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Journal logoSTRUCTURAL
CHEMISTRY
ISSN: 2053-2296

2,6-Di­bromo-3,5-di­methyl­pyridine and 2,6-di­iodo-3,5-di­methyl­pyridine

aDepartment of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, England
*Correspondence e-mail: dpugh1@soton.ac.uk

(Received 12 July 2006; accepted 16 August 2006; online 12 September 2006)

The title compounds 2,6-dibromo-3,5-dimethyl­pyridine, C7H7Br2N, (I), and 2,6-diiodo-3,5-dimethyl­pyridine, C7H7I2N, (II), constitute the first structurally characterized examples of 2,6-dihalo-3,5-dimethyl­pyridines. Compound (I) crystallizes as a racemic twin with two symmetry-independent mol­ecules in the asymmetric unit, while (II) is non-planar with the pyridine ring slightly deformed into a saddle shape, and exhibits crystallographically imposed twofold symmetry. Both (I) and (II) exhibit aromatic face-to-face π-stacking in the solid state, although there are no other long-range inter­actions. In (I), alternate mol­ecules are oriented at 90°, resulting in X-shaped columns, while in (II), mol­ecules pack in a parallel fashion, leading to a zigzag array.

Comment

To date, 2,6-dihalo-3,5-dimethyl­pyridine compounds have not been structurally characterized. Indeed, the only known crystal structure of a 2,6-dihalo-3,5-dialkyl­pyridine was reported by Kasturi et al. (1992[Kasturi, T. R., Arumugam, S., Mathew, L., Jayaram, S. K., Dastidar, P. & Guru Row, T. N. (1992). Tetrahedron, 48, 6499-6510.]), although as part of a larger structure. Although several methods exist for synthesizing 2,6-dichloro-3,5-dimethyl­pyridine (Crouch & Lochte, 1943[Crouch, W. W. & Lochte, H. L. (1943). J. Am. Chem. Soc. 65, 270-272.]; Meerpoel et al., 1991[Meerpoel, L., Deroover, G., Van Aken, K., Lux, G. & Hoornaert, G. (1991). Synthesis, pp. 765-768.]; Gros et al., 2002[Gros, P., Viney, C. & Fort, Y. (2002). Synlett, pp. 628-630.]), only one route to the dibromide (I)[link] has been disclosed (Dunn & Guillermic, 1988[Dunn, A. D. & Guillermic, S. (1988). Z. Chem. 28, 59-60.]), and neither the difluoride nor the diiodide is known.

[Scheme 1]

2,6-Dibromo­pyridine is commonly used in the synthesis of (CNC) `pincer' ligands containing N-heterocyclic carbene groups. It has been used to form (CNC) `pincer' ligands (III)[link] by quaternization with the appropriately substituted imidazole at high temperature, followed by deprotonation of the resulting imidazolium salt with a base (Danopoulos et al., 2002[Danopoulos, A. A., Winston, S. & Motherwell, W. B. (2002). Chem. Commun. pp. 1376-1377.]).

[Scheme 2]

C—H activation at the 3- and 5-positions of the pyridine ring was seen with Fe and Ir complexes of (III)[link] (R is 2,6-diisopropyl­phenyl). To counter this, a `pincer' ligand with blocking groups in the 3- and 5-positions on the pyridine ring was desired, which led to the use of (I)[link] as a starting material. Despite the use of very high temperatures (> 473 K) and lengthy reaction times (14 days), the reaction did not afford the doubly quaternized product. In order to overcome this obstacle, compound (II)[link] with its weaker carbon–halogen bond was synthesized.

The asymmetric unit of (I)[link] (Fig. 1[link]) contains two independent mol­ecules with similar geometric parameters (Table 1[link]) and an overall Z of 8. The cell dimensions are close to tetra­gonal P42212, but the data do not merge; instead, the structure was refined in the ortho­rhom­bic space group P212121. The mol­ecular dimensions are unremarkable, but the structure is a racemic twin with a Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]) parameter of 0.471 (17). The mol­ecule is planar, and the Br1A—C1A—C2A—C6A and N1A—C1A—C2A—C3A torsion angles (Table 1[link]) do not indicate any significant steric inter­actions between the Br atoms and the methyl groups.

The mol­ecule of compound (II)[link] (Fig. 2[link]) is slightly deformed into a saddle shape due to steric repulsion between the I atoms and the respective ortho methyl groups. The extent of the distortion of the atoms bonded to the pyridine ring is indicated by the I1—C1—C2—C4 torsion angle (Table 2[link]), where atom I1 and the methyl group (C4) are located on either side of the ring. Substituents trans to each other are distorted in the same direction above or below the ring, resulting in a saddle-shaped mol­ecule. The saddle point can be found in the middle of the pyridine ring; this can be seen from the torsion angle for the atoms in the pyridine ring (N1—C1—C2—C3) being smaller than that for the atoms on the outside of the ring. The distortion of the ring can also be noted by the deviation out of the mean plane of all atoms in the ring, atom C2 lying 0.021 (2) Å out of the plane.

