Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106053571/hj3027sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270106053571/hj3027Isup2.hkl |
CCDC reference: 638342
For the preparations of 3-(phenylazo)carbazole, 3-nitrosocarbazole (1.96 g, 10 mmol) and freshly distilled aniline (1.01 ml, 11 mmol) were dissolved in a mixture of methanol (50 ml) and acetic acid (50 ml). A brown solution was maintained at 323 K for 4 h and evaporated in vacuum. A tarry residue was chromatographed on the column (40 × 5 cm, silica gel, type 60) using benzene as the eluant. The orange solution was concentrated to ca 100 ml, diluted with an equal volume of isooctane and cooled. 3-(Phenylazo)-carbazole (1.35 g, 50%) was collected by filtration and dried in vacuum (m.p. 473–474 K). Recrystallization from ethanol did not change the melting point. MS, m/z (int.): 271 (38, M+), 241 (3), 194 (11), 167 (17), 166 (100), 138 (21), 92 (5), 91 (7), 77 (18). IR (KBr): 3405 (pyrrole H atom); 3060 (stretching vibrations of aromatic H atoms); 1610, 1455, 1330, 1250 (skeletal vibrations); 825 (out-of-plane wagging vibrations, two adjacent pH atoms); 760, 735 (four adjacent hydrogen wag); 700 (sextant ring bend). 13C NMR (CDCl3): phenyl ring 153.1 (C1B), 130.4 (C34B), 129.3 (C3B and C5B), 122.8 (C2B and C6B); carbazole system 146.9 (C3), 141.5 (C9A) 140.4 (C8A), 126.7 (C7), 124.1 (C4A), 124.0 (C5A), 121.3 (C2), 121.0 (C5), 120.5 (C6), 117.0 (C4), 111.2 (C1), 111.0 (C8). Analysis calculated for C18H13N3 (271.30): C 79.68, H 4.83%; found: C 79.79, H 4.98%. For the preparation of (I), 3-(phenylazo)carbazole (2.71 g, 10 mmol), methyl iodide (2.84 g, 20 mmol) and tetra-n-butylammonium iodide (0.1 g) were dissolved in dimethyl sulfoxide (10 ml). To the stirred solution, potassium hydroxide (4.6 g, 0.1 mol), as a concentrated aqueous solution, was added and the stirring was continued for 2 h. The mixture was poured on to ice, and a yellow precipitate was collected by filtration and crystallized twice from ethanol. Compound (I) (2.19, 80%) was obtained as orange needles (m.p. 405–406 K). MS, m/z (int.): 285 (44, M+), 208 (3), 180 (100), 164 (4), 152 (24), 77 (12). IR (KBr): 3050 (aromatic H atoms); 2932, 2822 (N-methyl group); 1425 (deformations of N-methyl group); 745 (deformations of four and five adjacent aromatic h atoms); 686 (mono substituted benzene ring bend). 13C NMR (CDCl3): phenyl ring 153.1 (C1B), 130.3 (C4B), 129.3 (C3B and C5B) 122.7 (C2 and C6B); carbazole system 146.4 (C3), 142.9 (C9A), 141.9 (C8A), 126.5 (C7), 123.6 (C4A), 123.3 (C5A), 121.3 (C2), 120.9 (C5), 120 C6, 116.8 (C4), 109.2 (C1), 108.8 (C8). The crystal-state geometry of (I) was used as starting structure for full optimization using standard DFT and employing the B3LYP hybrid functional (Becke, 1988; Lee et al., 1988; Becke, 1993). Geometry optimization and vibrational analysis were performed without constraints on isolated molecules with the 6–311+G** basis set. All normal frequencies at the optimized geometry are real, showing that it is indeed a stable minimum. The calculations were carried out using GAUSSIAN03 (Frisch et al., 2004).
The H atoms of the CH3 group were generated in idealized positions, with the torsion angle optimized (C—H = 0.96 Å). The remaining H atoms were localized successfully from a Fourier map and in the final refinement their positions and the isotropic displacement parameters were refined; the final C—H distance ranged from 0.951 (13) to 1.034 (14) Å.
Data collection: CrysAlis CCD (Oxford Diffraction, 2002); cell refinement: CrysAlis RED (Oxford Diffraction, 2002); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1990); software used to prepare material for publication: SHELXL97.
