Ammonium 4-nitrophenylarsonate

In the crystal structure of the title compound, (NH₄)[AsO₂(OH)(C₆H₄NO₂)], the 4-nitro­phenyl­arsonate anions and ammonium cations are linked through hydrogen bonds to form infinite chains along the b axis. The hydroxyl O atom of the 4-nitro­phenyl­arsonate anion acts as both an acceptor and a donor of hydrogen bonds. All atoms are located in general positions.

S1. Comment

The realm of phosphonate chemistry has developed rapidly and many new compounds have been prepared and characterized, due to interest in their potential applications in the areas of sorption and ion exchange (Wang et al., 1993), sensors (Cao et al., 1992; Alberti & Polombari, 1989), nonlinear optics (Thompson, 1994; Ungashe et al., 1992) and catalysis (Wan et al., 1986). In contrast, arsonate chemistry has received only limited attention. To our knowledge, few studies have been undertaken of the synthesis and characterization of metal arsonates with the goal of preparing functional compounds analogous to the reported metal phosphonates (Huan et al., 1990; Morizzi et al., 2000). In this context, the synthesis and structure of the title compound, (I), are presented here. \sch

The structure of (I) is shown in Fig. 1, and selected bond lengths and angles are given in Table 1. The arsonate anion contains an As atom tetrahedrally connected to one C atom of the benzene ring and three O atoms (Nuttall & Hunter, 1996; Percino et al., 2001). The As—O bond lengths range from 1.655 (3) to 1.732 (2) Å and the O—As—O angles vary from 108.8 (1) to 116.6 (1)°. The As—O5 (hydroxyl) bond is longer than the other two As—O bonds. The As—C distance of 1.93 Å is near to that reported (1.95 Å) in the 4-aminobenzenearsonic acid complex (Shimada, 1961). The phenyl ring and nitro group are not coplanar, with a dihedral angle of 6.4°.

The molecules of (I) are held together by an infinite chain of hydrogen bonds along the b axis (Fig. 2). The hydrogen bonds in this study have been considered with a liberal distance cut-off criterion of 2.5 < D···A < 3.0 Å and an angle cut-off criterion of 120 < D—H···A < 180°. Hydrogen-bond distances and angles are listed in Table 2.

From Fig. 2 it can be seen that there are five H atoms available for hydrogen bonding in the asymmetric unit. One of these comes from the arsonate hydroxyl group and the remaining four come from the ammonium cation. There are three hydrogen bonds between the ammonium cation and O atoms from three different symmetry-related 4-nitrophenylarsonate anions. In dicyclohexylammonium arsonomethylphosphonate, the N atoms of the cation and O atoms of the anion are also involved in hydrogen bonding (Falvello et al., 1977). There is another hydrogen bond between the arsonate hydroxyl group and an arsonate O atom from another arsonate anion.

A comparison of this structure with that of benezenearsonic acid (Shimada, 1959) is interesting. The two structures are closely similar in having endless chains formed by the hydrogen bonds. However, in 4-aminobenzenearsonic acid, there are additional hydrogen bonds to connect these chains to form a beautiful network (Shimada, 1961).

In summary, the 4-nitrophenylarsonate anions and ammonium cations of (I) are linked through hydrogen bonds to form infinite chains along the b axis. The hydroxyl O atom of the 4-nitrophenylarsonate anion acts as both acceptor and donor in the hydrogen bonds, and the N atom of the ammonium cation plays only the role of donor.

Table 2. Short O—H···O and N—H···O contacts (Å, °)

S2. Experimental

An aqueous solution of ammonia was added to an aqueous solution of 4-nitrophenylarsonic acid until pH 6.5 was reached. Pale-yellow needle crystals of (I) were obtained after evaporating the solution at room temperature for several weeks. Analysis calculated for C₆H₉AsN₂O₅: C 27.27, H 3.41%; found: C 27.41, H 3.26%. IR data (KBr, ν, cm^-1): 2814 (O—H), 1524 and 1349 (NO₂), 1089 (As—C), 1087 (As═O).

S3. Refinement

All H atoms on C atoms were generated geometrically and refined as riding atoms, with C—H = 0.93 Å and U_iso(H) = 1.2U_eq(C). The H atoms of the ammonium cation were located in the difference Fourier map and refined freely. The H atom of the hydroxyl group was generated theoretically and refined as a riding atom, with O—H = 0.82 Å and U_iso(H) = 1.5U_eq(O).

