research communications\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 72| Part 5| May 2016| Pages 667-670

Crystal structure of 4′-bromo-2,5-dihy­dr­oxy-2′,5′-dimeth­­oxy-[1,1′-biphen­yl]-3,4-dicarbo­nitrile

CROSSMARK_Color_square_no_text.svg

aDepartment of Chemistry, The University of Alabama, Box 870336, Tuscaloosa, AL 35487-0336, USA, and bDepartment of Chemistry, McGill University, 801 Sherbrooke St. West, Montreal, Quebec, H3A 0B8, Canada
*Correspondence e-mail: swoski@ua.edu

Edited by G. Smith, Queensland University of Technology, Australia (Received 25 February 2016; accepted 6 April 2016; online 12 April 2016)

In the crystal of the title substituted hemibi­quinone derivative, C16H11BrN2O4 or [BrHBQH2(CN)2], the substituted benzene rings are rotated about the central C—C bond, forming a dihedral angle of 53.59 (7)°. The ring systems inter­act through an intra­molecular O—H⋯Ometh­oxy hydrogen bond, which induces a geometry quite different from those in previously reported hemibi­quinone structures. In the crystal, the mol­ecules associate through an inter­molecular O—H⋯Nnitrile hydrogen bond, forming chains which extend along [100] and are inter­linked through very weak C—H⋯N hydrogen bonds, giving a overall two-dimensional structure lying parallel to (010).

1. Chemical context

Recently, a new class of mol­ecules (hemibi­quinones, HBQs) has been reported as potential mol­ecular rectifiers (Meany et al., 2015[Meany, J. E., Kelley, S. P., Metzger, R. M., Rogers, R. D. & Woski, S. A. (2015). Acta Cryst. E71, 1454-1456.]). Biphenyl derivatives have garnered great attention as conductors of electricity (Venkataraman et al., 2006[Venkataraman, L., Klare, J. E., Nuckolls, C., Hybertsen, M. S. & Steigerwald, M. L. (2006). Nature, 442, 904-907.]). The symmetric nature of the biphenyl and polyphenyl derivatives studied so far allows for reasonable conduction through the π orbitals. Biphenyl derivatives with one electron-rich and one electron-deficient ring may be able to preferentially bias the direction of electron flow through the mol­ecule, thus acting as a mol­ecular diode. The donor–bridge–acceptor model has long been accepted as a basis for the design of mol­ecular rectifiers (Aviram & Ratner, 1974[Aviram, A. & Ratner, M. A. (1974). Chem. Phys. Lett. 29, 277-283.]). The asymmetric biphenyl structure should allow for conductivity through each of the rings, while the dihedral angle between the two rings decreases orbital overlap and allows for partial isolation of the electron-rich donor and electron-poor acceptor moieties. The efficiency of conduction through a given mol­ecule can be tuned depending on the torsion angle between the two rings.

[Scheme 1]

As one of the series of mol­ecules made for testing rectification through HBQs, the title compound, C16H11BrN2O4, [BrHBQH2(CN)2], (I)[link] has been isolated as an inter­mediate in the preparation of an HBQ derivative which can self-assemble on a gold surface. We have developed a selective synthesis for this reduced hemibi­quinone derivative that is scalable to gram qu­anti­ties. Mol­ecule (I)[link] is predicted not to act as a mol­ecular diode itself because both rings act as donor moieties. The oxidation of the hydro­quinone ring of (I)[link] would produce a potential rectifier.

Di­cyano-functionalized hydro­quinones are known for their ability to form hydrogen-bonded networks (Reddy et al., 1996[Reddy, D. S., Ovchinnikov, Y. E., Shishkin, O. V., Struchkov, Y. T. & Desiraju, G. T. (1996). J. Am. Chem. Soc. 118, 4085-4089.]) and charge-transfer complexes (Bock et al., 1996[Bock, H., Seitz, W., Sievert, M., Kleine, M. & Bats, J. W. (1996). Angew. Chem. Int. Ed. Engl. 35, 2244-2246.]), sometimes both at once (Ghorai & Mani, 2014[Ghorai, D. & Mani, G. (2014). RSC Adv. 4, 45603-45611.]). They have also been used as rigid ligands in coordination polymers (Kuroda-Sowa et al., 1997[Kuroda-Sowa, T., Horino, T., Yamamoto, M., Ohno, Y., Maekawa, M. & Munakata, M. (1997). Inorg. Chem. 36, 6382-6389.]). However, there are no crystal structures in which a di­cyano-functionalized hydro­quinone moiety has been appended to another aromatic ring. The present study affords an opportunity to investigate the mutual effects of these two functionalized ring systems on both the geometry of the mol­ecule and its inter­molecular inter­actions.

2. Structural commentary

In the title compound (Fig. 1[link]), the benzene rings are twisted out of a common plane, forming a dihedral angle of 53.59 (7)°, which appears to optimize the 2.7576 (18) Å O3—H⋯O2 intra­molecular hydrogen bond (Table 1[link]). The rings are essentially planar although the O3—H group, which participates in the intra­molecular hydrogen bond, is displaced slightly out of the plane. Also, the rings are not co-axial with the C4—C7 bond that bridges them. This can be seen in torsion angles involving three carbon atoms from one ring and the bridging carbon atom from the other, which deviate from linearity by ca 5° [C2—C3—C4—C7 = 173.88 (14)°, C6—C5—C4—C7 = −175.45 (14)°, C4—C7—C8—C9 = 174.94 (13)°, C4—C7—C12—C11 = −175.62 (13)°]. This bending of the mol­ecule about its long axis may also be due to hydrogen bonding as it causes the meth­oxy group to approach the OH group more closely. The aromatic C—C bonds of both rings have a narrow range of distances [from 1.387 (2) to 1.412 (2) Å]. The C—C, C—O, C—N, and C N distances for the mol­ecule are similar to the corresponding distances in 2,3,5,6-tetra­cyano­hydro­quinone (Bock et al., 1993[Bock, H., Seitz, W., Havlas, Z. & Bats, J. W. (1993). Angew. Chem. Int. Ed. Engl. 32, 411-414.]). The C—C bond distances around the bromo­dimeth­oxy­benzene ring are close to those in the other hemibi­quinone mol­ecules containing this ring (Meany et al., 2015[Meany, J. E., Kelley, S. P., Metzger, R. M., Rogers, R. D. & Woski, S. A. (2015). Acta Cryst. E71, 1454-1456.], 2016[Meany, J. E., Gerlach, D. L., Papish, E. T. & Woski, S. A. (2016). Acta Cryst. E72, 600-603.]). The C9—C10 bond in (I)[link] [1.408 (2) Å] is longer than the corresponding C1—C6 bond in BrHBQBr (1.334 Å; Meany et al., 2015[Meany, J. E., Kelley, S. P., Metzger, R. M., Rogers, R. D. & Woski, S. A. (2015). Acta Cryst. E71, 1454-1456.]). The stronger polarization of (I)[link] relative to the starting material should weaken the bond through repulsive effects. The Br1—C1 bond is slightly shorter in (I)[link] [1.885 (1) Å] compared to the starting material [1.898 (4) Å] as well, also suggesting decreased electron density on the di­meth­oxy­benzene ring due to increased polarization. The calculated dipole (B3LYP-DGDZVP) of BrHBQBr is only 1.33 D, compared to 6.17 D for (I)[link].

