The two title compounds are isomers of C6H3ClN2 containing a pyridine ring, a nitrile group, and a chloro substituent. The mol-ecules of each compound pack together in the solid state with offset face-to-face π-stacking, and inter-molecular C-H⋯Nnitrile and C-H⋯Npyridine inter-actions. 4-Chloro-pyridine-2-carbo-nitrile, (I), exhibits pairwise centrosymmetric head-to-head C-H⋯Nnitrile and C-H⋯Npyridine inter-actions, forming one-dimensional chains, which are π-stacked in an offset face-to-face fashion. The inter-molecular packing of the isomeric 6-chloro-pyridine-2-carbo-nitrile, (II), which differs only in the position of the chloro substituent on the pyridine ring, exhibits head-to-tail C-H⋯Nnitrile and C-H⋯Npyridine inter-actions, forming two-dimensional sheets which are π-stacked in an offset face-to-face fashion. In contrast to (I), the offset face-to-face π-stacking in (II) is formed between mol-ecules with alternating orientations of the chloro and nitrile substituents.
The two title compounds are isomers of C6H3ClN2 containing a pyridine ring, a nitrile group, and a chloro substituent. The mol-ecules of each compound pack together in the solid state with offset face-to-face π-stacking, and inter-molecular C-H⋯Nnitrile and C-H⋯Npyridine inter-actions. 4-Chloro-pyridine-2-carbo-nitrile, (I), exhibits pairwise centrosymmetric head-to-head C-H⋯Nnitrile and C-H⋯Npyridine inter-actions, forming one-dimensional chains, which are π-stacked in an offset face-to-face fashion. The inter-molecular packing of the isomeric 6-chloro-pyridine-2-carbo-nitrile, (II), which differs only in the position of the chloro substituent on the pyridine ring, exhibits head-to-tail C-H⋯Nnitrile and C-H⋯Npyridine inter-actions, forming two-dimensional sheets which are π-stacked in an offset face-to-face fashion. In contrast to (I), the offset face-to-face π-stacking in (II) is formed between mol-ecules with alternating orientations of the chloro and nitrile substituents.
Chloropyridinecarbonitriles are members of a class of compounds containing the ubiquitous six-membered nitrogen-containing heterocycle pyridine. The pyridine heterocycle features prominently in many valuable synthetic compounds (Bull et al., 2012 ▸). While several of the ten possible isomers of chloropyridinecarbonitrile are commercially available, none of their crystal structures have been reported in the literature, although the structure of 2-chloropyridine-4-carbonitrile has been deposited in the Cambridge Structural Database (Version 5.31, June 2015 with updates; Groom & Allen, 2014 ▸) as a private communication (refcode LOBVIJ). The title compounds represent two isomers of chloropyridine-2-carbonitrile, namely 4-chloropyridine-2-carbonitrile, (I), and 6-chloropyridine-2-carbonitrile, (II). In both cases, the intramolecular packing exhibits weak intermolecular C—H⋯N interactions, which are well documented (Desiraju & Steiner, 1999 ▸), as well as aromatic π-stacking interactions (Hunter & Saunders, 1990 ▸; Lueckheide et al., 2013 ▸).4-Chloron class="Chemical">pyridine-2-carbonitrile, (I), may be synthesized by the cyanation of 4-chloropyridine N-oxide with trimethylsilanecarbonitrile (TMSCN) (Sakamoto et al., 1985 ▸). More recently, it has been shown that (I) can be prepared in a one-step process from 4-nitropyridine N-oxide with ethyl chloroformate and TMSCN (Veerareddy et al., 2011 ▸). (I) has found use as a building block for a family of chiral catalysts (Busto et al., 2005 ▸).
6-Chloropyridine-2-carbonitrile, (II), may be synthesized by the vapor-phase chlorination of 2-cyanopyridine (Ruetman & Taplin, 1971 ▸), or by the cyanation of 2-chloropyridine N-oxide hydrochloride with sodium cyanide (Tsukamoto et al., 2009 ▸). This compound has found applications in the preparation of biologically active or pharmaceutical compounds, such as heteroaromatic carboxylic acids (Kiener et al., 1996 ▸) and 2-arylamino-substituted pyridinyl nitriles (Guo et al., 2013 ▸).
Structural commentary
4-Chloron class="Chemical">pyridine-2-carbonitrile, (I) (Fig. 1 ▸), and 6-chloropyridine-2-carbonitrile, (II) (Fig. 2 ▸), exhibit similar metrical parameters. The nitrile bond length C1—N2 of 1.156 (3) Å in (I) and 1.138 (2) Å in (II) are similar to those seen in the related structure 2-chloropyridine-4-carbonitrile, with the nitrile C≡N distance is 1.141 Å (CSD refcode LOBVIJ). The nitrile bond lengths in 2- and 3-cyanopyridine [1.145 (2) and 1.150 (1) Å, respectively; Kubiak et al., 2002 ▸] and 4-cyanopyridine [1.137 (8) Å; Laing et al., 1971 ▸] are also similar to those found in the title compounds. The aromatic chlorine bond lengths, viz. C4—Cl and C6—Cl of 1.740 (3) Å in (I) and 1.740 (1) Å in (II), are similar to those seen in the related structures 2-chloropyridine-4-carbonitrile (1.732 Å; CSD refcode LOBVIJ), 2- and 3-chloropyridine hydrochloride (1.710 and 1.727 Å, respectively; Freytag & Jones, 2001 ▸), and 4-chloropyridine hydrochloride (1.730 Å; Freytag et al., 1999 ▸).