Computing details

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL-Plus (Sheldrick, 1990).

Figures

	Fig. 1. A view of the cation and anion of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. The infinite chains of (I) linked by hydrogen bonds along the b axis.

Ammonium 4-nitrophenylarsonate

Crystal data

(NH4)[AsO2(OH)(C6H4NO2)]	F(000) = 528
Mr = 264.07	Dx = 1.913 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 24 reflections
a = 11.670 (3) Å	θ = 4.7–8.9°
b = 6.5073 (16) Å	µ = 3.71 mm^−1
c = 12.693 (3) Å	T = 293 K
β = 107.975 (18)°	Prism, pale yellow
V = 916.9 (4) Å^3	0.52 × 0.36 × 0.23 mm
Z = 4

Data collection

Siemens P4 diffractometer	1285 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.036
Graphite monochromator	θmax = 25.0°, θmin = 2.1°
ω scans	h = −1→13
Absorption correction: ψ scan (North et al., 1968)	k = −1→7
Tmin = 0.223, Tmax = 0.426	l = −15→14
2283 measured reflections	3 standard reflections every 97 reflections
1602 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)] = 0.030	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.077	w = 1/[σ^2(Fo^2) + (0.0412P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.98	(Δ/σ)max < 0.001
1602 reflections	Δρmax = 0.49 e Å^−3
144 parameters	Δρmin = −0.57 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: 0.0271 (17)

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
As	0.32227 (3)	0.07896 (6)	0.49177 (3)	0.02143 (18)
O1	−0.0982 (3)	0.5224 (5)	0.6879 (3)	0.0445 (8)
O2	0.0302 (3)	0.7704 (5)	0.7164 (2)	0.0420 (7)
O3	0.4218 (2)	0.2402 (4)	0.4657 (2)	0.0323 (6)
O4	0.2365 (2)	−0.0536 (4)	0.3853 (2)	0.0331 (7)
O5	0.3985 (2)	−0.0896 (4)	0.5953 (2)	0.0317 (6)
H5	0.4409	−0.1659	0.5718	0.048*
N1	−0.0025 (3)	0.5946 (5)	0.6866 (2)	0.0298 (7)
N2	0.3531 (3)	0.5938 (6)	0.3338 (3)	0.0291 (7)
C1	0.2247 (3)	0.2361 (6)	0.5608 (3)	0.0215 (7)
C2	0.1221 (3)	0.1489 (6)	0.5766 (3)	0.0285 (9)
H2	0.1036	0.0120	0.5579	0.034*
C3	0.0481 (3)	0.2631 (6)	0.6194 (3)	0.0289 (9)
H3	−0.0204	0.2058	0.6304	0.035*
C4	0.0787 (3)	0.4661 (6)	0.6457 (3)	0.0243 (8)
C5	0.1815 (3)	0.5542 (6)	0.6344 (3)	0.0268 (8)
H5A	0.2010	0.6896	0.6559	0.032*
C6	0.2549 (3)	0.4394 (6)	0.5908 (3)	0.0251 (8)
H6	0.3241	0.4970	0.5815	0.030*
H12	0.316 (4)	0.552 (8)	0.268 (2)	0.073 (19)*
H13	0.307 (4)	0.697 (7)	0.354 (3)	0.031 (11)*
H11	0.374 (4)	0.480 (7)	0.379 (3)	0.034 (12)*
H14	0.425 (2)	0.640 (7)	0.347 (4)	0.058 (16)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
As	0.0243 (2)	0.0171 (2)	0.0265 (2)	0.00235 (18)	0.01314 (15)	0.00002 (18)
O1	0.0293 (15)	0.049 (2)	0.063 (2)	−0.0015 (15)	0.0256 (15)	−0.0152 (16)
O2	0.0451 (16)	0.0299 (17)	0.0595 (17)	0.0037 (15)	0.0284 (15)	−0.0122 (15)
O3	0.0312 (14)	0.0222 (14)	0.0514 (15)	0.0048 (13)	0.0244 (12)	0.0058 (13)
O4	0.0372 (15)	0.0325 (17)	0.0294 (13)	0.0024 (14)	0.0100 (12)	−0.0087 (12)
O5	0.0364 (14)	0.0306 (15)	0.0320 (13)	0.0110 (14)	0.0160 (12)	0.0070 (13)
N1	0.0286 (17)	0.0347 (19)	0.0274 (15)	0.0070 (17)	0.0105 (13)	−0.0042 (16)
N2	0.0296 (18)	0.0246 (19)	0.0354 (19)	−0.0003 (18)	0.0134 (16)	0.0023 (18)
C1	0.0217 (17)	0.0209 (19)	0.0233 (16)	0.0033 (17)	0.0090 (14)	0.0013 (16)
C2	0.030 (2)	0.0177 (18)	0.039 (2)	−0.0035 (17)	0.0130 (17)	−0.0023 (17)
C3	0.0280 (19)	0.030 (2)	0.0328 (18)	−0.0052 (19)	0.0161 (16)	−0.0019 (19)
C4	0.0250 (19)	0.026 (2)	0.0232 (17)	0.0055 (17)	0.0095 (15)	−0.0002 (15)
C5	0.0299 (19)	0.019 (2)	0.0317 (19)	−0.0016 (18)	0.0102 (16)	−0.0028 (17)
C6	0.0231 (18)	0.021 (2)	0.0330 (19)	−0.0019 (18)	0.0116 (16)	−0.0033 (17)

