Hydrogen phosphate and dihydrogen phosphate salts of 4-amino­azobenzene

4-Amino-trans-azobenzene {or 4-[(E)-phenyl­diazen­yl]aniline} can form isomeric salts depending on the site of protonation. Both orange bis{4-[(E)-phenyl­diazen­yl]anilinium} hydrogen phos­phate, 2C₁₂H₁₂N₃⁺·HPO₄²⁻, and purple 4-[(E)-phenyl­diazen­yl]­anilinium dihydrogen phosphate phosphoric acid solvate, C₁₂H₁₂N₃⁺·H₂PO₄⁻·H₃PO₄, (II), have layered structures formed through O—H...O and N—H...O hydrogen bonds. Additionally, azobenzene fragments in (I) are assembled through C—H...π inter­actions and in (II) through π–π inter­actions. Arguments for the colour difference are tentatively proposed.

S1. Comment

4-Aminoazobenzene has three N atoms, each possessing an unshaired electron pair. In addition to the cis–trans isomerism, each of the N atoms can be protonated and isomeric cations can thus be formed. This property is potentially applicable in the design of piezochromic materials because two groups of salts, according to colour, can be distinguished. So far, purple and orange salts have been isolated. In our preliminary studies we have found that the orange hydrogenphosphate salt of 4-amino-trans-azobenzene {4-[(E)-phenyldiazenyl]aniline}, when pressed into a KBr pellet, turns purple over a period of a few minutes to a few days (Lukić et al., 2007). We have encountered difficulties in determining the exact reaction taking place in the KBr pellet that causes the colour change. To the best of our knowledge, no work has reported results on colour changes in the solid state of salts of 4-aminoazobenzene. Even though the number of salts of 4-aminoazobenzene characterized in the solid state is still relatively small, an assumption can be made about the cause of the colour change. Tentatively, we propose that the colour of 4-aminoazobenzene salts depends on the site of protonation. In the Cambridge Structural Database (Version 5.27; August 2006; Allen, 2002) are reported three orange salts, all having the amino group protonated, and one purple salt with only the azo group protonated. Undoubtedly, finding an unequivocal answer about the origin of this effect requires a broader study. In this paper, as a first step in this investigation, we report the crystal structures of the hydrogenphosphate, (I), and dihydrogenphosphate, (II), salts of 4-aminoazobenzene.

The formula unit of the orange salt (I) consists of two 4-aminoazobenzene molecules, both in the trans configuration and protonated on the amino N atom, along with a hydrogenphosphate anion (Fig. 1). The purple compound (II) consists of one 4-aminoazobenzene molecule, also in the trans configuration, protonated on an azo group N atom, a dihydrogenphosphate anion and one solvent molecule of phosphoric acid (Fig. 2). In compound (II), alternatively, the hydrogen-bonded phosphoric acid and dihydrogenphosphate units could be considered as jointly forming the anion. Different sites of protonation of 4-aminoazobenzene result in quite different geometries for the cations. This is probably the cause of the different colours of these salts. In both compounds the geometry of the cation deviates significantly from planarity, but the deviation is more pronounced in the purple salt (II). The relative twist of the second benzene [phenyl?] ring is 18.0 (1)° in compound (II), and 2.2 (3) and 6.8 (2)° for compound (I). This larger value in (II) can be explained by repulsions between H atoms of the benzene [phenyl?] ring and a hydrogen-bond acceptor which approaches the protonated azo group.

Both compounds have many possible hydrogen-bond donor groups of the type NH or OH and they are all, in accord with Etter's first rule (Etter et al. 1990), involved in hydrogen bonds. In (I) the anions are linked through O—H···O hydrogen bonds (Table 1) and form a chain running in the [001] direction (Fig. 3). There are adjacent chains of anions in the (100) plane, which are related by inversion. In this way, layers of anions are formed even though there is no hydrogen bonding between the chains. A layer of anions is surrounded by cations which, through N—H···O hydrogen bonds, connect the chains. This forms a complex hydrogen-bonding network and a sheet structure parallel to the (100) plane (Fig. 4). There are no strong interactions between the sheets. The morphology of the orange crystals also reveals this. Crystals, obtained by evaporation from ethanol, are plate-like with {100} as the two most developed planes. Crystals also show pronounced cleavage parallel to the same planes. The hydroxyl group of the hydrogenphosphate ion is involved in hydrogen bonding only as a donor group so that, with altogether seven remaining hydrogen-bond donor groups in (I), two O atoms are acceptors in two interactions and one in three (Table 1). The relative orientation of the non-polar azobenzene fragments is such that a C—H···π interaction is formed. Atoms H2 and H8 are at distances of 3.304 and 3.090 Å, respectively, from the mean planes of the benzene rings of the azobenzene fragment at (x, 1.5 − y, −1/2 + z), and at 3.322 and 3.140 Å, respectively, from the centroids of these rings. The second independent azobenzene fragment forms C—H···π interactions with two adjacent molecules. Firstly, atoms H14 and H20 lie 2.885 and 3.061 Å, respectively, from the mean planes (2.999 Å and 3.101 Å, respectively, from the centroids) of the benzene rings of the azobenzene fragment at (x, 1/2 − y, −1/2 + z). The second interaction is towards one benzene ring of the azobenzene fragment at (x, 1/2 − y, 1/2 + z). The distance of H23 from the mean plane of the benzene ring is 3.47 Å (2.96 Å from its centroid). This interaction could also account for the deviation from planarity of the azobenzene fragment.