The mol­ecular dimensions of (II)[link] are unremarkable. Although only three structurally characterized compounds with 2-iodo­pyridine groups exist, the C1—I1 bond lengths are similar, as are the C1—N1 bond lengths (Table 2[link]; Holmes et al., 2002[Holmes, B. T., Padgett, C. W. & Pennington, W. T. (2002). Acta Cryst. C58, o602-o603.]; Saha et al., 2005[Saha, B. K., Aitipamula, S., Banerjee, R., Nangia, A., Jetti, R. K. R., Boese, R., Lam, C.-K. & Mak, T. C. W. (2005). Mol. Cryst. Liq. Cryst. Sci. Technol. Sect. A, 440, 295-316.]).

A packing diagram of (I)[link] is shown in Fig. 3[link]. The only supra­molecular inter­action is face–face π-stacking, with no face–edge π-stacking. The mol­ecules are arranged in alternating columns, resulting in an `X' shape when viewed down the b axis. The dihedral angle between planes of the pyridine rings in successive mol­ecules in a column is 72.69 (10)°.

Compound (II)[link] exhibits the same supra­molecular inter­actions as (I)[link], with face–face π-stacking the only supra­molecular inter­action. However, the mol­ecules pack in a slightly different way, with alternating slanted columns of mol­ecules resulting in a zigzag arrangement when viewed down the b axis (Fig. 4[link]). Although 2,6-diiodo­pyridine exhibits both weak hydrogen-bonding inter­actions and weak halogen–halogen inter­actions (Holmes et al., 2002[Holmes, B. T., Padgett, C. W. & Pennington, W. T. (2002). Acta Cryst. C58, o602-o603.]), neither is present in (II)[link]; the inter­molecular I⋯I distance of 4.233 Å is greater than the sum of the van der Waals radii, estimated as 4.00 Å by Rowland & Taylor (1996[Rowland, R. S. & Taylor, R. (1996). J. Phys. Chem. 100, 7384-7391.]).

[Figure 1]
Figure 1
The two independent mol­ecules of (I) in the asymmetric unit, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2]
Figure 2
A representation of (II), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted. Atoms marked with a prime (′) are at the equivalent position ([1-x, y, {3\over2}-z]).
[Figure 3]
Figure 3
The packing of (I).
[Figure 4]
Figure 4
The packing of (II).

Experimental

Compound (I)[link] was synthesized according to the method of Dunn & Guillermic (1988[Dunn, A. D. & Guillermic, S. (1988). Z. Chem. 28, 59-60.]) in 64% yield and was crystallized from ethanol. Compound (II)[link] was synthesized via an aromatic Finkelstein reaction from the reaction of (I)[link] (15.00 g, 56.6 mmol), anhydrous NaI (34.13 g, 227.7 mmol), CuI (1.08 g, 5.7 mmol) and N,N-dimethylethylene­diamine (DMEDA; 1.20 ml, 11.3 mmol) in refluxing 1,4-dioxane (250 ml) for 40 h under an inert atmosphere. After cooling, water (100 ml) was added, and the product was extracted into CH2Cl2, dried over MgSO4, filtered and concentrated in vacuo. The resulting pale-orange solid was recrystallized from ethanol, affording colourless crystals in 83% yield. 1H NMR (400 MHz, CDCl3): δ 7.20 (1H, s, Ar), 2.30 (6H, s, Me); 13C NMR (100.6 MHz, CDCl3): δ 138.69 (C, C2/6), 137.49 (CH, C4), 119.38 (C, C3/5), 25.20 (CH3, Me).

Compound (I)[link]

Crystal data
  • C7H7Br2N

  • Mr = 264.96

  • Orthorhombic, P 21 21 21

  • a = 10.5429 (3) Å

  • b = 12.4821 (4) Å

  • c = 12.6458 (3) Å

  • V = 1664.16 (8) Å3

  • Z = 8

  • Dx = 2.115 Mg m−3

  • Mo Kα radiation

  • μ = 9.66 mm−1

  • T = 120 (2) K

  • Fragment, colourless

  • 0.10 × 0.10 × 0.02 mm

Data collection
  • Bruker–Nonius KappaCCD diffractometer

  • φ and ω scans

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. Version 2.10. University of Göttingen, Germany.]) Tmin = 0.397, Tmax = 0.826

  • 14709 measured reflections

  • 2175 independent reflections

  • 1984 reflections with I > 2σ(I)

  • Rint = 0.043

  • θmax = 27.5°

Refinement
  • Refinement on F2

  • R[F2 > 2σ(F2)] = 0.026

  • wR(F2) = 0.049

  • S = 1.08

  • 2175 reflections

  • 186 parameters

  • H-atom parameters constrained

  • w = 1/[σ2(Fo2) + (0.0144P)2 + 1.0475P] where P = (Fo2 + 2Fc2)/3

  • (Δ/σ)max = 0.022

  • Δρmax = 0.46 e Å−3

  • Δρmin = −0.50 e Å−3

  • Absolute structure: Flack (1983[Flack, H. D. (1983). Acta Cryst. A39, 876-881.]), 1623 Friedel pairs

  • Flack parameter: 0.471 (17)

Table 1
Selected geometric parameters (Å, °) for (I)[link]