C19H15N3 | F(000) = 600 |
Mr = 285.34 | Dx = 1.330 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2yn | Cell parameters from 10582 reflections |
a = 10.8631 (9) Å | θ = 2.9–25.5° |
b = 5.3684 (5) Å | µ = 0.08 mm−1 |
c = 24.661 (2) Å | T = 90 K |
β = 97.833 (7)° | Cube, orange |
V = 1424.7 (2) Å3 | 0.28 × 0.25 × 0.22 mm |
Z = 4 |
Xcalibur diffractometer | 1400 reflections with I > 2σ(I) |
Radiation source: fine-focus sealed tube | Rint = 0.048 |
Graphite monochromator | θmax = 25.5°, θmin = 2.9° |
Detector resolution: 1024x1024 with blocks 2x2 pixels mm-1 | h = −13→13 |
ω scans | k = −5→6 |
10582 measured reflections | l = −27→29 |
2656 independent reflections |
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)] = 0.034 | Hydrogen site location: difference Fourier map |
wR(F2) = 0.058 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.84 | w = 1/[σ2(Fo2) + (0.0778P)2 + 0.1154P] where P = (Fo2 + 2Fc2)/3 |
2656 reflections | (Δ/σ)max < 0.001 |
247 parameters | Δρmax = 0.14 e Å−3 |
0 restraints | Δρmin = −0.19 e Å−3 |
C19H15N3 | V = 1424.7 (2) Å3 |
Mr = 285.34 | Z = 4 |
Monoclinic, P21/n | Mo Kα radiation |
a = 10.8631 (9) Å | µ = 0.08 mm−1 |
b = 5.3684 (5) Å | T = 90 K |
c = 24.661 (2) Å | 0.28 × 0.25 × 0.22 mm |
β = 97.833 (7)° |
Xcalibur diffractometer | 1400 reflections with I > 2σ(I) |
10582 measured reflections | Rint = 0.048 |
2656 independent reflections |
R[F2 > 2σ(F2)] = 0.034 | 0 restraints |
wR(F2) = 0.058 | H atoms treated by a mixture of independent and constrained refinement |
S = 0.84 | Δρmax = 0.14 e Å−3 |
2656 reflections | Δρmin = −0.19 e Å−3 |
247 parameters |
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. |
x | y | z | Uiso*/Ueq | ||
N1 | 0.45088 (11) | 0.4012 (2) | 0.24874 (5) | 0.0213 (4) | |
N2 | 0.54651 (11) | 0.2672 (3) | 0.24705 (5) | 0.0216 (4) | |
C1 | 0.37048 (15) | 0.9338 (3) | 0.33226 (7) | 0.0201 (4) | |
C1B | 0.53410 (13) | 0.0878 (3) | 0.20403 (6) | 0.0176 (4) | |
C2 | 0.36696 (14) | 0.7478 (3) | 0.29336 (7) | 0.0201 (5) | |
C2B | 0.43547 (15) | 0.0789 (3) | 0.16143 (7) | 0.0229 (4) | |
C3 | 0.46604 (13) | 0.5810 (3) | 0.29199 (6) | 0.0177 (4) | |
C3B | 0.43370 (16) | −0.1052 (4) | 0.12223 (7) | 0.0262 (5) | |
C4 | 0.57138 (14) | 0.5962 (3) | 0.33076 (6) | 0.0185 (4) | |
C4B | 0.52881 (15) | −0.2805 (3) | 0.12454 (7) | 0.0219 (5) | |
C4A | 0.57711 (13) | 0.7810 (3) | 0.37019 (6) | 0.0172 (4) | |
C5 | 0.78376 (14) | 0.7458 (3) | 0.43785 (7) | 0.0208 (4) | |