Compound (II) is also in accord with Etter's rule as it has eight independent possible hydrogen-bond donor groups and all of them are involved in hydrogen bonds. A network is formed through five O—H···O and three N—H···O hydrogen bonds (Table 2). Dihydrogenphosphate anions and molecules of phosphoric acid are connected through O—H···O hydrogen bonds and form a chain running in the [100] direction. This chain is surrounded by cations, each forming three hydrogen bonds of the N—H···O type and linking anionic chains. Thus is formed a two-dimensional network parallel to the (001) plane (Fig. 5). Azobenzene fragments within this layer are related by translation in the [100] direction and are in contact through π–π stacking interactions.

In order to elucidate the chemical reaction taking place in the KBr pellet, we shall try to obtain further structural evidence with other salts of 4-amino-trans-azobenzene and to record UV–vis spectra of these salts in KBr pellets.

S2. Experimental

For the preparation of (I), 4-aminoazobenzene (5 mmol, 0.986 g) and H₃PO₄ (5.5 mmol, 5.5 ml of 1.0 mol dm⁻³ aqueous solution) were dissolved in 10 ml of 96% EtOH, with mild heating and stirring over a period of hours. This resulted in a dark-purple solution. Orange crystals precipitated after cooling. The crystals were rinsed three times with 96% EtOH and dried in air (1.08 g, 88%). Crystals of (I) suitable for single-crystal X-ray diffraction were obtained after one week by slow evaporation of an EtOH solution [50 mg of (I) in 5 ml of 96% EtOH] at room temperature. For the preparation of (II), a further 10 ml of H₃PO₄(aqueous, c = 1.0 mol dm⁻³) was added to the mother liquour left from the preparation of (I) and the resulting purple solution was left to evaporate at room temperature. After approximately three weeks, elongated purple plates of (II) were isolated and used as obtained in the diffraction experiment.

S3. Refinement

In both structures the H atoms bonded to N and O atoms were located from a difference Fourier map and then isotropically refined with a common U_iso value and with N—H bond distances restrained to 0.86 Å and O—H bond distances restrained to 0.90 Å. H atoms bonded to C atoms were placed at geometrically calculated positions with C—H bond distances fixed at 0.93 Å and U_iso(H) values of 1.2U_eq(C). Refinement of the Flack parameter (Flack, 1983; Flack & Bernardinelli, 2000) was attempted for structure (II) using TWIN and BASF commands in SHELXL97 (Sheldrick, 1997) but it did not converge (shift/s.u.=1.06 consecutively in an indefinite number of refinement cycles). Attempted refinement of the inverted structure led to instabilities in SHELXL97, but we observed that the value of x had settled at approximately 1.08 (9). If the Flack parameter was refined without refining the other parameters the value x= −0.1 (1) was found. For the inverted structure, also without refinement of the atomic parameters, the result was x=1.1 (1). From these results (high s.u. and lack of convergence) we cannot make a definite decision about the absolute structure of (II). The reported absolute structure was chosen as the more probable one.

Computing details

For both compounds, data collection: CrysAlis CCD (Oxford Diffraction, 2003); cell refinement: CrysAlis RED (Oxford Diffraction, 2003); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997). Molecular graphics: ORTEP-3 (Farrugia, 1997) and SCHAKAL99 (Keller, 1999) for (I); ORTEP-3 (Farrugia, 1997 )and SCHAKAL99 (Keller, 1999) for (II). For both compounds, software used to prepare material for publication: PARST (Nardelli, 1995) and SHELXL97 (Sheldrick, 1997).

Figures

	Fig. 1. A view of (I), with the atom-labeling sheme. Displacement ellipsoids are drawn at the 50% probability level
	Fig. 2. A view of (II), with the atom-labeling sheme. Displacement ellipsoids are drawn at the 50% probability level
	Fig. 3. A layer of anions in (I) in the (100) plane. Chains of anions formed in the [001] direction. Hydrogen bonds connecting hydrogenphosphate ions are shown with thicker dashed lines. [Symmetry code: (i) x, 1/2 − y, −1/2 + z.]
	Fig. 4. The two-dimensional network of hydrogen bonds in (I), extending in the (100) plane, perpendicular to the plane of the drawing.
	Fig. 5. The two-dimensional network of hydrogen bonds in (II), extending in the (001) plane.

