A monoclinic polymorph of (R,R)-4,4′-dibromo-2,2′-[cyclo­hexane-1,2-diylbis(nitrilo­methanylyl­idene)]diphenol

Kwang Ha

doi:10.1107/S1600536812016376

. 2012 Apr 21;68(Pt 5):o1449. doi: 10.1107/S1600536812016376

A monoclinic polymorph of (R,R)-4,4′-dibromo-2,2′-[cyclohexane-1,2-diylbis(nitrilomethanylylidene)]diphenol

Kwang Ha ^a,^*

PMCID: PMC3344566 PMID: 22590328

Abstract

The title compound, C₂₀H₂₀Br₂N₂O₂, a tetradentate Schiff base, is the enantiomerically pure R,R-diastereomer of four possible stereoisomers. The molecular structure reveals two strong intramolecular O—H⋯N hydrogen bonds between the hydroxy O atom and the imino N atom, which each generate S(6) rings. In the crystal, molecules are stacked in columns along the a axis; when viewed down the b axis, successive columns are stacked in the opposite direction. The structure reported herein is the monoclinic polymorph of the previously reported orthorhombic form [Yi & Hu (2009 ▶). Acta Cryst. E65, o2643], in which the complete molecule is generated by a crystallographic twofold axis.

Related literature

For the orthorhombic polymorph, see: Yi & Hu (2009 ▶).

Experimental

Crystal data

C₂₀H₂₀Br₂N₂O₂
M _r = 480.20
Monoclinic,
a = 5.9082 (5) Å
b = 18.8626 (15) Å
c = 9.0088 (7) Å
β = 91.867 (2)°
V = 1003.44 (14) Å³
Z = 2
Mo Kα radiation
μ = 4.06 mm⁻¹
T = 200 K
0.31 × 0.17 × 0.16 mm

Data collection

Bruker SMART 1000 CCD diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2000 ▶) T _min = 0.786, T _max = 1.000
7343 measured reflections
3868 independent reflections
2484 reflections with I > 2σ(I)
R _int = 0.031

Refinement

R[F ² > 2σ(F ²)] = 0.039
wR(F ²) = 0.108
S = 1.03
3868 reflections
235 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.88 e Å⁻³
Δρ_min = −0.47 e Å⁻³
Absolute structure: Flack (1983 ▶), 1331 Friedel pairs
Flack parameter: −0.010 (16)

Data collection: SMART (Bruker, 2000 ▶); cell refinement: SAINT (Bruker, 2000 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶) and PLATON (Spek, 2009 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536812016376/hb6734sup1.cif

e-68-o1449-sup1.cif^{(27KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812016376/hb6734Isup2.hkl

e-68-o1449-Isup2.hkl^{(189.6KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O1—H1O⋯N1	0.84	1.82	2.581 (7)	150
O2—H2O⋯N2	0.84	1.87	2.626 (7)	149

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Acknowledgments

This work was supported by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2011–0030747).

supplementary crystallographic information

Comment

The crystal structure of the title compound, C₂₀H₂₀Br₂N₂O₂, was previously reported in the orthorhombic space group P2₁2₁2 (Yi & Hu, 2009). The structure presented herein is essentially the same as the published structure and represents a monoclinic polymorph.

The title compound is a tetradentate Schiff base (Fig. 1), which can act as a dibasic ligand, i.e. the N and O donor atoms can coordinate one metal ion. The compound has two chiral C centres and is one of four possible stereoisomers. Crystallographically, the absolute configuration has been established by anomalous dispersion effects, and the R configuration of the asymmetric C atoms (C1 and C6) could be assigned. The Schiff base reveals strong intramolecular O—H···N hydrogen bonds between the hydroxy O atom and the imino N atom, with O···N distances of 2.581 (7) and 2.626 (7) Å, forming nearly planar six-membered rings (Fig. 2, Table 1). In the crystal structure, the benzene rings are not parallel: the dihedral angle between the benzene rings is 67.20 (15)°. The N—C bond lengths and the C—N—C bond angles indicate that the imino N atoms are sp²-hybridized [N1═C7 = 1.274 (8) Å, N1—C1 = 1.461 (8) Å, <C7—N1—C1 = 118.7 (6)°; N2═C14 = 1.280 (8) Å, N2—C6 = 1.474 (8) Å, <C14—N2—C6 = 118.3 (6)°]. The molecules are stacked in columns along the a axis. When viewed down the b axis, the successive compounds are stacked in the opposite direction. In the columns, the shortest centroid-centroid distance between aromatic rings is 4.709 (3) Å.

Experimental

1,2-Diaminocyclohexane (0.8007 g, 7.012 mmol) and 5-bromosalicylaldehyde (2.8204 g, 14.031 mmol) in EtOH (20 ml) were stirred for 1 h at room temperature. After addition of pentane (30 ml) to the reaction mixture, the formed precipitate was separated by filtration, washed with ether, and dried at 323 K, to give a yellow powder (1.7660 g). Yellow blocks were obtained by slow evaporation from a CH₃CN solution at room temperature. The previous polymorph (Yi & Hu, 2009) was crystallised from methanol.