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Hindered rotation about the partial double C—N bonds between the amine and pyridine moieties in the title mol­ecule, C16H14N4, results in two different conformations of the N-aryl-2-amino­pyridine units. One, assuming an E conformation, is involved in a pair of N—H...N hydrogen bonds that generate a centrosymmetric R_2^2(8) motif. The second, adopting a Z conformation, is not engaged in any hydrogen bonding and is flattened, the dihedral angle between the benzene and pyridine rings being 12.07 (7)°. This conformation is stabilized by an intramolecular C—H...N interaction [C...N = 2.9126 (19) Å, H...N = 2.31 Å and C—H...N = 120°].

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010400068X/av1160sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S010827010400068X/av1160Isup2.hkl
Contains datablock I

CCDC reference: 235352

Comment top

N,N'-Bis(2-pyridyl)aryldiamines are versatile building blocks for syntheses of extended supramolecular arrays (Bensemann et al., 2002; Gdaniec et al., 2002; Bensemann et al., 2003). Bearing two self-complementary 2-aminopyridine units, these molecules are able to form in crystals one-dimensional hydrogen-bonding networks using the cyclic R22(8) motif, or to assemble via a catemeric C(4) motif into one-, two- or even three-dimensional networks (Bensemann et al., 2002). In the first case, the N-aryl-2-aminopyridine units have to assume the E conformation, whereas the C(4) motif requires the units to adopt the Z conformation. A search of Cambridge Structural Database (CSD; Version 5.24, 272066 entries, plus three 2003 updates; Allen, 2002) revealed that the mean values of the dihedral angles between pyridine and aryl planes in the N-aryl-2-aminopyridine moieties, which are involved in hydrogen bonding as H-atom donor and H-atom acceptor, are similar for the E and Z forms [51 (7) and 47 (3)°, respectively].

However, in contrast to the E form, which cannot be planar for steric reason, the N-aryl-2-aminopyridine unit in the Z form is also able to adopt a conformation with nearly coplanar pyridine and aryl rings. In this arrangement, the pyridine N atom, being a hydrogen-bond acceptor, is blocked by the intramolecular C—H···N interaction and thus the N-aryl-2-aminopyridine unit can act only as an NH donor in the intermolecular hydrogen bonding. Among symmetrical N,N'-bis(2-pyridyl)aryldiamines studied so far, E,E or Z,Z conformations have been observed, but the E,Z form has never been reported (Bensemann et al., 2002; Kempe & Hillebrand, 2000). We report here the crystal structure of N,N'-bis(2-pyridyl)-1,2-diaminobenzene, (I), the first example of this class of compounds that exists in the E,Z form in the crystalline state.

The structure of (I), with the atom numbering scheme, is presented in Fig. 1, which shows one of the N-aryl-2-aminopyridine units (N1/C13) adopting a strongly flattened Z conformation, with N1—C2—N7—C8 and C2—N7—C8—C13 torsion angles equal to 2.0 (2) and −14.1 (2)°, respectively. This conformation is stabilized by the intramolecular C—H···N interaction between pyridine atom N1 and benzene atom H13 [C13···N1 = 2.9126 (19) Å, H13···N1 = 2.31 Å and C13—H13···N1 = 120°]. The second N-aryl-2-aminopyridine unit (C8–C20), adopting the E conformation, is significantly non-planar, with the aromatic rings strongly twisted about the C—N bonds to the amine group [C9—N14—C15—C20 = 14.3 (2)° and C10—C9—N14—C15 = 49.39 (19)°]. In this conformation, the H atoms of the two N—H groups in the molecule of (I) are separated by 2.16 (2) Å. A search of the CSD for N-aryl-2-aminopyridines showed that the dihedral angle between the pyridine ring and the plane of the amine group is generally smaller than that between the amine and N-aryl groups. This difference is probably a consequence of a stronger conjugation of the amine N π electrons with the pyridine π system. It? is further confirmed by the shortening of the C—N bond to the amine N atom; the mean value of the C—N bond length to the pyridine ring is significantly shorter than that to the aryl substituent [1.369 (7) and 1.413 (8) Å, respectively]. A similar trend can be observed for the C—N bond lengths in (I) (Table 1).

In the crystal, the molecules of (I) are joined by a pair of nearly linear N—H···N hydrogen bonds into discrete dimers (Fig. 1 and Table 2). These interactions between the N-aryl-2-aminopyridine units assuming the E conformation generate a centrosymmetric R22(8) motif. As indicated above, the second N-aryl-2-aminopyridine unit adopts a nearly planar Z conformation and therefore cannot act as an H-atom acceptor in intermolecular hydrogen bonding. The NH group of this unit has no additional acceptor accessible and therefore is not involved in any hydrogen bonding.

