Bis(β-alanine) hydrogen nitrate

In the title compound, 2C₃H₇NO₂.H⁺·NO₃⁻, both the alanine residues, related by a center of symmetry, are linked by a strong symmetric O—H...O hydrogen bond with an O...O distance of 2.467 (2) Å. The N atom and one of the O atoms of the nitrate anion lie on the twofold axis.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.033
• wR factor = 0.092
• Data-to-parameter ratio = 8.8

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

In amino acid–inorganic acid complexes, when the number of H atoms liberated from the inorganic acid is less than the number of amino acids, the H atom is shared by two amino acids, resulting in short symmetric O—H···O hydrogen bonds, as evidenced in triglycine sulfate (Kay, 1977), leading to phase transitions. In order to look for similar compounds, a systematic study of the behaviour of hydrogen bonding in amino acid–inorganic acid complexes was undertaken. In this context, the crystal structure of L-phenylalanine L-phenylalaninium perchlorate (Srinivasan & Rajaram, 1997), hydrogen bis[L-lysinium (2+)] dichloride perchlorate (Srinivasan et al., 2001a), L-lysine L-lysinium dichloride nitrate (Srinivasan et al., 2001b), L-phenylalanine-nitric acid (2/1) (Srinivasan et al., 2001c) and bis(L-proline) hydrogen perchlorate (Pandiarajan et al., 2001) have been reported. A similar stucture, L-phenylalanine L-phenylalaninium formate, has been reported by Gorbitz & Etter (1992). As part of this programme, the crystal structure of β-alanine with nitric acid was undertaken to study the nature of the hydrogen bonding in the presence of an inorganic acid.

The asymmetric unit contains one β-alanine residue and a nitrate anion which lies on the twofold axis. The backbone conformation angles ψ¹ and ψ² are -5.2 (2) and 174.9 (1)°, respectively, for the alanine residue. The straight-chain conformation angle χ¹ is in gauche I form [63.6 (2)°]. This tendency of twisting of the C—N bond is found in various amino acids (Lakshminarayanan et al., 1967).

The nitrate anion plays a vital role in forming hydrogen bonds with the alanine residue and stabilizing the structure. The H1B atom, which lies on a center of symmetry, links the two alanine residues through a strong symmetric O—H···O hydrogen bond [O1B···O1B(1/2 - x, 1/2 - y, 1 - z) 2.467 (2) Å]. The large U_iso value of H1B suggests that this atom may have positional or flip–flop disorder, leading to the switching of roles of the cation and zwitterion in a time-averaged equilibrium (Jeffrey & Saenger, 1991). A similar feature of short hydrogen bonding has been observed in L-phenylalanine L-phenylalaninium formate, L-phenylalanine L-phenylalaninium perchlorate, hydrogen bis[L-lysinium (2+)] dichloride perchlorate, L-lysine L-lysinium dichloride nitrate, L-phenylalanine-nitric acid (2/1) and bis(L-proline) hydrogen perchlorate. In these compounds, the hydrogen bond can be termed as a possible symmetric hydrogen bond. At low temperature, the crystal of (I) may go into non-centrosymmetric space group Cc, triggering a structural phase transition leading to interesting physical properties.

The O1 and O2 atoms of the nitrate anion, as acceptors, links the amino N atom in a three-centred hydrogen bond involving the alanine residue. This O2 atom of the nitrate anion, sitting on the twofold axis, links two symmetry-related β-alanine residues. A three-centred hydrogen bond is observed involving the alanine residue (amino N atom) and the carboxyl O1A (intramolecular hydrogen bond) and O1B (Z2 head-to-tail sequence) atoms. A glide-related head-to-tail sequence is observed, since N11—H2B···O1B(x, -y, z - 1/2) connects two glide-related amino acids (Vijayan, 1988).

S2. Experimental

Crystals of (I) were grown from an aqueous solution of a 2:1 stoichiometric ratio of β-alanine and nitric acid by slow evaporation.

S3. Refinement

All the H atoms were located and refined isotropically. The C—H and N—H bond lengths are 0.94 (2)–0.97 (2) and 0.87 (2)–0.89 (2) Å, respectively.

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, 1997); 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 the atom-numbering scheme and 50% probability displacement ellipsoids (Johnson, 1976).
	Fig. 2. Packing diagram of (I) viewed down the b axis.

β-Alanine β-alaninium nitrate

Crystal data

2C3H7NO2·H^+·NO3^−	F(000) = 512
Mr = 241.21	Dx = 1.516 Mg m^−3 Dm = 1.502 Mg m^−3 Dm measured by flotation using a mixture of carbon tetrachloride and xylene
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 19.791 (1) Å	Cell parameters from 25 reflections
b = 5.3220 (3) Å	θ = 11.3–14.0°
c = 10.974 (1) Å	µ = 0.14 mm^−1
β = 113.923 (6)°	T = 293 K
V = 1056.57 (13) Å^3	Needle, colorless
Z = 4	0.6 × 0.4 × 0.2 mm

Data collection

Enraf-Nonius sealed tube diffractometer	798 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.014
Graphite monochromator	θmax = 25.0°, θmin = 2.3°
ω–2θ scans	h = 0→23
Absorption correction: ψ scan (North et al., 1968)	k = 0→6
Tmin = 0.863, Tmax = 0.970	l = −13→11
941 measured reflections	3 standard reflections every 60 min
914 independent reflections	intensity decay: none

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)] = 0.033	All H-atom parameters refined
wR(F^2) = 0.092	w = 1/[σ^2(Fo^2) + (0.0459P)^2 + 0.682P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max < 0.001
914 reflections	Δρmax = 0.31 e Å^−3
104 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: 0.103 (7)

