Sodium 2-nitro­ethanaloximate forms a layered-framework structure

In the title compound, [Na(C₂H₃N₂O₃)], the Na⁺ cation lies on a centre of inversion in space group P2₁/m and all the atoms of the anion lie on a mirror plane. Na is octahedrally coordinated by four O and two N atoms from six different anions and each anion is coordinated to six different Na⁺ cations, forming chains of confacial octahedra which link the anion layers. Within these layers, the individual anions are linked by both O-H...O and C-H...O hydrogen bonds.

S1. Comment

We report here the structure of sodium 2-nitroethanaloximate, Na[O₂NCHCHNOH], (I), an unexpected coupling product derived from nitromethane, which was isolated serendipitously following attempted crystallization from aqueous nitromethane of an organic salt of sodium. \sch

Both ions of (I) (Fig. 1) lie in special positions in space group P2₁/m, with Z' = 0.5. The Na lies at a centre of inversion, selected as that at (1/2, 1/2, 1/2), and the atoms of the anion all lie on a mirror plane, selected as that at y = 0.75. The overall structure thus consists of layers of anions at y = (n/2 + 1/4) (n = zero or integer) linked by Na at y = (1/2, n/2, 1/2) (n = zero or integer). Each Na is six coordinate and approximately octahedral (Table 1, Fig. 1). The coordinating atoms (4O + 2 N) around the Na at (1/2, 1/2, 1/2) lie in the anions at (x, 3/4, z), (-1 + x, 3/4, z), (1 - x, -.25, 1 - z), and (2 - x, 1/4, 1 - z) (O donors), and at (x, 3/4, 1 + z) and (1 - x, 1/4, -z) (N donors). Similarly each anion is coordinated to six different Na centres: in the reference anions, N1 is coordinated to Na at (1/2, 1/2, -0.5) and (1/2, 1, -0.5); O2 to Na at (1/2, 1/2, 1/2,) and (1/2, 1, 1/2); and O3 to Na at (1.5, 1/2, 1/2) and (1.5, 1, 1/2). These metal-ligand interactions thus generate a chain of confacial NaN₂O₄ octahedra running parallel to [010] (Fig. 1), propagation of which by translation links all the ions into a single layered-framework structure.

In addition, the anions within each layer are linked into a continuous sheet by hydrogen bonds (Table 2, Fig. 2). Oxime O1 at (x, y, z) acts as hydrogen-bond donor to nitro O3 at (x, y, -1 + z), so generating by translation a C(7) chain parallel to [001]. Adjacent [001] chains are linked by C—H···O hydrogen bonds: C1 and C2 at (x, y, z) act as hydrogen-bond donors to O1 and O2 at (-1 + x, y, z) and (1 + x, y, z) respectively (Table 2). In this manner, the [001] chains are linked into (010) sheets built from R²₂(10) and R⁴₄(14) rings (Fig. 2). The combination of the (010) anion layers and the [010] metal-ligand chains generates the overall layer structure.

In the strictly planar anion, O1 is cis to C2: the bond distances (Table 1) within the anion are highly unusual in comparison with typical values for these bond types (Allen et al., 1987), and they are consistent with extensive delocalization of the negative charge. The N—O bonds in the nitro group are both very long [mean distance, 1.218 Å (Allen et al., 1987)], while the N2—C2 and C2—C1 bonds are both rather short (mean distances, 1.468 and 1.455 Å, respectively); although the N—O distance in the oxime unit is unexceptional, the N1—C1 distance is somewhat long for its type (mean value 1.281 Å; upper quartile value 1.288 Å). These observations, taken together, can most simply be interpreted in terms of a dominant contribution from form (IIa) with a lesser involvement of form (IIb). The Na—O distances (Table 1) are significantly shorter than the Na—N distance. The fact that N1, O2 and O3 all act as bridging atoms between pairs of Na is consistent with the involvement of both (IIa) and (IIb): in form (IIa), N1 carries only a single lone pair and hence would not be expected to act as a bridging atom, whereas in (IIb) it carries two lone pairs.

A plausible mechanism for the formation of the anion in (I) (Scheme) involves nucleophilic addition of the conjugate anion of nitromethane to a neutral molecule in the enolized aci form, followed by loss of water and a proton shift.

Related literature

For related literature, see: Allen et al. (1987).

S2. Experimental

The sodium salt of [3-(α-acetonylbenzyl)-4-hydroxycoumarin] was dissolved at ambient temperature in water and then an equal volume of nitromethane was added: when this solution was set aside to crystallize at ambient temperature, a solid orange-brown mass resulted, from which thin orange plates of (I) were isolated manually.

S3. Refinement

Compound (I) crystallized in the monoclinic system; space group P2₁/m or P2₁ from the systematic absences; P2₁/m was assumed and confirmed by the analysis. H atoms bonded to C were treated as riding atoms with C—H 0.95 Å. The H atom bonded to O1 was refined isotropically. The chemical types of all the atoms in the anion were confirmed by refinement of their site occupation factors.