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
O3—H3A⋯O2 0.72 (3) 2.11 (3) 2.7576 (18) 152 (3)
O4—H4A⋯N1i 0.79 (2) 2.03 (2) 2.8189 (18) 172 (2)
C2—H2A⋯N2ii 0.93 2.72 3.638 (2) 168
Symmetry codes: (i) x+1, y, z; (ii) [-x-1, y-{\script{1\over 2}}, -z-{\script{1\over 2}}].
[Figure 1]
Figure 1
The mol­ecular structure of (I)[link], showing the atom-numbering scheme. Displacement ellipsoids are displayed at the 50% probability level. The intra­molecular O3—H⋯O2 hydrogen bond is shown as a dashed line.

As in the other reported hemibi­quinone mol­ecules (Meany et al., 2015[Meany, J. E., Kelley, S. P., Metzger, R. M., Rogers, R. D. & Woski, S. A. (2015). Acta Cryst. E71, 1454-1456.]), we seek to use and compare the inter-ring torsion angles in the crystals as a guide compared to gas-phase calculated values. The intra­molecular hydrogen bond from the C8 phenol to the O2 meth­oxy group causes a greater torsion angle than that in the starting HBQ (Meany et al., 2015[Meany, J. E., Kelley, S. P., Metzger, R. M., Rogers, R. D. & Woski, S. A. (2015). Acta Cryst. E71, 1454-1456.]). In (I)[link], the C5—C4—C7—C8 torsion angle is −126.5 (2)°, compared to −110.9 (5)° in HBQ. DFT (B3LYP-DGDZVP) calculations performed on the target mol­ecule in the gas phase predict an angle of 48.85°. This significant discrepancy is due to packing inter­actions in the solid phase as well as the additional hydrogen bond. The hydrogen bond is indicated in Fig. 1[link], while the relative orientations of the rings can be seen in Fig. 2[link].

[Figure 2]
Figure 2
Ball-and-stick plot of (I)[link], viewed down the C4—C7 bond.

The O3—H⋯O2 intra­molecular hydrogen bond points toward the non-bonded electrons on O2 with a total bond angle of 152 (3)°. As a result of the influence of other short contacts and supra­molecular inter­actions (see below), the phenolic C—O—H bond angles deviate when compared to the meth­oxy C—O—C bond angles: C8—O3—H is 108 (2)°, C11—O4—H is 112.3 (2)°, C3—O2—C14 is 117.9 (1)°, and C6—O1—C13 is 117.2 (1)°. As in other structures, the meth­oxy groups are aligned mostly in-plane with the benzene ring, C5— C6—O1—C13 being bent out of plane by −4.5 (2)° and C2—C3—O2—C14 bent out of plane by −1.3 (2)°. The C12—C11—O4—H phenol group is also nearly planar, being bent out of plane by 1.3°. However, the hydrogen-bonded phenol is unsurprisingly bent out of plane, C7—C8—O3—H = 38 (2)°. The meth­oxy methyl groups point away from the sterically restricting groups ortho to these positions.

3. Supra­molecular features

Each mol­ecule makes short (less than the sum of the van der Waals radii) contacts to six neighboring mol­ecules (Fig. 3[link]). As in previously reported HBQ structures, rings of like identity are all aligned in parallel planes. All short contacts are associated with Lewis acid–base inter­actions of some kind, and for each inter­action there is one neighboring mol­ecule that acts as a donor and second that acts as an acceptor. Two central mol­ecules in the unit cell stack anti­parallel to one another, the quinone rings shifted off-center from one another in the a-axis direction. Both nitrile groups are involved in inter­molecular hydrogen-bonding inter­actions, the first one (O4—H⋯N1) strong, the second one (C2—H⋯N2) weaker but still highly directional. For details, see Table 1[link]. These inter­actions link mol­ecules along the crystallographic a- and b-axis directions, respectively, forming sheets parallel to (010) (Fig. 4[link]). The quinone rings are aligned parallel to the bc plane diagonal.

[Figure 3]
Figure 3
Short (less than the sum of the van der Waals radii) contact environment around [BrHBQH2(CN)2]. Dashed green lines indicate short contacts. Axes are color coded: red = a axis, green = b axis and blue = c axis.
[Figure 4]
Figure 4
Hydrogen-bonded sheets along ab. Dashed green lines indicate short contacts. Axes are color coded: red = a axis, green = b axis and blue = c axis.

The remaining two mol­ecules in the unit cell are oriented orthogonally to the central mol­ecules. These mol­ecules are anti­parallel to each other, where the di­meth­oxy­benzene rings stack with those of the central pair. Slightly repulsive π-inter­actions between mol­ecules along b and stacking along c can be seen in Fig. 5[link]. Inter­centroid distances for the rings are longer than expected for close ππ inter­actions at 4.107 (1) Å. However, since the rings are slightly offset from one another, this is not the correct centroid to use. Instead, a close 3.598 (1) Å π-inter­action between two inter­molecular C9—C10 centroids exists. A centroid calculated for the C7—C8—C9—C11—C12 ring sits 3.574 (1) Å from a centroid for N1—C15—C9—C10—C16—N2, which may be explained by the electron-donating character of the hydro­quinone as compared to the di­nitrile substituents. The planes of the di­meth­oxy­benzene rings are oriented parallel to the short diagonal of the ac plane.