C1A—N1A 1.323 (5)
C1A—Br1A 1.904 (4)
C5A—N1A 1.323 (5)
C5A—Br2A 1.905 (4)
C1B—N1B 1.317 (5)
C1B—Br1B 1.906 (4)
C5B—N1B 1.327 (5)
C5B—Br2B 1.898 (4)
N1A—C1A—C2A—C3A 1.1 (6)
Br1A—C1A—C2A—C6A 0.6 (6)

Compound (II)[link]

Crystal data
  • C7H7I2N

  • Mr = 358.94

  • Orthorhombic, P b c n

  • a = 7.6194 (3) Å

  • b = 14.6296 (6) Å

  • c = 8.1057 (2) Å

  • V = 903.53 (6) Å3

  • Z = 4

  • Dx = 2.639 Mg m−3

  • Mo Kα radiation

  • μ = 6.89 mm−1

  • T = 120 (2) K

  • Blade, colourless

  • 0.36 × 0.04 × 0.01 mm

Data collection
  • Bruker–Nonius KappaCCD diffractometer

  • φ and ω scans

  • Absorption correction: multi-scan (SADABS; Sheldrick, 2003[Sheldrick, G. M. (2003). SADABS. Version 2.10. University of Göttingen, Germany.]) Tmin = 0.191, Tmax = 0.934

  • 7765 measured reflections

  • 1049 independent reflections

  • 933 reflections with I > 2σ(I)

  • Rint = 0.035

  • θmax = 27.7°

Refinement
  • Refinement on F2

  • R[F2 > 2σ(F2)] = 0.021

  • wR(F2) = 0.047

  • S = 1.12

  • 1049 reflections

  • 48 parameters

  • H-atom parameters constrained

  • w = 1/[σ2(Fo2) + (0.0083P)2 + 2.3067P] where P = (Fo2 + 2Fc2)/3

  • (Δ/σ)max = 0.037

  • Δρmax = 0.60 e Å−3

  • Δρmin = −1.23 e Å−3

Table 2
Selected geometric parameters (Å, °) for (II)[link]

C1—N1 1.330 (4)
C1—I1 2.116 (3)
N1—C1—C2—C3 3.9 (4)
I1—C1—C2—C4 6.8 (4)

The unit cell of (I) is close to being metrically primitive tetra­gonal, but the data do not merge in this setting (Rmerge = 0.587). Compound (I)[link] was refined as a racemic twin using the TWIN and BASF instructions; the final value of the BASF parameter was 0.471 (17). 1623 Friedel pairs were merged in the final cycle of refinement. For both (I)[link] and (II)[link], H atoms were placed in geometrically assigned positions, with fixed bond lengths of 0.95 (CH) and 0.98 Å (CH3), and refined using a riding model, with Uiso(H) values of 1.2Ueq(CH) or 1.5Ueq(CH3) of the parent atom.

For both compounds, data collection: COLLECT (Hooft, 1998[Hooft, R. (1998). COLLECT. Nonius BV, Delft, The Netherlands.]); cell refinement: DENZO (Otwinowski & Minor, 1997[Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307-326. New York: Academic Press.]) and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SIR92 (Altomare et al., 1994[Altomare, A., Cascarano, G., Giacovazzo, C., Guagliardi, A., Burla, M. C., Polidori, G. & Camalli, M. (1994). J. Appl. Cryst. 27, 435.]) for (I) and SHELXS97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.]) for (II); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997[Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.]); molecular graphics: ORTEP-3 (Farrugia, 1997[Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.]); software used to prepare material for publication: PLATON (Spek, 2003[Spek, A. L. (2003). J. Appl. Cryst. 36, 7-13.]), WinGX (Farrugia, 1999[Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837-838.]) and enCIFer (Allen et al., 2004[Allen, F. H., Johnson, O., Shields, G. P., Smith, B. R. & Towler, M. (2004). J. Appl. Cryst. 37, 335-338.]).

Supporting information


Comment top

To date, 2,6-dihalo-3,5-dimethylpyridine compounds have not been structurally characterized. Indeed, the only known crystal structure of a 2,6-dihalo-3,5-dialkylpyridine was reported by Kasturi et al. (1992), although as part of a larger structure. Although several methods exist for synthesizing 2,6-dichloro-3,5-dimethylpyridine (Crouch & Lochte, 1943; Meerpoel et al., 1991; Gros et al., 2002), only one route to the dibromide (I) has been disclosed (see Scheme 1) (Dunn & Guillermic, 1988), and neither the difluoride nor the diiodide is known.

2,6-Dibromopyridine is commonly used in the synthesis of (CNC) 'pincer' ligands containing N-heterocyclic carbene moieties. It has been used to form (CNC) 'pincer' ligands (III) (Scheme 2) by quaternizing (III) with the appropriately substituted imidazole at high temperature, followed by deprotonation of the resulting imidazolium salt with a base (Danopoulos et al., 2002).