Geometric parameters (Å, º)

As—O4	1.655 (3)	N2—H14	0.86 (2)
As—O3	1.673 (3)	C1—C6	1.392 (5)
As—O5	1.732 (2)	C1—C2	1.395 (5)
As—C1	1.930 (3)	C2—C3	1.372 (5)
O1—N1	1.216 (4)	C2—H2	0.9300
O2—N1	1.229 (4)	C3—C4	1.382 (5)
O5—H5	0.8200	C3—H3	0.9300
N1—C4	1.472 (5)	C4—C5	1.377 (5)
N2—H12	0.86 (2)	C5—C6	1.375 (5)
N2—H13	0.94 (4)	C5—H5A	0.9300
N2—H11	0.92 (4)	C6—H6	0.9300
O4—As—O3	116.59 (13)	C6—C1—As	119.6 (3)
O4—As—O5	109.22 (14)	C2—C1—As	120.2 (3)
O3—As—O5	108.79 (13)	C3—C2—C1	120.7 (4)
O4—As—C1	110.75 (14)	C3—C2—H2	119.6
O3—As—C1	107.48 (15)	C1—C2—H2	119.6
O5—As—C1	103.16 (13)	C2—C3—C4	117.8 (3)
As—O5—H5	109.5	C2—C3—H3	121.1
O1—N1—O2	123.6 (3)	C4—C3—H3	121.1
O1—N1—C4	118.6 (3)	C5—C4—C3	122.8 (3)
O2—N1—C4	117.8 (3)	C5—C4—N1	118.4 (3)
H12—N2—H13	110 (4)	C3—C4—N1	118.8 (3)
H12—N2—H11	108 (4)	C6—C5—C4	119.2 (3)
H13—N2—H11	118 (4)	C6—C5—H5A	120.4
H12—N2—H14	118 (5)	C4—C5—H5A	120.4
H13—N2—H14	108 (4)	C5—C6—C1	119.4 (3)
H11—N2—H14	96 (4)	C5—C6—H6	120.3
C6—C1—C2	120.2 (3)	C1—C6—H6	120.3
O4—As—C1—C6	−135.8 (3)	C2—C3—C4—N1	177.0 (3)
O3—As—C1—C6	−7.4 (3)	O1—N1—C4—C5	173.9 (3)
O5—As—C1—C6	107.5 (3)	O2—N1—C4—C5	−5.3 (5)
O4—As—C1—C2	41.8 (3)	O1—N1—C4—C3	−5.5 (5)
O3—As—C1—C2	170.2 (3)	O2—N1—C4—C3	175.3 (3)
O5—As—C1—C2	−75.0 (3)	C3—C4—C5—C6	2.8 (6)
C6—C1—C2—C3	1.5 (5)	N1—C4—C5—C6	−176.6 (3)
As—C1—C2—C3	−176.0 (3)	C4—C5—C6—C1	−1.0 (5)
C1—C2—C3—C4	0.2 (5)	C2—C1—C6—C5	−1.1 (5)
C2—C3—C4—C5	−2.4 (6)	As—C1—C6—C5	176.4 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H11···O3	0.92 (4)	1.89 (4)	2.813 (4)	176 (3)
N2—H12···O4^i	0.86 (3)	1.97 (3)	2.819 (3)	169 (su)
N2—H13···O4^ii	0.94 (5)	1.92 (5)	2.844 (4)	168 (su)
O5—H5···O3^iii	0.82	1.87	2.638 (4)	156

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