(I) 4-[(E)-phenyldiazenyl]anilinium hydrogenphosphate

Crystal data

2C12H12N3^+·HO4P^2^−	F(000) = 1032
Mr = 492.47	Dx = 1.363 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 2158 reflections
a = 26.757 (4) Å	θ = 2.9–19.6°
b = 11.2998 (15) Å	µ = 0.16 mm^−1
c = 7.9943 (12) Å	T = 293 K
β = 96.709 (12)°	Plates, orange
V = 2400.5 (6) Å^3	0.45 × 0.40 × 0.04 mm
Z = 4

Data collection

Oxford Xcalibur 3 CCD area-detector diffractometer	3382 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.058
Graphite monochromator	θmax = 26.0°, θmin = 3.9°
ω scans	h = −33→33
17388 measured reflections	k = −13→13
4676 independent reflections	l = −9→9

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)] = 0.075	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.229	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + (0.140P)^2 + 1.0658P] where P = (Fo^2 + 2Fc^2)/3
4676 reflections	(Δ/σ)max = 0.003
338 parameters	Δρmax = 0.95 e Å^−3
7 restraints	Δρmin = −0.55 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
P1	0.48444 (3)	0.36912 (7)	0.22093 (9)	0.0330 (3)
O1	0.46821 (8)	0.47852 (19)	0.3105 (2)	0.0378 (5)
O2	0.46545 (8)	0.25731 (19)	0.2945 (2)	0.0427 (6)
O3	0.54141 (8)	0.36427 (18)	0.2211 (3)	0.0389 (5)
O4	0.45861 (9)	0.3840 (2)	0.0352 (2)	0.0457 (6)
H1P	0.4664 (14)	0.332 (3)	−0.037 (4)	0.062 (4)*
N1	0.57194 (10)	0.5718 (3)	0.3981 (3)	0.0378 (6)
H1A	0.5698 (14)	0.506 (2)	0.340 (4)	0.062 (4)*
H2A	0.5555 (13)	0.565 (4)	0.487 (3)	0.062 (4)*
H3A	0.5590 (15)	0.634 (3)	0.343 (5)	0.062 (4)*
N4	0.57214 (10)	0.1466 (2)	0.3963 (3)	0.0361 (6)
H5A	0.5558 (13)	0.140 (3)	0.486 (4)	0.062 (4)*
H4A	0.5624 (14)	0.214 (2)	0.348 (4)	0.062 (4)*
H6A	0.5609 (14)	0.088 (3)	0.330 (4)	0.062 (4)*
N2	0.77723 (11)	0.6536 (3)	0.6140 (4)	0.0544 (8)
N3	0.79648 (11)	0.5908 (3)	0.7313 (4)	0.0584 (8)
N5	0.78103 (12)	0.1566 (3)	0.6022 (4)	0.0598 (9)
N6	0.79578 (12)	0.0937 (3)	0.7212 (4)	0.0590 (8)
C1	0.62499 (11)	0.5917 (3)	0.4512 (4)	0.0361 (7)
C2	0.64937 (13)	0.6883 (3)	0.3942 (4)	0.0503 (9)
H2	0.6322	0.7414	0.3194	0.060*
C3	0.69985 (13)	0.7054 (3)	0.4496 (5)	0.0525 (9)
H3	0.7167	0.7698	0.4101	0.063*
C4	0.72559 (13)	0.6281 (3)	0.5626 (4)	0.0455 (8)
C5	0.70034 (13)	0.5315 (3)	0.6194 (5)	0.0525 (9)
H5	0.7173	0.4784	0.6948	0.063*
C6	0.65042 (13)	0.5144 (3)	0.5646 (4)	0.0496 (9)
H6	0.6335	0.4501	0.6042	0.059*
C7	0.84825 (14)	0.6136 (4)	0.7844 (5)	0.0525 (9)
C8	0.87518 (14)	0.7099 (4)	0.7378 (5)	0.0592 (10)
H8	0.8596	0.7672	0.6660	0.071*
C9	0.92524 (16)	0.7204 (4)	0.7984 (5)	0.0693 (12)
H9	0.9433	0.7857	0.7678	0.083*
C10	0.94910 (15)	0.6362 (4)	0.9035 (6)	0.0689 (12)
H10	0.9832	0.6436	0.9408	0.083*
C11	0.92231 (16)	0.5410 (4)	0.9531 (6)	0.0688 (12)
H11	0.9381	0.4845	1.0257	0.083*
C12	0.87165 (15)	0.5295 (4)	0.8946 (5)	0.0632 (11)
H12	0.8533	0.4658	0.9289	0.076*
C13	0.62623 (11)	0.1424 (3)	0.4408 (4)	0.0349 (7)
C14	0.65597 (12)	0.2328 (3)	0.3928 (4)	0.0453 (8)
H14	0.6418	0.2939	0.3252	0.054*
C15	0.70691 (13)	0.2323 (4)	0.4454 (4)	0.0527 (9)
H15	0.7272	0.2927	0.4122	0.063*
C16	0.72768 (12)	0.1430 (3)	0.5466 (4)	0.0469 (9)
C17	0.69829 (13)	0.0484 (3)	0.5891 (4)	0.0503 (9)
H17	0.7129	−0.0141	0.6528	0.060*
