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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, 2C
12H
12N
3+·HPO
42−, and purple 4-[(
E)-phenyldiazenyl]anilinium dihydrogen phosphate phosphoric acid solvate, C
12H
12N
3+·H
2PO
4−·H
3PO
4, (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.
Supporting information
CCDC references: 634915; 634916
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.
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 Uiso 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 Uiso(H) values of 1.2Ueq(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.
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).
(I) 4-[(
E)-phenyldiazenyl]anilinium hydrogenphosphate
top
Crystal data top
2C12H12N3+·HO4P2− | 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) Å3 | 0.45 × 0.40 × 0.04 mm |
Z = 4 | |
Data collection top
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 top
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.075 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.229 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.05 | w = 1/[σ2(Fo2) + (0.140P)2 + 1.0658P] where P = (Fo2 + 2Fc2)/3 |
4676 reflections | (Δ/σ)max = 0.003 |
338 parameters | Δρmax = 0.95 e Å−3 |
7 restraints | Δρmin = −0.55 e Å−3 |
Crystal data top
2C12H12N3+·HO4P2− | V = 2400.5 (6) Å3 |
Mr = 492.47 | Z = 4 |
Monoclinic, P21/c | Mo Kα radiation |
a = 26.757 (4) Å | µ = 0.16 mm−1 |
b = 11.2998 (15) Å | T = 293 K |
c = 7.9943 (12) Å | 0.45 × 0.40 × 0.04 mm |
β = 96.709 (12)° | |
Data collection top
Oxford Xcalibur 3 CCD area-detector diffractometer | 3382 reflections with I > 2σ(I) |
17388 measured reflections | Rint = 0.058 |
4676 independent reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.075 | 7 restraints |
wR(F2) = 0.229 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.05 | Δρmax = 0.95 e Å−3 |
4676 reflections | Δρmin = −0.55 e Å−3 |
338 parameters | |
Special details top
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 (Å2) top | 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 (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
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) top
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) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H3A···O2i | 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···O1ii | 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···O1iii | 0.88 (2) | 1.78 (3) | 2.663 (3) | 173 (3) |
N4—H5A···O3iv | 0.88 (2) | 1.96 (3) | 2.816 (3) | 161 (3) |
O4—H1P···O2v | 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)
top
Crystal data top
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) Å3 | Prism, purple |
Z = 4 | 0.55 × 0.15 × 0.02 mm |
Data collection top
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 top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.040 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.101 | w = 1/[σ2(Fo2) + (0.0585P)2] where P = (Fo2 + 2Fc2)/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) |
Crystal data top
C12H12N3+·H3O4P−·H2O4P | V = 1673.9 (3) Å3 |
Mr = 393.23 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 4.5515 (4) Å | µ = 0.31 mm−1 |
b = 10.5973 (9) Å | T = 293 K |
c = 34.705 (3) Å | 0.55 × 0.15 × 0.02 mm |
Data collection top
Oxford Xcalibur 3 CCD area-detector diffractometer | 4015 independent reflections |
Absorption correction: analytical (Alcock, 1970) | 3323 reflections with I > 2σ(I) |
Tmin = 0.911, Tmax = 0.993 | Rint = 0.041 |
22198 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.040 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.101 | Δρmax = 0.23 e Å−3 |
S = 1.07 | Δρmin = −0.24 e Å−3 |
4015 reflections | Absolute structure: Flack (1983), 1631 Friedel pairs |
251 parameters | Absolute structure parameter: −0.11 (10) |
8 restraints | |
Special details top
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 (Å2) top | 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 (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
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) top
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) top
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···O1i | 0.87 (4) | 1.71 (4) | 2.568 (3) | 168 (4) |
O7—H7···O6i | 0.82 (3) | 1.72 (3) | 2.537 (2) | 171 (3) |
N1—H2···O7ii | 0.90 (4) | 2.17 (3) | 2.994 (3) | 149 (3) |
O8—H8···O5iii | 0.85 (4) | 1.75 (4) | 2.579 (3) | 167 (4) |
N1—H1···O6iv | 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. |
Experimental details
| (I) | (II) |
Crystal data |
Chemical formula | 2C12H12N3+·HO4P2− | C12H12N3+·H3O4P−·H2O4P |
Mr | 492.47 | 393.23 |
Crystal system, space group | Monoclinic, P21/c | Orthorhombic, P212121 |
Temperature (K) | 293 | 293 |
a, b, c (Å) | 26.757 (4), 11.2998 (15), 7.9943 (12) | 4.5515 (4), 10.5973 (9), 34.705 (3) |
α, β, γ (°) | 90, 96.709 (12), 90 | 90, 90, 90 |
V (Å3) | 2400.5 (6) | 1673.9 (3) |
Z | 4 | 4 |
Radiation type | Mo Kα | Mo Kα |
µ (mm−1) | 0.16 | 0.31 |
Crystal size (mm) | 0.45 × 0.40 × 0.04 | 0.55 × 0.15 × 0.02 |
|
Data collection |
Diffractometer | Oxford Xcalibur 3 CCD area-detector diffractometer | Oxford Xcalibur 3 CCD area-detector diffractometer |
Absorption correction | – | Analytical (Alcock, 1970) |
Tmin, Tmax | – | 0.911, 0.993 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 17388, 4676, 3382 | 22198, 4015, 3323 |
Rint | 0.058 | 0.041 |
(sin θ/λ)max (Å−1) | 0.617 | 0.662 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.075, 0.229, 1.05 | 0.040, 0.101, 1.07 |
No. of reflections | 4676 | 4015 |
No. of parameters | 338 | 251 |
No. of restraints | 7 | 8 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.95, −0.55 | 0.23, −0.24 |
Absolute structure | ? | Flack (1983), 1631 Friedel pairs |
Absolute structure parameter | ? | −0.11 (10) |
Hydrogen-bond geometry (Å, º) for (I) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H3A···O2i | 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···O1ii | 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···O1iii | 0.88 (2) | 1.78 (3) | 2.663 (3) | 173 (3) |
N4—H5A···O3iv | 0.88 (2) | 1.96 (3) | 2.816 (3) | 161 (3) |
O4—H1P···O2v | 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. |
Hydrogen-bond geometry (Å, º) for (II) top
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···O1i | 0.87 (4) | 1.71 (4) | 2.568 (3) | 168 (4) |
O7—H7···O6i | 0.82 (3) | 1.72 (3) | 2.537 (2) | 171 (3) |
N1—H2···O7ii | 0.90 (4) | 2.17 (3) | 2.994 (3) | 149 (3) |
O8—H8···O5iii | 0.85 (4) | 1.75 (4) | 2.579 (3) | 167 (4) |
N1—H1···O6iv | 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. |
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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.