Crystal and mol­ecular structure of meso-2,6-di­bromo­hepta­nedioic acid (meso-2,6-di­bromo­pimelic acid)

Dirda, N.D.A.; Zavalij, P.Y.; Kao, J.P.Y.

doi:10.1107/S2056989016001754

research communications

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ISSN: 2056-9890

Volume 72| Part 3| March 2016| Pages 322-324

doi:10.1107/S2056989016001754

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Crystal and molecular structure of meso-2,6-dibromoheptanedioic acid (meso-2,6-dibromopimelic acid)

Nathaniel D. A. Dirda,^a Peter Y. Zavalij ^b and Joseph P. Y. Kao ^a,^c ^*

^aCenter for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD 21201, USA, ^bDepartment of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA, and ^cDepartment of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
^*Correspondence e-mail: jkao@umaryland.edu

Edited by S. Parkin, University of Kentucky, USA (Received 23 January 2016; accepted 27 January 2016; online 10 February 2016)

The molecular structure of the title compound, C₇H₁₀Br₂O₄, confirms the meso (2R,6S) configuration. In the crystal, molecules are linked by pairs of O—H⋯O=C hydrogen bonds between their terminal carboxyl groups in an R₂²(8) motif, forming extended chains that propagate parallel to the c axis. Adjacent chains are linked by C=O⋯Br halogen bonds.

Keywords: crystal structure; hydrogen bonding; halogen bonding.

CCDC reference: 1450356

1. Chemical context

meso-2,6-Dibromopimelic acid is a convenient starting point for preparing derivatives 2,6-disubstituted with non-halogen functional groups (for examples: Schotte, 1956b ; Lingens, 1960 ; Yuan & Lu, 2009 ). It also has utility in the synthesis of heterocycles (Schotte, 1956b; Miyake et al., 2000 ; Peters et al., 2006 ; Hamon et al., 2007 ). In an ongoing study of disulfides, the title compound was required as precursor to meso-3,7-dicarboxy-1,2-dithiepane. Surprisingly, other than the melting point reported by Schotte (1956a ), no further analytical data have been published on the dibromo acid. Original stereochemical assignment was based on the lack of optical activity of the acid isolated through crystallization of the acid brucine salt (Schotte, 1956a). The need to confirm the meso configuration motivated the crystal structure determination.

2. Structural commentary

The molecular structure of the title compound is shown in Fig. 1; the (2R,6S) configuration is apparent, confirming the meso form of the compound. All bond lengths and angles are within normal ranges.

Figure 1
The molecular structure of the title compound, with non-H atoms labeled. Displacement ellipsoids are shown at the 60% probability level.

3. Supramolecular features

In the crystal, the molecules are linked in head-to-tail fashion by pairs of O—H⋯O=C hydrogen bonds (Table 1) between their terminal carboxyl groups in an R₂²(8) motif, forming extended chains that propagate parallel to the c axis (Fig. 2a). Adjacent chains are cross-linked by interactions between a carboxyl C=O group in one chain with a Br atom in an adjacent chain. These linkages meet the criteria for halogen bonds (Desiraju et al., 2013 ): (i) the =O⋯Br—C bonds are nearly linear [the =O1⋯Br2—C2 and =O3⋯Br6—C6 angles being 168.06 (8) and 170.26 (8)°, respectively], and (ii) the O⋯Br distances [3.224 (2) and 3.058 (2) Å for O1⋯Br2ⁱⁱⁱ and O3⋯Br6^iv, respectively [symmetry codes: (iii) $[{1\over 2}]$ − x, y − $[{1\over 2}]$ , z; (iv) $[{3\over 2}]$ − x, y − $[{1\over 2}]$ , z] are less than the sum of the van der Waals radii of 3.35 Å (Mantina et al., 2009 ; Alvarez, 2013 ). H and Br bonding are shown in Fig. 2.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O2—H2⋯O3ⁱ	0.84	1.80	2.635 (3)	177
O4—H4⋯O1ⁱⁱ	0.84	1.83	2.669 (3)	176
Symmetry codes: (i) $[x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (ii) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ .

