Two-dimensional hydrogen-bonded arrays in p-phenyl­azoanilinium oxalate

In the title compound, 2C₆H₅N=NC₆H₄NH₃⁺·C₂O₄²⁻ or 2C₁₂H₁₂N₃⁺·C₂O₄²⁻, p-phenyl­azo­anil­ine is protonated at the amine site to form an organic ammonium cation, and oxalic acid is deprotonated forming an oxalate dianion. The latter occupies a special position at the inversion centre. The structure exhibits a layered hydrogen-bonded framework built up by N—H...O hydrogen bonds.

Key indicators

• Single-crystal X-ray study
• T = 297 K
• Mean [sigma](C-C) = 0.002 Å
• R factor = 0.041
• wR factor = 0.129
• Data-to-parameter ratio = 16.6

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level B:



PLAT_369  Alert B Long   C(sp2)-C(sp2) Bond  C(13)  -   C(13)a =       1.57 Ang.


 Alert Level C:



PLAT_715  Alert C D-H     Unknown or Inconsistent Label ........       (A)N3
                           (A)N3  H31

PLAT_715  Alert C D-H     Unknown or Inconsistent Label ........       (B)N3
                           (B)N3  H31

PLAT_715  Alert C D-H     Unknown or Inconsistent Label ........       (C)N3
                           (C)N3  H32

PLAT_715  Alert C D-H     Unknown or Inconsistent Label ........       (D)N3
                           (D)N3  H33

PLAT_715  Alert C D-H     Unknown or Inconsistent Label ........       (E)C2
                           (E)C2  H2

PLAT_717  Alert C D...A   Unknown or Inconsistent Label ........       (A)N3
                           (A)N3  O1

PLAT_717  Alert C D...A   Unknown or Inconsistent Label ........       (B)N3
                           (B)N3  O2

PLAT_717  Alert C D...A   Unknown or Inconsistent Label ........       (C)N3
                           (C)N3  O1

PLAT_717  Alert C D...A   Unknown or Inconsistent Label ........       (D)N3
                           (D)N3  O2

PLAT_717  Alert C D...A   Unknown or Inconsistent Label ........       (E)C2
                           (E)C2  O1

PLAT_718  Alert C D-H..A  Unknown or Inconsistent label ........       (A)N3
                           (A)N3  H31    O1

PLAT_718  Alert C D-H..A  Unknown or Inconsistent label ........       (B)N3
                           (B)N3  H31    O2

PLAT_718  Alert C D-H..A  Unknown or Inconsistent label ........       (C)N3
                           (C)N3  H32    O1

PLAT_718  Alert C D-H..A  Unknown or Inconsistent label ........       (D)N3
                           (D)N3  H33    O2

PLAT_718  Alert C D-H..A  Unknown or Inconsistent label ........       (E)C2
                           (E)C2  H2     O1


 0 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 15 Alert Level C = Please check

---

S1. Comment

Carboxylic acids have been widely used as pattern-controlling functional groups for rational design of organic solids (Desiraju, 1989; Melendez & Hamilton, 1998). Oxalic acid is a dicarboxylic acid which has been of interest in fundamental research and industrial applications. It can be deprotonated to form hydrogenoxalate or oxalate anions as two species in solution and the solid state. The oxalate ion is a bidentate ligand used in the preparation of metal complexes and inorganic salts, while hydrogenoxalate is the dominant form in the organic salts of oxalic acid. Data mining in the Cambridge Structural Database (Allen & Kennard, 1993; CSD Version 5.21, updated April 2001 with 233218 entries) for the structures of organic salts comprising hydrogenoxalate and oxalate ions shows that there are some reports which can be used to understand the packing patterns and utilize them in the context of crystal engineering. For instance, in the structure of methylammonium hydrogenoxalate (Thomas, 1975), hydrogen bonding is a complex three-dimensional network, while for anilinium hydrogenoxalate monohydrate (Paixäo et al., 2000), a two-dimensional hydrogen-bonded network is formed from a bilayer of alternative cations and anions, and water molecules are sandwiched between the bilayers. A series of diammonium salts of oxalic acid, with the general formula H₃N(CH₂)_nNH₃²⁺·2HC₂O₄^-·H₂O, where n = 2, 3, 4 and 6, are reported (Babu et al., 1998; Barnes et al., 1998; Vijayalakshmi & Srinivasan, 1983), in which hydrogenoxalate anions are involved in hydrogen bonds with organic ammonium cations. The packing of the homologue with n = 2, ethylenediammonium bis(monohydrogenoxalate) monohydrate (Barnes et al., 1998), is unique in this series since it exhibits pillared–layered hydrogen-bonded arrays in which water molecules are sandwiched between the bilayer sheets.