C—H activation at the 3- and 5-positions of the pyridine ring was seen with Fe and Ir complexes of (III) (R = 2,6-diisopropylphenyl, DiPP). To counter this, a 'pincer' ligand with blocking groups in the 3- and 5-positions on the pyridine ring was desired, which led to the use of (I) as a starting material. Despite the use of very high temperatures (>473 K) and lengthy reaction times (14 days), the reaction did not afford the doubly quaternized product. In order to overcome this obstacle, compound (II) with its weaker C—halogen bond was synthesized.

The asymmetric unit of (I) is presented in Fig. 1, and contains two independent molecules with similar geometric parameters (Table 1) and an overall Z of 8. The cell dimensions are close to tetragonal P42212, but the data do not merge; instead, the structure was refined in the orthorhombic spacegroup P212121. The molecular dimensions are unremarkable, but the structure is a racemic twin with a Flack (1983) parameter of 0.471 (17). The molecule is planar, and torsion angles of 0.6 (6)° (Br1—C1—C2—C6) and 1.1 (6)° (N1—C1—C2—C3) do not indicate any significant steric interactions between the Br atoms and the methyl groups.

Compound (II) is presented in Fig. 2. It is slightly deformed into a saddle shape due to the steric repulsion between the I atoms and the respective ortho methyl group. The extent of the distortion of the atoms bonded to the pyridine ring is indicated by a torsion angle of 6.8 (4)° (I1—C1—C2—C4), with atom I1 and the methyl group (C4) located on either side of the ring. Substituents trans to each other are distorted in the same direction above or below the ring, resulting in a saddle-shaped molecule. The saddle point can be found in the middle of the pyridine ring; this can be seen from the torsion angle for the atoms in the pyridine ring (N1—C1—C2—C3) being smaller, at 3.9 (4)°, than that for the atoms on the outside of the ring. The distortion of the ring can also be noted by the deviation out of the mean plane of all atoms in the ring, C2 being 0.021 (2) Å out of the plane.

The molecular dimensions of (II) are unremarkable. Although only three structurally characterized compounds with 2-iodopyridine groups exist, the C1—I1 bond length of 2.116 (3) Å is similar, as is the C1—N1 bond length of 1.330 (4) Å (Holmes et al., 2002; Saha et al., 2005).

A packing diagram of (I) is shown in Fig. 3. The only supramolecular interaction is face–face π stacking, with no face–edge π stacking. The molecules are arranged in alternating columns resulting in an X shape when viewed down the b axis. The dihedral angle between planes of the pyridine rings in successive molecules in a column is 72.69 (10)°.

Compound (II) exhibits the same supramolecular interactions as (I), with face–face π stacking the only supramolecular interaction. However, the molecules pack in a slightly different way, with alternating slanted columns of molecules resulting in a zigzag arrangement when viewed down the b axis (Fig. 4). Although 2,6-diiodopyridine exhibits both weak hydrogen-bonding interactions and weak halogen–halogen interactions (Holmes et al., 2002), neither is present in (II); the intermolecular I···I distance of 4.233 Å is greater than the sum of the van der Waals radii, estimated at 4.00 Å by Rowland & Taylor (1996).

Experimental top

Compound (I) was synthesized according to the method of Dunn & Guillermic (1988) in 64% yield and crystallized from ethanol. Compound (II) was synthesized via an aromatic Finkelstein reaction from the reaction of (I) (15.00 g, 56.6 mmol), anhydrous NaI (34.13 g, 227.7 mmol), CuI (1.08 g, 5.7 mmol) and DMEDA (define) (1.20 ml, 11.3 mmol) in refluxing 1,4-dioxane (250 ml) for 40 h in an inert atmosphere. After cooling, water (100 ml) was added, and the product was extracted into CH2Cl2, dried over MgSO4, filtered and concentrated in vacuo. The resulting pale-orange solid was recrystallized from ethanol, affording white crystals in 83% yield. 1H NMR (400 MHz, CDCl3): δ 7.20 (1H, s, Ar), 2.30 (6H, s, Me); 13C NMR (100.6 MHz, CDCl3): δ 138.69 (C, C2/6), 137.49 (CH, C4), 119.38 (C, C3/5), 25.20 (CH3, Me).

Refinement top

The unit cell of (I) is close to being metrically primitive tetragonal, but the data do not merge in this setting (Rmerge = 0.587). Compound (I) was refined as a racemic twin using the TWIN and BASF instructions; the final value of the BASF parameter was 0.471 (17). 1623 Friedel pairs were merged in the final cycle of refinement. For both (I) and (II), H atoms were placed in geometrically assigned positions with fixed bond lengths of 0.95 Å (CH) and 0.98 Å (CH3), and refined using a riding model with a Uiso(H) value of 1.2Ueq (CH) or 1.5Ueq (CH3) of the parent atom.

Computing details top

For both compounds, data collection: COLLECT (Hooft, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT; data reduction: DENZO and COLLECT. Program(s) used to solve structure: SIR92 (Altomare et al., 1994) for (I); SHELXS97 (Sheldrick, 1997) for (II). For both compounds, program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: PLATON (Spek, 2003), WinGX (Farrugia, 1999) and enCIFer (Allen et al., 2004).