Figure 2
The molecular packing, viewed along the b and a axes [panels (a) and (b)]. Intermolecular hydrogen bonding (cyan) between terminal carboxyl groups results in head-to-tail linkage of the molecules into chains extending along [001]. Adjacent chains are linked by halogen bonding (C=O⋯Br, green).

4. Synthesis and crystallization

The title compound was first prepared in pure form and its stereochemistry deduced by Fehnel & Oppenlander (1953 ). The synthesis for the present work followed the method of Schotte (1956a). Pimelic (heptanedioic) acid was converted into the diacid chloride by heating with thionyl chloride. Removal of excess SOCl₂ under reduced pressure left the liquid diacid chloride. Over 1 h, bromine (2.3 equivalents) was added dropwise to the stirred diacid chloride maintained at 363 K. Thereafter, stirring and heating continued for an additional hour. The dibrominated acid chloride was hydrolyzed by gradual addition to vigorously stirred formic acid maintained at 353–363 K. When gas evolution ceased, the reaction mixture was refluxed for 15 min, and then allowed to cool to room temperature. Upon cooling in the refrigerator, over two days, the reaction mixture yielded two crops of solids, which were combined and extracted by shaking with ice-cold CHCl₃. The remaining solids were recrystallized three times from formic acid to give meso-2,6-dibroheptanedioic acid (26% yield).

The ¹H NMR spectrum, acquired in Me₂SO-d₆, is consistent with the molecular structure, with the following resonances (δ referenced to Me₄Si): 13.22, singlet, 2H; 4.43, triplet, 2H, J = 7 Hz; 2.01, multiplet, 2H; 1.88, multiplet, 2H; 1.54, multiplet, 1H; 1.39, multiplet, 1H. The high-resolution mass spectrum (electrospray) showed the expected manifold arising from the two stable isotopes of bromine, with the base peak at m/z = 316.884; species containing halogens other than bromine were not observed. To produce crystals suitable for diffraction, 10 mg of the title compound was dissolved in a capped glass vial in minimal formic acid with warming. Once a few seeds became visible, slow evaporation of the solvent over 14 days yielded crystals of good quality.

5. Refinement details

Crystal data, data collection and structure refinement details are summarized in Table 2. H-atom U_iso parameters were refined to confirm proper positioning of the H atoms; this was particularly important for the carboxyl H atoms. Uniquely for H3, its U_iso [0.013 (7)] is smaller than the U_eq of C3 [0.022 (4)], to which it is attached, but by less than two s.u.'s. All other H-atom U_iso values are consistent with expectation: 0.02–0.3 for CH and CH₂, and 0.05 for CO₂H. These values are in line with H-atom U_iso values in C₂–C₁₂ aliphatic acids without heavy-atom substitution, whose structures had been determined at the same temperature (150 K) or lower (Thalladi et al., 2000 ; Mitchell et al.,2001 ; Peppel et al., 2015a ,b ; Sonneck et al., 2015a ,b ). In these structures, U_iso values average 0.033±0.006 for CH and CH₂, and 0.068±0.033 for reciprocally hydrogen-bonded CO₂H.

Table 2
Experimental details

Crystal data
Chemical formula	C₇H₁₀Br₂O₄
M_r	317.97
Crystal system, space group	Orthorhombic, Pbca
Temperature (K)	150
a, b, c (Å)	10.4277 (7), 10.7014 (7), 18.7154 (13)
V (Å³)	2088.5 (2)
Z	8
Radiation type	Mo Kα
μ (mm⁻¹)	7.74
Crystal size (mm)	0.35 × 0.27 × 0.09

Data collection
Diffractometer	Bruker SMART APEXII CCD
Absorption correction	Multi-scan (SADABS; Sheldrick, 2008 )
T_min, T_max	0.231, 0.498
No. of measured, independent and observed [I > 2σ(I)] reflections	35789, 4598, 3488
R_int	0.037
(sin θ/λ)_max (Å⁻¹)	0.807

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.084, 1.08
No. of reflections	4598
No. of parameters	130
H-atom treatment	Only H-atom displacement parameters refined
Δρ_max, Δρ_min (e Å⁻³)	2.07, −1.15
Computer programs: APEX2, SAINT and XSHELL (Bruker, 2010 ), SHELXS97 (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2015 ), Mercury (Macrae et al., 2008 ), PLATON (Spek, 2009 ) and publCIF (Westrip, 2010 ).