[Figure 5]
Figure 5
Unit-cell packing of (I)[link], viewed along the a axis. Short contacts show the long ring stacking along the c axis.

4. Synthesis and crystallization

2-Bromo-5-(4-bromo-2,5-di­meth­oxy­phen­yl)cyclo­hexa-2,5-diene-1,4-dione, BrHBQBr, (0.300 g, 0.744 mmol) was dissolved in 350 mL of aceto­nitrile. In a separate beaker, potassium cyanide (0.124 g, 1.90 mmol) was dissolved in 50 mL of H2O. Upon pouring the aqueous solution into the organic solution, the mixture immediately changed from a vibrant red to a deep purple. After stirring for 1 h, 50 µL of concentrated HCl solution was added, changing the color of the mixture from purple to bright orange. The mixture was diluted with 50 mL of water and the aceto­nitrile was removed by rotary evaporation. A tan powder precipitated, which was recovered by filtration and washed with water to yield the crude product. This material was recrystallized from acetone giving 0.196 g (70.4%) of pure material as yellow–orange prisms. 1H NMR (360 MHz, d6-acetone) δ = 10.02 (s, 1H, ArOH), 8.75 (s, 1H, ArOH), 7.34 (s, 1H, ArH), 7.24 (s, 1H, ArH), 7.05 (s, 1H, ArH), 3.88 (s, 3H, OCH3), 3.82 (s, 3H, OCH3).

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. Hydroxyl hydrogen atoms were located from the difference map and their coordinates were refined while the thermal parameters were constrained to ride on the carrier atom with Uiso = 1.5Ueq(O). Hydrogen atoms bonded to carbon were placed in calculated positions with C—H = 0.93 Å (aromatic) or 0.96 Å (meth­yl) and their coordin­ates and thermal parameters were constrained to ride on the carrier atom, with Uiso = 1.5Ueq(aromatic C) or 1.5Ueq(methyl C).

Table 2
Experimental details

Crystal data
Chemical formula C16H11BrN2O4
Mr 375.18
Crystal system, space group Monoclinic, P21/c
Temperature (K) 296
a, b, c (Å) 8.4726 (3), 23.7748 (8), 8.0833 (3)
β (°) 111.6985 (17)
V3) 1512.88 (9)
Z 4
Radiation type Mo Kα
μ (mm−1) 2.74
Crystal size (mm) 0.35 × 0.20 × 0.09
 
Data collection
Diffractometer Bruker APEXII CCD
Absorption correction Multi-scan (SADABS; Bruker, 2010[Bruker (2010). APEX2, SAINT and SADABS. Bruker AXS, Inc., Madison, Wisconsin, USA.])
Tmin, Tmax 0.428, 0.747
No. of measured, independent and observed [I > 2σ(I)] reflections 65083, 6269, 4739
Rint 0.037
(sin θ/λ)max−1) 0.796
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.089, 1.03
No. of reflections 6269
No. of parameters 216
H-atom treatment H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3) 0.59, −0.26
Computer programs: APEX2 and SAINT (Bruker, 2010[Bruker (2010). APEX2, SAINT and SADABS. Bruker AXS, Inc., Madison, Wisconsin, USA.]), SHELXS97 and SHELXTL (Sheldrick 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]) and SHELXL2014 (Sheldrick, 2015[Sheldrick, G. M. (2015). Acta Cryst. C71, 3-8.]).

Supporting information


Chemical context top

Recently, a new class of molecules (hemibi­quinones, HBQs) has been reported as potential molecular rectifiers (Meany et al., 2015). Bi­phenyl derivatives have garnered great attention as conductors of electricity (Venkataraman et al., 2006). The symmetric nature of the bi­phenyl and polyphenyl derivatives studied so far allows for reasonable conduction through the π orbitals. Bi­phenyl derivatives with one electron-rich and one electron-deficient ring may be able to preferentially bias the direction of electron flow through the molecule, thus acting as a molecular diode. The donor–bridge–acceptor model has long been accepted as a basis for the design of molecular rectifiers (Aviram & Ratner, 1974). The asymmetric bi­phenyl structure should allow for conductivity through each of the rings, while the dihedral angle between the two rings decreases orbital overlap and allows for partial isolation of the electron-rich donor and electron-poor acceptor moieties. The efficiency of conduction through a given molecule can be tuned depending on the torsion angle between the two rings.

As one of the series of molecules made for testing rectification through HBQs, the title compound, C16H11BrN2O4, [BrHBQH2(CN)2], (I) has been isolated as an inter­mediate in the preparation of an HBQ derivative which can self-assemble on a gold surface. We have developed a selective synthesis for this reduced hemibi­quinone derivative that is scalable to gram qu­anti­ties. Molecule (I) is predicted not to act as a molecular diode itself because both rings act as donor moieties. The oxidation of the hydro­quinone ring of (I) would produce a potential rectifier.

Di­cyano-functionalized hydro­quinones are known for their ability to form hydrogen-bonded networks (Reddy et al., 1996) and charge-transfer complexes (Bock et al., 1996), sometimes both at once (Ghorai & Mani, 2014). They have also been used as rigid ligands in coordination polymers (Kuroda-Sowa et al., 1997). However, there are no crystal structures in which a di­cyano-functionalized hydro­quinone moiety has been appended to another aromatic ring. The present study affords an opportunity to investigate the mutual effects of these two functionalized ring systems on both the geometry of the molecule and its inter­molecular inter­actions.

