Glycine sodium nitrate

The glycine mol­ecule in the title compound, Na(NO₃)·C₂H₅NO₂, exists in the zwitterionic form. The Na atom exhibits eightfold coordination and the polyhedron may be visualized as a distorted hexagonal bipyramid. The glycine mol­ecules are linked through head-to-tail hydrogen bonds and are found `sandwiched' between the Na(NO₃) layers.

S1. Comment

Glycine has the distinction of being the only amino acid which forms very many addition compounds with inorganic acids and salts, besides forming metallic complexes. The present study of the title compound, (I), seems to be the only work on an amino acid complex which contains both sodium and nitrate ions. The crystal structures of glycine sodium iodide hydrate (Verbist et al., 1971) and glycine potassium triodide (Herbstein & Kapon, 1980) are the only other complexes involving glycine and alkali metals that have been reported so far. \sch

The glycine molecule in (I) exists in the zwitterionic form. The nitrate group exhibits non-crystallographic D_{3 h} symmetry, with the three N—O bond distances having equal values [mean 1.241 (5) Å] and the three O—N—O angles not deviating significantly from 120°. Fig. 1 shows the coordination environment around the Na, which has a coordination number of eight. The coordination polyhedron may be visualized as a distorted hexagonal bipyramid, with the carboxyl O atoms of the amino acid occupying the apical sites. The Na—O distances range from 2.324 (3) to 2.719 (3) Å.

Fig. 2 shows the layer formed by the sodium and nitrate ions, in which the O atoms of the nitrate groups coordinate to Na, forming a two-dimensional layered network. These layers are separated by a distance of a/2 and are interconnected through coordination of the carboxyl O atoms of the glycine molecules to Na. Almost linear O1—Na—O2 chains involving carboxyl O atoms run along the (202) plane along the [101] direction.

The glycine molecules are seen `sandwiched' between layers of NaNO₃ (Fig. 3). Both carboxyl O atoms participate in hydrogen bonding as acceptors, forming two N—H···O head-to-tail hydrogen bonds, one along the b direction and the other related by a c glide to it. In addition, an N—H···O and a C—H···O hydrogen bond are also observed, involving atom O4 of the nitrate group as acceptor.

Interestingly, in the crystal structure of glycine silver nitrate (Mohana Rao & Viswamitra, 1972), which is found to be ferroelectric below 218 K (Pepinsky et al., 1957), all three H atoms attached to the N atom are shared by the O atoms of the nitrate group in forming hydrogen bonds, and the carboxyl O atoms of the amino acid molecule do not take part in the hydrogen-bonding network.

S2. Experimental

Colourless single crystals of (I) were grown as transparent plates, from a saturated aqueous solution containing glycine and sodium nitrate in stoichiometric ratio. The density was determined by the flotation method, using a liquid mixture of carbon tetrachloride and bromoform.

S3. Refinement

All H atoms were located from a difference Fourier map and were allowed to ride on their parent atoms, with default values for bond distances and displacement parameters. Friedel pairs were merged before the final refinement cycles.

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: SHELXS93 (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 showing the coordination environment around Na. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii [symmetry codes: (i) x, 1 - y, z; (ii) x, 1 - y, z - 1/2; (iii) x - 1/2, 3/2 - y, z - 1/2]. Query - (iii) not in Fig.
	Fig. 2. A view showing the O atoms of the nitrate groups coordinating to Na atoms, forming a two-dimensional layered network.
	Fig. 3. The unit-cell packing of molecules in (I), showing the glycine molecules `sandwiched' between the NaNO3 layers.

Glycine sodium nitrate

Crystal data

[NaNO3]·C2H5NO2	F(000) = 328
Mr = 160.07	Dx = 1.769 Mg m^−3 Dm = 1.76 Mg m^−3 Dm measured by flotation
Monoclinic, Cc	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C -2yc	Cell parameters from 25 reflections
a = 14.329 (3) Å	θ = 7–16°
b = 5.2662 (11) Å	µ = 0.23 mm^−1
c = 9.1129 (18) Å	T = 293 K
β = 119.10 (3)°	Plate, colourless
V = 600.9 (2) Å^3	0.32 × 0.21 × 0.18 mm
Z = 4

Data collection

Enraf-Nonius CAD4 diffractometer	Rint = 0.017
Radiation source: fine-focus sealed tube	θmax = 25.0°, θmin = 3.3°
Graphite monochromator	h = −16→5
ω/2θ scans	k = −5→6
1077 measured reflections	l = −9→10
531 independent reflections	2 standard reflections every 60 min
523 reflections with I > 2σ(I)	intensity decay: <2%

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) = 0.078	w = 1/[σ^2(Fo^2) + (0.0597P)^2 + 0.1988P] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
531 reflections	Δρmax = 0.26 e Å^−3
92 parameters	Δρmin = −0.28 e Å^−3
2 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.020 (4)