Residual electron density is somewhat high (Δρ_max and Δρ_min being 2.07 and −1.14 e Å³, respectively) and localizes near the heavier Br atoms, which suggests Fourier truncation as a possible cause. Other reasons could be translational pseudosymmetry (for example, see Kiessling & Zeller, 2011 ), or the high geometric anisotropy of the crystal (ratio of largest-to-smallest dimensions being 4), which can yield less accurate absorption correction performed through SADABS software. The irregular shape of the crystal precluded more accurate absorption correction through face indexing.

Supporting information

CCDC reference: 1450356

Crystal structure: contains datablock I. DOI: 10.1107/S2056989016001754/pk2573sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S2056989016001754/pk2573Isup2.hkl

Supporting information file. DOI: 10.1107/S2056989016001754/pk2573Isup3.cml

checkCIF report

Chemical context top

meso-2,6-Dibromopimelic acid is a convenient starting point for preparing derivatives 2,6-disubstituted with non-halogen functional groups (for examples: Schotte, 1956b; Lingens, 1960; Yuan & Lu, 2009). It also has utility in the synthesis of heterocycles (Schotte, 1956b; Miyake et al., 2000; Peters et al., 2006; Hamon et al., 2007). In an ongoing study of disulfides, the title compound was required as precursor to meso-3,7-dicarboxy-1,2-dithiepane. Surprisingly, other than the melting point reported by Schotte (1956a), no further analytical data have been published on the dibromo acid. Original stereochemical assignment was based on the lack of optical activity of the acid isolated through crystallization of the acid brucine salt (Schotte, 1956a). The need to confirm the meso configuration motivated the crystal structure determination.

Structural commentary top

Supramolecular features top

In the crystal, the molecules are linked in head-to-tail fashion by pairs of O—H···O═C hydrogen bonds (Table 1) between their terminal carboxyl groups in an R₂²(8) motif, forming extended chains that propagate parallel to the c axis (Fig. 2a). Adjacent chains are cross-linked by interactions between a carboxyl C═O group in one chain with a Br atom in an adjacent chain. These linkages meet the criteria for halogen bonds (Desiraju et al., 2013): (i) the ═O···Br—C bonds are nearly linear [the ═O1···Br2—C2 and ═O3···Br6—C6 angles being 168.06 (8) and 170.26 (8)°, respectively], and (ii) the O···Br distances [3.224 (2) and 3.058 (2) Å for O1···Br2ⁱⁱⁱ and O3···Br6^iv, respectively [symmetry codes: (iii) 1/2 − x, y − 1/2, z; (iv) 3/2 − x, y − 1/2, z] are less than the sum of the van der Waals radii of 3.35 Å (Mantina et al., 2009; Alvarez, 2013). H and Br bonding are shown in Fig. 2.

Synthesis and crystallization top

The title compound was first prepared in pure form and its stereochemistry deduced by Fehnel & Oppenlander (1953). The synthesis for the present work followed the method of Schotte (1956a). Pimelic (heptanedioic) acid was converted into the diacid chloride by heating with thionyl chloride. Removal of excess SOCl₂ under reduced pressure left the liquid diacid chloride. Over 1 h, bromine (2.3 equivalents) was added dropwise to the stirred diacid chloride maintained at ~363 K. Thereafter, stirring and heating continued for an additional hour. The dibrominated acid chloride was hydrolyzed by gradual addition to vigorously stirred formic acid maintained at 353–363 K. When gas evolution ceased, the reaction mixture was refluxed for 15 min, and then allowed to cool to room temperature. Upon cooling in the refrigerator, over two days, the reaction mixture yielded two crops of solids, which were combined and extracted by shaking with ice-cold CHCl₃. The remaining solids were recrystallized three times from formic acid to give meso-2,6-dibroheptanedioic acid (26% yield).