C18	0.64706 (12)	0.0482 (3)	0.5357 (4)	0.0443 (8)
H18	0.6269	−0.0143	0.5633	0.053*
C19	0.84859 (14)	0.1102 (4)	0.7801 (5)	0.0544 (9)
C20	0.87796 (15)	0.2040 (4)	0.7356 (5)	0.0638 (11)
H20	0.8641	0.2621	0.6618	0.077*
C21	0.92788 (16)	0.2099 (4)	0.8021 (6)	0.0712 (12)
H21	0.9477	0.2721	0.7718	0.085*
C22	0.94870 (15)	0.1252 (4)	0.9123 (6)	0.0709 (13)
H22	0.9826	0.1288	0.9545	0.085*
C23	0.91851 (16)	0.0344 (4)	0.9596 (6)	0.0693 (12)
H23	0.9320	−0.0223	1.0362	0.083*
C24	0.86878 (15)	0.0274 (4)	0.8942 (5)	0.0640 (11)
H24	0.8488	−0.0336	0.9274	0.077*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0403 (5)	0.0319 (5)	0.0268 (4)	0.0000 (3)	0.0036 (3)	0.0006 (3)
O3	0.0410 (13)	0.0359 (12)	0.0399 (12)	0.0004 (9)	0.0061 (9)	0.0004 (9)
O1	0.0424 (12)	0.0409 (13)	0.0302 (10)	0.0013 (9)	0.0045 (8)	−0.0040 (9)
N1	0.0405 (15)	0.0387 (16)	0.0342 (14)	−0.0001 (12)	0.0046 (11)	−0.0017 (11)
N4	0.0370 (14)	0.0392 (16)	0.0318 (13)	−0.0009 (11)	0.0027 (10)	0.0008 (11)
C13	0.0367 (16)	0.0397 (18)	0.0283 (14)	0.0013 (13)	0.0041 (11)	−0.0024 (12)
O2	0.0534 (14)	0.0403 (13)	0.0338 (11)	−0.0084 (10)	0.0030 (9)	0.0066 (9)
O4	0.0652 (16)	0.0433 (14)	0.0267 (11)	0.0106 (11)	−0.0032 (10)	−0.0010 (9)
C1	0.0349 (16)	0.0433 (18)	0.0300 (14)	−0.0008 (13)	0.0030 (11)	−0.0020 (13)
C16	0.0360 (18)	0.061 (2)	0.0440 (18)	0.0012 (15)	0.0055 (14)	−0.0100 (16)
C6	0.047 (2)	0.049 (2)	0.0512 (19)	−0.0046 (16)	0.0015 (15)	0.0127 (16)
C4	0.0406 (18)	0.053 (2)	0.0423 (17)	−0.0007 (15)	0.0038 (14)	−0.0007 (15)
C22	0.041 (2)	0.094 (4)	0.074 (3)	0.002 (2)	−0.0069 (19)	−0.003 (3)
C18	0.0419 (18)	0.0460 (19)	0.0447 (18)	0.0013 (15)	0.0033 (14)	0.0050 (15)
C19	0.0408 (19)	0.070 (3)	0.051 (2)	0.0018 (18)	0.0006 (15)	−0.0073 (18)
C14	0.0448 (19)	0.047 (2)	0.0436 (17)	−0.0028 (15)	0.0038 (14)	0.0058 (15)
C7	0.043 (2)	0.066 (3)	0.0467 (19)	−0.0007 (17)	0.0003 (15)	0.0040 (17)
C2	0.048 (2)	0.051 (2)	0.0503 (19)	−0.0020 (16)	−0.0018 (15)	0.0119 (17)
C15	0.045 (2)	0.062 (2)	0.052 (2)	−0.0102 (17)	0.0054 (15)	0.0030 (18)
N2	0.0421 (17)	0.067 (2)	0.0535 (18)	−0.0024 (14)	0.0006 (13)	0.0051 (16)
C17	0.051 (2)	0.052 (2)	0.0475 (19)	0.0089 (16)	−0.0003 (15)	0.0028 (16)
N6	0.0526 (19)	0.068 (2)	0.0564 (19)	0.0048 (16)	0.0044 (14)	0.0063 (17)
C10	0.044 (2)	0.091 (4)	0.069 (3)	−0.003 (2)	−0.0054 (19)	−0.002 (2)
C3	0.044 (2)	0.056 (2)	0.057 (2)	−0.0089 (16)	0.0003 (15)	0.0132 (18)
C12	0.057 (2)	0.067 (3)	0.063 (2)	−0.002 (2)	0.0005 (18)	0.015 (2)
C5	0.047 (2)	0.054 (2)	0.054 (2)	0.0004 (16)	−0.0053 (15)	0.0132 (17)
C24	0.053 (2)	0.074 (3)	0.064 (2)	−0.001 (2)	0.0022 (18)	0.006 (2)
C20	0.052 (2)	0.081 (3)	0.057 (2)	0.005 (2)	−0.0045 (17)	0.001 (2)
N5	0.0481 (19)	0.075 (2)	0.0561 (19)	0.0068 (16)	0.0054 (14)	0.0012 (17)
N3	0.0451 (18)	0.073 (2)	0.0549 (18)	0.0010 (15)	−0.0016 (14)	0.0074 (17)
C8	0.051 (2)	0.065 (3)	0.059 (2)	0.0001 (18)	−0.0043 (17)	−0.0001 (19)
C11	0.056 (2)	0.080 (3)	0.067 (3)	0.008 (2)	−0.0078 (19)	0.010 (2)
C23	0.058 (3)	0.082 (3)	0.066 (3)	0.010 (2)	−0.0028 (19)	0.008 (2)
C21	0.056 (3)	0.086 (3)	0.069 (3)	−0.008 (2)	−0.001 (2)	−0.004 (2)
C9	0.058 (3)	0.082 (3)	0.066 (2)	−0.012 (2)	−0.0015 (19)	−0.003 (2)