Figures top
[Figure 1] Fig. 1. The two independent molecules of (I) in the asymmetric unit, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
[Figure 2] Fig. 2. A representation of (II), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted.
[Figure 3] Fig. 3. The packing of (I).
[Figure 4] Fig. 4. The packing of (II).
(I) 2,6-dibromo-3,5-dimethylpyridine top
Crystal data top
C7H7Br2NF(000) = 1008
Mr = 264.96Dx = 2.115 Mg m3
Orthorhombic, P212121Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2ac 2abCell parameters from 2177 reflections
a = 10.5429 (3) Åθ = 2.9–27.5°
b = 12.4821 (4) ŵ = 9.67 mm1
c = 12.6458 (3) ÅT = 120 K
V = 1664.16 (8) Å3Fragment, colourless
Z = 80.10 × 0.10 × 0.02 mm
Data collection top
Bruker–Nonius KappaCCD
diffractometer
2175 independent reflections
Radiation source: Bruker-Nonius FR591 rotating anode1984 reflections with I > 2σ(I)
10cm confocal mirrors monochromatorRint = 0.043
Detector resolution: 9.091 pixels mm-1θmax = 27.5°, θmin = 3.6°
ϕ and ω scansh = 1313
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
k = 1116
Tmin = 0.397, Tmax = 0.826l = 1616
14709 measured reflections
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.026H-atom parameters constrained
wR(F2) = 0.049 w = 1/[σ2(Fo2) + (0.0144P)2 + 1.0475P]
where P = (Fo2 + 2Fc2)/3
S = 1.08(Δ/σ)max = 0.022
2175 reflectionsΔρmax = 0.46 e Å3
186 parametersΔρmin = 0.50 e Å3
0 restraintsAbsolute structure: Flack (1983), 1623 Friedel pairs
Primary atom site location: structure-invariant direct methodsAbsolute structure parameter: 0.471 (17)
Crystal data top
C7H7Br2NV = 1664.16 (8) Å3
Mr = 264.96Z = 8
Orthorhombic, P212121Mo Kα radiation
a = 10.5429 (3) ŵ = 9.67 mm1
b = 12.4821 (4) ÅT = 120 K
c = 12.6458 (3) Å0.10 × 0.10 × 0.02 mm
Data collection top
Bruker–Nonius KappaCCD
diffractometer
2175 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
1984 reflections with I > 2σ(I)
Tmin = 0.397, Tmax = 0.826Rint = 0.043
14709 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.026H-atom parameters constrained
wR(F2) = 0.049Δρmax = 0.46 e Å3
S = 1.08Δρmin = 0.50 e Å3
2175 reflectionsAbsolute structure: Flack (1983), 1623 Friedel pairs
186 parametersAbsolute structure parameter: 0.471 (17)
0 restraints
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.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

