5,5′-Bis[(2,2,2-trifluoro­eth­oxy)meth­yl]-2,2′-bipyridine

Norman Lu; Wen-Han Tu; Wei-Hsuan Chang; Zong-Wei Wu; Han-Chang Su

doi:10.1107/S1600536811000730

. 2011 Jan 12;67(Pt 2):o355–o356. doi: 10.1107/S1600536811000730

5,5′-Bis[(2,2,2-trifluoroethoxy)methyl]-2,2′-bipyridine

Norman Lu ^a,^*, Wen-Han Tu ^a, Wei-Hsuan Chang ^a, Zong-Wei Wu ^a, Han-Chang Su ^a

PMCID: PMC3051693 PMID: 21523035

Abstract

The complete molecule of the title compound, C₁₆H₁₄F₆N₂O₂, is generated by crystallographic inversion symmetry, which results in two short intramolecular C—H⋯N hydrogen-bond contacts per molecule. In the crystal, aromatic π–π stacking [centroid–centroid distance = 3.457 (2) Å] and weak C—H⋯π interactions occur. A short H⋯H [2.32 (3) Å] contact is present.

Related literature

For related structures and background to the anti-planar geometry of bpy, see: Lu, Tu, Wu et al. (2010 ▶); Iyer et al. (2005 ▶); Heirtzler et al. (2002 ▶); Maury et al. (2001 ▶); Vogtle et al. (1990 ▶). For background to the bipyridine (bpy) ligand, see: Bain et al. (1989 ▶); Chambron & Sauvage (1986 ▶, 1987 ▶); Grätzel (2001 ▶); Haga et al. (2000 ▶); Lu, Tu, Hou et al. (2010 ▶); Lu, Tu, Wen et al. (2010 ▶); Lu et al. (2007 ▶). For C—H⋯H—C interactions, see: Wolstenholme & Cameron (2006 ▶).

Experimental

Crystal data

C₁₆H₁₄F₆N₂O₂
M _r = 380.29
Triclinic,
a = 4.6573 (2) Å
b = 5.6842 (3) Å
c = 15.7273 (8) Å
α = 94.298 (3)°
β = 98.473 (3)°
γ = 105.689 (4)°
V = 393.57 (3) Å³
Z = 1
Mo Kα radiation
μ = 0.15 mm⁻¹
T = 100 K
0.2 × 0.14 × 0.12 mm

Data collection

Bruker APEXII CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2008 ▶) T _min = 0.664, T _max = 0.746
6627 measured reflections
1577 independent reflections
1348 reflections with I > 2σ(I)
R _int = 0.024

Refinement

R[F ² > 2σ(F ²)] = 0.031
wR(F ²) = 0.104
S = 1.12
1577 reflections
146 parameters
All H-atom parameters refined
Δρ_max = 0.29 e Å⁻³
Δρ_min = −0.27 e Å⁻³

Data collection: APEX2 (Bruker, 2010 ▶); cell refinement: SAINT (Bruker, 2009 ▶); 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 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: WinGX (Farrugia, 1999 ▶).

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811000730/fk2030sup1.cif

e-67-0o355-sup1.cif^{(14.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811000730/fk2030Isup2.hkl

e-67-0o355-Isup2.hkl^{(76.1KB, hkl)}

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

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

Cg is the centroid of the N,C1–C5 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C4—H4⋯Nⁱ	0.925 (17)	2.464 (18)	2.809 (2)	102.3 (12)
C6—H6A⋯Cgⁱⁱ	0.990 (19)	2.59	3.5089 (16)	155

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Symmetry codes: (i) Inline graphic ; (ii) .

Acknowledgments

NL thanks the Taiwan NSC for financial support (NSC 98-2113-M- 027-002-MY3). We also thank Mr T. S. Kuo (Department of Chemistry, National Taiwan Normal University, Taiwan) for the assistance with the structure analysis.

supplementary crystallographic information

Comment

Bipyridine (bpy) ligand is among the most versatile ligands in organometallics. It has been extensively used to prepare various chelating compounds with different metal ions (Haga et al., 2000; Bain et al., 1989; Grätzel, 2001; Chambron & Sauvage, 1987, 1986). Structures with the motif {[4,4'-bis(R_fCH₂OCH₂) -2,2'-bpy]MCl₂, M = Pd or Pt} are interesting and reveal the blue shifting C–H···F–C hydrogen bonding (Lu, Tu, Hou et al., 2010; Lu, Tu, Wen et al., 2010; Lu, et al., 2007). However, the X-ray crystal structure of poly-fluorinated bpy ligands still remains elusive until recent elucidation of the structure on simplest 4,4'-bis(CF₃CH₂OCH₂)-2,2'-bpy (Lu, Tu, Wu et al., 2010). Reported here is the significantly different crystal structure on its 5,5'-isomer. They vary only on the positions of two identical substituents, yet features of packing in the solid state show little in similarity.

