A 2:1 co-crystal of 3,5-di­bromo-4-cyano­benzoic acid and anthracene

Noland, W.E.; Rieger, J.L.; Tu, Z.H.; Tritch, K.J.

doi:10.1107/S2056989017014815

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Volume 73| Part 11| November 2017| Pages 1743-1746

https://doi.org/10.1107/S2056989017014815

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A 2:1 co-crystal of 3,5-dibromo-4-cyanobenzoic acid and anthracene

Wayland E. Noland,^a ^* Janel L. Rieger,^a Zoe H. Tu ^a and Kenneth J. Tritch ^a

^aDepartment of Chemistry, University of Minnesota, 207 Pleasant St SE, Minneapolis, MN 55455, USA
^*Correspondence e-mail: nolan001@umn.edu

Edited by A. J. Lough, University of Toronto, Canada (Received 13 September 2017; accepted 12 October 2017; online 20 October 2017)

The title co-crystal, C₈H₃Br₂NO₂·0.5C₁₄H₁₀, was self-assembled from a 2:1 mixture of the components in slowly evaporating dichloromethane. The molecules adopt a sheet structure parallel to (1-12) in which carboxy hydrogen-bonded dimers and anthracene molecules stagger in both dimensions. Within the sheets, six individual cyano acid molecules surround each anthracene molecule. Cyano acid molecules form one of the two possible R₂²(10) rings between neighboring cyano and bromo groups. Compared to the dichloro analog [Britton (2012 ). J. Chem. Crystallogr. 42, 851–855], the dihedral angle between the best-fit planes of acid and anthracene molecules has decreased from 7.1 to 0.9 (2)°.

Keywords: crystal structure; co-crystal; carboxylic acid; N⋯Br contacts.

CCDC reference: 1525811

1. Chemical context

Doyle Britton (1930–2015) published roughly 30 crystallographic articles on solid-phase cyano–halo interactions from variously substituted halobenzonitriles and isocyanides. Britton postulated that 3,5-dichloro-4-cyanobenzoic acid might assemble into a honeycomb-like sheet structure (Fig. 1a) via a combination of carboxy hydrogen-bond dimerization and CN⋯Cl short contacts. In 2012, he found that the cyano acid molecules alone do not pack in this way, but slow evaporation of mixtures containing naphthalene or anthracene afforded 2:1 acid:hydrocarbon co-crystals roughly matching his proposed structure (Britton, 2012). However, no CN⋯Cl contacts were observed (Fig. 1b). Anthracene was the better fit, although it was too large to allow the ideal molecular arrangement. There is no obvious substitute for anthracene or naphthalene. Thus, we have prepared anthracene co-crystals with the dibromo analog in hopes that the larger Br bond and contact radii might close the CN⋯X gaps observed with Cl.

Figure 1
(a) The honeycomb-like structure envisioned by Doyle Britton. (b) A 2:1 co-crystal of 3,5-dichloro-4-cyanobenzoic acid with anthracene, viewed along 28 $[\overline{1}]$ (Britton, 2012

). Magenta dashed lines represent short contacts.

2. Structural commentary

The benzene (C2–C5/C7/C8) and anthracene (C9–C15 and symmetry equivalents, Fig. 2) ring systems are nearly planar. The mean deviation of atoms from the planes of best fit are 0.0074 (17) Å and 0.0041 (14) Å, respectively, both of which are comparable to the corresponding values in the dichloro crystal. However, the dihedral angle between the carboxy group (O1–C1–O2) and the benzene ring is 3.2 (4)°, compared with 7.2° in the dichloro analog.

Figure 2
The molecular structures of the components of the title co-crystal, with atom labeling and displacement ellipsoids at the 50% probability level. Only the symmetry-unique 3,5-dibromo-4-cyanobenzoic acid molecule is shown. Unlabeled anthracene atoms are generated by the (–x, –y, –z) symmetry operation.