Here, we report the crystal structure of bis(p-phenylazoanilinium) oxalate, I). This compound crystallizes in the triclinic system with space group P1 (No. 2). The asymmeric unit consists of an independent organic ammonium cation and a half of an oxalate anion since it lies at center of symmetry (see Fig. 1). They are linked together by N—H···O hydrogen bonds forming sheets parallel to the ab plane, as shown in Fig. 2. The p-phenylazoaniline molecules are protonated at the amine site forming ammonium cations which act as hydrogen-bond donors. There is no sign of protonation of azo groups or its participation in hydrogen bonding similar to what we have found in the crystal structure of p-phenylazoanilinium phenylphosphonate (Mahmoudkhani & Langer, 2001). This behavior of organic cation is different from what is found in the crystal structure of p-phenylazoaniline hydrochloride, where protonation occurs at the azo group. Oxalic acid, on the other hand, is deprotonated to form an organic dianion which acts as the acceptor of hydrogen bonds.

The hydrogen-bonding pattern is presented in Fig. 3. For its analysis, we used the graph-set methodology of Bernstein et al. (1995) and Grell et al. (1999).

Although the first-level graph set contains only D descriptors, the second-level graph set comprises several motifs including C₂²(6), C₂²(7), D₂²(6), R₁²(5), R₄²(8),R₂⁴(8), R₄⁴(12) and R₄⁴(14). The assignment of graph-set descriptors were performed using the PLUTO program, as described by Motherwell et al. (1999). The N3 atom acts as a donor of N—H···O bifurcated hydrogen bonds to the O1 and O2 atoms, or a and b hydrogen bonds according to Table 2, forming a R₁²(5) ring motif. The O1 and O2 atoms act as bifurcated acceptors of hydrogen bonds. A pair of ammonium cations are linked together via N—H···O hydrogen bonds with the O1 or O2 atoms (a and c hydrogen bonds), forming R₄²(8) ring motifs. A R₄⁴(12) motif is also formed by hydrogen bonding of two cations and two anions (c and d hydrogen bonds). The arrangement of supramolecular motifs, including rings, provides two-dimensional hydrogen-bonded network in the crystal structure of the title compound.

S2. Experimental

Compound (I) was prepared by the reaction of oxalic acid and p-phenylazoaniline in ethanol and subsequent reflux for about 1 h. Crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of the solution over a period of a few days.

S3. Refinement

The (N—)H atoms were located from difference Fourier map and refined isotropically with a restrained bond distance of 0.87 Å; other H atoms were placed in idealized positions and refined in the isotropic approximation (N—H = 0.90–0.93 Å and C—H 0.96–1.02%A).

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SAINT (Siemens, 1995); data reduction: SAINT and SADABS (Sheldrick, 1996); program(s) used to solve structure: SHELXTL (Bruker, 2001); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg, 2000).

Figures

	Fig. 1. The molecular structure of (I) showing the atom-numbering scheme. Displacement ellipsoids are shown at the 50% probability level. The symmetry-dependent part of the oxalate ion is shown by semi-transparent colors.
	Fig. 2. A space-filling representation of a hydrogen-bonded sheet in the crystal structure of (I). Aromatic tails are pointing out from the layer.
	Fig. 3. Representation of the hydrogen-bonding pattern in the structure of (I). Only α-C atoms are shown for clarity. A label is assigned to each hydrogen bond (see Table 2).

Bis(p-phenylazoanilinium) oxalate

Crystal data

2C12H12N3^+·C2O4^2^−	Z = 1
Mr = 484.51	F(000) = 254
Triclinic, P1	Dx = 1.373 Mg m^−3
a = 6.4875 (1) Å	Mo Kα radiation, λ = 0.71073 Å
b = 7.0151 (1) Å	Cell parameters from 5443 reflections
c = 14.2991 (1) Å	θ = 1–30°
α = 92.044 (1)°	µ = 0.10 mm^−1
β = 100.045 (1)°	T = 297 K
γ = 112.955 (1)°	Needle, yellow-orange
V = 586.17 (1) Å^3	1.00 × 0.50 × 0.25 mm