The ¹H NMR spectrum, acquired in Me₂SO-d₆, is consistent with the molecular structure, with the following resonances (δ referenced to Me₄Si): 13.22, singlet, 2H; 4.43, triplet, 2H, J = 7 Hz; 2.01, multiplet, 2H; 1.88, multiplet, 2H; 1.54, multiplet, 1H; 1.39, multiplet, 1H. The high-resolution mass spectrum (electrospray) showed the expected manifold arising from the two stable isotopes of bromine, with the base peak at m/z = 316.884; species containing halogens other than bromine were not observed. To produce crystals suitable for diffraction, ~10 mg of the title compound was dissolved in a capped glass vial in minimal formic acid with warming. Once a few seeds became visible, slow evaporation of the solvent over 14 days yielded crystals of good quality.

Refinement details top

Crystal data, data collection and structure refinement details are summarized in Table 2. H-atom U_iso parameters were refined to confirm proper positioning of the H atoms; this was particularly important for the carboxyl H atoms. Uniquely for H3, its U_iso [0.013 (7)] is smaller than the U_eq of C3 [0.022 (4)], to which it is attached, but by less than two s.u.'s. All other H-atom U_iso values are consistent with expectation: ~0.02–0.3 for CH and CH₂, and ~0.05 for CO₂H. These values are in line with H-atom U_iso values in C₂–C₁₂ aliphatic acids without heavy-atom substitution, whose structures had been determined at the same temperature (150 K) or lower (Thalladi et al., 2000; Mitchell et al.,2001; Peppel et al., 2015a,b; Sonneck et al., 2015a,b). In these structures, U_iso values average 0.033±0.006 for CH and CH₂, and 0.068±0.033 for reciprocally hydrogen-bonded CO₂H.

Residual electron density is somewhat high (Δρ_max and Δρ_min being 2.07 and −1.14 e Å³, respectively) and localizes near the heavier Br atoms, which suggests Fourier truncation as a possible cause. Other reasons could be translational pseudosymmetry (for example, see Kiessling & Zeller, 2011), or the high geometric anisotropy of the crystal (ratio of largest-to-smallest dimensions being ~4), which can yield less accurate absorption correction performed through SADABS software. The irregular shape of the crystal precluded more accurate absorption correction through face indexing.

Related literature top

The title compound was first prepared in pure form and its stereochemistry deduced by Fehnel and Oppenlander (1953). The meso and racemic forms of 2,6-dibromoheptanedioic acid (2,6-dibromopimelic acid) were prepared by Schotte (1956a), who also resolved the enantiomorphs by crystallization of the acid brucine and chiconidine salts. Conversion of the title compound into derivatives 2,6-disubstituted with non-halogen functional groups is exemplified in Schotte (1956b), Lingens (1960), and Yuan & Lu (2009). Use of the title compound in heterocycle synthesis has been reported (Schotte, 1956b; Miyake et al., 2000; Peters et al., 2006; Hamon et al., 2007).

Structure description top

meso-2,6-Dibromopimelic acid is a convenient starting point for preparing derivatives 2,6-disubstituted with non-halogen functional groups (for examples: Schotte, 1956b; Lingens, 1960; Yuan & Lu, 2009). It also has utility in the synthesis of heterocycles (Schotte, 1956b; Miyake et al., 2000; Peters et al., 2006; Hamon et al., 2007). In an ongoing study of disulfides, the title compound was required as precursor to meso-3,7-dicarboxy-1,2-dithiepane. Surprisingly, other than the melting point reported by Schotte (1956a), no further analytical data have been published on the dibromo acid. Original stereochemical assignment was based on the lack of optical activity of the acid isolated through crystallization of the acid brucine salt (Schotte, 1956a). The need to confirm the meso configuration motivated the crystal structure determination.