The structure was refined as a racemic twin and the component scale factor refined to a value of 0.471. 1623 Friedel pairs were merged in the final cycle of refinement.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C1A0.1899 (4)0.7712 (3)0.7014 (3)0.0181 (9)
C2A0.1864 (4)0.6619 (4)0.6807 (3)0.0205 (9)
C3A0.2526 (4)0.6298 (3)0.5909 (3)0.0205 (9)
H3A0.25380.55590.57300.025*
C4A0.3174 (4)0.7022 (3)0.5261 (3)0.0180 (9)
C5A0.3091 (4)0.8087 (3)0.5581 (3)0.0180 (9)
C6A0.1170 (4)0.5831 (3)0.7493 (3)0.0245 (9)
H6A10.12360.51140.71830.037*
H6A20.02750.60370.75420.037*
H6A30.15470.58280.82010.037*
C7A0.3902 (4)0.6659 (4)0.4309 (3)0.0275 (10)
H7A10.35910.70380.36810.041*
H7A20.37860.58860.42130.041*
H7A30.48050.68150.44090.041*
N1A0.2481 (3)0.8439 (3)0.6427 (3)0.0176 (7)
Br1A0.10517 (4)0.82680 (4)0.82250 (3)0.02592 (11)
Br2A0.39131 (4)0.91662 (4)0.47668 (3)0.02766 (11)
C1B0.6757 (4)0.8022 (3)0.8098 (3)0.0192 (9)
C2B0.6780 (4)0.6948 (3)0.7797 (3)0.0208 (9)
C3B0.7527 (4)0.6285 (3)0.8416 (3)0.0208 (9)
H3B0.75750.55440.82460.025*
C4B0.8210 (4)0.6670 (4)0.9279 (3)0.0178 (9)
C5B0.8085 (4)0.7769 (3)0.9468 (3)0.0199 (9)
C6B0.6016 (4)0.6529 (4)0.6877 (3)0.0278 (10)
H6B10.51100.66160.70260.042*
H6B20.62060.57680.67700.042*
H6B30.62360.69300.62370.042*
C7B0.9028 (4)0.5958 (4)0.9942 (3)0.0294 (10)
H7B10.99110.61980.98960.044*
H7B20.89640.52190.96840.044*
H7B30.87440.59901.06790.044*
N1B0.7377 (3)0.8437 (3)0.8905 (3)0.0191 (8)
Br1B0.57822 (4)0.90160 (4)0.72923 (4)0.03317 (13)
Br2B0.89866 (4)0.84133 (4)1.06013 (3)0.02859 (12)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C1A0.015 (2)0.022 (2)0.018 (2)0.0011 (18)0.0010 (17)0.0017 (17)
C2A0.016 (2)0.018 (2)0.027 (2)0.0031 (18)0.0048 (19)0.001 (2)
C3A0.021 (2)0.015 (2)0.025 (2)0.0012 (17)0.007 (2)0.0015 (18)
C4A0.016 (2)0.018 (2)0.020 (2)0.0006 (17)0.0034 (18)0.0010 (18)
C5A0.015 (2)0.019 (2)0.021 (2)0.0012 (17)0.0004 (18)0.0066 (18)
C6A0.024 (2)0.021 (2)0.029 (2)0.001 (2)0.004 (2)0.005 (2)
C7A0.030 (2)0.028 (2)0.025 (2)0.012 (2)0.000 (2)0.0033 (19)
N1A0.0127 (17)0.0200 (19)0.0202 (16)0.0004 (15)0.0018 (15)0.0009 (15)
Br1A0.0282 (2)0.0251 (2)0.0245 (2)0.0021 (2)0.0056 (2)0.00355 (18)
Br2A0.0293 (2)0.0232 (2)0.0305 (2)0.0037 (2)0.0062 (2)0.00665 (19)
C1B0.016 (2)0.020 (2)0.022 (2)0.0018 (17)0.0042 (18)0.0073 (18)
C2B0.020 (2)0.022 (2)0.021 (2)0.0025 (18)0.0051 (19)0.0009 (18)
C3B0.024 (2)0.014 (2)0.024 (2)0.0034 (18)0.005 (2)0.0000 (17)
C4B0.015 (2)0.017 (2)0.021 (2)0.0012 (18)0.0045 (17)0.0014 (19)
C5B0.020 (2)0.018 (2)0.022 (2)0.0059 (18)0.0023 (19)0.0025 (18)
C6B0.033 (3)0.029 (2)0.021 (2)0.008 (2)0.002 (2)0.003 (2)
C7B0.028 (2)0.025 (2)0.035 (2)0.003 (2)0.001 (2)0.008 (2)
N1B0.0198 (18)0.0138 (17)0.0236 (18)0.0016 (15)0.0032 (16)0.0030 (16)
Br1B0.0324 (3)0.0304 (3)0.0366 (2)0.0056 (2)0.0074 (2)0.0091 (2)
Br2B0.0291 (3)0.0310 (3)0.0257 (2)0.0058 (2)0.0039 (2)0.00555 (19)
Geometric parameters (Å, º) top
C1A—N1A1.323 (5)C1B—N1B1.317 (5)
C1A—C2A1.389 (6)C1B—C2B1.394 (6)
C1A—Br1A1.904 (4)C1B—Br1B1.906 (4)
C2A—C3A1.392 (6)C2B—C3B1.385 (6)
C2A—C6A1.501 (6)C2B—C6B1.509 (6)
C3A—C4A1.399 (6)C3B—C4B1.394 (6)
C3A—H3A0.9500C3B—H3B0.9500
C4A—C5A1.391 (6)C4B—C5B1.399 (6)
C4A—C7A1.498 (6)C4B—C7B1.496 (6)
C5A—N1A1.323 (5)C5B—N1B1.327 (5)
C5A—Br2A1.905 (4)C5B—Br2B1.898 (4)
C6A—H6A10.9800C6B—H6B10.9800
C6A—H6A20.9800C6B—H6B20.9800
C6A—H6A30.9800C6B—H6B30.9800
C7A—H7A10.9800C7B—H7B10.9800
C7A—H7A20.9800C7B—H7B20.9800
C7A—H7A30.9800C7B—H7B30.9800
N1A—C1A—C2A125.5 (4)N1B—C1B—C2B125.5 (4)
N1A—C1A—Br1A114.8 (3)N1B—C1B—Br1B115.2 (3)
C2A—C1A—Br1A119.8 (3)C2B—C1B—Br1B119.3 (3)
C1A—C2A—C3A115.0 (4)C3B—C2B—C1B115.5 (4)
C1A—C2A—C6A123.2 (4)C3B—C2B—C6B122.1 (4)
C3A—C2A—C6A121.8 (4)C1B—C2B—C6B122.3 (4)
C2A—C3A—C4A122.5 (4)C2B—C3B—C4B122.0 (4)
C2A—C3A—H3A118.7C2B—C3B—H3B119.0
C4A—C3A—H3A118.7C4B—C3B—H3B119.0
C5A—C4A—C3A114.5 (4)C3B—C4B—C5B115.1 (4)
C5A—C4A—C7A123.7 (4)C3B—C4B—C7B122.1 (4)
C3A—C4A—C7A121.7 (4)C5B—C4B—C7B122.8 (4)
N1A—C5A—C4A125.7 (4)N1B—C5B—C4B125.3 (4)
N1A—C5A—Br2A115.0 (3)N1B—C5B—Br2B114.9 (3)
C4A—C5A—Br2A119.3 (3)C4B—C5B—Br2B119.8 (3)
C2A—C6A—H6A1109.5C2B—C6B—H6B1109.5
C2A—C6A—H6A2109.5C2B—C6B—H6B2109.5
H6A1—C6A—H6A2109.5H6B1—C6B—H6B2109.5
C2A—C6A—H6A3109.5C2B—C6B—H6B3109.5
H6A1—C6A—H6A3109.5H6B1—C6B—H6B3109.5