Data collection

Siemens SMART CCD diffractometer	3499 independent reflections
Radiation source: fine-focus sealed tube	2858 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
Detector resolution: no pixels mm^-1	θmax = 30.5°, θmin = 2.9°
ω scans	h = −9→9
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	k = −10→10
Tmin = 0.910, Tmax = 0.976	l = −20→20
7891 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)] = 0.041	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.129	All H-atom parameters refined
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0677P)^2 + 0.0807P] where P = (Fo^2 + 2Fc^2)/3
3499 reflections	(Δ/σ)max < 0.001
211 parameters	Δρmax = 0.32 e Å^−3
3 restraints	Δρmin = −0.22 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	0.58318 (11)	0.76598 (10)	0.48700 (5)	0.03369 (18)
N1	−0.14184 (16)	0.74518 (16)	0.04159 (7)	0.0394 (2)
C1	0.08350 (15)	0.79559 (15)	0.33855 (7)	0.0286 (2)
O2	0.79716 (11)	0.58262 (12)	0.52064 (6)	0.0380 (2)
N2	−0.32444 (17)	0.76653 (17)	0.01430 (7)	0.0407 (2)
C2	−0.11676 (17)	0.82239 (17)	0.30468 (8)	0.0344 (2)
H2	−0.199 (2)	0.854 (2)	0.3535 (11)	0.050 (4)*
N3	0.16503 (14)	0.81488 (13)	0.44204 (6)	0.02889 (18)
H33	0.047 (2)	0.746 (2)	0.4699 (10)	0.049 (4)*
C3	−0.19630 (18)	0.80539 (18)	0.20688 (8)	0.0361 (2)
H3	−0.339 (2)	0.822 (2)	0.1802 (10)	0.046 (4)*
C4	−0.07316 (17)	0.76438 (16)	0.14373 (7)	0.0337 (2)
C5	0.12801 (19)	0.73936 (19)	0.17838 (8)	0.0388 (2)
H5	0.214 (3)	0.705 (2)	0.1317 (11)	0.052 (4)*
C6	0.20651 (17)	0.75391 (18)	0.27639 (8)	0.0358 (2)
H6	0.343 (3)	0.734 (2)	0.3013 (11)	0.055 (4)*
C7	−0.39778 (18)	0.74820 (17)	−0.08718 (7)	0.0356 (2)
C8	−0.6040 (2)	0.7661 (2)	−0.11869 (8)	0.0421 (3)
H8	−0.686 (3)	0.793 (3)	−0.0683 (12)	0.058 (4)*
C9	−0.6907 (2)	0.7481 (2)	−0.21620 (9)	0.0444 (3)
H9	−0.837 (3)	0.759 (3)	−0.2406 (12)	0.060 (4)*
C10	−0.5701 (2)	0.7156 (2)	−0.28159 (9)	0.0445 (3)
H10	−0.635 (3)	0.701 (3)	−0.3485 (13)	0.065 (5)*
C11	−0.3627 (2)	0.6996 (2)	−0.24997 (9)	0.0453 (3)
H11	−0.276 (3)	0.677 (3)	−0.2974 (13)	0.063 (5)*
C12	−0.2759 (2)	0.71477 (19)	−0.15315 (8)	0.0411 (3)
H12	−0.132 (3)	0.702 (3)	−0.1313 (11)	0.055 (4)*
C13	0.61097 (14)	0.60138 (14)	0.50227 (6)	0.02527 (18)
H32	0.235 (2)	0.9518 (19)	0.4666 (9)	0.038 (3)*
H31	0.277 (2)	0.763 (2)	0.4568 (11)	0.051 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0299 (3)	0.0251 (3)	0.0444 (4)	0.0099 (3)	0.0057 (3)	0.0056 (3)
N1	0.0395 (5)	0.0458 (5)	0.0341 (5)	0.0191 (4)	0.0059 (4)	0.0054 (4)
C1	0.0251 (4)	0.0252 (4)	0.0332 (5)	0.0083 (3)	0.0043 (3)	0.0049 (3)
O2	0.0234 (3)	0.0375 (4)	0.0539 (5)	0.0118 (3)	0.0094 (3)	0.0135 (3)
N2	0.0415 (5)	0.0497 (6)	0.0328 (5)	0.0212 (4)	0.0049 (4)	0.0056 (4)
C2	0.0296 (4)	0.0421 (5)	0.0352 (5)	0.0178 (4)	0.0073 (4)	0.0068 (4)
N3	0.0249 (4)	0.0275 (4)	0.0328 (4)	0.0098 (3)	0.0038 (3)	0.0044 (3)
C3	0.0302 (5)	0.0437 (6)	0.0368 (5)	0.0181 (4)	0.0048 (4)	0.0073 (4)
C4	0.0332 (5)	0.0339 (5)	0.0330 (5)	0.0131 (4)	0.0051 (4)	0.0051 (4)
C5	0.0358 (5)	0.0468 (6)	0.0382 (5)	0.0207 (5)	0.0093 (4)	0.0037 (5)
C6	0.0295 (4)	0.0428 (6)	0.0385 (5)	0.0188 (4)	0.0054 (4)	0.0049 (4)
C7	0.0381 (5)	0.0359 (5)	0.0317 (5)	0.0148 (4)	0.0051 (4)	0.0037 (4)
C8	0.0423 (6)	0.0491 (7)	0.0384 (6)	0.0224 (5)	0.0072 (4)	0.0053 (5)
C9	0.0440 (6)	0.0461 (6)	0.0420 (6)	0.0204 (5)	0.0005 (5)	0.0060 (5)
C10	0.0543 (7)	0.0409 (6)	0.0328 (5)	0.0163 (5)	0.0022 (5)	0.0032 (4)
C11	0.0525 (7)	0.0480 (7)	0.0362 (6)	0.0204 (5)	0.0113 (5)	0.0023 (5)
C12	0.0404 (6)	0.0451 (6)	0.0388 (6)	0.0186 (5)	0.0075 (4)	0.0035 (5)
C13	0.0240 (4)	0.0259 (4)	0.0244 (4)	0.0084 (3)	0.0050 (3)	0.0031 (3)