Geometric parameters (Å, º)

P1—O2	1.507 (2)	C19—C20	1.390 (6)
P1—O1	1.517 (2)	C19—N6	1.448 (5)
P1—O3	1.525 (2)	C14—C15	1.379 (4)
P1—O4	1.572 (2)	C14—H14	0.9300
N1—C1	1.451 (4)	C7—C8	1.380 (5)
N1—H3A	0.88 (2)	C7—C12	1.393 (5)
N1—H2A	0.88 (2)	C7—N3	1.424 (5)
N1—H1A	0.88 (2)	C2—C3	1.385 (5)
N4—C13	1.450 (4)	C2—H2	0.9300
N4—H4A	0.88 (2)	C15—H15	0.9300
N4—H6A	0.88 (2)	N2—N3	1.239 (4)
N4—H5A	0.89 (2)	C17—H17	0.9300
C13—C14	1.376 (4)	N6—N5	1.216 (5)
C13—C18	1.386 (4)	C10—C9	1.376 (6)
O4—H1P	0.87 (2)	C10—C11	1.377 (6)
C1—C2	1.376 (5)	C10—H10	0.9300
C1—C6	1.380 (5)	C3—H3	0.9300
C16—C15	1.370 (5)	C12—C11	1.387 (5)
C16—C17	1.392 (5)	C12—H12	0.9300
C16—N5	1.453 (4)	C5—H5	0.9300
C6—C5	1.370 (5)	C24—C23	1.374 (5)
C6—H6	0.9300	C24—H24	0.9300
C4—C3	1.381 (5)	C20—C21	1.380 (5)
C4—C5	1.388 (5)	C20—H20	0.9300
C4—N2	1.424 (4)	C8—C9	1.375 (5)
C22—C21	1.374 (6)	C8—H8	0.9300
C22—C23	1.386 (6)	C11—H11	0.9300
C22—H22	0.9300	C23—H23	0.9300
C18—C17	1.387 (5)	C21—H21	0.9300
C18—H18	0.9300	C9—H9	0.9300
C19—C24	1.373 (6)
O2—P1—O1	111.78 (12)	C12—C7—N3	114.5 (3)
O2—P1—O3	110.61 (12)	C1—C2—C3	119.1 (3)
O1—P1—O3	111.71 (12)	C1—C2—H2	120.4
O2—P1—O4	109.10 (13)	C3—C2—H2	120.4
O1—P1—O4	103.90 (12)	C16—C15—C14	120.1 (3)
O3—P1—O4	109.50 (12)	C16—C15—H15	120.0
C1—N1—H3A	110 (3)	C14—C15—H15	120.0
C1—N1—H2A	110 (2)	N3—N2—C4	114.0 (3)
H3A—N1—H2A	106 (4)	C18—C17—C16	119.5 (3)
C1—N1—H1A	107 (3)	C18—C17—H17	120.3
H3A—N1—H1A	115 (4)	C16—C17—H17	120.3
H2A—N1—H1A	110 (4)	N5—N6—C19	113.2 (3)
C13—N4—H4A	112 (3)	C9—C10—C11	119.8 (4)
C13—N4—H6A	112 (3)	C9—C10—H10	120.1
H4A—N4—H6A	109 (4)	C11—C10—H10	120.1
C13—N4—H5A	112 (3)	C4—C3—C2	121.0 (3)
H4A—N4—H5A	106 (4)	C4—C3—H3	119.5
H6A—N4—H5A	105 (4)	C2—C3—H3	119.5
C14—C13—C18	120.9 (3)	C11—C12—C7	119.9 (4)
C14—C13—N4	120.0 (3)	C11—C12—H12	120.0
C18—C13—N4	119.0 (3)	C7—C12—H12	120.0
P1—O4—H1P	116 (3)	C6—C5—C4	120.0 (3)
C2—C1—C6	120.2 (3)	C6—C5—H5	120.0
C2—C1—N1	120.8 (3)	C4—C5—H5	120.0
C6—C1—N1	119.0 (3)	C19—C24—C23	120.1 (4)
C15—C16—C17	120.5 (3)	C19—C24—H24	119.9
C15—C16—N5	114.8 (3)	C23—C24—H24	119.9
C17—C16—N5	124.7 (3)	C21—C20—C19	119.3 (4)
C5—C6—C1	120.5 (3)	C21—C20—H20	120.4
C5—C6—H6	119.7	C19—C20—H20	120.4
C1—C6—H6	119.7	N6—N5—C16	113.3 (3)
C3—C4—C5	119.1 (3)	N2—N3—C7	115.2 (3)
C3—C4—N2	117.0 (3)	C9—C8—C7	119.4 (4)
C5—C4—N2	123.9 (3)	C9—C8—H8	120.3
C21—C22—C23	119.0 (4)	C7—C8—H8	120.3
C21—C22—H22	120.5	C10—C11—C12	119.8 (4)
C23—C22—H22	120.5	C10—C11—H11	120.1
C13—C18—C17	119.1 (3)	C12—C11—H11	120.1
C13—C18—H18	120.4	C24—C23—C22	120.6 (4)
C17—C18—H18	120.4	C24—C23—H23	119.7
C24—C19—C20	120.0 (4)	C22—C23—H23	119.7
C24—C19—N6	114.9 (4)	C22—C21—C20	121.0 (4)
C20—C19—N6	125.0 (4)	C22—C21—H21	119.5
C13—C14—C15	119.7 (3)	C20—C21—H21	119.5
C13—C14—H14	120.1	C8—C9—C10	121.2 (4)
C15—C14—H14	120.1	C8—C9—H9	119.4
C8—C7—C12	119.9 (4)	C10—C9—H9	119.4
C8—C7—N3	125.6 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H3A···O2^i	0.88 (2)	1.84 (3)	2.721 (3)	173 (3)
N4—H4A···O3	0.88 (2)	2.02 (3)	2.901 (3)	176 (3)
N1—H2A···O1^ii	0.89 (2)	1.86 (3)	2.737 (3)	166 (3)
N1—H1A···O3	0.87 (2)	1.97 (3)	2.811 (3)	161 (3)
N4—H6A···O1^iii	0.88 (2)	1.78 (3)	2.663 (3)	173 (3)
N4—H5A···O3^iv	0.88 (2)	1.96 (3)	2.816 (3)	161 (3)
O4—H1P···O2^v	0.87 (2)	1.68 (3)	2.523 (3)	164 (3)