3. Supramolecular features

The dihedral angle between the benzene and anthracene planes is 0.9 (2)°, which is much lower than 7.1° of the dichloro analog. As expected, $[R_{2}^{2}]$ (8) carboxy hydrogen-bonded dimers are observed (Table 1); these are located on an inversion center. $[R_{2}^{2}]$ (10) rings form about another inversion center based on C6≡N1⋯Br2 contacts (Table 2); however, the corresponding N1⋯Br1 contacts are not observed (Fig. 3). Instead, 3.5534 (5) Å Br1⋯Br1 contacts form, slightly closer than the 3.70 Å non-bonded contact diameter of Br (Rowland & Taylor, 1996 ). In the title co-crystal, two corners of the anthracene molecule contact the cyano acid network (Fig. 3), whereas all four corners made contact in the Cl analog (Fig. 1b). Overall, substitution of Cl atoms with Br atoms has facilitated the formation of half of the envisioned CN⋯X short contacts and also improved the coplanarity of the acid and hydrocarbon molecules, but anthracene is slightly too large to allow the ideal arrangement of cyano acid molecules. It is possible that upon substitution of Br atoms with I atoms, the improvements would continue and the envisioned sheet structure might occur. This possibility is currently being studied in our laboratory.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1A⋯O2ⁱ	0.84	1.79	2.627 (2)	178
Symmetry code: (i) -x, -y+1, -z+1.

Table 2
Contact geometry (Å, °)

C—X⋯Br	C—X	X⋯Br	C—X⋯Br
C6≡N1⋯Br2ⁱⁱ	1.143 (4)	3.307 (2)	115.9 (2)
C4—Br1⋯Br1ⁱⁱⁱ	1.886 (2)	3.5534 (5)	133.43 (7)
Symmetry codes: (ii) −x + 2, −y + 1, −z + 2; (iii) −x + 1, −y, −z + 2.

Figure 3
The sheet structure observed in the title co-crystal, viewed along [011].

4. Database survey

A search of the Cambridge Structural Database (Version 5.38, update May 2017; Groom et al., 2016 ) found no 4-cyano-3-halobenzoic acids other than the six structures reported by Britton (2012). Among 3-halobenzoic acids, no entries were found in which carboxy dimers formed and assembled into a honeycomb-like sheet, with or without a co-former. Of the 40 entries for 3,5-dihalo-2,6-unsubstituted benzoic acids, 11 of them are co-crystals with carboxy monomers hydrogen-bonded to an O or N atom in the co-former (i.e., Dubey & Desiraju, 2014 ; Back et al., 2012 ). Hydroxy acid (I) (Prout et al., 1988 ; Fig. 4) and amino acids (II) (Pant, 1965 ; Ueda et al., 2014 ) form interlocking ribbons in which adjacent carboxy dimers are connected by I⋯I contacts, or amino-carboxy hydrogen-bonds, respectively. 4-Cyanobenzoic acid (III) forms a sheet structure in which carboxy dimers are connected lengthwise by $[R_{2}^{2}]$ (10) rings formed by CN⋯H contacts, and laterally by R₃³(7) rings formed by weak C—H⋯O bonds flanking each pair of carboxy groups (Higashi & Osaki, 1981 ).

Figure 4
Selected structures from the database survey.

5. Synthesis and crystallization

Methyl 4-amino-3,5-dibromobenzoate (V): Bromine (3.9 mL) and then pyridine (5.7 mL) were added dropwise to ice-cold methanol (35 mL). This mixture was added dropwise to a solution of methyl 4-aminobenzoate [(IV), commercially available, Fig. 5] in methanol (50 mL). The resulting mixture was refluxed for 4 h and then cooled to room temperature. The methanol was removed on a rotary evaporator. Dichloromethane (50 mL) and water (50 mL) were added. Aliquots (5 mL) of Na₂CO₃ solution (aq., sat.) were added until the aqueous phase remained slightly alkaline after 10 min. The organic phase was separated and then washed with Na₂S₂O₃ solution (aq., sat., 25 mL), water (25 mL), brine (25 mL), and was then concentrated on a rotary evaporator. The resulting brown residue was recrystallized from ethyl acetate, giving colorless needles (18.1 g, 93%). M.p. 406–408 K (lit. 404–406 K; Otto & Juppe, 1965 ); ¹H NMR (300 MHz, CDCl₃) δ 8.063 (s, 2H), 4.996 (s, 2H), 3.866 (s, 3H); ¹³C NMR (75 MHz, CDCl₃) δ 165.1 (1C), 145.9 (1C), 133.5 (2C), 121.0 (1C), 107.5 (2C), 52.3 (1C); IR (NaCl, cm⁻¹) 3321, 3076, 2958, 1723, 1713, 1610, 1432, 1303, 1268, 975, 855, 761; MS (ESI, m/z) [M+Na]⁺ calculated for C₈H₇Br₂NO₂ 331.8715, found 331.8709.

Figure 5
The three-step synthesis of the title cyano acid (VII).

