A new polymorph of 2,6-di­amino­pyridine

2,6-Di­amino­pyridine (26-DAP, C₅H₇N₃) is a common inter­mediate in the synthesis of aromatic azo chromophores, which are widespread in the dyes and pigments industry. Sublimation of commercial 26-DAP powder yielded a new polymorph, denoted Form II, which grew as colorless ortho­rhom­bic needles. Recrystallization from acetone or toluene also yielded Form II as the major phase. Thermal analysis shows that Form II is a less stable polymorph and it converts upon heating at 335 K to the previously reported Form I.

Computing details

Data collection: APEX2 (Bruker, 2014); cell refinement: SAINT (Bruker, 2014); data reduction: SAINT (Bruker, 2014), XPREP (Bruker, 2014) and SADABS (Bruker, 2014); program(s) used to solve structure: SHELXT2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: SHELXTL (Bruker, 2014); software used to prepare material for publication: XCIF (Bruker, 2014).

Pyridine-2,6-diamine

Crystal data

C5H7N3	Dx = 1.313 Mg m^−3
Mr = 109.14	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 10034 reflections
a = 5.1217 (9) Å	θ = 3.7–19.6°
b = 9.8397 (14) Å	µ = 0.09 mm^−1
c = 21.914 (4) Å	T = 100 K
V = 1104.4 (3) Å^3	Needle, colorless
Z = 8	0.44 × 0.05 × 0.02 mm
F(000) = 464

Data collection

Bruker APEX DUO/APEXII CCD diffractometer	948 independent reflections
Radiation source: fine-focus sealed tube	559 reflections with I > 2σ(I)
Multilayer mirrors monochromator	Rint = 0.180
profile data from φ and ω scans	θmax = 24.9°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Bruker, 2014)	h = −6→6
Tmin = 0.518, Tmax = 0.745	k = −11→11
8750 measured reflections	l = −25→25

Refinement

Refinement on F^2	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.056	w = 1/[σ^2(Fo^2) + (0.0763P)^2] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.149	(Δ/σ)max < 0.001
S = 0.98	Δρmax = 0.32 e Å^−3
948 reflections	Δρmin = −0.24 e Å^−3
86 parameters	Extinction correction: SHELXL2014 (Sheldrick, 2015b), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
4 restraints	Extinction coefficient: 0.018 (4)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.0267 (5)	0.6215 (2)	0.18272 (11)	0.0207 (7)
N2	−0.3151 (5)	0.4730 (3)	0.17132 (13)	0.0272 (8)
H2A	−0.460 (5)	0.456 (4)	0.1506 (14)	0.041*
H2B	−0.343 (7)	0.487 (4)	0.2108 (9)	0.041*
N3	0.3660 (6)	0.7692 (3)	0.20060 (12)	0.0237 (7)
H3A	0.399 (7)	0.730 (3)	0.2371 (10)	0.036*
H3B	0.511 (5)	0.806 (3)	0.1854 (15)	0.036*
C1	−0.1445 (6)	0.5638 (3)	0.14421 (14)	0.0231 (8)
C2	−0.1450 (7)	0.5874 (3)	0.08154 (14)	0.0298 (9)
H2	−0.2679	0.5442	0.0555	0.036*
C3	0.0409 (7)	0.6765 (4)	0.05851 (16)	0.0333 (10)
H3	0.0474	0.6948	0.0160	0.040*
C4	0.2160 (6)	0.7385 (3)	0.09735 (14)	0.0257 (8)
H4	0.3418	0.8007	0.0820	0.031*
C5	0.2056 (6)	0.7086 (3)	0.15879 (13)	0.0201 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0239 (15)	0.0110 (13)	0.0272 (15)	0.0011 (12)	−0.0006 (12)	−0.0004 (11)
N2	0.0247 (17)	0.0129 (14)	0.0440 (18)	−0.0037 (13)	−0.0045 (14)	0.0018 (12)
N3	0.0268 (16)	0.0154 (15)	0.0289 (16)	−0.0050 (13)	−0.0012 (14)	0.0028 (11)
C1	0.0240 (18)	0.0096 (16)	0.0358 (18)	0.0068 (14)	−0.0018 (16)	−0.0022 (13)
C2	0.032 (2)	0.025 (2)	0.0318 (19)	0.0052 (17)	−0.0055 (17)	−0.0057 (13)
C3	0.038 (2)	0.036 (2)	0.0258 (19)	0.0085 (18)	0.0016 (17)	0.0043 (15)
C4	0.0289 (19)	0.0192 (18)	0.0290 (18)	0.0016 (16)	−0.0001 (15)	0.0033 (13)
C5	0.0222 (18)	0.0103 (16)	0.0279 (18)	0.0058 (14)	0.0010 (14)	−0.0014 (12)

Geometric parameters (Å, º)

N1—C1	1.343 (4)	C1—C2	1.393 (4)
N1—C5	1.360 (4)	C2—C3	1.389 (5)
N2—C1	1.384 (4)	C2—H2	0.9500
N2—H2A	0.886 (18)	C3—C4	1.378 (5)
N2—H2B	0.888 (18)	C3—H3	0.9500
N3—C5	1.368 (4)	C4—C5	1.379 (4)
N3—H3A	0.902 (18)	C4—H4	0.9500
N3—H3B	0.891 (18)
C1—N1—C5	117.6 (3)	C3—C2—H2	121.2
C1—N2—H2A	115 (2)	C1—C2—H2	121.2
C1—N2—H2B	115 (2)	C4—C3—C2	120.0 (3)
H2A—N2—H2B	113 (3)	C4—C3—H3	120.0
C5—N3—H3A	121 (2)	C2—C3—H3	120.0
C5—N3—H3B	115 (2)	C3—C4—C5	118.9 (3)
H3A—N3—H3B	110 (3)	C3—C4—H4	120.5
N1—C1—N2	114.5 (3)	C5—C4—H4	120.5
N1—C1—C2	123.4 (3)	N1—C5—N3	114.9 (3)
N2—C1—C2	122.0 (3)	N1—C5—C4	122.5 (3)
C3—C2—C1	117.5 (3)	N3—C5—C4	122.6 (3)
C5—N1—C1—N2	178.0 (3)	C2—C3—C4—C5	1.1 (5)
C5—N1—C1—C2	0.9 (4)	C1—N1—C5—N3	176.9 (3)
N1—C1—C2—C3	−0.7 (5)	C1—N1—C5—C4	−0.2 (4)
N2—C1—C2—C3	−177.5 (3)	C3—C4—C5—N1	−0.8 (5)
C1—C2—C3—C4	−0.4 (5)	C3—C4—C5—N3	−177.7 (3)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3A···N1^i	0.90 (2)	2.16 (2)	3.054 (4)	171 (3)
N3—H3B···N2^ii	0.89 (2)	2.29 (2)	3.118 (4)	155 (3)

Symmetry codes: (i) x+1/2, y, −z+1/2; (ii) −x+1/2, y+1/2, z.