Structural commentary top

In the title compound (Fig. 1), the benzene rings are twisted out of a common plane, forming a dihedral angle of 53.59 (7)°, which appears to optimize the 2.7576 (18) Å O3—H···O2 intra­molecular hydrogen bond (Table 1). The rings are essentially planar although the O3—H group, which participates in the intra­molecular hydrogen bond, is displaced slightly out of the plane. Also, the rings are not co-axial with the C4—C7 bond that bridges them. This can be seen in torsion angles involving three carbon atoms from one ring and the bridging carbon atom from the other, which deviate from linearity by ca 5° [C2—C3—C4—C7 = 173.88 (14)°, C6—C5—C4—C7 = -175.45 (14)°, C4—C7—C8—C9 = 174.94 (13)°, C4—C7—C12—C11 = -175.62 (13)°]. This bending of the molecule about its long axis may also be due to hydrogen bonding as it causes the meth­oxy group to approach the OH group more closely. The aromatic C—C bonds of both rings have a narrow range of distances [from 1.387 (2) to 1.412 (2) Å]. The C—C, C—O, C—N, and CN distances for the molecule are similar to the corresponding distances in 2,3,5,6-tetra­cyano­hydro­quinone (Bock et al., 1993). The C—C bond distances around the bromo­dimeth­oxy­benzene ring are close to those in the other hemibi­quinone molecules containing this ring (Meany et al., 2015, 2016). The C9—C10 bond in (I) [1.408 (2) Å] is longer than the corresponding C1—C6 bond in BrHBQBr (1.334 Å; Meany et al., 2015). The stronger polarization of (I) relative to the starting material should weaken the bond through repulsive effects. The Br1—C1 bond is slightly shorter in (I) [1.885 (1) Å] compared to the starting material [1.898 (4) Å] as well, also suggesting decreased electron density on the di­meth­oxy­benzene ring due to increased polarization. The calculated dipole (B3LYP-DGDZVP) of BrHBQBr is only 1.33 D, compared to 6.17 D for (I) .

As in the other reported hemibi­quinone molecules (Meany et al., 2015), we seek to use and compare the inter-ring torsion angles in the crystals as a guide compared to gas-phase calculated values. The intra­molecular hydrogen bond from the C8 phenol to the O2 meth­oxy group causes a greater torsion angle than that in the starting HBQ (Meany et al., 2015). In (I), the C5—C4—C7—C8 torsion angle is -126.5 (2)°, compared to -110.9 (5)° in HBQ. DFT (B3LYP-DGDZVP) calculations performed on the target molecule in the gas phase predict an angle of 48.85°. This significant discrepancy is due to packing inter­actions in the solid phase as well as the additional hydrogen bond. The hydrogen bond is indicated in Fig. 1, while the relative orientations of the rings can be seen in Fig. 2.

The O3—H···O2 intra­molecular hydrogen bond points toward the non-bonded electrons on O2 with a total bond angle of 152 (3)°. As a result of the influence of other short contacts and supra­molecular inter­actions (see below), the phenolic C—O—H bond angles deviate when compared to the meth­oxy C—O—C bond angles: C8—O3—H is 108 (2)°, C11—O4—H is 112.3 (2)°, C3—O2—C14 is 117.9 (1)°, and C6—O1—C13 is 117.2 (1)°. As in other structures, the meth­oxy groups are aligned mostly in-plane with the benzene ring, C5— C6—O1—C13 being bent out of plane by -4.5 (2)° and C2—C3—O2—C14 bent out of plane by -1.3 (2)°. The C12—C11—O4—H phenol group is also nearly planar, being bent out of plane by 1.3°. However, the hydrogen-bonded phenol is unsurprisingly bent out of plane, C7—C8—O3—H = 38 (2)°. The meth­oxy methyl groups point away from the sterically restricting groups ortho to these positions.

Supra­molecular features top

Each molecule makes short (less than the sum of the van der Waals radii) contacts to six neighboring molecules (Fig. 3). As in previously reported HBQ structures, rings of like identity are all aligned in parallel planes. All short contacts are associated with Lewis acid–base inter­actions of some kind, and for each inter­action there is one neighboring molecule that acts as a donor and second that acts as an acceptor. Two central molecules in the unit cell stack anti­parallel to one another, the quinone rings shifted off-center from one another in the a-axis direction. Both nitrile groups are involved in inter­molecular hydrogen-bonding inter­actions, the first one (O4—H···N1) strong , the second one (C2—H···N2) weaker but still highly directional. For details, see Table 1. These inter­actions link molecules along the crystallographic a- and b-axis directions, respectively, forming sheets parallel to (010) (Fig. 4). The quinone rings are aligned parallel to the bc plane diagonal.

The remaining two molecules in the unit cell are oriented orthogonally to the central molecules. These molecules are anti­parallel to each other, where the di­meth­oxy­benzene rings stack with those of the central pair. Slightly repulsive π-inter­actions between molecules along b and stacking along c can be seen in Fig. 5. Inter­centroid distances for the rings are longer than expected for close π inter­actions at 4.107 (1) Å. However, since the rings are slightly offset from one another, this is not the correct centroid to use. Instead, a close 3.598 (1) Å π-inter­action between two inter­molecular C9—C10 centroids exists. A centroid calculated for the C7—C8—C9—C11—C12 ring sits 3.574 (1) Å from a centroid for N1—C15—C9—C10—C16—N2, which may be explained by the electron-donating character of the hydro­quinone as compared to the di­nitrile substituents. The planes of the di­meth­oxy­benzene rings are oriented parallel to the short diagonal of the ac plane.

Synthesis and crystallization top

2-Bromo-5-(4-bromo-2,5-di­meth­oxy­phenyl)­cyclo­hexa-2,5-diene-1,4-dione, BrHBQBr, (0.300 g, 0.744 mmol) was dissolved in 350 mL of aceto­nitrile. In a separate beaker, potassium cyanide (0.124 g, 1.90 mmol) was dissolved in 50 mL of H2O. Upon pouring the aqueous solution into the organic solution, the mixture immediately changed from a vibrant red to a deep purple. After stirring for 1 h, 50 µL of concentrated HCl solution was added, changing the color of the mixture from purple to bright orange. The mixture was diluted with 50 mL of water and the aceto­nitrile was removed by rotary evaporation. A tan powder precipitated, which was recovered by filtration and washed with water to yield the crude product. This material was recrystallized from acetone giving 0.196 g (70.4%) of pure material as yellow–orange prisms. 1H NMR (360 MHz, d6-acetone) δ = 10.02 (s, 1H, ArOH), 8.75 (s, 1H, ArOH), 7.34 (s, 1H, ArH), 7.24 (s, 1H, ArH), 7.05 (s, 1H, ArH), 3.88 (s, 3H, OCH3), 3.82 (s, 3H, OCH3).

Refinement top

Crystal data, data collection and structure refinement details are summarized in Table 2. Hydroxyl hydrogen atoms were located from the difference map and their coordinates were refined while the thermal parameters were constrained to ride on the carrier atom with Uiso = 1.5Ueq(O). Hydrogen atoms bonded to carbon were placed in calculated positions with C—H = 0.93 Å (aromatic) or 0.96 Å (methyl) and their coordinates and thermal parameters were constrained to ride on the carrier atom, with Uiso = 1.5Ueq(aromatic C) or 1.5Ueq(methyl C).