H6A2—C6A—H6A3109.5H6B2—C6B—H6B3109.5
C4A—C7A—H7A1109.5C4B—C7B—H7B1109.5
C4A—C7A—H7A2109.5C4B—C7B—H7B2109.5
H7A1—C7A—H7A2109.5H7B1—C7B—H7B2109.5
C4A—C7A—H7A3109.5C4B—C7B—H7B3109.5
H7A1—C7A—H7A3109.5H7B1—C7B—H7B3109.5
H7A2—C7A—H7A3109.5H7B2—C7B—H7B3109.5
C1A—N1A—C5A116.8 (4)C1B—N1B—C5B116.6 (4)
N1A—C1A—C2A—C3A1.1 (6)N1B—C1B—C2B—C3B0.0 (6)
Br1A—C1A—C2A—C3A179.3 (3)Br1B—C1B—C2B—C3B179.0 (3)
N1A—C1A—C2A—C6A179.0 (4)N1B—C1B—C2B—C6B178.4 (4)
Br1A—C1A—C2A—C6A0.6 (6)Br1B—C1B—C2B—C6B2.5 (5)
C1A—C2A—C3A—C4A0.2 (6)C1B—C2B—C3B—C4B0.1 (6)
C6A—C2A—C3A—C4A179.9 (4)C6B—C2B—C3B—C4B178.6 (4)
C2A—C3A—C4A—C5A0.7 (6)C2B—C3B—C4B—C5B0.2 (6)
C2A—C3A—C4A—C7A178.8 (4)C2B—C3B—C4B—C7B179.4 (4)
C3A—C4A—C5A—N1A0.9 (6)C3B—C4B—C5B—N1B0.6 (6)
C7A—C4A—C5A—N1A178.6 (4)C7B—C4B—C5B—N1B179.8 (4)
C3A—C4A—C5A—Br2A179.4 (3)C3B—C4B—C5B—Br2B178.8 (3)
C7A—C4A—C5A—Br2A1.1 (6)C7B—C4B—C5B—Br2B0.4 (6)
C2A—C1A—N1A—C5A0.9 (6)C2B—C1B—N1B—C5B0.4 (6)
Br1A—C1A—N1A—C5A179.5 (3)Br1B—C1B—N1B—C5B178.7 (3)
C4A—C5A—N1A—C1A0.2 (6)C4B—C5B—N1B—C1B0.7 (6)
Br2A—C5A—N1A—C1A179.9 (3)Br2B—C5B—N1B—C1B178.7 (3)
(II) 2,6-diiodo-3,5-dimethylpyridine top
Crystal data top
C7H7I2NF(000) = 648
Mr = 358.94Dx = 2.639 Mg m3
Orthorhombic, PbcnMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2n 2abCell parameters from 1217 reflections
a = 7.6194 (3) Åθ = 2.9–27.5°
b = 14.6296 (6) ŵ = 6.89 mm1
c = 8.1057 (2) ÅT = 120 K
V = 903.53 (6) Å3Blade, colourless
Z = 40.36 × 0.04 × 0.01 mm
Data collection top
Bruker–Nonius KappaCCD
diffractometer
1049 independent reflections
Radiation source: Bruker-Nonius FR591 rotating anode933 reflections with I > 2σ(I)
10cm confocal mirrors monochromatorRint = 0.035
Detector resolution: 9.091 pixels mm-1θmax = 27.7°, θmin = 3.0°
ϕ and ω scansh = 99
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
k = 1718
Tmin = 0.191, Tmax = 0.934l = 810
7765 measured reflections
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)] = 0.021Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.047H-atom parameters constrained
S = 1.12 w = 1/[σ2(Fo2) + (0.0083P)2 + 2.3067P]
where P = (Fo2 + 2Fc2)/3
1049 reflections(Δ/σ)max = 0.037
48 parametersΔρmax = 0.60 e Å3
0 restraintsΔρmin = 1.23 e Å3
Crystal data top
C7H7I2NV = 903.53 (6) Å3
Mr = 358.94Z = 4
Orthorhombic, PbcnMo Kα radiation
a = 7.6194 (3) ŵ = 6.89 mm1
b = 14.6296 (6) ÅT = 120 K
c = 8.1057 (2) Å0.36 × 0.04 × 0.01 mm
Data collection top
Bruker–Nonius KappaCCD
diffractometer
1049 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2003)
933 reflections with I > 2σ(I)
Tmin = 0.191, Tmax = 0.934Rint = 0.035
7765 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0210 restraints
wR(F2) = 0.047H-atom parameters constrained
S = 1.12Δρmax = 0.60 e Å3
1049 reflectionsΔρmin = 1.23 e Å3
48 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.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.6231 (4)0.1112 (2)0.6711 (4)0.0170 (6)
C20.6355 (4)0.0162 (2)0.6694 (4)0.0148 (6)
C30.50000.0294 (3)0.75000.0176 (9)
H30.50000.09430.75000.021*
C40.7841 (4)0.0352 (2)0.5916 (4)0.0225 (7)
H4A0.78740.02210.47300.034*
H4B0.76720.10100.60850.034*
H4C0.89510.01620.64220.034*
N10.50000.1586 (2)0.75000.0176 (8)
I10.80626 (3)0.190295 (14)0.53659 (3)0.02337 (10)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0135 (15)0.0182 (15)0.0192 (15)0.0036 (12)0.0005 (13)0.0010 (12)
C20.0150 (15)0.0159 (14)0.0136 (14)0.0007 (12)0.0047 (12)0.0007 (11)
C30.019 (2)0.016 (2)0.018 (2)0.0000.0034 (18)0.000
C40.0203 (17)0.0221 (16)0.0250 (17)0.0032 (13)0.0019 (14)0.0051 (14)
N10.0169 (19)0.0153 (17)0.0208 (19)0.0000.0012 (16)0.000
I10.02093 (15)0.01828 (14)0.03090 (16)0.00283 (8)0.00815 (8)0.00004 (9)
Geometric parameters (Å, º) top
C1—N11.330 (4)C3—H30.9500
C1—C21.393 (4)C4—H4A0.9800
C1—I12.116 (3)C4—H4B0.9800
C2—C31.391 (4)C4—H4C0.9800
C2—C41.499 (4)
N1—C1—C2124.9 (3)C2i—C3—H3118.6
N1—C1—I1115.3 (2)C2—C4—H4A109.5
C2—C1—I1119.7 (2)C2—C4—H4B109.5
C3—C2—C1115.0 (3)H4A—C4—H4B109.5
C3—C2—C4121.2 (3)C2—C4—H4C109.5
C1—C2—C4123.8 (3)H4A—C4—H4C109.5
C2—C3—C2i122.8 (4)H4B—C4—H4C109.5
C2—C3—H3118.6C1i—N1—C1117.2 (4)
N1—C1—C2—C33.9 (4)C1—C2—C3—C2i1.8 (4)
I1—C1—C2—C3174.71 (16)C4—C2—C3—C2i176.7 (3)
N1—C1—C2—C4174.6 (3)C2—C1—N1—C1i2.1 (2)
I1—C1—C2—C46.8 (4)I1—C1—N1—C1i176.6 (2)
Symmetry code: (i) x+1, y, z+3/2.