C5B | 0.62690 (16) | −0.2685 (3) | 0.16652 (7) | 0.0229 (5) | |
C5A | 0.66863 (13) | 0.8463 (3) | 0.41634 (6) | 0.0172 (4) | |
C6 | 0.84906 (15) | 0.8549 (3) | 0.48394 (7) | 0.0223 (5) | |
N9 | 0.50592 (11) | 1.1170 (2) | 0.41314 (5) | 0.0207 (4) | |
C6B | 0.62977 (15) | −0.0843 (3) | 0.20614 (7) | 0.0193 (4) | |
C7 | 0.80121 (16) | 1.0640 (3) | 0.50803 (7) | 0.0239 (5) | |
C8 | 0.68759 (14) | 1.1666 (3) | 0.48755 (7) | 0.0219 (4) | |
C8A | 0.62164 (14) | 1.0551 (3) | 0.44159 (6) | 0.0193 (4) | |
C9A | 0.47699 (14) | 0.9515 (3) | 0.37024 (6) | 0.0177 (4) | |
C10 | 0.42681 (13) | 1.3175 (3) | 0.42815 (6) | 0.0256 (5) | |
H10A | 0.3803 | 1.2604 | 0.4562 | 0.038* | |
H10B | 0.3706 | 1.3676 | 0.3966 | 0.038* | |
H10C | 0.4774 | 1.4568 | 0.4416 | 0.038* | |
H1 | 0.3018 (11) | 1.055 (2) | 0.3342 (5) | 0.012 (4)* | |
H2 | 0.2956 (11) | 0.731 (2) | 0.2651 (5) | 0.011 (4)* | |
H2B | 0.3716 (11) | 0.207 (3) | 0.1603 (5) | 0.016 (4)* | |
H3B | 0.3656 (13) | −0.114 (3) | 0.0912 (6) | 0.034 (5)* | |
H4 | 0.6406 (11) | 0.476 (2) | 0.3303 (5) | 0.017 (4)* | |
H4B | 0.5260 (12) | −0.418 (3) | 0.0951 (6) | 0.032 (5)* | |
H5 | 0.8165 (12) | 0.598 (3) | 0.4198 (5) | 0.025 (5)* | |
H5B | 0.6929 (11) | −0.386 (3) | 0.1694 (5) | 0.019 (4)* | |
H6 | 0.9315 (11) | 0.788 (2) | 0.4996 (5) | 0.018 (4)* | |
H6B | 0.6970 (11) | −0.076 (2) | 0.2358 (5) | 0.019 (4)* | |
H7 | 0.8459 (12) | 1.145 (3) | 0.5406 (6) | 0.026 (5)* | |
H8 | 0.6529 (11) | 1.314 (3) | 0.5054 (5) | 0.017 (4)* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0218 (8) | 0.0210 (10) | 0.0214 (9) | −0.0020 (7) | 0.0044 (6) | −0.0011 (8) |
N2 | 0.0209 (8) | 0.0227 (9) | 0.0216 (9) | 0.0003 (7) | 0.0048 (6) | −0.0013 (8) |
C1 | 0.0185 (10) | 0.0210 (12) | 0.0209 (11) | 0.0026 (9) | 0.0028 (8) | 0.0036 (9) |
C1B | 0.0194 (10) | 0.0189 (11) | 0.0149 (10) | −0.0014 (8) | 0.0040 (8) | −0.0019 (9) |
C2 | 0.0164 (10) | 0.0246 (13) | 0.0184 (11) | −0.0019 (9) | −0.0004 (8) | 0.0031 (10) |
C2B | 0.0202 (10) | 0.0267 (13) | 0.0219 (11) | 0.0042 (9) | 0.0031 (8) | −0.0030 (10) |
C3 | 0.0197 (10) | 0.0184 (11) | 0.0154 (10) | −0.0028 (8) | 0.0040 (8) | −0.0019 (9) |
C3B | 0.0232 (11) | 0.0341 (14) | 0.0199 (11) | −0.0017 (10) | −0.0015 (9) | −0.0042 (10) |
C4 | 0.0174 (10) | 0.0177 (12) | 0.0211 (11) | −0.0001 (9) | 0.0054 (8) | 0.0024 (9) |
C4B | 0.0252 (11) | 0.0204 (12) | 0.0207 (11) | −0.0043 (9) | 0.0055 (9) | −0.0035 (10) |