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
O1A	0.19302 (7)	0.4346 (2)	0.27700 (10)	0.0452 (4)
O1B	0.21345 (6)	0.1038 (2)	0.41024 (9)	0.0381 (4)
H1B	0.2500	0.2500	0.5000	0.116 (14)*
C11	0.18276 (8)	0.2140 (3)	0.29461 (14)	0.0321 (4)
C12	0.13324 (9)	0.0474 (3)	0.18276 (14)	0.0369 (4)
H12A	0.0973 (11)	−0.033 (4)	0.2091 (19)	0.050 (5)*
H12B	0.1631 (11)	−0.083 (4)	0.1728 (18)	0.045 (5)*
C13	0.09337 (9)	0.1853 (3)	0.05321 (15)	0.0377 (4)
H13A	0.0660 (10)	0.324 (4)	0.0621 (17)	0.042 (5)*
H13B	0.0597 (11)	0.077 (4)	−0.015 (2)	0.050 (5)*
N11	0.14535 (8)	0.2912 (3)	−0.00011 (14)	0.0389 (4)
H1A	0.1805 (12)	0.375 (4)	0.062 (2)	0.052 (5)*
H2B	0.1670 (11)	0.179 (4)	−0.0288 (19)	0.055 (6)*
H3C	0.1196 (13)	0.386 (4)	−0.071 (2)	0.061 (6)*
N1	0.5000	0.0750 (4)	0.7500	0.0379 (5)
O1	0.45215 (7)	0.1894 (3)	0.65579 (12)	0.0553 (4)
O2	0.5000	−0.1571 (4)	0.7500	0.0753 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1A	0.0592 (8)	0.0348 (7)	0.0367 (6)	−0.0082 (5)	0.0143 (5)	−0.0005 (5)
O1B	0.0423 (6)	0.0377 (7)	0.0277 (6)	−0.0011 (5)	0.0074 (4)	0.0007 (4)
C11	0.0317 (7)	0.0343 (9)	0.0303 (8)	0.0006 (6)	0.0126 (6)	−0.0012 (6)
C12	0.0394 (8)	0.0352 (8)	0.0318 (8)	−0.0027 (7)	0.0100 (7)	−0.0014 (6)
C13	0.0314 (8)	0.0471 (10)	0.0316 (8)	−0.0014 (7)	0.0097 (6)	−0.0003 (7)
N11	0.0390 (8)	0.0441 (9)	0.0320 (8)	−0.0008 (7)	0.0127 (6)	−0.0002 (6)
N1	0.0377 (10)	0.0440 (11)	0.0341 (9)	0.000	0.0168 (8)	0.000
O1	0.0497 (7)	0.0541 (8)	0.0507 (8)	0.0099 (6)	0.0086 (6)	0.0069 (6)
O2	0.0956 (16)	0.0438 (11)	0.0539 (12)	0.000	−0.0034 (11)	0.000

Geometric parameters (Å, º)

O1A—C11	1.2204 (19)	C13—H13A	0.94 (2)
O1B—C11	1.3030 (17)	C13—H13B	0.96 (2)
O1B—H1B	1.2333 (10)	N11—H1A	0.87 (2)
C11—C12	1.509 (2)	N11—H2B	0.87 (2)
C12—C13	1.507 (2)	N11—H3C	0.89 (2)
C12—H12A	0.97 (2)	N1—O2	1.235 (3)
C12—H12B	0.94 (2)	N1—O1^i	1.2419 (15)
C13—N11	1.486 (2)	N1—O1	1.2419 (15)
C11—O1B—H1B	112.62 (10)	N11—C13—H13B	107.2 (12)
O1A—C11—O1B	123.06 (13)	C12—C13—H13B	111.9 (12)
O1A—C11—C12	122.09 (13)	H13A—C13—H13B	107.4 (15)
O1B—C11—C12	114.84 (13)	C13—N11—H1A	110.2 (13)
C13—C12—C11	113.58 (13)	C13—N11—H2B	113.9 (14)
C13—C12—H12A	109.3 (11)	H1A—N11—H2B	106.2 (19)
C11—C12—H12A	109.3 (12)	C13—N11—H3C	108.4 (14)
C13—C12—H12B	111.1 (11)	H1A—N11—H3C	113 (2)
C11—C12—H12B	107.1 (11)	H2B—N11—H3C	105.5 (19)
H12A—C12—H12B	106.2 (16)	O2—N1—O1^i	119.35 (10)
N11—C13—C12	112.02 (13)	O2—N1—O1	119.35 (10)
N11—C13—H13A	105.2 (11)	O1^i—N1—O1	121.3 (2)
C12—C13—H13A	112.7 (11)
O1A—C11—C12—C13	−5.2 (2)	C11—C12—C13—N11	63.60 (19)
O1B—C11—C12—C13	174.93 (13)

Symmetry code: (i) −x+1, y, −z+3/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1B—H1B···O1B^ii	1.23 (1)	1.23 (1)	2.467 (2)	180
N11—H1A···O1A	0.87 (2)	2.29 (2)	2.8971 (18)	126.5 (17)
N11—H1A···O1B^iii	0.87 (2)	2.34 (2)	3.0517 (18)	139.1 (17)
N11—H2B···O1B^iv	0.87 (2)	2.01 (3)	2.877 (2)	175 (2)
N11—H3C···O1^iii	0.89 (2)	2.10 (3)	2.908 (2)	150 (2)
N11—H3C···O2^v	0.89 (2)	2.40 (2)	3.0779 (15)	133.2 (18)

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