of investigations being carried out in our laboratory on crystalline amino acid–carboxylic acid complexes. The crystal structures of glycinium maleate (Rajagopal et al., 2001) and L-alaninium maleate (Alagar, Krishnakumar, Subha Nandhini & Natarajan, 2001) have been reported recently.

Fig. 1 shows the molecular structure with the atom-numbering scheme. The DL-valinium molecule exists in the cationic form with a protonated amino group and an uncharged carboxylic acid group. The maleic acid molecule exists in the mono-ionized state. The semi-maleate ion is essentially planar as observed in the crystal structures of similar complexes. The angle between the planes of the half-molecule is 8.1 (1)°. This value is somewhat larger than that found in L-phenylalaninium maleate [3.5 (1)°; Alagar, Krishnakumar & Natarajan, 2001], where the intramolecular hydrogen bond between atoms O3 and O5 is symmetric. The larger value observed in (I) may be attributed to asymmetric nature of the intramolecular hydrogen bond. An asymmetric intramolecular hydrogen bond is observed in the crystal structures of maleic acid (James & Williams, 1974), glycinium maleate and L-alaninium maleate; it is found to be symmetric 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) with an H atom shared between the respective oxygen atoms.

Fig. 2 shows the packing of the molecules of (I) viewed down the a axis. The semi-maleate ions do not have direct hydrogen-bonded interactions among themselves except for a weak C—H···O hydrogen bond which links them to form an infinite one-dimensional chain down the a axis. There is a head-to-tail hydrogen bond among the centrosymmetrically related amino acid molecules leading to the formation of a dimer. The non-polar side chains of the DL-valinium cations form alternating hydrophobic columns down the a axis. The crystal packing is characterized by O—H···O and N—H···O hydrogen bonds. However, considering the presence of many strong O—H···O and N—H···O bonds, it seems unlikely that weak hydrogen bonds of the type C—H···O play a role in determining the packing modes of the molecules. The aggregation pattern has some similarities with that observed in L-phenylalaninium maleate, but is distinctly different from glycinium maleate and L-alaninium maleate.

S2. Experimental

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

S3. Refinement

All the H atoms were generated geometrically and were allowed to ride on their parent atoms with SHELXL97 (Sheldrick, 1997) defaults for bond lengths and displacement parameters.

Computing details

Data collection: SMART (Bruker, 1999); cell refinement: SMART; 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: PLATON (Spek, 1999); software used to prepare material for publication: SHELXL97.

Figures

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

DL-valinium maleate

Crystal data

C5H12NO2^+·C4H3O4^−	Z = 2
Mr = 233.22	F(000) = 248
Triclinic, P1	Dx = 1.417 Mg m^−3 Dm = 1.42 Mg m^−3 Dm measured by flotation in a mixture of xylene and carbon tetrachloride
a = 6.1830 (12) Å	Mo Kα radiation, λ = 0.71073 Å
b = 9.6480 (19) Å	Cell parameters from 1024 reflections
c = 10.534 (2) Å	θ = 2.2–26.3°
α = 104.92 (3)°	µ = 0.12 mm^−1
β = 106.32 (3)°	T = 150 K
γ = 104.40 (3)°	Prismatic, colorless
V = 546.71 (19) Å^3	0.3 × 0.3 × 0.3 mm

Data collection

BRUKER SMART diffractometer	2225 independent reflections
Radiation source: fine-focus sealed tube	1991 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.036
Detector resolution: 8 pixels mm^-1	θmax = 26.4°, θmin = 2.2°
ω scan	h = −7→7
Absorption correction: empirical (using intensity measurements) (SADABS; Bruker, 1998)	k = −12→11
Tmin = 0.968, Tmax = 0.968	l = −13→12
5585 measured reflections