Computing details

Data collection: Collect (Nonius, 1997-2000); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2001); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).

Figures

Fig. 1. Part of the crystal structure of (I) showing the ionic components and the coordination geometry at Na. Displacement ellipsoids are drawn at the 30% probability level. Atoms Na1a and Na1b are at (1/2, 1, 1/2) and (1/2, 0, 1/2) respectively; N1c and O3d are at (x, 3/4, 1 + z) and (-1 + x, 3/4, z), respectively; and N1e, O2f and O3g are at (1 - x, 1/4, -z), (1 - x, 1/4, 1 - z), and (2 - x, 1/4, 1 - z), respectively.

Fig. 2. Part of the crystal structure of (I) showing formation of (010) sheet built from R^22(10) and R^44(14) rings. Atoms marked with a star (*), hash (#) or dollar sign () are at the symmetry positions (x, y, -1 + z), (-1 + x, y, z) and (1 + x, y, z), respectively.

Sodium 2-nitroethanaloximate

Crystal data

Na^+·C2H3N2O3^−	F(000) = 128
Mr = 126.05	Dx = 1.897 Mg m^−3
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71073 Å
a = 4.9640 (15) Å	Cell parameters from 355 reflections
b = 6.346 (2) Å	θ = 2.6–25.0°
c = 7.336 (2) Å	µ = 0.25 mm^−1
β = 107.25 (2)°	T = 150 K
V = 220.70 (11) Å^3	Plate, orange
Z = 2	0.42 × 0.12 × 0.03 mm

Data collection

Kappa-CCD diffractometer	406 independent reflections
Radiation source: fine-focus sealed X-ray tube	308 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.091
ϕ scans, and ω scans with κ offsets	θmax = 25.0°, θmin = 4.3°
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997)	h = 0→5
Tmin = 0.902, Tmax = 0.993	k = 0→7
1075 measured reflections	l = −8→8

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)] = 0.059	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.162	H atoms treated by a mixture of independent and constrained refinement
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0449P)^2 + 0.064P] where P = (Fo^2 + 2Fc^2)/3
406 reflections	(Δ/σ)max < 0.001
52 parameters	Δρmax = 0.48 e Å^−3
0 restraints	Δρmin = −0.42 e Å^−3

Special details

Experimental. The program DENZO-SMN (Otwinowski & Minor, 1997) uses a scaling algorithm [Fox, G·C. & Holmes, K·C. (1966). Acta Cryst. 20, 886–891]which effectively corrects for absorption effects. High redundancy data were used in the scaling program hence the 'multi-scan' code word was used. No transmission coefficients are available from the program (only scale factors for each frame). The scale factors in the experimental table are calculated from the 'size' command in the SHELXL97 input file.

Geometry. Mean-plane data from the final SHELXL97 refinement run:-

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Na1	0.5000	0.5000	0.5000	0.0350 (7)
O1	1.0402 (7)	0.7500	−0.2181 (6)	0.0440 (11)
O2	0.6608 (6)	0.7500	0.3103 (5)	0.0355 (10)
O3	1.1278 (6)	0.7500	0.4454 (4)	0.0346 (10)
N1	0.7565 (8)	0.7500	−0.2246 (6)	0.0378 (11)
N2	0.9105 (8)	0.7500	0.2873 (6)	0.0324 (10)
C1	0.7297 (10)	0.7500	−0.0538 (8)	0.0382 (13)
C2	0.9554 (10)	0.7500	0.1189 (7)	0.0351 (12)
H1	1.030 (14)	0.7500	−0.371 (10)	0.063 (19)*
H1A	0.5434	0.7500	−0.0435	0.046*
H2	1.1439	0.7500	0.1129	0.042*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Na1	0.0250 (11)	0.0413 (14)	0.0412 (13)	0.0003 (7)	0.0135 (9)	0.0001 (8)
O1	0.0268 (18)	0.060 (3)	0.047 (3)	0.000	0.0132 (17)	0.000
O2	0.0209 (16)	0.047 (2)	0.043 (2)	0.000	0.0155 (14)	0.000
O3	0.0201 (16)	0.047 (2)	0.037 (2)	0.000	0.0087 (14)	0.000
N1	0.024 (2)	0.045 (3)	0.044 (3)	0.000	0.0092 (17)	0.000
N2	0.0222 (19)	0.037 (3)	0.039 (2)	0.000	0.0111 (17)	0.000
C1	0.029 (2)	0.044 (3)	0.043 (3)	0.000	0.015 (2)	0.000
C2	0.030 (2)	0.039 (3)	0.042 (3)	0.000	0.019 (2)	0.000

Geometric parameters (Å, º)