Figure 1
A view of 4-chloropyridine-2-carbonitrile, (I), with the atom-numbering scheme. Displacement ellipsoids are shown at the 50% probability level.
Figure 2
A view of 6-chloropyridine-2-carbonitrile, (II), with the atom-numbering scheme. Displacement ellipsoids are shown at the 50% probability level.
Both (I) and (II) are almost planar, with r.m.s. deviations from the mean planes of all non-H atoms of 0.0077 and 0.0161 Å, respectively. As may be expected, the heterocyclic rings are slightly wedge shaped as the pyridine C—N bond are shorter than the C—C bonds in each aromatic ring. In (I), the ring C2—N1 and C6—N1 bond lengths of 1.361 (3) and 1.350 (3) Å are similar to those found in (II) of 1.349 (1) and 1.322 (1) Å. The average ring C—C bond lengths are 1.403 (2) Å in (I) and 1.391 (5) Å in (II). The lengths are comparable to those found in the parent compound, pyridine, with C—N of 1.34 Å and C—C of 1.38 Å (Mootz & Wussow, 1981 ▸), and in the related structure 2-chloropyridine-4-carbonitrile, with C—N bond lengths of 1.328 and 1.340 Å, and an average C—C bond length of 1.377 (7) Å (CSD refcode LOBVIJ).
Supramolecular features
The molecules of each of the title compounds pack together in the solid state with π-stacking, and intermolecular C—H⋯Nnitrile and C—H⋯Npyridine interactions, however, the packing motifs are unique, and also different than those found in the related structure 2-chloropyridine-4-carbonitrile (CSD refcode LOBVIJ). For a discussion of weak C—H⋯X interactions, see Desiraju & Steiner (1999 ▸).The molecules of (I) pack together in the solid state via alternating centrosymmetric head-to-head intermolecular C—H⋯Nnitrile and C—H⋯Npyridine interactions to form a one-dimensional zigzag chain (Fig. 3 ▸ and Table 1 ▸). The chains further pack together through offset face-to-face π-stacking (Fig. 4 ▸). This π-stacking is characterized by a centroid-to-centroid distance of 3.813 (5) Å, a plane-to-centroid distance of 3.454 (4) Å, and a ring offset or ring-slippage distance of 1.615 (3) Å (Hunter & Saunders, 1990 ▸; Lueckheide et al., 2013 ▸). The π-stacking in (I) is similar to that found in the related unpublished structure 2-chloropyridine-4-carbonitrile (CSD refcode LOBVIJ).
Figure 3
A view of the intermolecular C—H⋯Nnitrile and C—H⋯Npyridine contacts (dashed lines) in 4-chloropyridine-2-carbonitrile, (I), that form a one-dimensional chain. [Symmetry codes: (i) −x − 1, −y + 1, −z; (ii) −x, −y + 1, −z + 1.]
Table 1
Hydrogen-bond geometry (Å, °) for (I)
D—H⋯A
D—H
H⋯A
D⋯A
D—H⋯A
C3—H3A⋯N2i
0.95
2.64
3.462 (5)
146
C6—H6A⋯N1ii
0.95
2.75
3.493 (5)
136
Symmetry codes: (i) ; (ii) .
Figure 4
A view of the offset face-to-face π-stacking in 4-chloropyridine-2-carbonitrile, (I), with the thick dashed line indicating a centroid-to-centroid interaction. [Symmetry code: (i) x + 1, y, z.]
In contrast to (I), the molecules of (II) pack together via head-to-tail C—H⋯Nnitrile and C—H⋯Npyridine interactions to form two-dimensional sheets that are parallel to the (001) plane (Fig. 5 ▸ and Table 2 ▸). As in (I), the parallel planes of the molecules engage in offset face-to-face π-stacking between the two-dimensional sheets, which is characterized by a ring centroid-to-centroid distance of 3.7204 (7) Å, a centroid-to-plane distance of 3.41 (1) Å, and a ring-offset slippage of 1.48 (2) Å (Fig. 6 ▸). However, in constrast to (I), the π-stacking in (II) is formed between molecules with alternating orientations of the chloro and nitrile substituents with a plane-to-plane angle of 0.23 (5)°. For a more thorough description of π-stacking, see Hunter & Saunders (1990 ▸) and Lueckheide et al. (2013 ▸).
Figure 5
A view of the intermolecular C—H⋯Nnitrile and C—H⋯Npyridine contacts (dashed lines) in 6-chloropyridine-2-carbonitrile, (I), that form a two-dimensional sheet. [Symmetry codes: (i) x − 1, y, z; (ii) −x + , y − , −z + .]