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)] = 0.045	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.134	H-atom parameters constrained
S = 1.09	w = 1/[σ^2(Fo^2) + (0.0837P)^2 + 0.1505P] where P = (Fo^2 + 2Fc^2)/3
2225 reflections	(Δ/σ)max < 0.001
149 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	0.84000 (19)	0.58264 (12)	0.66233 (12)	0.0260 (3)
H1	0.7346	0.6207	0.6717	0.039*
O2	0.77880 (19)	0.49747 (12)	0.83331 (11)	0.0262 (3)
O3	0.21319 (19)	0.07564 (12)	0.18678 (14)	0.0319 (3)
H3	0.2074	−0.0121	0.1430	0.048*
O4	0.49219 (19)	0.30302 (12)	0.31668 (12)	0.0276 (3)
O5	0.20543 (18)	−0.18088 (12)	0.07529 (12)	0.0257 (3)
O6	0.46732 (18)	−0.29285 (11)	0.04021 (11)	0.0246 (3)
N1	1.1539 (2)	0.40441 (13)	0.87416 (12)	0.0199 (3)
H1A	1.2715	0.3636	0.8733	0.030*
H1B	1.0254	0.3350	0.8756	0.030*
H1C	1.2105	0.4901	0.9523	0.030*
C1	0.8829 (2)	0.51190 (15)	0.75313 (14)	0.0197 (3)
C2	1.0790 (2)	0.44473 (15)	0.74446 (14)	0.0193 (3)
H2	1.2194	0.5260	0.7478	0.023*
C3	0.9927 (2)	0.30887 (16)	0.60556 (15)	0.0206 (3)
H3A	0.9326	0.3456	0.5266	0.025*
C4	0.7835 (3)	0.17424 (17)	0.59202 (17)	0.0283 (4)
H4A	0.6532	0.2099	0.6048	0.042*
H4B	0.8384	0.1310	0.6645	0.042*
H4C	0.7251	0.0956	0.4981	0.042*
C5	1.2001 (3)	0.25776 (19)	0.58620 (17)	0.0283 (4)
H5A	1.3313	0.3458	0.5954	0.042*
H5B	1.1442	0.1797	0.4923	0.042*
H5C	1.2575	0.2150	0.6586	0.042*
C6	0.4337 (3)	0.16786 (16)	0.24253 (15)	0.0223 (3)
C7	0.6296 (2)	0.11276 (16)	0.21831 (15)	0.0215 (3)
H7	0.7831	0.1903	0.2544	0.026*
C8	0.6235 (2)	−0.02778 (16)	0.15418 (15)	0.0215 (3)
H8	0.7734	−0.0340	0.1518	0.026*
C9	0.4182 (2)	−0.17747 (15)	0.08529 (14)	0.0201 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0286 (6)	0.0281 (6)	0.0340 (6)	0.0151 (4)	0.0188 (5)	0.0178 (5)
O2	0.0267 (5)	0.0329 (6)	0.0280 (6)	0.0135 (4)	0.0175 (5)	0.0138 (5)
O3	0.0209 (5)	0.0226 (6)	0.0538 (7)	0.0082 (4)	0.0184 (5)	0.0101 (5)
O4	0.0275 (6)	0.0219 (5)	0.0351 (6)	0.0101 (4)	0.0141 (5)	0.0086 (5)
O5	0.0170 (5)	0.0226 (5)	0.0380 (6)	0.0047 (4)	0.0123 (4)	0.0110 (5)
O6	0.0238 (5)	0.0204 (5)	0.0289 (6)	0.0067 (4)	0.0113 (4)	0.0067 (4)
N1	0.0186 (6)	0.0204 (6)	0.0212 (6)	0.0066 (4)	0.0087 (5)	0.0065 (5)
C1	0.0193 (6)	0.0167 (6)	0.0216 (7)	0.0039 (5)	0.0086 (5)	0.0053 (5)
C2	0.0184 (6)	0.0191 (6)	0.0223 (7)	0.0049 (5)	0.0109 (5)	0.0083 (5)
C3	0.0209 (7)	0.0223 (7)	0.0206 (7)	0.0078 (5)	0.0104 (5)	0.0073 (5)
C4	0.0272 (8)	0.0235 (7)	0.0284 (8)	0.0029 (6)	0.0128 (6)	0.0031 (6)
C5	0.0262 (7)	0.0346 (8)	0.0282 (8)	0.0147 (6)	0.0144 (6)	0.0087 (6)
C6	0.0219 (7)	0.0229 (7)	0.0274 (7)	0.0082 (5)	0.0129 (6)	0.0128 (6)
C7	0.0174 (6)	0.0219 (7)	0.0259 (7)	0.0044 (5)	0.0100 (5)	0.0097 (6)
C8	0.0165 (6)	0.0242 (7)	0.0268 (7)	0.0064 (5)	0.0120 (5)	0.0098 (6)
C9	0.0197 (7)	0.0220 (7)	0.0216 (7)	0.0062 (5)	0.0101 (5)	0.0105 (5)