Structure description top

Recently, a new class of molecules (hemibi­quinones, HBQs) has been reported as potential molecular rectifiers (Meany et al., 2015). Bi­phenyl derivatives have garnered great attention as conductors of electricity (Venkataraman et al., 2006). The symmetric nature of the bi­phenyl and polyphenyl derivatives studied so far allows for reasonable conduction through the π orbitals. Bi­phenyl derivatives with one electron-rich and one electron-deficient ring may be able to preferentially bias the direction of electron flow through the molecule, thus acting as a molecular diode. The donor–bridge–acceptor model has long been accepted as a basis for the design of molecular rectifiers (Aviram & Ratner, 1974). The asymmetric bi­phenyl structure should allow for conductivity through each of the rings, while the dihedral angle between the two rings decreases orbital overlap and allows for partial isolation of the electron-rich donor and electron-poor acceptor moieties. The efficiency of conduction through a given molecule can be tuned depending on the torsion angle between the two rings.

As one of the series of molecules made for testing rectification through HBQs, the title compound, C16H11BrN2O4, [BrHBQH2(CN)2], (I) has been isolated as an inter­mediate in the preparation of an HBQ derivative which can self-assemble on a gold surface. We have developed a selective synthesis for this reduced hemibi­quinone derivative that is scalable to gram qu­anti­ties. Molecule (I) is predicted not to act as a molecular diode itself because both rings act as donor moieties. The oxidation of the hydro­quinone ring of (I) would produce a potential rectifier.

Di­cyano-functionalized hydro­quinones are known for their ability to form hydrogen-bonded networks (Reddy et al., 1996) and charge-transfer complexes (Bock et al., 1996), sometimes both at once (Ghorai & Mani, 2014). They have also been used as rigid ligands in coordination polymers (Kuroda-Sowa et al., 1997). However, there are no crystal structures in which a di­cyano-functionalized hydro­quinone moiety has been appended to another aromatic ring. The present study affords an opportunity to investigate the mutual effects of these two functionalized ring systems on both the geometry of the molecule and its inter­molecular inter­actions.

In the title compound (Fig. 1), the benzene rings are twisted out of a common plane, forming a dihedral angle of 53.59 (7)°, which appears to optimize the 2.7576 (18) Å O3—H···O2 intra­molecular hydrogen bond (Table 1). The rings are essentially planar although the O3—H group, which participates in the intra­molecular hydrogen bond, is displaced slightly out of the plane. Also, the rings are not co-axial with the C4—C7 bond that bridges them. This can be seen in torsion angles involving three carbon atoms from one ring and the bridging carbon atom from the other, which deviate from linearity by ca 5° [C2—C3—C4—C7 = 173.88 (14)°, C6—C5—C4—C7 = -175.45 (14)°, C4—C7—C8—C9 = 174.94 (13)°, C4—C7—C12—C11 = -175.62 (13)°]. This bending of the molecule about its long axis may also be due to hydrogen bonding as it causes the meth­oxy group to approach the OH group more closely. The aromatic C—C bonds of both rings have a narrow range of distances [from 1.387 (2) to 1.412 (2) Å]. The C—C, C—O, C—N, and CN distances for the molecule are similar to the corresponding distances in 2,3,5,6-tetra­cyano­hydro­quinone (Bock et al., 1993). The C—C bond distances around the bromo­dimeth­oxy­benzene ring are close to those in the other hemibi­quinone molecules containing this ring (Meany et al., 2015, 2016). The C9—C10 bond in (I) [1.408 (2) Å] is longer than the corresponding C1—C6 bond in BrHBQBr (1.334 Å; Meany et al., 2015). The stronger polarization of (I) relative to the starting material should weaken the bond through repulsive effects. The Br1—C1 bond is slightly shorter in (I) [1.885 (1) Å] compared to the starting material [1.898 (4) Å] as well, also suggesting decreased electron density on the di­meth­oxy­benzene ring due to increased polarization. The calculated dipole (B3LYP-DGDZVP) of BrHBQBr is only 1.33 D, compared to 6.17 D for (I) .

As in the other reported hemibi­quinone molecules (Meany et al., 2015), we seek to use and compare the inter-ring torsion angles in the crystals as a guide compared to gas-phase calculated values. The intra­molecular hydrogen bond from the C8 phenol to the O2 meth­oxy group causes a greater torsion angle than that in the starting HBQ (Meany et al., 2015). In (I), the C5—C4—C7—C8 torsion angle is -126.5 (2)°, compared to -110.9 (5)° in HBQ. DFT (B3LYP-DGDZVP) calculations performed on the target molecule in the gas phase predict an angle of 48.85°. This significant discrepancy is due to packing inter­actions in the solid phase as well as the additional hydrogen bond. The hydrogen bond is indicated in Fig. 1, while the relative orientations of the rings can be seen in Fig. 2.

The O3—H···O2 intra­molecular hydrogen bond points toward the non-bonded electrons on O2 with a total bond angle of 152 (3)°. As a result of the influence of other short contacts and supra­molecular inter­actions (see below), the phenolic C—O—H bond angles deviate when compared to the meth­oxy C—O—C bond angles: C8—O3—H is 108 (2)°, C11—O4—H is 112.3 (2)°, C3—O2—C14 is 117.9 (1)°, and C6—O1—C13 is 117.2 (1)°. As in other structures, the meth­oxy groups are aligned mostly in-plane with the benzene ring, C5— C6—O1—C13 being bent out of plane by -4.5 (2)° and C2—C3—O2—C14 bent out of plane by -1.3 (2)°. The C12—C11—O4—H phenol group is also nearly planar, being bent out of plane by 1.3°. However, the hydrogen-bonded phenol is unsurprisingly bent out of plane, C7—C8—O3—H = 38 (2)°. The meth­oxy methyl groups point away from the sterically restricting groups ortho to these positions.