C4A | 0.0174 (9) | 0.0160 (11) | 0.0186 (10) | −0.0019 (8) | 0.0034 (8) | 0.0002 (9) |
C5 | 0.0232 (10) | 0.0190 (12) | 0.0209 (10) | −0.0018 (9) | 0.0052 (8) | 0.0010 (10) |
C5B | 0.0244 (11) | 0.0211 (12) | 0.0243 (11) | 0.0032 (9) | 0.0071 (9) | 0.0023 (10) |
C5A | 0.0189 (9) | 0.0168 (11) | 0.0165 (10) | −0.0022 (8) | 0.0041 (8) | 0.0025 (9) |
C6 | 0.0208 (10) | 0.0250 (13) | 0.0202 (11) | −0.0021 (9) | −0.0009 (9) | 0.0016 (10) |
N9 | 0.0203 (8) | 0.0194 (10) | 0.0225 (8) | 0.0042 (7) | 0.0032 (6) | −0.0019 (8) |
C6B | 0.0195 (10) | 0.0225 (12) | 0.0158 (10) | −0.0030 (9) | 0.0019 (8) | 0.0016 (10) |
C7 | 0.0275 (11) | 0.0253 (12) | 0.0186 (11) | −0.0072 (10) | 0.0019 (9) | −0.0027 (10) |
C8 | 0.0257 (11) | 0.0191 (12) | 0.0213 (11) | −0.0016 (9) | 0.0049 (9) | −0.0028 (10) |
C8A | 0.0204 (10) | 0.0202 (12) | 0.0180 (10) | −0.0009 (8) | 0.0048 (8) | 0.0041 (9) |
C9A | 0.0214 (10) | 0.0155 (11) | 0.0170 (10) | −0.0014 (8) | 0.0054 (8) | 0.0003 (9) |
C10 | 0.0269 (10) | 0.0229 (12) | 0.0280 (11) | 0.0033 (8) | 0.0070 (8) | −0.0010 (9) |
N1—N2 | 1.2687 (15) | C4A—C5A | 1.449 (2) |
N1—C3 | 1.4315 (17) | C5—C6 | 1.385 (2) |
N2—C1B | 1.4259 (18) | C5—C5A | 1.3985 (19) |
C1—C2 | 1.382 (2) | C5—H5 | 1.001 (13) |
C1—C9A | 1.389 (2) | C5B—C6B | 1.388 (2) |
C1—H1 | 0.996 (12) | C5B—H5B | 0.951 (13) |
C1B—C6B | 1.3862 (19) | C5A—C8A | 1.411 (2) |
C1B—C2B | 1.395 (2) | C6—C7 | 1.403 (2) |
C2—C3 | 1.404 (2) | C6—H6 | 0.992 (12) |
C2—H2 | 0.973 (11) | N9—C9A | 1.3846 (17) |
C2B—C3B | 1.381 (2) | N9—C8A | 1.3938 (17) |
C2B—H2B | 0.974 (13) | N9—C10 | 1.4563 (17) |
C3—C4 | 1.3898 (19) | C6B—H6B | 0.962 (12) |
C3B—C4B | 1.393 (2) | C7—C8 | 1.383 (2) |
C3B—H3B | 0.990 (13) | C7—H7 | 0.980 (13) |
C4—C4A | 1.385 (2) | C8—C8A | 1.391 (2) |
C4—H4 | 0.994 (12) | C8—H8 | 1.004 (13) |
C4B—C5B | 1.382 (2) | C10—H10A | 0.9600 |
C4B—H4B | 1.034 (14) | C10—H10B | 0.9600 |
C4A—C9A | 1.4217 (19) | C10—H10C | 0.9600 |
N2—N1—C3 | 113.27 (12) | C4B—C5B—H5B | 121.4 (8) |
N1—N2—C1B | 114.36 (12) | C6B—C5B—H5B | 118.5 (8) |
C2—C1—C9A | 117.33 (16) | C5—C5A—C8A | 119.85 (15) |
C2—C1—H1 | 123.7 (7) | C5—C5A—C4A | 133.40 (16) |
C9A—C1—H1 | 118.9 (7) | C8A—C5A—C4A | 106.75 (13) |
C6B—C1B—C2B | 120.02 (17) | C5—C6—C7 | 120.54 (16) |
C6B—C1B—N2 | 115.34 (14) | C5—C6—H6 | 120.1 (8) |
C2B—C1B—N2 | 124.64 (15) | C7—C6—H6 | 119.4 (8) |
C1—C2—C3 | 121.93 (16) | C9A—N9—C8A | 109.07 (13) |
C1—C2—H2 | 120.4 (8) | C9A—N9—C10 | 126.03 (13) |
C3—C2—H2 | 117.6 (8) | C8A—N9—C10 | 124.84 (13) |