O1—N1	1.395 (5)	O1—H1	1.11 (7)
N1—C1	1.299 (6)	O2—Na1^iii	2.398 (2)
C1—C2	1.421 (7)	O3—Na1^iv	2.377 (2)
Na1—O2	2.398 (2)	O3—Na1^v	2.377 (2)
Na1—O3^i	2.377 (2)	N1—Na1^vi	2.587 (3)
C2—N2	1.319 (6)	N1—Na1^vii	2.587 (3)
N2—O2	1.300 (5)	C1—H1A	0.9500
N2—O3	1.329 (5)	C2—H2	0.9500
Na1—N1^ii	2.587 (3)
O2—Na1—N1^ii	82.87 (10)	N1^x—Na1—Na1^iii	127.82 (6)
O2—Na1—O3^i	80.59 (9)	N1^ii—Na1—Na1^iii	52.18 (6)
O3^i—Na1—N1^ii	84.27 (9)	Na1^xi—Na1—Na1^iii	180
O3^viii—Na1—O3^i	180	N1—O1—H1	103 (4)
O3^viii—Na1—O2	99.41 (9)	N2—O2—Na1	124.74 (16)
O3^viii—Na1—O2^ix	80.59 (9)	N2—O2—Na1^iii	124.74 (16)
O3^i—Na1—O2^ix	99.41 (9)	Na1—O2—Na1^iii	82.86 (10)
O2—Na1—O2^ix	180	N2—O3—Na1^iv	122.41 (16)
O3^viii—Na1—N1^x	84.27 (9)	N2—O3—Na1^v	122.41 (16)
O3^i—Na1—N1^x	95.73 (9)	Na1^iv—O3—Na1^v	83.72 (9)
O2—Na1—N1^x	97.13 (10)	C1—N1—O1	111.0 (4)
O2^ix—Na1—N1^x	82.87 (10)	C1—N1—Na1^vi	125.87 (19)
O3^viii—Na1—N1^ii	95.73 (9)	O1—N1—Na1^vi	106.6 (2)
O2^ix—Na1—N1^ii	97.13 (10)	C1—N1—Na1^vii	125.87 (19)
N1^x—Na1—N1^ii	180	O1—N1—Na1^vii	106.6 (2)
O3^viii—Na1—Na1^xi	48.14 (5)	Na1^vi—N1—Na1^vii	75.65 (12)
O3^i—Na1—Na1^xi	131.86 (5)	O2—N2—C2	123.6 (4)
O2—Na1—Na1^xi	131.43 (5)	O2—N2—O3	116.4 (3)
O2^ix—Na1—Na1^xi	48.57 (5)	C2—N2—O3	119.9 (4)
N1^x—Na1—Na1^xi	52.18 (6)	N1—C1—C2	125.5 (4)
N1^ii—Na1—Na1^xi	127.82 (6)	N1—C1—H1A	117.2
O3^viii—Na1—Na1^iii	131.86 (5)	C2—C1—H1A	117.2
O3^i—Na1—Na1^iii	48.14 (5)	N2—C2—C1	121.9 (4)
O2—Na1—Na1^iii	48.57 (5)	N2—C2—H2	119.1
O2^ix—Na1—Na1^iii	131.43 (5)	C1—C2—H2	119.1
O3^viii—Na1—O2—N2	−11.4 (3)	Na1—O2—N2—O3	−53.63 (18)
O3^i—Na1—O2—N2	168.6 (3)	Na1^iii—O2—N2—O3	53.63 (18)
N1^x—Na1—O2—N2	−96.7 (3)	Na1^iv—O3—N2—O2	−127.77 (15)
N1^ii—Na1—O2—N2	83.3 (3)	Na1^v—O3—N2—O2	127.77 (15)
Na1^xi—Na1—O2—N2	−52.3 (3)	Na1^iv—O3—N2—C2	52.23 (15)
Na1^iii—Na1—O2—N2	127.7 (3)	Na1^v—O3—N2—C2	−52.23 (15)
O3^viii—Na1—O2—Na1^iii	−139.10 (8)	O1—N1—C1—C2	0.0
O3^i—Na1—O2—Na1^iii	40.90 (8)	Na1^vi—N1—C1—C2	130.82 (19)
N1^x—Na1—O2—Na1^iii	135.55 (9)	Na1^vii—N1—C1—C2	−130.82 (19)
N1^ii—Na1—O2—Na1^iii	−44.45 (9)	O2—N2—C2—C1	0.0
Na1—O2—N2—C2	126.37 (18)	O3—N2—C2—C1	180
Na1^iii—O2—N2—C2	−126.37 (18)	N1—C1—C2—N2	180

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3^vi	1.11 (7)	1.56 (7)	2.630 (5)	160 (6)
C1—H1A···O1^i	0.95	2.45	3.274 (7)	146
C2—H2···O2^v	0.95	2.55	3.364 (6)	145

Symmetry codes: (i) x−1, y, z; (v) x+1, y, z; (vi) x, y, z−1.