The title compound I is centro-symmetric and crystallizes in the space group of P-1, one half of the molecule being crystallographically independent. Two structural features of the title compound I are the planarity and the anti conformation of connected pyridyl units. The bpy exhibits a planar core and the N–C3–C3ⁱ–Nⁱ torsion angle is 180°, similar to the values in its 4,4'-isomer (Lu, Tu, Wu et al., 2010). Also noticed is the intramolecular weak hydrogen bonding interaction on C4–H4···Nⁱ, as suggested by the short H4···Nⁱ distance of 2.46 (2) Å and the C4–H4···Nⁱ angle of 102 (1)° (see Fig. 1).

Although both the title compound and its 4,4'-isomer (Lu, Tu, Wu et al., 2010) have the same molecular formula and their bpy cores are similarly planar, their identical side chains, positioned differently, show very different intermolecular interactions and packing methods. The intramolecular C–H···O and intermolecular C–H···N and C–H···F interactions, which were observed in 4,4'-bis(2,2,2-trifluoroethoxymethyl)-2,2'-bipyridine (Lu, Tu, Wu et al., 2010), are missing in I. There is almost no intramolecular C–H···O interaction in I, judged from the C5–C1–C6–O torsion angle of 41.5 (2)°, which deviates significantly from that reported for such a hydrogen-bonding system. In its 4,4'-isomer, the corresponding H3···O8 distance is 2.52 (1) Å and the C3–C4–C7–O8 torsion angle measures -21.9 (1)°.

Instead of intermolecular C–H···N and C–H···F interactions, stabilization of the structure of I is likely due to effective intermolecular C–H..π and F···F interactions. The π-π stacking is the driving force towards crystallization, with two adjacent bpy layers at a distance of 3.512 (2) Å. On top of this, the C6–H6A..π hydrogen bonding interaction has been observed between the methylene H atom and one of the adjacent bpy rings on the a-translation related direction. As shown in Table 1, the distance of H6A to bpy plane is 2.57 (2) Å, making less than 10° with the vector of H6A to centroid of the bpy ring. The terminal CF₃ groups shown in Fig. 2 are then fixed in crystalline state by the F···F interaction between two adjacent stacking layers. The F1···F3' distance is 2.857 (2) Å, the C8–F1···F3' angle 101.4 (1)°, and the C8–F3···F1" angle 166.0 (1)°.

In particular, the weak C4–H4···H4'–C4' (Wolstenholme et al., 2006) interaction shown in Fig. 2 has also been identified with H4···H4' distance of 2.32 (3) Å and the C4–H4···H4' angle of 113 (2)°. The C4–H4···H4'–C4' interaction connects two neighboring π stacking piles. Inside one π stacking pile, the π..π stacking distance between consecutive layers is 3.512 (2) Å, whereas the shifting step between two neighboring π stacking piles is 1.448 (2) Å. It is believed that this rare C–H···H–C supramolecular interaction seems to be derived from the dipole-induced interactions, defined by Wolstenholme, on the symmetry-related hydrogen atoms.

Experimental

5,5'-bis(CF₃CH₂OCH₂)-2,2'-bpy, (I), was prepared according to the general procedure described in Lu et al., (2007). The crude product was further purified by vacuum sublimation or chromatography to obtain the title compound as a colorless solid. Full characterization data are listed below.

Analytical data of (I): Yield 76 %, m.p. = 393 K. ¹H NMR (500 MHz, d-DMSO, room temperature), δ(ppm) Pyridine ring H: 8.66 s, H6, 2H), 8.39 (d, H4, ³J_HH=8.24 Hz, 2H), 7.92 (d, H3, ³J_HH=8.24 Hz, 2H), 4.77 (s, bpy-CH₂, 4H), 4.17 (q, -OCH₂CF₃, ³J_HF=9.34 Hz, 4H); ¹⁹F NMR (470.5 MHz, d-DMSO, room temperature), δ (ppm) -73.1 (t, -CH₂CF₃, ³J_HF = 9.7 Hz, 6F); ¹³C NMR (126 MHz,d-DMSO, room temperature) δ (ppm) 120.3, 133.1, 136.9, 148.7, 154.7 (s, bpy, 10C), 121.1-127.8 (q, -CF₃, ¹J_CF = 279.6 Hz, 2C), 70.6 (s, bpy-CH₂, 2C), 66.8 (q, -CH₂CF₃, ²J_CF = 33.2 Hz, 2C).

GC/MS (M/e) : M⁺ = 380, (M-C₂H₃F₃O)⁺ = 281, [M-(C₂H₃F₃O)₂]⁺= 182, (C₆H₅N)⁺ = 91.

FT-IR (cm^-1): 1601.5, 1553.8, 1469.4, 1360.1 (bpy-ring, m), 1155.8, 1122.6 (CF₂ stretch, s).

Recrystallization proceeded with dissolution of I in DMSO to form a saturated solution, to which the water overlayer (5 cm³) was added. Solvent diffusion over a period of ten days at 298 K afforded needle shaped crystals.