Geometric parameters (Å, º)

O1—C13	1.2571 (11)	C5—C6	1.3908 (15)
N1—N2	1.2487 (13)	C5—H5	1.02 (1)
N1—C4	1.4359 (13)	C6—H6	0.96 (1)
C1—C2	1.3911 (13)	C7—C8	1.3906 (16)
C1—C6	1.3868 (14)	C7—C12	1.3995 (16)
C1—N3	1.4645 (12)	C8—C9	1.3911 (17)
O2—C13	1.2494 (11)	C8—H8	1.02 (1)
N2—C7	1.4306 (14)	C9—C10	1.3848 (19)
C2—C3	1.3873 (15)	C9—H9	0.98 (2)
C2—H2	1.02 (1)	C10—C11	1.3915 (18)
N3—H33	0.90 (1)	C10—H10	0.96 (2)
N3—H32	0.91 (1)	C11—C12	1.3843 (16)
N3—H31	0.93 (1)	C11—H11	0.99 (2)
C3—C4	1.3960 (15)	C12—H12	0.97 (2)
C3—H3	0.99 (1)	C13—C13^i	1.5698 (17)
C4—C5	1.3924 (15)
N2—N1—C4	113.51 (9)	C1—C6—H6	119.8 (10)
C6—C1—C2	121.26 (9)	C5—C6—H6	120.9 (10)
C6—C1—N3	120.11 (8)	C8—C7—C12	120.27 (10)
C2—C1—N3	118.63 (9)	C8—C7—N2	115.57 (10)
N1—N2—C7	114.92 (9)	C12—C7—N2	124.16 (10)
C3—C2—C1	119.47 (9)	C7—C8—C9	119.81 (11)
C3—C2—H2	122.7 (8)	C7—C8—H8	117.7 (9)
C1—C2—H2	117.9 (8)	C9—C8—H8	122.5 (9)
C1—N3—H33	109.7 (10)	C10—C9—C8	120.02 (11)
C1—N3—H32	110.4 (8)	C10—C9—H9	118.4 (10)
H33—N3—H32	111.0 (13)	C8—C9—H9	121.6 (10)
C1—N3—H31	111.3 (9)	C9—C10—C11	120.13 (11)
H33—N3—H31	109.5 (13)	C9—C10—H10	118.4 (10)
H32—N3—H31	105.0 (12)	C11—C10—H10	121.5 (10)
C2—C3—C4	119.70 (9)	C12—C11—C10	120.42 (11)
C2—C3—H3	121.6 (8)	C12—C11—H11	119.9 (10)
C4—C3—H3	118.7 (8)	C10—C11—H11	119.7 (10)
C5—C4—C3	120.37 (10)	C11—C12—C7	119.36 (11)
C5—C4—N1	116.09 (9)	C11—C12—H12	120.2 (9)
C3—C4—N1	123.54 (9)	C7—C12—H12	120.5 (9)
C6—C5—C4	119.99 (10)	O2—C13—O1	126.67 (8)
C6—C5—H5	120.0 (8)	O2—C13—C13^i	116.66 (10)
C4—C5—H5	119.9 (8)	O1—C13—C13^i	116.66 (9)
C1—C6—C5	119.20 (9)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
(a)N3—H31···O1	0.93 (1)	1.95 (1)	2.8325 (15)	158 (1)
(b)N3—H31···O2^i	0.93 (1)	2.33 (1)	2.9520 (12)	124 (1)
(c)N3—H32···O1^ii	0.91 (1)	1.89 (1)	2.7939 (11)	172 (1)
(d)N3—H33···O2^iii	0.90 (1)	1.88 (1)	2.7654 (11)	175 (2)
(e)C2—H2···O1^iii	1.02 (1)	2.52 (1)	3.4620 (13)	153.3 (12)

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