Methyl 3,5-dibromo-4-cyanobenzoate (VI), adapted from the work of Toya et al. (1992 ): Cyanide suspension: NaCN (680 mg) and CuCN (480 mg) and water (40 mL) were combined in a 400 mL beaker. After the solids dissolved, NaHCO₃ (6.5 g) was added. The resulting suspension was cooled in an ice bath. Diazotization: Dibromo ester [(V), 720 mg] was ground in a mortar and then combined with acetic acid (2.6 mL) in a round-bottomed flask. H₂SO₄ (0.6 mL) was added dropwise over 1 min, followed by a solution of NaNO₂ (313 mg) in water (1.5 mL) over 30 min.. During the course of the additions, the reaction mixture was gradually warmed in an oil bath to 315 K. Cyanation: When no more starting material remained, as indicated by TLC, the diazotization mixture was removed from the heat and then added dropwise to the cyanide suspension. The ice bath was removed. The cyanation mixture was stirred overnight and then extracted with dichloromethane (3 × 20 mL). The combined organic portions were washed with water (20 mL), brine (20 mL), dried with Na₂SO₄, filtered, and then concentrated on a rotary evaporator. The resulting brown residue was separated by column chromatography. The desired fraction (R_f = 0.34 in 3:1 hexane:ethyl acetate on SiO₂) was concentrated on a rotary evaporator, giving a tan powder (681 mg, 92%). M.p. 410–411 K; ¹H NMR (500 MHz, CDCl₃) δ 8.264 (s, 2H), 3.974 (s, 3H); ¹³C NMR (126 MHz, CDCl₃) δ 163.4 (1C), 135.5 (1C), 132.6 (2C), 127.1 (2C), 122.5 (1C), 115.5 (1C), 53.5 (1C); IR (KBr, cm⁻¹) 3076, 2955, 2229, 1732, 1429, 1263, 1124, 971, 748; MS (ESI, m/z) [M+Na]⁺ calculated for C₉H₅Br₂NO₂ 341.8559, found 341.8547.

3,5-Dibromo-4-cyanobenzoic acid (VII), adapted from the work of Lepage et al. (2004 ; especially compound 24): Cyano ester [(VI), 231 mg], lithium iodide (128 mg), and pyridine (10 mL) were combined in a round-bottomed flask. The resulting mixture was refluxed for 24 h and then cooled to room temperature. Chloroform (25 mL), water (25 mL), and hydrochloric acid (12 M, 25 mL) were added. After being stirred for 10 min, the resulting mixture was separated by suction filtration, giving a light-brown powder (217 mg, 99%). M.p. 423–425 K; ¹H NMR (500 MHz, (CD₃)₂SO) δ 14.120 (s, H1A), 8.232 (s, H3A, H8A); ¹³C NMR (126 MHz, (CD₃)₂SO) δ 163.9 (C1), 137.0 (C2), 132.1 (C3, C8), 126.7 (C4, C7), 120.6 (C5), 115.9 (C6); IR (KBr, cm⁻¹) 3421, 3077, 2128, 1811, 1662, 1537, 1371, 1296, 1025, 825, 770, 748; MS (ESI, m/z) [M–H]⁻ calculated for C₈H₃Br₂NO₂ 303.8437, found 303.8443.

Crystallization: 3,5-Dibromo-4-cyanobenzoic acid (100 mg) and anthracene (29 mg) were dissolved in dichloromethane (25 mL) in a loosely covered beaker. Most of the solvent was allowed to evaporate gradually over 3 d. The resulting colorless or pale-orange plate-shaped crystals were collected after decantation and then washed with several drops of ice-cold 1:3 dichloromethane:pentane.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. A direct-methods solution was calculated, followed by full-matrix least squares/difference-Fourier cycles. All H atoms were placed in calculated positions (C—H = 0.95 Å, O—H = 0.84 Å) and refined as riding atoms with U_iso(H) set to 1.2U_eq(C) and 1.5U_eq(O).

