Crystal structure of 5-[2-(2,4,6-tri­bromo­phen­yl)diazen­yl]tropolone

Hill, T.N.; Savig, K.L.; Lemmerer, A.

doi:10.1107/S2056989018006151

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Volume 74| Part 5| May 2018| Pages 709-712

https://doi.org/10.1107/S2056989018006151

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Crystal structure of 5-[2-(2,4,6-tribromophenyl)diazenyl]tropolone

Tania N. Hill,^a ^* Kelsey L. Savig ^a and Andreas Lemmerer ^a

^aMolecular Sciences Institute, School of Chemistry, University of the Witwatersrand, PO WITS 2050, Johannesburg, South Africa
^*Correspondence e-mail: tania.hill@gmail.com

Edited by L. Fabian, University of East Anglia, England (Received 10 April 2018; accepted 23 April 2018; online 27 April 2018)

The title compound {systematic name: 2-hydroxy-5-[2-(2,4,6-tribromophenyl)diazen-1-yl]cyclohepta-2,4,6-trien-1-one}, C₁₃H₇Br₃N₂O₂, is essentially planar, with an r.m.s. deviation of 0.054 Å. The molecular structure is fixed in the azo tautomer by intramolecular C—H⋯N interactions, with O—H⋯O hydrogen bonds creating linked dimers. Charge-transfer interactions are observed, with the segregated stacks linked by Br⋯Br interactions.

Keywords: crystal structure; azotropolone; azo group.

CCDC reference: 1838908

1. Chemical context

In modern times, dyes have become an enormous market (approx. $13.4 billion) with over one million tons of various dyes and pigments being produced each year, and their uses ranging from textiles, cosmetics, food coloring, printing inks to optical recording media. Azo dyes form one of the largest groups of synthetic chemical dyes with the chemical structure of these compounds featuring substituted aromatic rings that are joined by one or more azo groups (R—N=N—R). The first of these dyes to be produced was aniline yellow, which contains an azo-substituted benzene group. Tropolone exhibits similar aromatic properties to benzene; as such, a study was undertaken to synthesize a series of azo-functionalized tropolones. A search of the Cambridge Structural Database (CSD; Groom et al., 2016 ) yielded twenty troponoid compounds with a mono-substituted 5-position. Of these, only eleven had the tropolone backbone, only two of which had an azo linking group. As part of this study, we report the crystal structure of the title compound, I (Fig. 1).

Figure 1
View of I with 50% probability displacement ellipsoids

2. Structural commentary

The title compound, I, shows no signs of azo-hydrazone tautomerization, a phenomenon known to the phenylazo-derivatives, because of the stabilizing intramolecular interaction of the hydrogen (H6) atom of the tropolone ring with the nitrogen (N2) atom of the azo group (Table 1, Fig. 2). Similar to 5-phenylazotropolone (Hill et al., 2012 ), I is essentially planar, with the dihedral angle between the least-squares planes A (O1, O2, C1–C7, N1) and B (N2, C11–C16) of 5.07 (6)° with an r.m.s. deviation of 0.054 Å. The largest variation from the molecular plane is for the phenyl carbon (C13) with a value of 0.096 (2) Å. However, this planarity does not extend to the other azotropolones: 5-(4-ethoxyphenylazo)tropolone (Kubo et al., 2008 ) was found to be twisted with an angle of 27.6 (1)°.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C6—H6⋯N2	0.95	2.36	2.705 (3)	101
O2—H2⋯O1	0.84	2.1	2.591 (2)	117
C3—H3⋯O2ⁱ	0.95	2.54	3.241 (3)	131
Symmetry code: (i) $[-x+1, y-{\script{1\over 2}}, -z+{\script{3\over 2}}]$ .

Figure 2
The packing of I as viewed along the b-axis. The top-right insert illustrates the Br⋯π and π→π^* CT interactions, while the bottom-right insert illustrates the O—H⋯O and C—H⋯N interactions as dashed bonds. Only selected hydrogen atoms are shown for clarity.

3. Supramolecular features

As with tropolone (Shimanouchi & Sasada, 1973 ) along with the azotropolones, I forms centrosymmetric homodimers through an O—H⋯O interaction (Table 1, Fig. 2). Steyl & Roodt (2008 ) proposed a general range for Br⋯Br interactions, with distances between 3.6 and 4.6 Å with an interaction angle of 40 to 180°. Two noteworthy Br⋯Br interactions are observed for compound I, firstly, a ring formed with the adjacent molecule with a distance of 3.8246 (3) Å [Br1⋯Br3(−x, 1 − y, 1 − z)], and secondly, a chain linking the molecules [Br3⋯Br3(−x, − $[{1\over 2}]$ + y, $[{3\over 2}]$ − z)] with a distance of 3.6841 (4) Å (Fig. 3). Although the triangle interaction, which was observed by Steyl & Roodt, was present for I, the distances are rather long [3.6441 (4), 3.8246 (3) and 4.0113 (4) Å], but still fall into the range set.

