A third polymorph of N,N′-bis­(pyridin-2-yl)benzene-1,4-diamine

Barbara Wicher; Maria Gdaniec

doi:10.1107/S1600536811044539

. 2011 Oct 29;67(Pt 11):o3095. doi: 10.1107/S1600536811044539

A third polymorph of N,N′-bis(pyridin-2-yl)benzene-1,4-diamine

Barbara Wicher ^a, Maria Gdaniec ^a,^*

PMCID: PMC3247481 PMID: 22220099

Abstract

A third polymorph of the title compound, C₁₆H₁₄N₄, has been obtained. The molecule adopts a non-planar conformation with an E configuration at the two partially double exo C N bonds of the 2-pyridylamine units. Like in the triclinic form [Bensemann et al. (2002 ▶). New J. Chem. 26, 448–456], the recognition process between 2-pyridylamine units takes place through formation of a cyclic R ₂ ²(8) hydrogen-bond motif, leading to the creation of tapes parallel to [001].

Related literature

For the structures of the orthorhombic and triclinic polymorphs of N,N′-di(pyridin-2-yl)benzene-1,4-diamine, see: Bensemann et al. (2002 ▶).

Experimental

Crystal data

C₁₆H₁₄N₄
M _r = 262.31
Monoclinic,
a = 7.2534 (2) Å
b = 20.8270 (6) Å
c = 9.0681 (3) Å
β = 106.746 (4)°
V = 1311.79 (7) Å³
Z = 4
Cu Kα radiation
μ = 0.65 mm⁻¹
T = 295 K
0.2 × 0.2 × 0.05 mm

Data collection

Oxford Diffraction SuperNova diffractometer
Absorption correction: multi-scan (CrysAlis PRO; Agilent, 2010 ▶) T _min = 0.799, T _max = 1.000
10413 measured reflections
2398 independent reflections
2221 reflections with I > 2/s(I)
R _int = 0.019

Refinement

R[F ² > 2σ(F ²)] = 0.035
wR(F ²) = 0.094
S = 1.07
2398 reflections
181 parameters
H-atom parameters constrained
Δρ_max = 0.11 e Å⁻³
Δρ_min = −0.19 e Å⁻³

Data collection: CrysAlis PRO (Agilent, 2010 ▶); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SIR2004 (Burla et al., 2005 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶) and Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536811044539/rz2657sup1.cif

e-67-o3095-sup1.cif^{(21.9KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811044539/rz2657Isup2.hkl

e-67-o3095-Isup2.hkl^{(117.8KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811044539/rz2657Isup3.cml

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
N7—H7N⋯N16ⁱ	0.90	2.25	3.1423 (13)	175
N14—H14N⋯N2ⁱⁱ	0.90	2.12	3.0141 (14)	175

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

supplementary crystallographic information

Comment

The compounds bearing two 2-pyridylamine groups separated by linkers can adopt either E,E, Z,Z or E,Z forms depending on the configuration of the partially double exo C≐ N bond of the 2-pyridylamine unit. In crystals the molecules in the E, E form tend to build one-dimensional networks via R²₂(8) synthons generated between self-complementary 2-pyridylamine groups. In turn, the Z,Z form generates the C(4) catemer motif that can lead to the formation of one-, two- and three-dimensional frameworks (Bensemann et al., 2002). These compounds are known to exhibit conformational polymorphism and for N,N'-di(pyridin-2-yl)benzene-1,4-diamine two polymorphic forms were identified. In the orthorhombic form (Pbca, Z'=0.5), obtained by crystallization from acetonitrile, the molecules are nonplanar and adopt the Z,Z form. Hydrogen bonds between 2-pyridylamine groups generate catemeric motifs that assemble molecules into a two-dimensional framework. In the triclinic P1 polymorph, obtained by crystallization from methanol, there are two symmetry independent molecules, each in the E,E form and located around inversion center. These molecules form tapes via strongly nonplanar R²₂(8) motif generated by N—H···N hydrogen bonds (Bensemann et al., 2002).

Recently, during an attempt to cocrystallize N,N'-di(pyridin-2-yl)benzene-1,4-diamine with pyrazine from 2-butanone, a new monoclinic polymorph of N,N'-di(pyridin-2-yl)benzene-1,4-diamine was obtained. When crystallization was repeated from 2-butanone without addition of pyrazine the triclinic polymorph was formed.

In the new monoclinic polymorph the molecules adopt the E,E form and are assembled into tapes via strongly non-planar R²₂(8) hydrogen-bond motif. The overall shape of the tapes and their crystal packing are different from the arrangement found in the triclinic polymorph. As shown in Fig. 2a, the hydrogen-bonded tapes extended along [0 0 1] are grouped into pairs, with no specific interactions occurring between the two tapes, and these pairs of tapes are further arranged in a herring-bone manner (Fig. 2b).

The three polymorphs of N,N'-di(pyridin-2-yl)benzene-1,4-diamine have identical or very similar melting points: 478–479 K for the orthorhombic and triclinic polymorphs and 479 K for the monoclinic form. The calculated crystal densities are also similar: 1.335, 1.314 and 1.328 g cm^-3 for orthorhombic, triclinic and monoclinic forms, respectively.

Experimental

N,N'-Di(pyridin-2-yl)benzene-1,4-diamine was prepared according to the published procedure (Bensemann et al., 2002). N,N'-Di(pyridin-2-yl)benzene-1,4-diamine (0.03 g, 0.11 mmol) and pyrazine (0.01 g, 0.11 mmol) were dissolved in 5 ml of 2-butanone and placed in a glass vial. After a few days colourless, plate-shaped crystals with a melting point of 479 K were obtained.