Geometric parameters (Å, º)

O1—C1	1.3170 (18)	C3—C5	1.5289 (19)
O1—H1	0.84	C3—C4	1.532 (2)
O2—C1	1.2117 (17)	C3—H3A	1.00
O3—C6	1.2932 (19)	C4—H4A	0.98
O3—H3	0.84	C4—H4B	0.98
O4—C6	1.2343 (19)	C4—H4C	0.98
O5—C9	1.2812 (17)	C5—H5A	0.98
O6—C9	1.2386 (17)	C5—H5B	0.98
N1—C2	1.4967 (18)	C5—H5C	0.98
N1—H1A	0.91	C6—C7	1.4963 (19)
N1—H1B	0.91	C7—C8	1.336 (2)
N1—H1C	0.91	C7—H7	0.95
C1—C2	1.5236 (19)	C8—C9	1.502 (2)
C2—C3	1.539 (2)	C8—H8	0.95
C2—H2	1.00
C1—O1—H1	109.5	C3—C4—H4B	109.5
C6—O3—H3	109.5	H4A—C4—H4B	109.5
C2—N1—H1A	109.5	C3—C4—H4C	109.5
C2—N1—H1B	109.5	H4A—C4—H4C	109.5
H1A—N1—H1B	109.5	H4B—C4—H4C	109.5
C2—N1—H1C	109.5	C3—C5—H5A	109.5
H1A—N1—H1C	109.5	C3—C5—H5B	109.5
H1B—N1—H1C	109.5	H5A—C5—H5B	109.5
O2—C1—O1	125.43 (13)	C3—C5—H5C	109.5
O2—C1—C2	122.63 (13)	H5A—C5—H5C	109.5
O1—C1—C2	111.93 (11)	H5B—C5—H5C	109.5
N1—C2—C1	106.47 (11)	O4—C6—O3	122.39 (14)
N1—C2—C3	113.72 (11)	O4—C6—C7	117.28 (13)
C1—C2—C3	111.40 (11)	O3—C6—C7	120.33 (13)
N1—C2—H2	108.4	C8—C7—C6	130.46 (13)
C1—C2—H2	108.4	C8—C7—H7	114.8
C3—C2—H2	108.4	C6—C7—H7	114.8
C5—C3—C4	111.08 (12)	C7—C8—C9	130.42 (13)
C5—C3—C2	111.31 (12)	C7—C8—H8	114.8
C4—C3—C2	112.87 (12)	C9—C8—H8	114.8
C5—C3—H3A	107.1	O6—C9—O5	123.48 (13)
C4—C3—H3A	107.1	O6—C9—C8	116.58 (12)
C2—C3—H3A	107.1	O5—C9—C8	119.94 (12)
C3—C4—H4A	109.5
O2—C1—C2—N1	−15.48 (17)	C1—C2—C3—C4	−63.27 (15)
O1—C1—C2—N1	165.83 (11)	O4—C6—C7—C8	173.59 (15)
O2—C1—C2—C3	109.03 (15)	O3—C6—C7—C8	−6.5 (2)
O1—C1—C2—C3	−69.66 (15)	C6—C7—C8—C9	−0.2 (3)
N1—C2—C3—C5	−68.65 (15)	C7—C8—C9—O6	−176.16 (15)
C1—C2—C3—C5	171.02 (11)	C7—C8—C9—O5	4.0 (2)
N1—C2—C3—C4	57.05 (16)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O4^i	0.84	1.76	2.5963 (15)	178
O3—H3···O5	0.84	1.60	2.4330 (17)	174
N1—H1A···O6^ii	0.91	1.99	2.8323 (17)	154
N1—H1B···O5^iii	0.91	2.07	2.9572 (18)	166
N1—H1C···O2^iv	0.91	2.21	2.8542 (17)	127
N1—H1C···O6^v	0.91	2.07	2.828 (2)	140
C2—H2···O4^vi	1.00	2.48	3.453 (2)	164
C7—H7···O1^vi	0.95	2.51	3.458 (2)	172
C8—H8···O3^vii	0.95	2.54	3.4229 (19)	155

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