Figure 3
The Br⋯Br interactions of I illustrated with dashed bonds. Hydrogen atoms omitted for clarity.

The π–π interactions that were observed for 5-phenylazotropolone and 5-(4-ethoxyphenylazo)tropolone are not observed for I. Instead, a π→π^* charge-transfer (CT) interaction between the aromatic phenyl and tropolone with the diazenyl group is seen (Fig. 2), with ring centroid to N=N midpoint distances of 3.3463 (3) and 3.3415 (3) Å, respectively. Additionally, a Br⋯π interaction is found with a Br to benzene ring centroid distance of 3.4563 (3) Å.

As a result of the observed O—H⋯O, Br⋯Br, Br⋯π and π→π^* CT interactions, the assembly of I is seen as forming segregated stacks along the b-axis direction (Fig. 2).

4. Hirshfeld Surface Analysis

Hirshfeld surface plots were generated for tropolone (CSD refcode: TROPOL10; Shimanouchi & Sasada, 1973), 5-phenylazotropolone (CSD refcode: YDIVYZ; Hill et al., 2012) and I based on the crystallographic information file (CIF) using CrystalExplorer17.5 (Turner et al., 2017 ), to explore and compare the location of atom-to-atom short contacts along with the quantitative ratios of these interactions. Unfortunatly, the Hirshfeld surfaces for 5-(4-ethoxyphenylazo)tropolone could not be generated as the co-ordinates were not inputted into the CSD. The curvedness plots of tropolone and 5-phenyltropolone show large regions of green. This is attributed to a relatively flat surface area (planar), whilst the blue regions illustrate areas of curvature (Fig. 4). For tropolone and 5-phenyltropolone, it can be seen that the molecules are essentially planar, as mentioned previously, with 5-phenyltropolone having a dihedral angle (between the least-squares planes of the tropolone and phenyl moieties) of 1.57 (8)°. This is smaller than the corresponding angle found for I [5.07 (6)°], where the additional twist of the dihedral planes can clearly be seen in the curvedness plot, as there are additional blue regions which snake over the `planar' surface of the molecule. The curvedness plots of the compounds show flat surface areas, which is consistent with the planar packing arrangement that has been observed for both tropolone and 5-phenylazotropolone. It is interesting to note that in the curvedness plots, the Br⋯Br interactions are clearly visible as curved (red) regions and contribute 9% to the total surface area. These interactions are mirrored in the shape-index plots but are a little harder to observe.

Figure 4
Hirshfeld surfaces for tropolone, 5-phenyltropolone and I, mapped with curvedness (top) and shape index (bottom).

On the shape-index surface plots for tropolone, 5-phenylazotropolone and I (Fig. 4), convex blue regions represent donor groups, whilst the red concave regions are the acceptor groups. The π–π interactions are generally indicated by adjacent red and blue triangles. These triangles are clearly observed for both tropolone (17.5% surface contribution) and 5-phenyltropolone (10.5% surface contribution), whereas this triangle formation was not found for I, further supporting the finding of no π–π interactions. As mentioned in the Supramolecular features section, I is seen to have both Br⋯π (7.1% surface contribution) and CT (9.2% surface contribution) interactions (Fig. 2). This is further supported by the Hirshfeld shape-index surface illustrating the blue region of the donor azo group and the red accepting region of the tropolone moiety (Fig. 4).

5. Synthesis and crystallization

The reagents were commercially obtained and used without further purification.

Sodium nitrite (1.4 mmol) dissolved in water (1 cm³) was added dropwise to a solution containing 2,4,6-tribromoaniline (1.6 mmol), hydrochloric acid (2 cm³, conc.) and water (7 cm³). Upon cooling the resultant mixture to ca 277 K, it was added slowly to a solution of sodium hydroxide (1.8 mmol) and tropolone (1.6 mmol) in water (4 cm³), keeping the temperature below 278 K. The resulting solution was stirred for 30 min., filtered and air-dried. Crystals suitable for X-ray diffraction were obtained by recrystallization with CHCl₃. Yield: 281 mg (38%), IR_ATR: 3231, 1602, 1541, 1524, 1507, 1439, 1411, 1439, 1304, 1258, 1190, 1052, 872, 852, 799, 730, 705, 669, 620, 604, 546, 490 cm⁻¹.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were positioned geometrically and refined using a riding model, with C—H = 0.95 Å, U_iso(H) = 1.2U_eq(C) for aromatic H atoms and with O—H = 0.84 Å, U_iso(H)=1.5U_eq(O) for the hydroxy H atom.