Experimental details

(I)(II)
Crystal data
Chemical formulaC7H7Br2NC7H7I2N
Mr264.96358.94
Crystal system, space groupOrthorhombic, P212121Orthorhombic, Pbcn
Temperature (K)120120
a, b, c (Å)10.5429 (3), 12.4821 (4), 12.6458 (3)7.6194 (3), 14.6296 (6), 8.1057 (2)
V3)1664.16 (8)903.53 (6)
Z84
Radiation typeMo KαMo Kα
µ (mm1)9.676.89
Crystal size (mm)0.10 × 0.10 × 0.020.36 × 0.04 × 0.01
Data collection
DiffractometerBruker–Nonius KappaCCD
diffractometer
Bruker–Nonius KappaCCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2003)
Multi-scan
(SADABS; Sheldrick, 2003)
Tmin, Tmax0.397, 0.8260.191, 0.934
No. of measured, independent and
observed [I > 2σ(I)] reflections
14709, 2175, 1984 7765, 1049, 933
Rint0.0430.035
(sin θ/λ)max1)0.6490.653
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.026, 0.049, 1.08 0.021, 0.047, 1.12
No. of reflections21751049
No. of parameters18648
H-atom treatmentH-atom parameters constrainedH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.46, 0.500.60, 1.23
Absolute structureFlack (1983), 1623 Friedel pairs?
Absolute structure parameter0.471 (17)?

Computer programs: COLLECT (Hooft, 1998), DENZO (Otwinowski & Minor, 1997) and COLLECT, DENZO and COLLECT, SIR92 (Altomare et al., 1994), SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ORTEP-3 (Farrugia, 1997), PLATON (Spek, 2003), WinGX (Farrugia, 1999) and enCIFer (Allen et al., 2004).

Selected geometric parameters (Å, º) for (I) top
C1A—N1A1.323 (5)C1B—N1B1.317 (5)
C1A—Br1A1.904 (4)C1B—Br1B1.906 (4)
C5A—N1A1.323 (5)C5B—N1B1.327 (5)
C5A—Br2A1.905 (4)C5B—Br2B1.898 (4)
N1A—C1A—C2A—C3A1.1 (6)Br1A—C1A—C2A—C6A0.6 (6)
Selected geometric parameters (Å, º) for (II) top
C1—N11.330 (4)C1—I12.116 (3)
N1—C1—C2—C33.9 (4)I1—C1—C2—C46.8 (4)
 

Acknowledgements

The author acknowledges the financial support of the EPSRC and thanks Professor Mike Hursthouse for use of the National Crystallography Service diffractometers. Additional thanks go to Drs Andreas Danopoulos, Mark Light and Joseph Wright for their invaluable assistance in compiling this manuscript.

References

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