Each molecule makes short (less than the sum of the van der Waals radii) contacts to six neighboring molecules (Fig. 3). As in previously reported HBQ structures, rings of like identity are all aligned in parallel planes. All short contacts are associated with Lewis acid–base inter­actions of some kind, and for each inter­action there is one neighboring molecule that acts as a donor and second that acts as an acceptor. Two central molecules in the unit cell stack anti­parallel to one another, the quinone rings shifted off-center from one another in the a-axis direction. Both nitrile groups are involved in inter­molecular hydrogen-bonding inter­actions, the first one (O4—H···N1) strong , the second one (C2—H···N2) weaker but still highly directional. For details, see Table 1. These inter­actions link molecules along the crystallographic a- and b-axis directions, respectively, forming sheets parallel to (010) (Fig. 4). The quinone rings are aligned parallel to the bc plane diagonal.

The remaining two molecules in the unit cell are oriented orthogonally to the central molecules. These molecules are anti­parallel to each other, where the di­meth­oxy­benzene rings stack with those of the central pair. Slightly repulsive π-inter­actions between molecules along b and stacking along c can be seen in Fig. 5. Inter­centroid distances for the rings are longer than expected for close π inter­actions at 4.107 (1) Å. However, since the rings are slightly offset from one another, this is not the correct centroid to use. Instead, a close 3.598 (1) Å π-inter­action between two inter­molecular C9—C10 centroids exists. A centroid calculated for the C7—C8—C9—C11—C12 ring sits 3.574 (1) Å from a centroid for N1—C15—C9—C10—C16—N2, which may be explained by the electron-donating character of the hydro­quinone as compared to the di­nitrile substituents. The planes of the di­meth­oxy­benzene rings are oriented parallel to the short diagonal of the ac plane.

Synthesis and crystallization top

2-Bromo-5-(4-bromo-2,5-di­meth­oxy­phenyl)­cyclo­hexa-2,5-diene-1,4-dione, BrHBQBr, (0.300 g, 0.744 mmol) was dissolved in 350 mL of aceto­nitrile. In a separate beaker, potassium cyanide (0.124 g, 1.90 mmol) was dissolved in 50 mL of H2O. Upon pouring the aqueous solution into the organic solution, the mixture immediately changed from a vibrant red to a deep purple. After stirring for 1 h, 50 µL of concentrated HCl solution was added, changing the color of the mixture from purple to bright orange. The mixture was diluted with 50 mL of water and the aceto­nitrile was removed by rotary evaporation. A tan powder precipitated, which was recovered by filtration and washed with water to yield the crude product. This material was recrystallized from acetone giving 0.196 g (70.4%) of pure material as yellow–orange prisms. 1H NMR (360 MHz, d6-acetone) δ = 10.02 (s, 1H, ArOH), 8.75 (s, 1H, ArOH), 7.34 (s, 1H, ArH), 7.24 (s, 1H, ArH), 7.05 (s, 1H, ArH), 3.88 (s, 3H, OCH3), 3.82 (s, 3H, OCH3).

Refinement details top

Crystal data, data collection and structure refinement details are summarized in Table 2. Hydroxyl hydrogen atoms were located from the difference map and their coordinates were refined while the thermal parameters were constrained to ride on the carrier atom with Uiso = 1.5Ueq(O). Hydrogen atoms bonded to carbon were placed in calculated positions with C—H = 0.93 Å (aromatic) or 0.96 Å (methyl) and their coordinates and thermal parameters were constrained to ride on the carrier atom, with Uiso = 1.5Ueq(aromatic C) or 1.5Ueq(methyl C).