Table 3
Experimental details

Crystal data
Chemical formula	C₈H₃Br₂NO₂·0.5C₁₄H₁₀
M_r	394.04
Crystal system, space group	Triclinic, P $[\overline{1}]$
Temperature (K)	123
a, b, c (Å)	8.8963 (8), 9.4701 (9), 9.5839 (9)
α, β, γ (°)	115.356 (3), 106.876 (3), 94.119 (3)
V (Å³)	680.03 (11)
Z	2
Radiation type	Cu Kα
μ (mm⁻¹)	7.57
Crystal size (mm)	0.18 × 0.09 × 0.03

Data collection
Diffractometer	Bruker VENTURE PHOTON-1000
Absorption correction	Multi-scan (SADABS; Sheldrick, 1996 )
T_min, T_max	0.509, 0.754
No. of measured, independent and observed [I > 2σ(I)] reflections	9139, 2745, 2607
R_int	0.035
(sin θ/λ)_max (Å⁻¹)	0.625

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.026, 0.068, 1.06
No. of reflections	2745
No. of parameters	182
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.40, −0.53
Computer programs: APEX2 and SAINT (Bruker, 2012 ), SHELXS97 (Sheldrick 2015a ), SHELXL2014 (Sheldrick, 2015b ), Mercury (Macrae et al., 2008 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1525811

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2056989017014815/lh5854sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989017014815/lh5854Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2056989017014815/lh5854Isup3.cml

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2008); software used to prepare material for publication: publCIF (Westrip, 2010).

3,5-Dibromo-4-cyanobenzoic acid–anthracene (2/1) top

Crystal data top

C₈H₃Br₂NO₂·0.5C₁₄H₁₀	Z = 2
M_r = 394.04	F(000) = 382
Triclinic, P1	D_x = 1.924 Mg m⁻³
a = 8.8963 (8) Å	Cu Kα radiation, λ = 1.54178 Å
b = 9.4701 (9) Å	Cell parameters from 2967 reflections
c = 9.5839 (9) Å	θ = 5.3–74.6°
α = 115.356 (3)°	µ = 7.57 mm⁻¹
β = 106.876 (3)°	T = 123 K
γ = 94.119 (3)°	Plate, pale orange
V = 680.03 (11) Å³	0.18 × 0.09 × 0.03 mm

Data collection top

Bruker VENTURE PHOTON-1000 diffractometer	2607 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.035
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	θ_max = 74.6°, θ_min = 5.3°
T_min = 0.509, T_max = 0.754	h = −11→11
9139 measured reflections	k = −11→11
2745 independent reflections	l = −11→11

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.026	H-atom parameters constrained
wR(F²) = 0.068	w = 1/[σ²(F_o²) + (0.0369P)² + 0.5603P] where P = (F_o² + 2F_c²)/3
S = 1.06	(Δ/σ)_max = 0.001
2745 reflections	Δρ_max = 0.40 e Å⁻³
182 parameters	Δρ_min = −0.53 e Å⁻³