Special details

Experimental. The automated lattice search routine of the CAD-4 diffractometer had failed to notice what the authors noticed later - that the linear combination (h+k+l) of indices assigned to all 25 defining reflections used to obtain the unit cell was a multiple of 2. The cell parameters obtained were a = 7.636 (4), b = 8.820 (4) and c = 10.523 (2) Å, and α = 113.80 (4), β = 102.83 (5) and γ = 100.82 (4)°. Consequently, the intensity data had reflections with linear combinations of indices odd absent, leading to an unconventional body-centered triclinic cell. The authors realised the problem only after attempting structure solution in the triclinic space group P1 with the above unit-cell dimensions. A careful look at the coordinates of the four molecules obtained in the space group P1 had systematic symmetry relationships, i.e. the coordinates of pairs of atoms are related, very closely, by the n-glide plane in Cc. The revised unit cells were obtained with the lattice vectors (-3/2, 1/2, 1/2), (1/2, 1/2, 1/2) and (1/2, 1/2, -1/2), and the structure was solved.

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
Na1	0.02620 (10)	0.7440 (2)	0.34703 (14)	0.0350 (4)
O1	0.21304 (19)	0.6855 (4)	0.4361 (3)	0.0443 (6)
O2	0.34212 (17)	0.7003 (5)	0.7013 (3)	0.0395 (6)
O3	0.0158 (3)	0.4537 (5)	0.5714 (3)	0.0587 (7)
O4	0.0420 (2)	0.2460 (5)	0.3923 (3)	0.0479 (7)
O5	0.0408 (2)	0.0492 (5)	0.5980 (3)	0.0523 (7)
N1	0.24303 (19)	0.1973 (5)	0.3921 (3)	0.0311 (6)
H1A	0.2575	0.0325	0.3947	0.047*
H1B	0.2590	0.2758	0.3207	0.047*
H1C	0.1739	0.2176	0.3586	0.047*
N2	0.0333 (2)	0.2482 (4)	0.5213 (3)	0.0295 (6)
C1	0.2859 (2)	0.5888 (5)	0.5655 (4)	0.0279 (5)
C2	0.3073 (2)	0.3068 (6)	0.5620 (4)	0.0348 (7)
H2A	0.3825	0.2813	0.5988	0.042*
H2B	0.2906	0.2185	0.6398	0.042*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Na1	0.0296 (6)	0.0342 (8)	0.0378 (7)	0.0027 (4)	0.0138 (5)	0.0032 (5)
O1	0.0341 (11)	0.0235 (9)	0.0528 (14)	0.0020 (10)	0.0035 (10)	0.0012 (10)
O2	0.0347 (12)	0.0390 (11)	0.0446 (13)	−0.0061 (9)	0.0191 (11)	−0.0153 (10)
O3	0.087 (2)	0.0381 (12)	0.0571 (14)	0.0179 (14)	0.0401 (15)	−0.0030 (12)
O4	0.0459 (14)	0.068 (2)	0.0383 (13)	−0.0073 (10)	0.0274 (12)	−0.0057 (9)
O5	0.0681 (16)	0.0323 (11)	0.0491 (13)	−0.0029 (12)	0.0226 (12)	0.0128 (11)
N1	0.0336 (12)	0.0218 (9)	0.0398 (14)	−0.0017 (9)	0.0194 (11)	−0.0047 (10)
N2	0.0330 (13)	0.0261 (13)	0.0293 (11)	0.0010 (10)	0.0150 (10)	0.0005 (8)
C1	0.0259 (11)	0.0224 (12)	0.0375 (12)	−0.0026 (11)	0.0171 (10)	−0.0026 (12)
C2	0.0378 (16)	0.0223 (12)	0.0349 (15)	−0.0007 (12)	0.0104 (13)	−0.0011 (13)

Geometric parameters (Å, º)