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

(II) 4-[(E)-phenyldiazenyl]anilinium dihydrogenphosphate–phosphoric acid (1/1)

Crystal data

C12H12N3^+·H3O4P^−·H2O4P	F(000) = 816
Mr = 393.23	Dx = 1.560 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2ab	Cell parameters from 3527 reflections
a = 4.5515 (4) Å	θ = 2.9–21.3°
b = 10.5973 (9) Å	µ = 0.31 mm^−1
c = 34.705 (3) Å	T = 293 K
V = 1673.9 (3) Å^3	Prism, purple
Z = 4	0.55 × 0.15 × 0.02 mm

Data collection

Oxford Xcalibur 3 CCD area-detector diffractometer	4015 independent reflections
Radiation source: fine-focus sealed tube	3323 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.041
ω scans	θmax = 28.1°, θmin = 4.0°
Absorption correction: analytical (Alcock, 1970)	h = −6→6
Tmin = 0.911, Tmax = 0.993	k = −14→13
22198 measured reflections	l = −45→45

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)] = 0.040	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.101	w = 1/[σ^2(Fo^2) + (0.0585P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.07	(Δ/σ)max < 0.001
4015 reflections	Δρmax = 0.23 e Å^−3
251 parameters	Δρmin = −0.24 e Å^−3
8 restraints	Absolute structure: Flack (1983), 1631 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.11 (10)