Synthesis and crystallization top

The title compound was first prepared in pure form and its stereochemistry deduced by Fehnel & Oppenlander (1953). The synthesis for the present work followed the method of Schotte (1956a). Pimelic (heptanedioic) acid was converted into the diacid chloride by heating with thionyl chloride. Removal of excess SOCl₂ under reduced pressure left the liquid diacid chloride. Over 1 h, bromine (2.3 equivalents) was added dropwise to the stirred diacid chloride maintained at ~363 K. Thereafter, stirring and heating continued for an additional hour. The dibrominated acid chloride was hydrolyzed by gradual addition to vigorously stirred formic acid maintained at 353–363 K. When gas evolution ceased, the reaction mixture was refluxed for 15 min, and then allowed to cool to room temperature. Upon cooling in the refrigerator, over two days, the reaction mixture yielded two crops of solids, which were combined and extracted by shaking with ice-cold CHCl₃. The remaining solids were recrystallized three times from formic acid to give meso-2,6-dibroheptanedioic acid (26% yield).

The ¹H NMR spectrum, acquired in Me₂SO-d₆, is consistent with the molecular structure, with the following resonances (δ referenced to Me₄Si): 13.22, singlet, 2H; 4.43, triplet, 2H, J = 7 Hz; 2.01, multiplet, 2H; 1.88, multiplet, 2H; 1.54, multiplet, 1H; 1.39, multiplet, 1H. The high-resolution mass spectrum (electrospray) showed the expected manifold arising from the two stable isotopes of bromine, with the base peak at m/z = 316.884; species containing halogens other than bromine were not observed. To produce crystals suitable for diffraction, ~10 mg of the title compound was dissolved in a capped glass vial in minimal formic acid with warming. Once a few seeds became visible, slow evaporation of the solvent over 14 days yielded crystals of good quality.

Refinement details top

Crystal data, data collection and structure refinement details are summarized in Table 2. H-atom U_iso parameters were refined to confirm proper positioning of the H atoms; this was particularly important for the carboxyl H atoms. Uniquely for H3, its U_iso [0.013 (7)] is smaller than the U_eq of C3 [0.022 (4)], to which it is attached, but by less than two s.u.'s. All other H-atom U_iso values are consistent with expectation: ~0.02–0.3 for CH and CH₂, and ~0.05 for CO₂H. These values are in line with H-atom U_iso values in C₂–C₁₂ aliphatic acids without heavy-atom substitution, whose structures had been determined at the same temperature (150 K) or lower (Thalladi et al., 2000; Mitchell et al.,2001; Peppel et al., 2015a,b; Sonneck et al., 2015a,b). In these structures, U_iso values average 0.033±0.006 for CH and CH₂, and 0.068±0.033 for reciprocally hydrogen-bonded CO₂H.

Residual electron density is somewhat high (Δρ_max and Δρ_min being 2.07 and −1.14 e Å³, respectively) and localizes near the heavier Br atoms, which suggests Fourier truncation as a possible cause. Other reasons could be translational pseudosymmetry (for example, see Kiessling & Zeller, 2011), or the high geometric anisotropy of the crystal (ratio of largest-to-smallest dimensions being ~4), which can yield less accurate absorption correction performed through SADABS software. The irregular shape of the crystal precluded more accurate absorption correction through face indexing.

Computing details top

Data collection: APEX2 (Bruker, 2010); cell refinement: APEX2 (Bruker, 2010); data reduction: APEX2 and SAINT (Bruker, 2010); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: XSHELL (Bruker, 2010) and Mercury (Macrae et al., 2008); software used to prepare material for publication: APEX2 (Bruker, 2010), SHELXL2014 (Sheldrick, 2015), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