Table 2
Experimental details

Crystal data
Chemical formula	C₁₃H₇Br₃N₂O₂
M_r	462.94
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	173
a, b, c (Å)	18.1742 (3), 4.7885 (1), 16.0308 (3)
β (°)	104.560 (1)
V (Å³)	1350.31 (4)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	8.96
Crystal size (mm)	0.4 × 0.12 × 0.07

Data collection
Diffractometer	Bruker APEXII CCD area detector
Absorption correction	Multi-scan (SADABS; Bruker, 2004 )
T_min, T_max	0.124, 0.573
No. of measured, independent and observed [I > 2σ(I)] reflections	27599, 3258, 2744
R_int	0.055
(sin θ/λ)_max (Å⁻¹)	0.661

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.023, 0.051, 1.02
No. of reflections	3258
No. of parameters	182
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.77, −0.68
Computer programs: APEX2 (Bruker, 2005 ), SAINT-Plus and XPREP (Bruker, 2004), SHELXS97 and SHELXL97 (Sheldrick, 2008 ), DIAMOND (Brandenburg & Putz, 2005 ) and WinGX (Farrugia, 2012 ).

Supporting information

CCDC reference: 1838908

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2056989018006151/fy2127sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989018006151/fy2127Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989018006151/fy2127Isup3.cml

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT-Plus (Bruker, 2004); data reduction: SAINT-Plus (Bruker, 2004) and XPREP (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg & Putz, 2005); software used to prepare material for publication: WinGX (Farrugia, 2012).

2-Hydroxy-5-[2-(2,4,6-tribromophenyl)diazen-1-yl]cyclohepta-2,4,6-trien-1-one top

Crystal data top

C₁₃H₇Br₃N₂O₂	F(000) = 880
M_r = 462.94	D_x = 2.277 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 8182 reflections
a = 18.1742 (3) Å	θ = 2.3–28.2°
b = 4.7885 (1) Å	µ = 8.96 mm⁻¹
c = 16.0308 (3) Å	T = 173 K
β = 104.560 (1)°	Plate, red
V = 1350.31 (4) Å³	0.4 × 0.12 × 0.07 mm
Z = 4

Data collection top

Bruker APEXII CCD area detector diffractometer	3258 independent reflections
Radiation source: fine-focus sealed tube	2744 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.055
Detector resolution: 512 pixels mm^-1	θ_max = 28°, θ_min = 2.3°
φ and ω scans	h = −24→24
Absorption correction: multi-scan (SADABS; Bruker, 2004)	k = −6→6
T_min = 0.124, T_max = 0.573	l = −20→21
27599 measured reflections

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.023	w = 1/[σ²(F_o²) + (0.0151P)² + 1.5233P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.051	(Δ/σ)_max = 0.001
S = 1.01	Δρ_max = 0.77 e Å⁻³
3258 reflections	Δρ_min = −0.68 e Å⁻³
182 parameters