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
Br1	0.38562 (3)	0.12356 (3)	0.93908 (3)	0.01483 (9)
Br2	0.81803 (2)	0.51847 (3)	0.84679 (3)	0.01686 (9)
O1	0.21809 (18)	0.54610 (19)	0.5615 (2)	0.0154 (3)
H1A	0.1338	0.5671	0.5146	0.023*
O2	0.04198 (18)	0.38413 (18)	0.5858 (2)	0.0139 (3)
N1	0.8230 (2)	0.2641 (3)	1.0526 (3)	0.0211 (4)
C1	0.1800 (3)	0.4429 (2)	0.6097 (3)	0.0102 (4)
C2	0.3217 (2)	0.4018 (2)	0.7011 (2)	0.0092 (4)
C3	0.2929 (2)	0.2999 (2)	0.7650 (2)	0.0096 (4)
H3A	0.1859	0.2573	0.7495	0.011*
C4	0.4229 (3)	0.2615 (2)	0.8516 (2)	0.0100 (4)
C5	0.5815 (2)	0.3249 (2)	0.8767 (2)	0.0102 (4)
C6	0.7162 (3)	0.2888 (3)	0.9728 (3)	0.0135 (4)
C7	0.6057 (3)	0.4265 (3)	0.8107 (3)	0.0116 (4)
C8	0.4777 (3)	0.4647 (2)	0.7223 (2)	0.0103 (4)
H8A	0.4958	0.5328	0.6766	0.012*
C9	0.4142 (3)	0.8993 (2)	0.5372 (3)	0.0131 (4)
H9A	0.3562	0.8307	0.5622	0.016*
C10	0.5827 (3)	0.9268 (2)	0.5908 (3)	0.0126 (4)
C11	0.6714 (3)	0.8552 (3)	0.6831 (3)	0.0179 (5)
H11A	0.6149	0.7875	0.7102	0.022*
C12	0.8344 (3)	0.8823 (3)	0.7326 (3)	0.0230 (5)
H12A	0.8912	0.8345	0.7947	0.028*
C13	0.9206 (3)	0.9822 (3)	0.6915 (3)	0.0247 (5)
H13A	1.0347	0.9989	0.7249	0.030*
C14	0.8420 (3)	1.0540 (3)	0.6055 (3)	0.0198 (5)
H14A	0.9019	1.1211	0.5803	0.024*
C15	0.6700 (3)	1.0296 (2)	0.5522 (3)	0.0121 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Br1	0.01625 (14)	0.01597 (13)	0.01776 (14)	0.00482 (9)	0.00336 (10)	0.01426 (10)
Br2	0.00653 (13)	0.02493 (15)	0.02190 (14)	0.00266 (9)	0.00341 (10)	0.01464 (11)
O1	0.0098 (7)	0.0197 (8)	0.0244 (8)	0.0037 (6)	0.0021 (6)	0.0196 (7)
O2	0.0079 (7)	0.0163 (7)	0.0211 (8)	0.0027 (6)	0.0017 (6)	0.0141 (6)
N1	0.0163 (10)	0.0255 (10)	0.0221 (10)	0.0110 (8)	0.0021 (8)	0.0136 (9)
C1	0.0104 (10)	0.0099 (9)	0.0095 (9)	0.0028 (7)	0.0010 (7)	0.0053 (7)
C2	0.0092 (9)	0.0086 (9)	0.0081 (9)	0.0037 (7)	−0.0007 (7)	0.0046 (7)
C3	0.0084 (9)	0.0091 (9)	0.0107 (9)	0.0020 (7)	0.0014 (7)	0.0054 (7)
C4	0.0115 (10)	0.0100 (9)	0.0090 (9)	0.0045 (7)	0.0011 (8)	0.0062 (8)
C5	0.0080 (9)	0.0111 (9)	0.0082 (9)	0.0045 (7)	−0.0005 (7)	0.0035 (8)
C6	0.0117 (10)	0.0140 (10)	0.0131 (10)	0.0048 (8)	0.0025 (8)	0.0059 (8)
C7	0.0088 (9)	0.0128 (9)	0.0112 (9)	0.0016 (7)	0.0028 (8)	0.0044 (8)
C8	0.0113 (9)	0.0095 (9)	0.0108 (9)	0.0021 (7)	0.0025 (8)	0.0063 (8)
C9	0.0162 (10)	0.0082 (9)	0.0148 (10)	0.0001 (8)	0.0070 (8)	0.0047 (8)
C10	0.0172 (11)	0.0081 (9)	0.0113 (9)	0.0016 (8)	0.0056 (8)	0.0033 (8)
C11	0.0245 (12)	0.0125 (10)	0.0156 (10)	0.0033 (9)	0.0049 (9)	0.0069 (9)
C12	0.0257 (13)	0.0167 (11)	0.0196 (11)	0.0055 (9)	−0.0010 (10)	0.0082 (9)
C13	0.0135 (11)	0.0222 (12)	0.0276 (13)	0.0018 (9)	0.0007 (9)	0.0071 (10)
C14	0.0131 (11)	0.0152 (11)	0.0261 (12)	−0.0012 (8)	0.0052 (9)	0.0072 (9)
C15	0.0138 (10)	0.0073 (9)	0.0131 (9)	0.0000 (7)	0.0057 (8)	0.0027 (8)

Geometric parameters (Å, º) top

Br1—C4	1.886 (2)	C8—H8A	0.9500
Br2—C7	1.890 (2)	C9—C15ⁱ	1.394 (3)
O1—C1	1.309 (3)	C9—C10	1.400 (3)
O1—H1A	0.8400	C9—H9A	0.9500
O2—C1	1.224 (3)	C10—C11	1.432 (3)
N1—C6	1.142 (3)	C10—C15	1.432 (3)
C1—C2	1.493 (3)	C11—C12	1.356 (4)
C2—C3	1.390 (3)	C11—H11A	0.9500
C2—C8	1.391 (3)	C12—C13	1.423 (4)
C3—C4	1.386 (3)	C12—H12A	0.9500
C3—H3A	0.9500	C13—C14	1.359 (4)
C4—C5	1.402 (3)	C13—H13A	0.9500
C5—C7	1.394 (3)	C14—C15	1.433 (3)
C5—C6	1.446 (3)	C14—H14A	0.9500
C7—C8	1.381 (3)	C15—C9ⁱ	1.394 (3)