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
P1	0.48750 (13)	0.81316 (6)	0.128846 (16)	0.03570 (15)
O1	0.2474 (4)	0.75052 (15)	0.15063 (5)	0.0447 (4)
O2	0.7364 (4)	0.8519 (2)	0.15612 (7)	0.0725 (7)
H4	0.894 (7)	0.807 (3)	0.1547 (10)	0.080 (4)*
O3	0.3721 (5)	0.93537 (17)	0.11026 (5)	0.0632 (6)
H5	0.414 (7)	0.951 (3)	0.0864 (8)	0.080 (4)*
O4	0.6077 (4)	0.72266 (16)	0.09777 (5)	0.0481 (5)
H6	0.716 (6)	0.757 (3)	0.0808 (9)	0.080 (4)*
P2	0.77257 (13)	0.92323 (5)	0.018088 (17)	0.03558 (15)
O6	0.5232 (4)	0.99005 (15)	0.03851 (5)	0.0431 (4)
O7	1.0141 (4)	1.02416 (16)	0.01074 (5)	0.0473 (4)
H7	1.172 (6)	1.007 (3)	0.0215 (9)	0.080 (4)*
O5	0.8891 (4)	0.81371 (16)	0.04054 (5)	0.0472 (4)
O8	0.6831 (5)	0.88634 (18)	−0.02311 (5)	0.0631 (6)
H8	0.565 (7)	0.826 (3)	−0.0274 (10)	0.080 (4)*
N1	−0.3687 (6)	0.2693 (2)	0.04604 (7)	0.0551 (6)
H1	−0.418 (7)	0.187 (3)	0.0406 (9)	0.080 (4)*
H2	−0.462 (7)	0.337 (3)	0.0354 (9)	0.080 (4)*
N2	0.3563 (5)	0.39153 (19)	0.16585 (6)	0.0453 (5)
N3	0.4095 (5)	0.50276 (19)	0.17883 (6)	0.0437 (5)
H3	0.318 (7)	0.572 (3)	0.1682 (9)	0.080 (4)*
C1	−0.1965 (6)	0.3016 (2)	0.07502 (7)	0.0419 (6)
C2	−0.0516 (6)	0.2085 (2)	0.09755 (7)	0.0482 (6)
H2C	−0.0818	0.1234	0.0924	0.058*
C3	0.1306 (7)	0.2439 (2)	0.12650 (7)	0.0489 (6)
H3C	0.2276	0.1824	0.1407	0.059*
C4	0.1760 (6)	0.3729 (2)	0.13548 (7)	0.0420 (6)
C5	0.0290 (6)	0.4661 (2)	0.11322 (7)	0.0470 (6)
H5C	0.0570	0.5512	0.1186	0.056*
C6	−0.1500 (6)	0.4314 (2)	0.08443 (7)	0.0476 (6)
H6C	−0.2462	0.4933	0.0702	0.057*
C7	0.5853 (6)	0.5164 (2)	0.21240 (6)	0.0412 (6)
C8	0.7525 (6)	0.4168 (2)	0.22619 (7)	0.0502 (6)
H8C	0.7601	0.3409	0.2128	0.060*
C9	0.9070 (7)	0.4319 (3)	0.25994 (8)	0.0586 (8)
H9C	1.0172	0.3651	0.2696	0.070*
C10	0.9004 (7)	0.5445 (3)	0.27953 (7)	0.0583 (8)
H10C	1.0058	0.5540	0.3023	0.070*
C11	0.7368 (7)	0.6430 (3)	0.26526 (8)	0.0575 (7)
H11C	0.7310	0.7190	0.2786	0.069*
C12	0.5810 (6)	0.6306 (2)	0.23131 (7)	0.0514 (7)
H12C	0.4751	0.6983	0.2214	0.062*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0346 (3)	0.0367 (3)	0.0358 (3)	−0.0002 (3)	0.0012 (3)	−0.0008 (2)
O1	0.0371 (10)	0.0451 (9)	0.0520 (10)	−0.0014 (9)	0.0045 (9)	0.0086 (8)
O2	0.0338 (10)	0.1034 (18)	0.0804 (14)	0.0054 (11)	−0.0091 (11)	−0.0451 (13)
O3	0.0991 (15)	0.0397 (9)	0.0508 (10)	0.0190 (11)	0.0209 (11)	0.0073 (8)
O4	0.0654 (12)	0.0380 (9)	0.0411 (9)	0.0073 (8)	0.0078 (9)	−0.0010 (7)
P2	0.0358 (3)	0.0348 (3)	0.0362 (3)	−0.0025 (3)	−0.0006 (3)	−0.0002 (2)
O6	0.0332 (8)	0.0480 (9)	0.0482 (9)	0.0041 (8)	0.0009 (8)	0.0006 (7)
O7	0.0339 (9)	0.0454 (9)	0.0626 (11)	−0.0041 (9)	−0.0049 (9)	0.0113 (8)
O5	0.0566 (11)	0.0423 (9)	0.0427 (8)	0.0118 (9)	0.0108 (8)	0.0036 (7)
O8	0.0964 (17)	0.0537 (11)	0.0393 (9)	−0.0230 (11)	−0.0106 (11)	−0.0013 (8)
N1	0.0671 (17)	0.0412 (12)	0.0571 (14)	0.0006 (12)	−0.0179 (12)	−0.0029 (10)
N2	0.0554 (13)	0.0390 (11)	0.0414 (10)	−0.0016 (10)	−0.0015 (10)	−0.0014 (9)
C7	0.0436 (14)	0.0440 (13)	0.0361 (11)	−0.0055 (11)	−0.0002 (11)	0.0037 (10)
C12	0.0622 (18)	0.0437 (13)	0.0483 (13)	0.0017 (13)	−0.0068 (14)	0.0009 (12)
C1	0.0480 (15)	0.0379 (12)	0.0398 (12)	−0.0011 (12)	−0.0034 (11)	0.0003 (10)
N3	0.0521 (13)	0.0391 (11)	0.0399 (10)	−0.0006 (10)	−0.0055 (10)	0.0025 (9)
C8	0.0545 (15)	0.0477 (14)	0.0485 (13)	0.0040 (15)	−0.0036 (13)	−0.0002 (11)
C6	0.0585 (16)	0.0365 (12)	0.0477 (13)	0.0006 (12)	−0.0065 (12)	0.0059 (11)
C4	0.0494 (15)	0.0387 (12)	0.0378 (12)	−0.0013 (11)	−0.0037 (11)	0.0021 (10)
C5	0.0563 (15)	0.0346 (11)	0.0502 (13)	−0.0026 (12)	−0.0090 (14)	0.0013 (10)
C2	0.0640 (18)	0.0338 (12)	0.0468 (13)	−0.0020 (12)	−0.0068 (13)	−0.0014 (10)
C11	0.072 (2)	0.0532 (15)	0.0471 (14)	−0.0046 (16)	−0.0123 (16)	−0.0059 (13)
C9	0.0658 (19)	0.0616 (17)	0.0486 (14)	0.0108 (16)	−0.0117 (14)	0.0040 (13)
C3	0.0667 (17)	0.0370 (12)	0.0430 (13)	0.0042 (12)	−0.0046 (14)	0.0060 (10)
C10	0.0677 (18)	0.0628 (17)	0.0446 (14)	−0.0009 (16)	−0.0141 (14)	−0.0017 (13)