Figures top

	Fig. 1. The molecular structure of the title compound, with non-H atoms labeled. Displacement ellipsoids are shown at the 60% probability level.
	Fig. 2. The molecular packing, viewed along the b and a axes [panels (a) and (b)]. Intermolecular hydrogen bonding (cyan) between terminal carboxyl groups results in head-to-tail linkage of the molecules into chains extending along [001]. Adjacent chains are linked by halogen bonding (C═O···Br, green).

meso-2,6-Dibromoheptanedioic acid top

Crystal data top

C₇H₁₀Br₂O₄	D_x = 2.023 Mg m⁻³
M_r = 317.97	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 9811 reflections
a = 10.4277 (7) Å	θ = 2.2–34.7°
b = 10.7014 (7) Å	µ = 7.74 mm⁻¹
c = 18.7154 (13) Å	T = 150 K
V = 2088.5 (2) Å³	Plate, colourless
Z = 8	0.35 × 0.27 × 0.09 mm
F(000) = 1232

Data collection top

Bruker SMART APEXII CCD diffractometer	4598 independent reflections
Radiation source: sealed tube	3488 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.037
Detector resolution: 8.333 pixels mm^-1	θ_max = 35.0°, θ_min = 2.2°
φ and ω scans	h = −16→16
Absorption correction: multi-scan (SADABS; Sheldrick, 2008)	k = −17→17
T_min = 0.231, T_max = 0.498	l = −30→30
35789 measured reflections

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.036	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.084	Only H-atom displacement parameters refined
S = 1.08	w = 1/[σ²(F_o²) + (0.020P)² + 6.P] where P = (F_o² + 2F_c²)/3
4598 reflections	(Δ/σ)_max = 0.001
130 parameters	Δρ_max = 2.07 e Å⁻³
0 restraints	Δρ_min = −1.14 e Å⁻³

Crystal data top

C₇H₁₀Br₂O₄	V = 2088.5 (2) Å³
M_r = 317.97	Z = 8
Orthorhombic, Pbca	Mo Kα radiation
a = 10.4277 (7) Å	µ = 7.74 mm⁻¹
b = 10.7014 (7) Å	T = 150 K
c = 18.7154 (13) Å	0.35 × 0.27 × 0.09 mm

Data collection top

Bruker SMART APEXII CCD diffractometer	4598 independent reflections
Absorption correction: multi-scan (SADABS; Sheldrick, 2008)	3488 reflections with I > 2σ(I)
T_min = 0.231, T_max = 0.498	R_int = 0.037
35789 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.036	0 restraints
wR(F²) = 0.084	Only H-atom displacement parameters refined
S = 1.08	Δρ_max = 2.07 e Å⁻³
4598 reflections	Δρ_min = −1.14 e Å⁻³
130 parameters