Experimental top

1,2-Diaminobenzene (2.7 g, 25 mmol) was dissolved in 2-chloropyridine (7 ml, 75 mmol) and refluxed for 1 h. After cooling, the precipitated hydrochloride was filtered off and washed with diethyl ether. The crude hydrochloride (8.5 g) was dissolved in water, 25% aqueous ammonia (25 ml) was added and the precipitated product was extracted with ethyl acetate. The organic layer was dried (Na2SO4), evaporated to dryness and the residue was crystallized from ethanol [yield 4.59 g, 70%; m.p. 440–441 K, literature 439–440 K (Fischer, 1902)]; 1H NMR (CDCl3): δ 8.16 (m, 2 H), 7.71 (dd, J = 3.6 and 6.0 Hz, 2 H), 7.42 (m, 2 H), 7.12 (dd, J = 3.5 and 6.0 Hz, 2 H), 6.86 (br s, 2 H), 6.70 (m, 2 H) and 6.59 (m, 2 H); 13C NMR (DMSO-d6): δ 156.8, 147.8, 137.8, 133.7, 123.7, 114.5 and 109.6.

Refinement top

H atoms attached to N atoms were located in a difference Fourier map and refined isotropically. H atoms attached to C atoms were placed in calculated positions (0.96 Å) and treated as riding. Their isotropic displacement parameters were refined.