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.41630 (13)	1.5974 (5)	0.51392 (14)	0.0173 (5)
C2	0.45286 (13)	1.6351 (5)	0.60559 (14)	0.0171 (4)
C3	0.43788 (13)	1.5012 (5)	0.67536 (15)	0.0189 (5)
H3	0.4684	1.5592	0.7298	0.023*
C4	0.38490 (13)	1.2934 (5)	0.67894 (14)	0.0191 (5)
H4	0.3844	1.2338	0.7353	0.023*
C5	0.33337 (12)	1.1622 (5)	0.61327 (14)	0.0163 (4)
C6	0.32247 (13)	1.2070 (5)	0.52358 (14)	0.0181 (5)
H6	0.285	1.0929	0.4873	0.022*
C7	0.35821 (13)	1.3907 (5)	0.48232 (15)	0.0190 (5)
H7	0.3419	1.3811	0.4213	0.023*
C11	0.20015 (13)	0.6200 (5)	0.62034 (14)	0.0171 (4)
C12	0.14250 (13)	0.4963 (5)	0.55595 (14)	0.0184 (5)
C13	0.09308 (13)	0.2960 (5)	0.57313 (15)	0.0208 (5)
H13	0.0542	0.2182	0.5282	0.025*
C14	0.10233 (13)	0.2135 (5)	0.65781 (16)	0.0213 (5)
C15	0.15835 (14)	0.3243 (5)	0.72361 (15)	0.0208 (5)
H15	0.1639	0.263	0.7812	0.025*
C16	0.20691 (13)	0.5268 (5)	0.70536 (14)	0.0186 (5)
N1	0.28798 (11)	0.9647 (4)	0.64541 (13)	0.0221 (4)
N2	0.24557 (11)	0.8171 (4)	0.58994 (12)	0.0200 (4)
O1	0.43793 (10)	1.7538 (4)	0.46231 (10)	0.0230 (4)
O2	0.50700 (10)	1.8299 (3)	0.62292 (11)	0.0225 (4)
H2	0.511	1.9037	0.5767	0.034*
Br1	0.128145 (15)	0.60750 (6)	0.439523 (15)	0.02966 (7)
Br2	0.282839 (16)	0.65030 (6)	0.802286 (15)	0.03009 (8)
Br3	0.036554 (14)	−0.06019 (5)	0.684700 (18)	0.02738 (7)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0184 (11)	0.0153 (11)	0.0192 (11)	0.0027 (9)	0.0069 (9)	0.0010 (9)
C2	0.0160 (11)	0.0147 (10)	0.0201 (11)	0.0005 (8)	0.0038 (9)	−0.0016 (9)
C3	0.0193 (11)	0.0198 (11)	0.0164 (11)	−0.0005 (9)	0.0021 (9)	0.0002 (9)
C4	0.0199 (12)	0.0211 (12)	0.0155 (11)	0.0000 (9)	0.0029 (9)	0.0042 (9)
C5	0.0150 (11)	0.0146 (10)	0.0206 (11)	0.0007 (9)	0.0068 (9)	0.0025 (9)
C6	0.0179 (11)	0.0156 (11)	0.0195 (11)	−0.0001 (9)	0.0022 (9)	−0.0011 (9)
C7	0.0208 (12)	0.0202 (12)	0.0152 (11)	0.0008 (9)	0.0030 (9)	0.0006 (9)
C11	0.0164 (11)	0.0142 (11)	0.0217 (11)	0.0004 (8)	0.0064 (9)	0.0004 (9)
C12	0.0178 (11)	0.0190 (11)	0.0191 (11)	0.0018 (9)	0.0060 (9)	0.0013 (9)
C13	0.0183 (12)	0.0177 (11)	0.0266 (12)	−0.0010 (9)	0.0060 (10)	−0.0033 (9)
C14	0.0200 (12)	0.0135 (11)	0.0347 (13)	0.0007 (9)	0.0146 (10)	0.0009 (10)
C15	0.0248 (12)	0.0179 (11)	0.0221 (12)	0.0019 (10)	0.0102 (10)	0.0021 (9)
C16	0.0203 (12)	0.0165 (11)	0.0195 (11)	0.0000 (9)	0.0058 (9)	−0.0020 (9)
N1	0.0217 (10)	0.0220 (10)	0.0224 (10)	−0.0043 (8)	0.0055 (8)	0.0043 (8)
N2	0.0185 (10)	0.0199 (10)	0.0217 (10)	−0.0047 (8)	0.0051 (8)	0.0012 (8)
O1	0.0287 (9)	0.0202 (8)	0.0207 (8)	−0.0039 (7)	0.0076 (7)	0.0027 (7)
O2	0.0253 (9)	0.0214 (8)	0.0213 (8)	−0.0088 (7)	0.0070 (7)	0.0012 (7)
Br1	0.02972 (14)	0.03815 (15)	0.01879 (12)	−0.00894 (11)	0.00180 (10)	0.00365 (10)
Br2	0.04013 (16)	0.03091 (14)	0.01657 (12)	−0.01094 (11)	0.00216 (10)	0.00090 (10)
Br3	0.02564 (13)	0.01662 (12)	0.04556 (16)	−0.00247 (10)	0.01955 (11)	0.00277 (11)