C3B—C2B—C1B | 119.18 (17) | C1B—C6B—C5B | 120.26 (16) |
C3B—C2B—H2B | 122.9 (8) | C1B—C6B—H6B | 118.9 (8) |
C1B—C2B—H2B | 117.9 (8) | C5B—C6B—H6B | 120.8 (8) |
C4—C3—C2 | 120.54 (16) | C8—C7—C6 | 121.87 (17) |
C4—C3—N1 | 123.53 (15) | C8—C7—H7 | 116.2 (8) |
C2—C3—N1 | 115.93 (14) | C6—C7—H7 | 122.0 (8) |
C2B—C3B—C4B | 121.02 (17) | C7—C8—C8A | 117.46 (16) |
C2B—C3B—H3B | 120.7 (9) | C7—C8—H8 | 121.6 (8) |
C4B—C3B—H3B | 118.2 (9) | C8A—C8—H8 | 120.9 (7) |
C4A—C4—C3 | 118.62 (15) | C8—C8A—N9 | 129.53 (15) |
C4A—C4—H4 | 120.9 (8) | C8—C8A—C5A | 121.62 (15) |
C3—C4—H4 | 120.5 (8) | N9—C8A—C5A | 108.85 (13) |
C5B—C4B—C3B | 119.42 (18) | N9—C9A—C1 | 129.82 (15) |
C5B—C4B—H4B | 120.4 (8) | N9—C9A—C4A | 108.66 (13) |
C3B—C4B—H4B | 120.2 (8) | C1—C9A—C4A | 121.50 (16) |
C4—C4A—C9A | 120.05 (15) | N9—C10—H10A | 109.5 |
C4—C4A—C5A | 133.28 (15) | N9—C10—H10B | 109.5 |
C9A—C4A—C5A | 106.66 (15) | H10A—C10—H10B | 109.5 |
C6—C5—C5A | 118.66 (16) | N9—C10—H10C | 109.5 |
C6—C5—H5 | 121.9 (8) | H10A—C10—H10C | 109.5 |
C5A—C5—H5 | 119.5 (8) | H10B—C10—H10C | 109.5 |
C4B—C5B—C6B | 120.09 (17) | ||
C3—N1—N2—C1B | −179.54 (12) | N2—C1B—C6B—C5B | 179.57 (13) |
N1—N2—C1B—C6B | −170.91 (13) | C4B—C5B—C6B—C1B | 0.4 (2) |
N1—N2—C1B—C2B | 9.8 (2) | C5—C6—C7—C8 | 0.9 (2) |
C9A—C1—C2—C3 | 0.4 (2) | C6—C7—C8—C8A | −0.2 (2) |
C6B—C1B—C2B—C3B | 1.1 (2) | C7—C8—C8A—N9 | 179.24 (16) |
N2—C1B—C2B—C3B | −179.70 (14) | C7—C8—C8A—C5A | −0.5 (2) |
C1—C2—C3—C4 | 0.9 (2) | C9A—N9—C8A—C8 | −179.38 (16) |
C1—C2—C3—N1 | −178.67 (13) | C10—N9—C8A—C8 | −1.9 (2) |
N2—N1—C3—C4 | −4.4 (2) | C9A—N9—C8A—C5A | 0.35 (16) |
N2—N1—C3—C2 | 175.20 (13) | C10—N9—C8A—C5A | 177.85 (13) |
C1B—C2B—C3B—C4B | −0.3 (3) | C5—C5A—C8A—C8 | 0.5 (2) |
C2—C3—C4—C4A | −0.9 (2) | C4A—C5A—C8A—C8 | −179.75 (14) |
N1—C3—C4—C4A | 178.71 (14) | C5—C5A—C8A—N9 | −179.24 (14) |
C2B—C3B—C4B—C5B | −0.5 (3) | C4A—C5A—C8A—N9 | 0.49 (16) |
C3—C4—C4A—C9A | −0.5 (2) | C8A—N9—C9A—C1 | 177.38 (16) |
C3—C4—C4A—C5A | 178.32 (16) | C10—N9—C9A—C1 | −0.1 (3) |
C3B—C4B—C5B—C6B | 0.4 (3) | C8A—N9—C9A—C4A | −1.08 (17) |
C6—C5—C5A—C8A | 0.1 (2) | C10—N9—C9A—C4A | −178.53 (13) |
C6—C5—C5A—C4A | −179.50 (16) | C2—C1—C9A—N9 | 179.97 (15) |
C4—C4A—C5A—C5 | −0.4 (3) | C2—C1—C9A—C4A | −1.7 (2) |
C9A—C4A—C5A—C5 | 178.55 (16) | C4—C4A—C9A—N9 | −179.56 (14) |
C4—C4A—C5A—C8A | 179.97 (17) | C5A—C4A—C9A—N9 | 1.36 (17) |
C9A—C4A—C5A—C8A | −1.12 (17) | C4—C4A—C9A—C1 | 1.8 (2) |