Computing details top

Data collection: CrysAlis (Oxford Diffraction, 2000); cell refinement: CrysAlis; data reduction: CrysAlis; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: 'Stereochemical Workstation (Siemens, 1989)'; software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. : The dimers of (I), formed via the cyclic R22(8) hydrogen-bond motif displacement ellipsoids are shown at the 50% probability level.
N,N'-Bis(2-pyridyl)-1,2-diaminobenzene top
Crystal data top
C16H14N4F(000) = 552
Mr = 262.31Dx = 1.334 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P2ynCell parameters from 4833 reflections
a = 9.1835 (6) Åθ = 4–25°
b = 7.8999 (6) ŵ = 0.08 mm1
c = 18.2023 (13) ÅT = 110 K
β = 98.598 (6)°Block, colorless
V = 1305.71 (16) Å30.40 × 0.40 × 0.20 mm
Z = 4
Data collection top
Kuma KM-4 CCD
diffractometer
2319 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.031
Graphite monochromatorθmax = 26.4°, θmin = 3.5°
ω scansh = 1111
6639 measured reflectionsk = 99
2655 independent reflectionsl = 2217
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)] = 0.046Hydrogen site location: mixed
wR(F2) = 0.125H atoms treated by a mixture of independent and constrained refinement
S = 1.08 w = 1/[σ2(Fo2) + (0.0717P)2 + 0.3063P]
where P = (Fo2 + 2Fc2)/3
2655 reflections(Δ/σ)max < 0.001
201 parametersΔρmax = 0.20 e Å3
0 restraintsΔρmin = 0.25 e Å3
Crystal data top
C16H14N4V = 1305.71 (16) Å3
Mr = 262.31Z = 4
Monoclinic, P21/nMo Kα radiation
a = 9.1835 (6) ŵ = 0.08 mm1
b = 7.8999 (6) ÅT = 110 K
c = 18.2023 (13) Å0.40 × 0.40 × 0.20 mm
β = 98.598 (6)°
Data collection top
Kuma KM-4 CCD
diffractometer
2319 reflections with I > 2σ(I)
6639 measured reflectionsRint = 0.031
2655 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0460 restraints
wR(F2) = 0.125H atoms treated by a mixture of independent and constrained refinement
S = 1.08Δρmax = 0.20 e Å3
2655 reflectionsΔρmin = 0.25 e Å3
201 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
xyzUiso*/Ueq
N10.06342 (13)0.69506 (15)0.30881 (6)0.0239 (3)
C20.10734 (15)0.77340 (17)0.25114 (7)0.0211 (3)
C30.25440 (17)0.82451 (19)0.25111 (9)0.0284 (3)
H3A0.28260.88100.20880.029 (4)*
C40.35691 (16)0.79234 (19)0.31243 (9)0.0299 (3)
H4A0.45740.82730.31370.033 (4)*
C50.31310 (16)0.70857 (19)0.37287 (8)0.0288 (3)
H5A0.38240.68210.41620.036 (5)*
C60.16702 (17)0.66474 (19)0.36800 (8)0.0278 (3)
H6A0.13640.60870.40990.033 (4)*
N70.00640 (13)0.80816 (15)0.18831 (6)0.0237 (3)
H70.0430 (18)0.874 (2)0.1560 (9)0.026 (4)*
C80.14579 (15)0.77847 (16)0.17315 (7)0.0207 (3)
C90.22453 (15)0.85996 (17)0.11013 (7)0.0211 (3)
C100.37580 (15)0.83763 (17)0.09312 (8)0.0242 (3)
H10A0.42840.89140.04990.028 (4)*
C110.45232 (16)0.73926 (18)0.13750 (8)0.0263 (3)
H11A0.55750.72880.12650.030 (4)*
C120.37415 (16)0.65587 (18)0.19818 (8)0.0270 (3)
H12A0.42600.58570.22860.029 (4)*
C130.22250 (16)0.67226 (18)0.21539 (8)0.0249 (3)
H13A0.17000.61070.25650.029 (4)*
N140.14696 (13)0.96227 (15)0.06474 (6)0.0235 (3)
H140.069 (2)0.919 (2)0.0446 (10)0.041 (5)*
C150.18829 (14)1.12400 (17)0.04170 (7)0.0196 (3)
N160.11729 (12)1.18788 (14)0.01178 (6)0.0212 (3)
C170.14821 (16)1.34886 (18)0.03364 (8)0.0251 (3)
H17A0.09691.39580.07110.029 (4)*
C180.24899 (17)1.45022 (18)0.00539 (8)0.0292 (3)
H18A0.26801.56390.02280.032 (4)*
C190.32205 (17)1.38154 (19)0.04925 (8)0.0285 (3)
H19A0.39341.44800.07000.033 (4)*
C200.29234 (15)1.21857 (18)0.07360 (8)0.0238 (3)
H20A0.34161.17060.11160.030 (4)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0241 (6)0.0269 (6)0.0211 (6)0.0017 (5)0.0050 (5)0.0007 (5)
C20.0215 (7)0.0205 (6)0.0222 (6)0.0030 (5)0.0057 (5)0.0012 (5)
C30.0248 (7)0.0313 (8)0.0301 (7)0.0001 (6)0.0079 (6)0.0060 (6)
C40.0217 (7)0.0322 (8)0.0357 (8)0.0010 (6)0.0043 (6)0.0025 (6)
C50.0267 (8)0.0334 (8)0.0249 (7)0.0078 (6)0.0002 (6)0.0023 (6)
C60.0318 (8)0.0302 (8)0.0218 (7)0.0039 (6)0.0057 (6)0.0016 (6)
N70.0211 (6)0.0291 (6)0.0220 (6)0.0003 (5)0.0064 (5)0.0061 (5)
C80.0219 (7)0.0204 (6)0.0204 (6)0.0006 (5)0.0053 (5)0.0025 (5)
C90.0238 (7)0.0196 (6)0.0215 (7)0.0035 (5)0.0084 (5)0.0003 (5)
C100.0237 (7)0.0240 (7)0.0251 (7)0.0049 (5)0.0043 (5)0.0015 (5)
C110.0212 (7)0.0252 (7)0.0330 (8)0.0017 (5)0.0056 (6)0.0037 (6)
C120.0283 (8)0.0254 (7)0.0290 (7)0.0053 (6)0.0104 (6)0.0006 (6)
C130.0276 (7)0.0250 (7)0.0225 (7)0.0012 (6)0.0052 (6)0.0007 (5)
N140.0227 (6)0.0243 (6)0.0257 (6)0.0071 (5)0.0111 (5)0.0057 (5)
C150.0176 (6)0.0225 (7)0.0182 (6)0.0001 (5)0.0011 (5)0.0001 (5)
N160.0193 (6)0.0233 (6)0.0215 (6)0.0012 (4)0.0043 (4)0.0019 (4)
C170.0256 (7)0.0243 (7)0.0256 (7)0.0004 (5)0.0045 (6)0.0045 (5)
C180.0333 (8)0.0196 (7)0.0353 (8)0.0044 (6)0.0069 (6)0.0028 (6)
C190.0304 (8)0.0250 (7)0.0315 (8)0.0064 (6)0.0092 (6)0.0025 (6)
C200.0233 (7)0.0266 (7)0.0225 (7)0.0024 (5)0.0070 (5)0.0008 (5)
Geometric parameters (Å, º) top
N1—C21.3320 (18)C10—H10A0.96
N1—C61.3480 (19)C11—C121.390 (2)
C2—N71.3877 (18)C11—H11A0.96
C2—C31.410 (2)C12—C131.387 (2)
C3—C41.372 (2)C12—H12A0.96
C3—H3A0.96C13—H13A0.96
C4—C51.394 (2)N14—C151.3802 (17)
C4—H4A0.96N14—H140.92 (2)
C5—C61.375 (2)C15—N161.3479 (17)
C5—H5A0.96C15—C201.4051 (19)
C6—H6A0.96N16—C171.3500 (18)
N7—C81.4033 (18)C17—C181.380 (2)
N7—H70.889 (17)C17—H17A0.96
C8—C131.3975 (19)C18—C191.390 (2)
C8—C91.4160 (19)C18—H18A0.96
C9—C101.3886 (19)C19—C201.376 (2)
C9—N141.4211 (17)C19—H19A0.9600
C10—C111.386 (2)C20—H20A0.96
C2—N1—C6116.86 (12)C10—C11—C12118.84 (13)
N1—C2—N7119.86 (12)C10—C11—H11A120.6
N1—C2—C3122.43 (13)C12—C11—H11A120.6
N7—C2—C3117.71 (13)C13—C12—C11121.13 (13)
C4—C3—C2119.18 (14)C13—C12—H12A119.5
C4—C3—H3A120.3C11—C12—H12A119.4
C2—C3—H3A120.5C12—C13—C8120.23 (13)
C3—C4—C5119.09 (14)C12—C13—H13A119.9
C3—C4—H4A120.5C8—C13—H13A119.8
C5—C4—H4A120.4C15—N14—C9124.34 (11)
C6—C5—C4117.55 (13)C15—N14—H14114.8 (12)
C6—C5—H5A121.2C9—N14—H14120.6 (12)
C4—C5—H5A121.2N16—C15—N14115.17 (11)
N1—C6—C5124.88 (14)N16—C15—C20122.12 (12)
N1—C6—H6A117.5N14—C15—C20122.67 (12)
C5—C6—H6A117.6C15—N16—C17117.54 (12)
C2—N7—C8130.68 (12)N16—C17—C18124.05 (13)
C2—N7—H7112.9 (11)N16—C17—H17A118.0
C8—N7—H7115.6 (11)C18—C17—H17A118.0
C13—C8—N7124.15 (12)C17—C18—C19117.54 (13)
C13—C8—C9118.70 (12)C17—C18—H18A121.3
N7—C8—C9117.14 (12)C19—C18—H18A121.2
C10—C9—C8119.71 (12)C20—C19—C18120.14 (13)
C10—C9—N14120.96 (12)C20—C19—H19A119.9
C8—C9—N14119.33 (12)C18—C19—H19A119.9
C11—C10—C9121.26 (13)C19—C20—C15118.61 (13)
C11—C10—H10A119.4C19—C20—H20A120.7
C9—C10—H10A119.4C15—C20—H20A120.7
N1—C2—N7—C82.0 (2)C10—C9—N14—C1549.39 (19)
C3—C2—N7—C8177.63 (13)C8—C9—N14—C15131.25 (14)
C2—N7—C8—C9167.00 (13)C9—N14—C15—N16168.21 (12)
C2—N7—C8—C1314.1 (2)C9—N14—C15—C2014.3 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C13—H13A···N10.962.312.9126 (19)120
N14—H14···N16i0.92 (2)2.07 (2)2.9874 (16)173.2 (16)
Symmetry code: (i) x, y+2, z.