Geometric parameters (Å, º)

P1—O1	1.4856 (17)	C12—C11	1.381 (4)
P1—O2	1.532 (2)	C12—H12C	0.9300
P1—O3	1.5393 (19)	C1—C2	1.421 (3)
P1—O4	1.5435 (18)	C1—C6	1.430 (3)
O2—H4	0.86 (3)	N3—H3	0.92 (3)
O3—H5	0.86 (3)	C8—C9	1.376 (4)
O4—H6	0.85 (3)	C8—H8C	0.9300
P2—O5	1.4950 (17)	C6—C5	1.340 (3)
P2—O6	1.5139 (17)	C6—H6C	0.9300
P2—O8	1.5371 (19)	C4—C3	1.417 (3)
P2—O7	1.5547 (18)	C4—C5	1.421 (3)
O7—H7	0.83 (3)	C5—H5C	0.9300
O8—H8	0.84 (3)	C2—C3	1.356 (4)
N1—C1	1.320 (3)	C2—H2C	0.9300
N1—H1	0.92 (3)	C11—C10	1.374 (4)
N1—H2	0.91 (3)	C11—H11C	0.9300
N2—N3	1.285 (3)	C9—C10	1.374 (4)
N2—C4	1.350 (3)	C9—H9C	0.9300
C7—C12	1.377 (3)	C3—H3C	0.9300
C7—C8	1.386 (3)	C10—H10C	0.9300
C7—N3	1.421 (3)
O1—P1—O2	110.45 (12)	N2—N3—C7	119.1 (2)
O1—P1—O3	109.77 (11)	N2—N3—H3	120 (2)
O2—P1—O3	106.59 (14)	C7—N3—H3	120 (2)
O1—P1—O4	109.81 (10)	C9—C8—C7	119.1 (2)
O2—P1—O4	109.64 (12)	C9—C8—H8C	120.4
O3—P1—O4	110.54 (10)	C7—C8—H8C	120.4
P1—O2—H4	116 (2)	C5—C6—C1	121.6 (2)
P1—O3—H5	119 (2)	C5—C6—H6C	119.2
P1—O4—H6	115 (2)	C1—C6—H6C	119.2
O5—P2—O6	112.64 (10)	N2—C4—C3	113.7 (2)
O5—P2—O8	112.40 (11)	N2—C4—C5	127.5 (2)
O6—P2—O8	110.85 (12)	C3—C4—C5	118.8 (2)
O5—P2—O7	111.64 (10)	C6—C5—C4	120.1 (2)
O6—P2—O7	106.56 (10)	C6—C5—H5C	120.0
O8—P2—O7	102.10 (11)	C4—C5—H5C	120.0
P2—O7—H7	113 (2)	C3—C2—C1	120.0 (2)
P2—O8—H8	122 (2)	C3—C2—H2C	120.0
C1—N1—H1	123 (2)	C1—C2—H2C	120.0
C1—N1—H2	112 (2)	C10—C11—C12	120.9 (3)
H1—N1—H2	123 (3)	C10—C11—H11C	119.5
N3—N2—C4	121.5 (2)	C12—C11—H11C	119.5
C12—C7—C8	120.8 (2)	C10—C9—C8	120.7 (3)
C12—C7—N3	118.2 (2)	C10—C9—H9C	119.6
C8—C7—N3	121.0 (2)	C8—C9—H9C	119.6
C7—C12—C11	118.8 (3)	C2—C3—C4	121.3 (2)
C7—C12—H12C	120.6	C2—C3—H3C	119.4
C11—C12—H12C	120.6	C4—C3—H3C	119.4
N1—C1—C2	121.0 (2)	C9—C10—C11	119.5 (2)
N1—C1—C6	120.8 (2)	C9—C10—H10C	120.2
C2—C1—C6	118.2 (2)	C11—C10—H10C	120.2

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H5···O6	0.86 (3)	1.78 (3)	2.647 (3)	176 (3)
O4—H6···O5	0.84 (3)	1.72 (3)	2.554 (3)	169 (3)
N3—H3···O1	0.91 (3)	2.03 (3)	2.899 (3)	161 (3)
O2—H4···O1^i	0.87 (4)	1.71 (4)	2.568 (3)	168 (4)
O7—H7···O6^i	0.82 (3)	1.72 (3)	2.537 (2)	171 (3)
N1—H2···O7^ii	0.90 (4)	2.17 (3)	2.994 (3)	149 (3)
O8—H8···O5^iii	0.85 (4)	1.75 (4)	2.579 (3)	167 (4)
N1—H1···O6^iv	0.91 (4)	2.12 (4)	3.011 (3)	168 (3)

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