C1—O1—H1A	109.5	C2—C8—H8A	120.5
O2—C1—O1	124.6 (2)	C15ⁱ—C9—C10	121.3 (2)
O2—C1—C2	121.29 (19)	C15ⁱ—C9—H9A	119.4
O1—C1—C2	114.08 (18)	C10—C9—H9A	119.4
C3—C2—C8	121.22 (19)	C9—C10—C11	122.1 (2)
C3—C2—C1	117.98 (18)	C9—C10—C15	119.3 (2)
C8—C2—C1	120.80 (19)	C11—C10—C15	118.6 (2)
C4—C3—C2	118.88 (19)	C12—C11—C10	121.2 (2)
C4—C3—H3A	120.6	C12—C11—H11A	119.4
C2—C3—H3A	120.6	C10—C11—H11A	119.4
C3—C4—C5	121.09 (19)	C11—C12—C13	120.0 (2)
C3—C4—Br1	119.34 (16)	C11—C12—H12A	120.0
C5—C4—Br1	119.57 (15)	C13—C12—H12A	120.0
C7—C5—C4	118.42 (19)	C14—C13—C12	121.0 (2)
C7—C5—C6	121.09 (19)	C14—C13—H13A	119.5
C4—C5—C6	120.47 (19)	C12—C13—H13A	119.5
N1—C6—C5	178.1 (2)	C13—C14—C15	120.7 (2)
C8—C7—C5	121.37 (19)	C13—C14—H14A	119.7
C8—C7—Br2	119.04 (16)	C15—C14—H14A	119.7
C5—C7—Br2	119.57 (16)	C9ⁱ—C15—C10	119.5 (2)
C7—C8—C2	119.02 (19)	C9ⁱ—C15—C14	122.1 (2)
C7—C8—H8A	120.5	C10—C15—C14	118.5 (2)

O2—C1—C2—C3	−2.9 (3)	Br2—C7—C8—C2	−177.60 (15)
O1—C1—C2—C3	176.48 (18)	C3—C2—C8—C7	−1.0 (3)
O2—C1—C2—C8	177.60 (19)	C1—C2—C8—C7	178.55 (18)
O1—C1—C2—C8	−3.1 (3)	C15ⁱ—C9—C10—C11	179.81 (19)
C8—C2—C3—C4	0.2 (3)	C15ⁱ—C9—C10—C15	−0.3 (3)
C1—C2—C3—C4	−179.35 (18)	C9—C10—C11—C12	179.4 (2)
C2—C3—C4—C5	0.6 (3)	C15—C10—C11—C12	−0.5 (3)
C2—C3—C4—Br1	179.97 (14)	C10—C11—C12—C13	−0.6 (4)
C3—C4—C5—C7	−0.7 (3)	C11—C12—C13—C14	1.2 (4)
Br1—C4—C5—C7	180.00 (14)	C12—C13—C14—C15	−0.7 (4)
C3—C4—C5—C6	177.55 (18)	C9—C10—C15—C9ⁱ	0.3 (3)
Br1—C4—C5—C6	−1.8 (3)	C11—C10—C15—C9ⁱ	−179.81 (19)
C4—C5—C7—C8	−0.1 (3)	C9—C10—C15—C14	−178.88 (19)
C6—C5—C7—C8	−178.35 (19)	C11—C10—C15—C14	1.0 (3)
C4—C5—C7—Br2	178.40 (14)	C13—C14—C15—C9ⁱ	−179.6 (2)
C6—C5—C7—Br2	0.2 (3)	C13—C14—C15—C10	−0.4 (3)
C5—C7—C8—C2	1.0 (3)

Symmetry code: (i) −x+1, −y+2, −z+1.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1A···O2ⁱⁱ	0.84	1.79	2.627 (2)	178

Symmetry code: (ii) −x, −y+1, −z+1.

Contact geometry (Å, °) top

C—X···Br	C—X	X···Br	C—X···Br
C6≡N1···Br2ⁱⁱ	1.143 (4)	3.307 (2)	115.9 (2)
C4—Br1···Br1ⁱⁱⁱ	1.886 (2)	3.5534 (5)	133.43 (7)

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

Acknowledgements

The authors thank Victor G. Young, Jr. (X-Ray Crystallographic Laboratory, University of Minnesota) for assistance with the crystallographic determination, the Wayland E. Noland Research Fellowship Fund at the University of Minnesota Foundation for generous financial support of this project, and Doyle Britton (deceased July 7, 2015) for providing the basis of this project. This work was taken in large part from the PhD thesis of KJT (Tritch, 2017 ).

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