Experimental details

Crystal data
Chemical formulaC16H14N4
Mr262.31
Crystal system, space groupMonoclinic, P21/n
Temperature (K)110
a, b, c (Å)9.1835 (6), 7.8999 (6), 18.2023 (13)
β (°) 98.598 (6)
V3)1305.71 (16)
Z4
Radiation typeMo Kα
µ (mm1)0.08
Crystal size (mm)0.40 × 0.40 × 0.20
Data collection
DiffractometerKuma KM-4 CCD
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
6639, 2655, 2319
Rint0.031
(sin θ/λ)max1)0.625
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.046, 0.125, 1.08
No. of reflections2655
No. of parameters201
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.20, 0.25

Computer programs: CrysAlis (Oxford Diffraction, 2000), CrysAlis, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), 'Stereochemical Workstation (Siemens, 1989)', SHELXL97.

Selected geometric parameters (Å, º) top
N1—C21.3320 (18)C9—N141.4211 (17)
N1—C61.3480 (19)N14—C151.3802 (17)
C2—N71.3877 (18)C15—N161.3479 (17)
N7—C81.4033 (18)N16—C171.3500 (18)
C2—N1—C6116.86 (12)C15—N14—C9124.34 (11)
C2—N7—C8130.68 (12)C15—N16—C17117.54 (12)
N1—C2—N7—C82.0 (2)C10—C9—N14—C1549.39 (19)
C2—N7—C8—C1314.1 (2)C9—N14—C15—C2014.3 (2)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C13—H13A···N10.962.312.9126 (19)120.1
N14—H14···N16i0.92 (2)2.07 (2)2.9874 (16)173.2 (16)
Symmetry code: (i) x, y+2, z.
 

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