Computing details top

Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT (Bruker, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are displayed at the 50% probability level. The intramolecular O3—H···O2 hydrogen bond is shown as a dashed line.
[Figure 2] Fig. 2. Ball-and-stick plot of (I), viewed down the C4—C7 bond.
[Figure 3] Fig. 3. Short (less than the sum of the van der Waals radii) contact environment around [BrHBQH2(CN)2]. Dashed green lines indicate short contacts. Axes are color coded: red = a axis, green = b axis and blue = c axis.
[Figure 4] Fig. 4. Hydrogen-bonded sheets along ab. Dashed green lines indicate short contacts. Axes are color coded: red = a axis, green = b axis and blue = c axis.
[Figure 5] Fig. 5. Unit-cell packing of (I), viewed along the a axis. Short contacts show the long ring stacking along the c axis.
4'-Bromo-2,5-dihydroxy-2',5'-dimethoxy-[1,1'-biphenyl]-3,4-dicarbonitrile top
Crystal data top
C16H11BrN2O4F(000) = 752
Mr = 375.18Dx = 1.647 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 8.4726 (3) ÅCell parameters from 9370 reflections
b = 23.7748 (8) Åθ = 2.6–29.9°
c = 8.0833 (3) ŵ = 2.74 mm1
β = 111.6985 (17)°T = 296 K
V = 1512.88 (9) Å3Tablet, yellow-orange
Z = 40.35 × 0.20 × 0.09 mm
Data collection top
Bruker APEXII CCD
diffractometer
4739 reflections with I > 2σ(I)
φ and ω scansRint = 0.037
Absorption correction: multi-scan
(SADABS; Bruker, 2010)
θmax = 34.5°, θmin = 1.7°
Tmin = 0.428, Tmax = 0.747h = 1313
65083 measured reflectionsk = 3737
6269 independent reflectionsl = 1212
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.035Hydrogen site location: mixed
wR(F2) = 0.089H atoms treated by a mixture of independent and constrained refinement
S = 1.03 w = 1/[σ2(Fo2) + (0.0431P)2 + 0.4609P]
where P = (Fo2 + 2Fc2)/3
6269 reflections(Δ/σ)max = 0.001
216 parametersΔρmax = 0.59 e Å3
0 restraintsΔρmin = 0.26 e Å3
Crystal data top
C16H11BrN2O4V = 1512.88 (9) Å3
Mr = 375.18Z = 4
Monoclinic, P21/cMo Kα radiation
a = 8.4726 (3) ŵ = 2.74 mm1
b = 23.7748 (8) ÅT = 296 K
c = 8.0833 (3) Å0.35 × 0.20 × 0.09 mm
β = 111.6985 (17)°
Data collection top
Bruker APEXII CCD
diffractometer
6269 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2010)
4739 reflections with I > 2σ(I)
Tmin = 0.428, Tmax = 0.747Rint = 0.037
65083 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0350 restraints
wR(F2) = 0.089H atoms treated by a mixture of independent and constrained refinement
S = 1.03Δρmax = 0.59 e Å3
6269 reflectionsΔρmin = 0.26 e Å3
216 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
xyzUiso*/Ueq
Br10.00177 (2)0.18718 (2)0.27906 (3)0.03808 (6)
O10.09291 (15)0.30658 (4)0.37344 (17)0.0372 (3)
O20.52102 (14)0.29007 (5)0.19615 (17)0.0400 (3)
O30.65570 (14)0.38022 (5)0.07840 (19)0.0393 (3)
H3A0.639 (3)0.3515 (11)0.093 (3)0.059*
O40.25442 (16)0.52226 (5)0.2911 (2)0.0502 (4)
H4A0.163 (3)0.5103 (10)0.276 (3)0.050*
N10.92239 (18)0.49008 (7)0.2525 (3)0.0524 (4)
N20.6248 (3)0.59864 (7)0.3963 (3)0.0594 (5)
C10.12247 (17)0.25158 (6)0.1689 (2)0.0269 (3)
C20.27623 (17)0.24472 (6)0.0277 (2)0.0290 (3)
H2A0.31870.20890.00980.035*
C30.36583 (17)0.29233 (6)0.0569 (2)0.0277 (3)
C40.30049 (16)0.34595 (5)0.00356 (19)0.0258 (2)
C50.14639 (17)0.35126 (6)0.1413 (2)0.0276 (3)
H5A0.10320.38700.17890.033*
C60.05661 (18)0.30449 (6)0.2301 (2)0.0271 (3)
C70.38125 (16)0.39804 (5)0.09918 (19)0.0258 (2)
C80.55087 (16)0.41297 (6)0.1289 (2)0.0269 (3)
C90.61363 (16)0.46445 (6)0.20684 (19)0.0270 (3)
C100.51175 (16)0.50206 (6)0.2583 (2)0.0283 (3)
C110.34649 (17)0.48643 (6)0.2341 (2)0.0312 (3)
C120.28382 (17)0.43499 (6)0.1544 (2)0.0300 (3)
H12A0.17280.42510.13770.036*
C130.1665 (2)0.36036 (8)0.4267 (3)0.0523 (5)
H13A0.27250.35630.52530.078*
H13B0.09080.38320.46180.078*
H13C0.18600.37800.32910.078*
C140.5909 (2)0.23599 (7)0.2582 (3)0.0411 (4)
H14A0.69670.24030.35680.062*
H14B0.60980.21610.16380.062*
H14C0.51310.21510.29570.062*
C150.78630 (18)0.47882 (7)0.2331 (2)0.0346 (3)
C160.5754 (2)0.55568 (7)0.3358 (2)0.0368 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br10.03661 (8)0.02562 (8)0.05028 (11)0.00760 (5)0.01403 (7)0.01143 (6)
O10.0332 (5)0.0295 (5)0.0380 (6)0.0005 (4)0.0002 (5)0.0032 (4)
O20.0303 (5)0.0276 (5)0.0480 (7)0.0015 (4)0.0019 (5)0.0029 (5)
O30.0287 (5)0.0312 (5)0.0611 (8)0.0015 (4)0.0201 (5)0.0066 (5)
O40.0361 (6)0.0334 (6)0.0905 (11)0.0093 (5)0.0344 (7)0.0259 (6)
N10.0283 (7)0.0508 (9)0.0779 (12)0.0084 (6)0.0192 (7)0.0051 (8)
N20.0674 (11)0.0381 (8)0.0724 (12)0.0203 (8)0.0255 (10)0.0161 (8)
C10.0264 (6)0.0219 (6)0.0334 (7)0.0039 (4)0.0122 (5)0.0046 (5)
C20.0286 (6)0.0202 (6)0.0380 (8)0.0004 (4)0.0120 (6)0.0003 (5)
C30.0233 (5)0.0233 (6)0.0342 (7)0.0003 (4)0.0079 (5)0.0003 (5)
C40.0238 (5)0.0205 (5)0.0325 (7)0.0019 (4)0.0098 (5)0.0025 (5)
C50.0261 (6)0.0208 (5)0.0341 (7)0.0007 (4)0.0090 (5)0.0009 (5)
C60.0254 (5)0.0251 (6)0.0296 (7)0.0018 (5)0.0088 (5)0.0024 (5)
C70.0223 (5)0.0206 (5)0.0322 (7)0.0021 (4)0.0073 (5)0.0005 (5)
C80.0211 (5)0.0249 (6)0.0330 (7)0.0002 (4)0.0082 (5)0.0005 (5)
C90.0208 (5)0.0251 (6)0.0330 (7)0.0031 (4)0.0073 (5)0.0011 (5)
C100.0259 (6)0.0229 (6)0.0354 (8)0.0052 (4)0.0105 (5)0.0035 (5)
C110.0262 (6)0.0232 (6)0.0462 (9)0.0034 (5)0.0158 (6)0.0067 (6)
C120.0226 (5)0.0243 (6)0.0433 (8)0.0044 (4)0.0122 (5)0.0060 (5)
C130.0467 (10)0.0336 (8)0.0546 (11)0.0069 (7)0.0069 (8)0.0022 (8)
C140.0353 (7)0.0336 (8)0.0483 (10)0.0086 (6)0.0083 (7)0.0100 (7)
C150.0262 (6)0.0302 (7)0.0455 (9)0.0038 (5)0.0109 (6)0.0008 (6)
C160.0364 (8)0.0297 (7)0.0453 (9)0.0088 (6)0.0165 (7)0.0063 (6)
Geometric parameters (Å, º) top
Br1—C11.8848 (13)C5—C61.3878 (19)
O1—C61.3655 (18)C5—H5A0.9300
O1—C131.418 (2)C7—C121.3876 (19)
O2—C31.3799 (17)C7—C81.4120 (18)
O2—C141.4266 (19)C8—C91.3892 (19)
O3—C81.3528 (17)C9—C101.408 (2)
O3—H3A0.72 (3)C9—C151.4396 (19)
O4—C111.3464 (18)C10—C111.3907 (18)
O4—H4A0.79 (2)C10—C161.434 (2)
N1—C151.137 (2)C11—C121.3927 (19)
N2—C161.143 (2)C12—H12A0.9300
C1—C21.388 (2)C13—H13A0.9600
C1—C61.3909 (19)C13—H13B0.9600
C2—C31.3933 (19)C13—H13C0.9600
C2—H2A0.9300C14—H14A0.9600
C3—C41.3933 (19)C14—H14B0.9600
C4—C51.4004 (19)C14—H14C0.9600
C4—C71.4860 (18)
C6—O1—C13117.15 (12)C9—C8—C7119.57 (12)
C3—O2—C14117.91 (12)C8—C9—C10121.32 (12)
C8—O3—H3A108 (2)C8—C9—C15118.27 (13)
C11—O4—H4A112.3 (17)C10—C9—C15120.41 (13)
C2—C1—C6121.99 (12)C11—C10—C9118.94 (12)
C2—C1—Br1118.91 (10)C11—C10—C16119.68 (13)
C6—C1—Br1119.09 (10)C9—C10—C16121.38 (12)
C1—C2—C3118.92 (12)O4—C11—C10117.60 (13)
C1—C2—H2A120.5O4—C11—C12122.95 (12)
C3—C2—H2A120.5C10—C11—C12119.45 (13)
O2—C3—C4115.96 (12)C7—C12—C11122.30 (12)
O2—C3—C2123.42 (13)C7—C12—H12A118.8
C4—C3—C2120.62 (12)C11—C12—H12A118.8
C3—C4—C5118.83 (12)O1—C13—H13A109.5
C3—C4—C7123.21 (12)O1—C13—H13B109.5
C5—C4—C7117.87 (12)H13A—C13—H13B109.5
C6—C5—C4121.56 (13)O1—C13—H13C109.5
C6—C5—H5A119.2H13A—C13—H13C109.5
C4—C5—H5A119.2H13B—C13—H13C109.5
O1—C6—C5124.67 (12)O2—C14—H14A109.5
O1—C6—C1117.32 (12)O2—C14—H14B109.5
C5—C6—C1118.01 (13)H14A—C14—H14B109.5
C12—C7—C8118.37 (12)O2—C14—H14C109.5
C12—C7—C4118.74 (11)H14A—C14—H14C109.5
C8—C7—C4122.82 (12)H14B—C14—H14C109.5
O3—C8—C9117.39 (12)N1—C15—C9179.5 (2)
O3—C8—C7122.99 (13)N2—C16—C10179.4 (2)
C13—O1—C6—C1175.14 (15)C4—C5—C6—O1179.10 (15)
C13—O1—C6—C54.5 (2)C4—C5—C6—C11.2 (2)
C14—O2—C3—C21.3 (2)C4—C7—C8—O32.4 (2)
C14—O2—C3—C4178.48 (15)C4—C7—C8—C9174.94 (13)
Br1—C1—C2—C3178.26 (12)C12—C7—C8—O3179.24 (14)
C6—C1—C2—C31.0 (2)C12—C7—C8—C91.9 (2)
Br1—C1—C6—O12.8 (2)C4—C7—C12—C11175.62 (13)
Br1—C1—C6—C5176.93 (12)C8—C7—C12—C111.4 (2)
C2—C1—C6—O1177.95 (14)O3—C8—C9—C10177.94 (14)
C2—C1—C6—C52.4 (2)O3—C8—C9—C151.7 (2)
C1—C2—C3—O2178.78 (14)C7—C8—C9—C100.5 (2)
C1—C2—C3—C41.5 (2)C7—C8—C9—C15179.13 (13)
O2—C3—C4—C5177.70 (14)C8—C9—C10—C111.6 (2)
O2—C3—C4—C75.9 (2)C8—C9—C10—C16178.84 (14)
C2—C3—C4—C52.6 (2)C15—C9—C10—C11178.81 (14)
C2—C3—C4—C7173.88 (14)C15—C9—C10—C160.8 (2)
C3—C4—C5—C61.2 (2)C9—C10—C11—O4177.38 (14)
C7—C4—C5—C6175.45 (14)C9—C10—C11—C122.1 (2)
C3—C4—C7—C857.1 (2)C16—C10—C11—O42.2 (2)
C3—C4—C7—C12126.09 (16)C16—C10—C11—C12178.27 (14)
C5—C4—C7—C8126.50 (16)O4—C11—C12—C7178.82 (14)
C5—C4—C7—C1250.37 (19)C10—C11—C12—C70.7 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3A···O20.72 (3)2.11 (3)2.7576 (18)152 (3)
O4—H4A···N1i0.79 (2)2.03 (2)2.8189 (18)172 (2)
C2—H2A···N2ii0.932.723.638 (2)168
Symmetry codes: (i) x+1, y, z; (ii) x1, y1/2, z1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O3—H3A···O20.72 (3)2.11 (3)2.7576 (18)152 (3)
O4—H4A···N1i0.79 (2)2.03 (2)2.8189 (18)172 (2)
C2—H2A···N2ii0.932.723.638 (2)168.2
Symmetry codes: (i) x+1, y, z; (ii) x1, y1/2, z1/2.