Na1—O1	2.410 (3)	O3—Na1^v	2.655 (3)
Na1—O2^i	2.324 (3)	O4—N2	1.241 (4)
Na1—O3	2.615 (3)	O4—Na1^vi	2.669 (3)
Na1—O3^ii	2.655 (3)	O5—N2	1.235 (4)
Na1—O4	2.647 (3)	O5—Na1^v	2.615 (3)
Na1—O4^iii	2.669 (3)	O5—Na1^vi	2.719 (3)
Na1—O5^iii	2.719 (3)	N1—C2	1.480 (4)
Na1—O5^ii	2.615 (3)	N1—H1A	0.8900
Na1—N2^ii	3.019 (3)	N1—H1B	0.8900
Na1—N2	3.032 (3)	N1—H1C	0.8900
O1—C1	1.242 (4)	N2—Na1^v	3.019 (3)
O2—C1	1.247 (4)	C1—C2	1.520 (4)
O2—Na1^iv	2.324 (3)	C2—H2A	0.9700
O3—N2	1.247 (3)	C2—H2B	0.9700
O2^i—Na1—O1	167.14 (12)	O3^ii—Na1—N2	97.47 (9)
O2^i—Na1—O3	92.30 (10)	O4^iii—Na1—N2	142.52 (8)
O1—Na1—O3	97.96 (11)	O5^iii—Na1—N2	95.68 (8)
O2^i—Na1—O5^ii	89.94 (10)	N2^ii—Na1—N2	121.21 (6)
O1—Na1—O5^ii	78.52 (10)	C1—O1—Na1	130.9 (2)
O3—Na1—O5^ii	168.82 (10)	C1—O2—Na1^iv	129.23 (18)
O2^i—Na1—O4	101.61 (9)	N2—O3—Na1	97.05 (19)
O1—Na1—O4	79.88 (8)	N2—O3—Na1^v	94.43 (19)
O3—Na1—O4	48.10 (8)	Na1—O3—Na1^v	166.09 (13)
O5^ii—Na1—O4	120.73 (8)	N2—O4—Na1	95.64 (16)
O2^i—Na1—O3^ii	89.02 (12)	N2—O4—Na1^vi	96.62 (17)
O1—Na1—O3^ii	79.09 (11)	Na1—O4—Na1^vi	164.39 (11)
O3—Na1—O3^ii	120.81 (5)	N2—O5—Na1^v	96.66 (19)
O5^ii—Na1—O3^ii	48.25 (9)	N2—O5—Na1^vi	94.32 (18)
O4—Na1—O3^ii	73.74 (8)	Na1^v—O5—Na1^vi	165.96 (11)
O2^i—Na1—O4^iii	87.16 (9)	C2—N1—H1A	109.5
O1—Na1—O4^iii	94.46 (8)	C2—N1—H1B	109.5
O3—Na1—O4^iii	119.41 (8)	H1A—N1—H1B	109.5
O5^ii—Na1—O4^iii	71.63 (8)	C2—N1—H1C	109.5
O4—Na1—O4^iii	164.39 (11)	H1A—N1—H1C	109.5
O3^ii—Na1—O4^iii	119.75 (9)	H1B—N1—H1C	109.5
O2^i—Na1—O5^iii	90.44 (10)	O5—N2—O4	120.5 (2)
O1—Na1—O5^iii	100.01 (11)	O5—N2—O3	120.4 (3)
O3—Na1—O5^iii	72.41 (9)	O4—N2—O3	119.0 (3)
O5^ii—Na1—O5^iii	118.54 (5)	O5—N2—Na1^v	59.36 (17)
O4—Na1—O5^iii	119.26 (8)	O4—N2—Na1^v	176.7 (2)
O3^ii—Na1—O5^iii	166.77 (9)	O3—N2—Na1^v	61.25 (17)
O4^iii—Na1—O5^iii	47.03 (7)	O5—N2—Na1	177.1 (2)
O2^i—Na1—N2^ii	90.46 (9)	O4—N2—Na1	60.32 (15)
O1—Na1—N2^ii	76.69 (10)	O3—N2—Na1	58.86 (17)
O3—Na1—N2^ii	144.98 (8)	Na1^v—N2—Na1	119.64 (7)
O5^ii—Na1—N2^ii	23.98 (7)	O1—C1—O2	126.0 (3)
O4—Na1—N2^ii	97.21 (7)	O1—C1—C2	117.7 (3)
O3^ii—Na1—N2^ii	24.32 (7)	O2—C1—C2	116.2 (3)
O4^iii—Na1—N2^ii	95.59 (7)	N1—C2—C1	111.9 (3)
O5^iii—Na1—N2^ii	142.50 (8)	N1—C2—H2A	109.2
O2^i—Na1—N2	98.50 (8)	C1—C2—H2A	109.2
O1—Na1—N2	87.98 (8)	N1—C2—H2B	109.2
O3—Na1—N2	24.09 (8)	C1—C2—H2B	109.2
O5^ii—Na1—N2	144.75 (8)	H2A—C2—H2B	107.9
O4—Na1—N2	24.04 (7)
O1—C1—C2—N1	6.7 (4)	O2—C1—C2—N1	−175.2 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···O1^vi	0.89	2.03	2.789 (4)	142
N1—H1B···O2^ii	0.89	1.97	2.780 (3)	151
C2—H2A···O4^vii	0.97	2.54	3.256 (4)	131
N1—H1C···O4	0.89	2.06	2.893 (4)	155

Symmetry codes: (ii) x, −y+1, z−1/2; (vi) x, y−1, z; (vii) x+1/2, −y+1/2, z+1/2.