C5A—C5—C6—C7 | −0.8 (2) | C5A—C4A—C9A—C1 | −177.26 (14) |
C2B—C1B—C6B—C5B | −1.1 (2) |
Experimental details
Crystal data | |
Chemical formula | C19H15N3 |
Mr | 285.34 |
Crystal system, space group | Monoclinic, P21/n |
Temperature (K) | 90 |
a, b, c (Å) | 10.8631 (9), 5.3684 (5), 24.661 (2) |
β (°) | 97.833 (7) |
V (Å3) | 1424.7 (2) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 0.08 |
Crystal size (mm) | 0.28 × 0.25 × 0.22 |
Data collection | |
Diffractometer | Xcalibur diffractometer |
Absorption correction | – |
No. of measured, independent and observed [I > 2σ(I)] reflections | 10582, 2656, 1400 |
Rint | 0.048 |
(sin θ/λ)max (Å−1) | 0.606 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.034, 0.058, 0.84 |
No. of reflections | 2656 |
No. of parameters | 247 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.14, −0.19 |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2002), CrysAlis RED (Oxford Diffraction, 2002), CrysAlis RED, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), SHELXTL (Sheldrick, 1990), SHELXL97.
Distance/angle | X-ray | DFT |
N1—N2 | 1.269 (2) | 1.255 |
N1—C3 | 1.432 (2) | 1.412 |
N2—C1B | 1.426 (2) | 1.419 |
N9—C9A | 1.385 (2) | 1.383 |
N9—C8A | 1.394 (2) | 1.393 |
N9—C10 | 1.456 (2) | 1.449 |
N2—N1—C3 | 113.3 (1) | 115.83 |
N1—N2—C1B | 114.4 (1) | 115.26 |
C6B—C1B—N2 | 115.3 (1) | 115.83 |
C2B—C1B—N2 | 124.6 (2) | 124.73 |
C9A—N9—C8A | 109.1 (1) | 108.84 |
C9A—N9—C10 | 126.0 (1) | 125.82 |
C8A—N9—C10 | 124.8 (1) | 125.22 |
N9—C8A—C5A | 108.9 (1) | 109.06 |
N9—C9A—C4A | 108.7 (1) | 109.05 |
C3—N1—N2—C1B | -179.5 (1) | 179.98 |
N1—N2—C1B—C6B | -170.9 (1) | 179.80 |
N1—N2—C1B—C2B | 9.8 (2) | -0.20 |
N2—N1—C3—C4 | -4.4 (2) | -0.48 |
N2—N1—C3—C2 | 175.2 (1) | 179.80 |
The carbazole system is susceptible to electrophilic attack but not enough to couple with diazonium salts. Carbazolyl-3-diazonium salts can be generated in situ and coupled with very reactive substrates such as 2-naphthol. A more general method of preparation involves condensation of nitrosoarenes and amines. 3-Phenylazocarbazole was prepared, in moderate yield, from 3-nitrosocarbazole and aniline, in acetic acid solution. Its 9-methyl derivative, (I), formed orange, well shaped crystals, suitable for X-ray diffraction studies. The reversed sequence of steps, viz. methylation and condensation, is less effective due to the side reactions that accompany alkylation of 3-nitrosocarbazole (Kyzioł, 1985).