Table 2
Hydrogen-bond geometry (Å, °) for (II)
D—H⋯A
D—H
H⋯A
D⋯A
D—H⋯A
C4—H4A⋯N1i
0.95
2.49
3.4099 (15)
164
C5—H5A⋯N2ii
0.95
2.70
3.5651 (17)
152
Symmetry codes: (i) ; (ii) .
Figure 6
A view of the alternating offset face-to-face π-stacking in 6-chloropyridine-2-carbonitrile, (II), with the thick dashed line indicating a centroid-to-centroid interaction. [Symmetry code: (i) x + , −y + , z + .]
Notably, there are no significant Cl⋯Cl contacts in (I) or (II), in contrast to 2-chloropyridine-4-carbonitrile (CSD refcode LOBVIJ), which exhibits a Cl⋯Cl contact distance of 3.371 Å that is shorter than the sum of the van der Waals radius of chlorine (3.5 Å; Bondi, 1964 ▸). For more information on halide–halide contacts, see Pedireddi et al. (1994 ▸) and Jelsch et al. (2015 ▸).
Synthesis and crystallization
4-Chloron class="Chemical">pyridine-2-carbonitrile (97%) and 6-chloropyridine-2-carbonitrile (96%) were purchased from Aldrich Chemical Company, USA. 4-Chloropyridine-2-carbonitrile was recrystallized from 95% ethanol.
Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. H atoms on C atoms were included in calculated positions and refined using a riding model, with C—H = 0.95 Å and U
iso(H) = 1.2U
eq(C) of the aryl C atoms.
Table 3
Experimental details
(I)
(II)
Crystal data
Chemical formula
C6H3ClN2
C6H3ClN2
Mr
138.55
138.55
Crystal system, space group
Monoclinic, P21/n
Monoclinic, P21/n
Temperature (K)
125
125
a, b, c (Å)
3.813 (5), 14.047 (19), 11.356 (15)
6.1739 (15), 15.238 (4), 7.0123 (18)
β (°)
96.806 (19)
112.492 (4)
V (Å3)
604.0 (14)
609.5 (3)
Z
4
4
Radiation type
Mo Kα
Mo Kα
μ (mm−1)
0.52
0.52
Crystal size (mm)
0.25 × 0.10 × 0.04
0.20 × 0.15 × 0.03
Data collection
Diffractometer
Bruker APEXII CCD
Bruker APEXII CCD
Absorption correction
Multi-scan (SADABS; Bruker, 2013 ▸)
Multi-scan (SADABS; Bruker, 2013 ▸)
Tmin, Tmax
0.67, 0.98
0.82, 0.98
No. of measured, independent and observed [I > 2σ(I)] reflections
12191, 1852, 1498
15460, 1868, 1657
Rint
0.063
0.031
(sin θ/λ)max (Å−1)
0.715
0.717
Refinement
R[F2 > 2σ(F2)], wR(F2), S
0.050, 0.135, 1.12
0.028, 0.082, 1.09
No. of reflections
1852
1868
No. of parameters
82
82
H-atom treatment
H-atom parameters constrained
H-atom parameters constrained
Δρmax, Δρmin (e Å−3)
0.53, −0.37
0.48, −0.19
Computer programs: APEX2 and SAINT (Bruker, 2013 ▸), SHELXS2014 and SHELXTL2014 (Sheldrick, 2008 ▸), SHELXL2014 (Sheldrick, 2015 ▸), OLEX2 (Dolomanov et al., 2009 ▸) and Mercury (Macrae et al., 2008 ▸).
Crystal structure: contains datablock(s) global, I, II. DOI: 10.1107/S2056989015011767/rz5161sup1.cifStructure factors: contains datablock(s) I. DOI: 10.1107/S2056989015011767/rz5161Isup2.hklStructure factors: contains datablock(s) II. DOI: 10.1107/S2056989015011767/rz5161IIsup3.hklClick here for additional data file.Supporting information file. DOI: 10.1107/S2056989015011767/rz5161Isup4.cmlClick here for additional data file.Supporting information file. DOI: 10.1107/S2056989015011767/rz5161IIsup5.cmlCCDC references: 1407613, 1407612Additional supporting information: crystallographic information; 3D view; checkCIF report
Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.050
H-atom parameters constrained
wR(F2) = 0.135
w = 1/[σ2(Fo2) + (0.0646P)2 + 0.4268P] where P = (Fo2 + 2Fc2)/3
S = 1.12
(Δ/σ)max < 0.001
1852 reflections
Δρmax = 0.53 e Å−3
82 parameters
Δρmin = −0.37 e Å−3
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.
Hydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.028
H-atom parameters constrained
wR(F2) = 0.082
w = 1/[σ2(Fo2) + (0.0424P)2 + 0.1697P] where P = (Fo2 + 2Fc2)/3
S = 1.09
(Δ/σ)max = 0.001
1868 reflections
Δρmax = 0.48 e Å−3
82 parameters
Δρmin = −0.19 e Å−3
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.