Geometric parameters (Å, º) top

C1—O1	1.250 (3)	C11—C12	1.404 (3)
C1—C7	1.443 (3)	C11—C16	1.410 (3)
C1—C2	1.464 (3)	C11—N2	1.419 (3)
C2—O2	1.333 (3)	C12—C13	1.388 (3)
C2—C3	1.375 (3)	C12—Br1	1.895 (2)
C3—C4	1.396 (3)	C13—C14	1.383 (3)
C3—H3	0.95	C13—H13	0.95
C4—C5	1.373 (3)	C14—C15	1.375 (3)
C4—H4	0.95	C14—Br3	1.895 (2)
C5—C6	1.417 (3)	C15—C16	1.391 (3)
C5—N1	1.433 (3)	C15—H15	0.95
C6—C7	1.360 (3)	C16—Br2	1.895 (2)
C6—H6	0.95	N1—N2	1.241 (3)
C7—H7	0.95	O2—H2	0.84

O1—C1—C7	120.2 (2)	C12—C11—C16	116.4 (2)
O1—C1—C2	116.8 (2)	C12—C11—N2	114.79 (19)
C7—C1—C2	123.0 (2)	C16—C11—N2	128.8 (2)
O2—C2—C3	116.3 (2)	C13—C12—C11	123.1 (2)
O2—C2—C1	114.9 (2)	C13—C12—Br1	117.00 (17)
C3—C2—C1	128.8 (2)	C11—C12—Br1	119.88 (17)
C2—C3—C4	130.2 (2)	C14—C13—C12	117.9 (2)
C2—C3—H3	114.9	C14—C13—H13	121.1
C4—C3—H3	114.9	C12—C13—H13	121.1
C5—C4—C3	129.7 (2)	C15—C14—C13	121.8 (2)
C5—C4—H4	115.1	C15—C14—Br3	118.70 (18)
C3—C4—H4	115.1	C13—C14—Br3	119.53 (18)
C4—C5—C6	127.1 (2)	C14—C15—C16	119.6 (2)
C4—C5—N1	111.70 (19)	C14—C15—H15	120.2
C6—C5—N1	121.2 (2)	C16—C15—H15	120.2
C7—C6—C5	129.0 (2)	C15—C16—C11	121.2 (2)
C7—C6—H6	115.5	C15—C16—Br2	114.52 (17)
C5—C6—H6	115.5	C11—C16—Br2	124.22 (17)
C6—C7—C1	132.0 (2)	N2—N1—C5	115.36 (19)
C6—C7—H7	114	N1—N2—C11	116.30 (19)
C1—C7—H7	114	C2—O2—H2	109.5

O1—C1—C2—O2	−1.7 (3)	C11—C12—C13—C14	−0.9 (4)
C7—C1—C2—O2	178.0 (2)	Br1—C12—C13—C14	−179.57 (17)
O1—C1—C2—C3	177.0 (2)	C12—C13—C14—C15	0.0 (4)
C7—C1—C2—C3	−3.4 (4)	C12—C13—C14—Br3	−179.80 (17)
O2—C2—C3—C4	179.1 (2)	C13—C14—C15—C16	0.6 (4)
C1—C2—C3—C4	0.5 (4)	Br3—C14—C15—C16	−179.58 (17)
C2—C3—C4—C5	0.9 (5)	C14—C15—C16—C11	−0.4 (4)
C3—C4—C5—C6	0.9 (4)	C14—C15—C16—Br2	−178.21 (18)
C3—C4—C5—N1	−178.5 (2)	C12—C11—C16—C15	−0.4 (3)
C4—C5—C6—C7	−1.8 (4)	N2—C11—C16—C15	−178.1 (2)
N1—C5—C6—C7	177.6 (2)	C12—C11—C16—Br2	177.20 (17)
C5—C6—C7—C1	−1.0 (4)	N2—C11—C16—Br2	−0.5 (4)
O1—C1—C7—C6	−176.5 (2)	C4—C5—N1—N2	−172.8 (2)
C2—C1—C7—C6	3.9 (4)	C6—C5—N1—N2	7.7 (3)
C16—C11—C12—C13	1.1 (3)	C5—N1—N2—C11	179.97 (19)
N2—C11—C12—C13	179.1 (2)	C12—C11—N2—N1	167.9 (2)
C16—C11—C12—Br1	179.71 (16)	C16—C11—N2—N1	−14.3 (4)
N2—C11—C12—Br1	−2.3 (3)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C6—H6···N2	0.95	2.36	2.705 (3)	101
O2—H2···O1	0.84	2.1	2.591 (2)	117
C3—H3···O2ⁱ	0.95	2.54	3.241 (3)	131

Symmetry code: (i) −x+1, y−1/2, −z+3/2.

Funding information

The University of the Witwatersand and the Molecular Sciences Institute are thanked for providing the infrastructure and financial support required to do this work.

References

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