The intense colour of (I) and its high dipole moment (µ = 7.47 × 10-30 Cm), suggested conjugation between the azo bridge and carbazole system (Frej et al., 1990). In the UV–vis spectrum (in THF), a strong band near the visible borderline (λmax = 390 nm, log ε = 3.98) corresponds to the K-band in azobenzene (λmax = 315 nm, log ε = 4.35). Such a bathochromic shift reflects enhanced polarizability of the carbazole system in comparison to the benzene ring and a conjugation between aromatic π-electrons and those of the azo bridge. Such an interaction should result in the planar conformation of the molecule of (I). Indeed, the mean deviation from the C3/N1/N2/C1B plane does not exceed 0.003 Å and both aromatic rings are nearly coplanar with the azo bridge. The torsion angle along the C1B—N2 bond is 9.8 (2)°, the other one about C3—N1 is even smaller [4.4 (2)°] and the aromatic rings are twisted in opposite directions. These small deformations result probably from the intermolecular interaction in the crystal lattice. A density functional theory (DFT) study predicts a completely planar conformation as the preferential one for the isolated molecule of (I), like that presented in the scheme (the N1—N2 bond syn to the C2—C3 bond). Another planar conformation (the N1—N2 bond anti to the C2—C3 bond) resulting from the former by rotation of 180° along the C3—N1 bond, is more stable by 0.3 kcal mol-1. However, in the crystal lattice, the latter is actually observed. Rotation along the Ar—N bonds is fast in the NMR time-scale. Comparison of the spectra of (I), azobenzene and 9,9'-dimethyl-3,3'-azocarbazole allows for uniquivocal assignment of the signals. There are only four peaks coming from the benzene ring since the signals of C2B and C6B and those of C3B and C5B are isochronic. The B3LYP/6–311+G** calculations indicated that the rotational barrier along the N2—C1B bond is ca 5 kcal mol-1 and slightly higher (ca 8 kcal mol-1) on the other side of the azo bridge. The torsion barrier of a phenyl ring corresponds well to the torsional potential found in trans-azobenzene (Tsuji et al., 2001).
The geometry of the azo bridge is typical of azoarenes; however, the N1—N2 bond [1.269 (2) Å] is slightly longer than in other compounds of this type (Allen et al., 1995). In azobenzene and its para-substituted derivatives, the N—N distance varies within the range 1.232–1.255 Å, characteristic of the strictly double-bond character (Allmann, 1975). The N1—C3 and N2—C1B bonds [1.432 (2) Å and 1.426 (2) Å, respectively] are longer than typical single bonds between sp2-hybridized N and C atoms (Allen et al., 1995). The valence angles centred on N1 and N2 are less than 120° [113.3 (1)° and 114.4 (1)°, respectively], and consequently the C3—N1 and C1B—N2 bonds are deviated from the symmetry axis of the benzene rings. Enhancement of the C4—C3—N1 and C2B—C1B—N2 valence angles increases the distance between ortho H atoms and azo N atoms to the acceptable values. The other geometric parameters of the N-methylcarbazole group in (I) correlate well with the corresponding values found in the crystal structure of 9-methylcarbazole (Popova & Chetkina, 1978) and its CT complexes (Hosomi et al., 2000). There are no significant differences between values of bond lengths and angles of (I) in the solid state and in the calculated structure; the differences do not exceed 0.02 Å for bond distances and 2° for bond angles.
Deformations of the benzene ring are not observed, in spite of the electron-withdrawing properties of the azo group (Domenicano, 1992); the HOMA (harmonic oscillator model of aromaticity) index (Kruszewski & Krygowski, 1973; Krygowski, 1993) indicates that aromaticity of the ring is not disturbed (HOMA = 0.993). The benzene rings belonging to the carbazole system are not regular hexagons but they do not differ significantly from the rings in 9-isopropylcarbazole (Baert et al., 1986), but the HOMA indices differ to some extent. The value for the substituted ring (0.937) is lower than that of the other ring (0.961). The same sequences of values were obtained for hypothetical conformations, viz. planar and twisted by 90°. Significant quinonoid deformation of the substituted carbazole ring was not observed, despite the delocalization of the electron pair on the pyrrole N atom. Atom N9 lies in the plane defined by the neighbouring C atoms. The N9—C8A and N9—C9A bond lengths [1.394 (2) and 1.385 (2) Å, respectively] correspond to the bond order of 1.2. The electron withdrawing properties of the phenylazo group (σp = +0.39) are insufficient to disturb the carbazole aromatic system. The conjugation between aromatic π-electrons and those of the azo bridge is not strong enough to cause significant deformations in the molecular structure.
The molecular arrangement of (I) in the crystal state is presented in Fig. 2. The molecules form columns with parallel arrangement; the distance between stacked molecules, measured as the distance between mean planes of non-H atoms, is 3.386 (1) Å. The molecules are shifted in the column in a staircase manner, so the azo atom N2 is 3.375 (1) Å from ring atom C5B. The molecules belonging to the neighbouring columns form a dihedral angle of 78.21 (1)°.