Special details top

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

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

	x	y	z	U_iso*/U_eq
O1	0.4428 (2)	0.35337 (18)	0.81180 (10)	0.0271 (4)
O2	0.5097 (2)	0.53602 (18)	0.85748 (10)	0.0289 (4)
H2	0.5328	0.4903	0.8916	0.044 (11)*
C1	0.4560 (2)	0.4669 (2)	0.80775 (12)	0.0200 (4)
C2	0.4148 (2)	0.5420 (2)	0.74305 (12)	0.0190 (4)
H2A	0.4858	0.6007	0.7303	0.024 (8)*
Br2	0.26550 (3)	0.64147 (3)	0.77267 (2)	0.02812 (7)
C3	0.3835 (2)	0.4638 (2)	0.67757 (12)	0.0221 (4)
H3A	0.3411	0.5169	0.6413	0.022 (8)*
H3B	0.3233	0.3963	0.6910	0.013 (7)*
C4	0.5050 (3)	0.4068 (3)	0.64587 (13)	0.0241 (5)
H4A	0.5692	0.4736	0.6380	0.030 (9)*
H4B	0.5417	0.3462	0.6802	0.033 (9)*
C5	0.4780 (2)	0.3408 (2)	0.57527 (13)	0.0212 (4)
H5A	0.4112	0.2765	0.5831	0.034 (9)*
H5B	0.4435	0.4024	0.5408	0.037 (10)*
C6	0.5957 (2)	0.2790 (2)	0.54304 (13)	0.0204 (4)
H6A	0.6299	0.2163	0.5778	0.029 (9)*
Br6	0.73130 (2)	0.40137 (2)	0.52174 (2)	0.02402 (6)
C7	0.5646 (2)	0.2132 (2)	0.47354 (12)	0.0204 (4)
O3	0.5852 (2)	0.10197 (18)	0.46621 (11)	0.0296 (4)
O4	0.5102 (2)	0.28358 (18)	0.42491 (10)	0.0300 (4)
H4	0.4863	0.2389	0.3905	0.053 (12)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.0382 (10)	0.0244 (9)	0.0188 (8)	−0.0048 (8)	−0.0049 (7)	0.0012 (7)
O2	0.0425 (11)	0.0238 (9)	0.0205 (8)	−0.0040 (8)	−0.0098 (8)	0.0008 (7)
C1	0.0205 (10)	0.0243 (11)	0.0152 (9)	0.0001 (8)	0.0009 (7)	0.0002 (8)
C2	0.0185 (9)	0.0204 (10)	0.0181 (10)	0.0006 (8)	0.0003 (7)	0.0012 (8)
Br2	0.02097 (11)	0.03372 (14)	0.02965 (13)	0.00479 (10)	0.00001 (10)	−0.00452 (10)
C3	0.0233 (11)	0.0270 (11)	0.0159 (9)	−0.0003 (9)	−0.0012 (8)	0.0008 (8)
C4	0.0264 (11)	0.0294 (12)	0.0166 (9)	0.0032 (9)	−0.0013 (8)	−0.0036 (9)
C5	0.0226 (11)	0.0239 (11)	0.0171 (9)	0.0003 (8)	−0.0008 (8)	−0.0005 (8)
C6	0.0255 (11)	0.0190 (10)	0.0169 (9)	0.0006 (8)	−0.0024 (8)	0.0009 (8)
Br6	0.02087 (10)	0.02733 (12)	0.02386 (11)	−0.00204 (9)	−0.00007 (9)	−0.00097 (9)
C7	0.0218 (10)	0.0228 (10)	0.0165 (9)	−0.0007 (8)	−0.0008 (8)	0.0014 (8)
O3	0.0387 (11)	0.0247 (9)	0.0253 (9)	0.0061 (8)	−0.0103 (8)	−0.0034 (7)
O4	0.0493 (12)	0.0215 (8)	0.0193 (8)	0.0027 (8)	−0.0100 (8)	−0.0001 (7)

Geometric parameters (Å, º) top

O1—C1	1.225 (3)	C4—H4A	0.9900
O2—C1	1.314 (3)	C4—H4B	0.9900
O2—H2	0.8400	C5—C6	1.520 (3)
C1—C2	1.516 (3)	C5—H5A	0.9900
C2—C3	1.519 (3)	C5—H5B	0.9900
C2—Br2	1.966 (2)	C6—C7	1.515 (3)
C2—H2A	1.0000	C6—Br6	1.968 (2)
C3—C4	1.526 (4)	C6—H6A	1.0000
C3—H3A	0.9900	C7—O3	1.217 (3)
C3—H3B	0.9900	C7—O4	1.310 (3)
C4—C5	1.524 (3)	O4—H4	0.8400