Experimental details

Crystal data
Chemical formulaC16H11BrN2O4
Mr375.18
Crystal system, space groupMonoclinic, P21/c
Temperature (K)296
a, b, c (Å)8.4726 (3), 23.7748 (8), 8.0833 (3)
β (°) 111.6985 (17)
V3)1512.88 (9)
Z4
Radiation typeMo Kα
µ (mm1)2.74
Crystal size (mm)0.35 × 0.20 × 0.09
Data collection
DiffractometerBruker APEXII CCD
Absorption correctionMulti-scan
(SADABS; Bruker, 2010)
Tmin, Tmax0.428, 0.747
No. of measured, independent and
observed [I > 2σ(I)] reflections
65083, 6269, 4739
Rint0.037
(sin θ/λ)max1)0.796
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.035, 0.089, 1.03
No. of reflections6269
No. of parameters216
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.59, 0.26

Computer programs: APEX2 (Bruker, 2010), SAINT (Bruker, 2010), SHELXS97 (Sheldrick 2008), SHELXL2014 (Sheldrick, 2015), SHELXTL (Sheldrick, 2008).

 

Acknowledgements

This research was supported by the National Science Foundation (CHE-08–48206). One of us (JEM) is grateful to the Department of Education's Graduate Assistance in Areas of National Need (GAANN) Program for fellowship support. We appreciate the assistance of Professor David Dixon and Dr Edward Garner in performing DFT calculations.

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Volume 72| Part 5| May 2016| Pages 667-670
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