C1—O2—H2	109.5	C5—C4—H4B	109.3
O1—C1—O2	124.2 (2)	C3—C4—H4B	109.3
O1—C1—C2	122.9 (2)	H4A—C4—H4B	108.0
O2—C1—C2	112.8 (2)	C6—C5—C4	113.3 (2)
C1—C2—C3	114.4 (2)	C6—C5—H5A	108.9
C1—C2—Br2	106.66 (16)	C4—C5—H5A	108.9
C3—C2—Br2	110.85 (16)	C6—C5—H5B	108.9
C1—C2—H2A	108.2	C4—C5—H5B	108.9
C3—C2—H2A	108.2	H5A—C5—H5B	107.7
Br2—C2—H2A	108.2	C7—C6—C5	111.7 (2)
C2—C3—C4	110.8 (2)	C7—C6—Br6	106.84 (16)
C2—C3—H3A	109.5	C5—C6—Br6	111.78 (16)
C4—C3—H3A	109.5	C7—C6—H6A	108.8
C2—C3—H3B	109.5	C5—C6—H6A	108.8
C4—C3—H3B	109.5	Br6—C6—H6A	108.8
H3A—C3—H3B	108.1	O3—C7—O4	124.1 (2)
C5—C4—C3	111.6 (2)	O3—C7—C6	120.9 (2)
C5—C4—H4A	109.3	O4—C7—C6	114.9 (2)
C3—C4—H4A	109.3	C7—O4—H4	109.5

O1—C1—C2—C3	−13.0 (3)	C3—C4—C5—C6	−178.1 (2)
O2—C1—C2—C3	165.5 (2)	C4—C5—C6—C7	179.3 (2)
O1—C1—C2—Br2	109.9 (2)	C4—C5—C6—Br6	−61.1 (2)
O2—C1—C2—Br2	−71.6 (2)	C5—C6—C7—O3	−122.1 (3)
C1—C2—C3—C4	−70.5 (3)	Br6—C6—C7—O3	115.4 (2)
Br2—C2—C3—C4	168.86 (17)	C5—C6—C7—O4	55.2 (3)
C2—C3—C4—C5	−173.3 (2)	Br6—C6—C7—O4	−67.3 (2)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O3ⁱ	0.84	1.80	2.635 (3)	177
O4—H4···O1ⁱⁱ	0.84	1.83	2.669 (3)	176

Symmetry codes: (i) x, −y+1/2, z+1/2; (ii) x, −y+1/2, z−1/2.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O3ⁱ	0.84	1.80	2.635 (3)	177
O4—H4···O1ⁱⁱ	0.84	1.83	2.669 (3)	176

Symmetry codes: (i) x, −y+1/2, z+1/2; (ii) x, −y+1/2, z−1/2.

Experimental details

Crystal data
Chemical formula	C₇H₁₀Br₂O₄
M_r	317.97
Crystal system, space group	Orthorhombic, Pbca
Temperature (K)	150
a, b, c (Å)	10.4277 (7), 10.7014 (7), 18.7154 (13)
V (Å³)	2088.5 (2)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	7.74
Crystal size (mm)	0.35 × 0.27 × 0.09

Data collection
Diffractometer	Bruker SMART APEXII CCD
Absorption correction	Multi-scan (SADABS; Sheldrick, 2008)
T_min, T_max	0.231, 0.498
No. of measured, independent and observed [I > 2σ(I)] reflections	35789, 4598, 3488
R_int	0.037
(sin θ/λ)_max (Å⁻¹)	0.807

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.036, 0.084, 1.08
No. of reflections	4598
No. of parameters	130
H-atom treatment	Only H-atom displacement parameters refined
Δρ_max, Δρ_min (e Å⁻³)	2.07, −1.14

Computer programs: APEX2 and SAINT (Bruker, 2010), SHELXS97 (Sheldrick, 2008), XSHELL (Bruker, 2010) and Mercury (Macrae et al., 2008), APEX2 (Bruker, 2010), SHELXL2014 (Sheldrick, 2015), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

Acknowledgements

This work was supported in part by the Nanobiology Fund of the University of Maryland Baltimore Foundation.

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Volume 72| Part 3| March 2016| Pages 322-324

doi:10.1107/S2056989016001754

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

Crystal and mol­ecular structure of meso-2,6-di­bromo­hepta­nedioic acid (meso-2,6-di­bromo­pimelic acid)

1. Chemical context

2. Structural commentary

3. Supra­molecular features

4. Synthesis and crystallization

5. Refinement details

Supporting information

Acknowledgements

References

research communications

Crystal and molecular structure of meso-2,6-dibromoheptanedioic acid (meso-2,6-dibromopimelic acid)

3. Supramolecular features