Crystal structure of 3,6-bis-(pyridin-2-yl)-1,4-di-hydro-1,2,4,5-tetra-zine.

The structure of the title compound, C12H10N6, at 100 K has monoclinic (P21/n) symmetry. Crystals were obtained as a yellow solid by reduction of 3,6-bis-(pyridin-2-yl)-1,2,4,5-tetra-zine. The structure displays inter-molecular hydrogen bonding of the N-H⋯N type, ordering mol-ecules into infinite ribbons extending along the [100] direction.

Chemical context

s-Tetra­zines represent a class of heterocyclic compounds. The substitution of four nitro­gen atoms in a six-membered benzene-like ring results in strong π-electron deficiency and concentration of negative charge on the heteroatoms. As a result of these properties, s-tetra­zines are used in organic synthesis (Saracoglu, 2007 ▸; Šečkutė & Deveraj et al., 2013 ▸; Churakov et al., 2004 ▸) as well as bridging ligands in metal complexes (Kaim, 2002 ▸; Clavier & Audebert, 2010 ▸). Moreover, their derivatives are often among biologically active compounds (Saghatforoush et al., 2016 ▸) and play an important role in anti-inflammatory (Kamal et al., 2006 ▸), anti­cancer, anti­viral drugs (Rao & Hu, 2006 ▸; Neunhoeffer et al., 1984 ▸) or as insecticidal products (Sauer et al.,1996 ▸; Brooker et al., 1987 ▸).

The title compound 3,6-bis­(pyridin-2-yl)-1,4-di­hydro-1,2,4,5-tetra­zine (I) was obtained as a yellow solid by reduction of 3,6-bis­(pyridin-2-yl)-1,2,4,5-tetra­zine (II) during its crystallization with 2-mercapto­pyridine N-oxide (III) in ethanol solution (Fig. 1 ▸).

Figure 1

Mol­ecular formulae of: 3,6-bis­(pyridin-2-yl)-1,4-di­hydro-1,2,4,5-tetra­zine (I), 3,6-bis­(pyridin-2-yl)-1,2,4,5-tetra­zine (II) and 2-mercapto­pyridine N-oxide (III).

Structural commentary

Compound (I) crystallizes in the monoclinic space group P21/n. The atomic labelling scheme is shown in Fig. 2 ▸. In (I), being a reduced form of (II), there are two hydrogen atoms at the 1 and 4 positions and two 2-pyridyl substituents at the 3 and 6 positions.

Figure 2

The mol­ecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.

The C—C bond lengths are within the expected values known for aromatic systems (Allen et al., 1987 ▸). However, there is a fluctuation of bond distances involving nitro­gen atoms. The N—N bonds within the central (A) ring are of almost equal length, being 1.4285 (15) and 1.4306 (16) Å. The C6—N1 and C3—N4 [1.3953 (17) and 1.4051 (17) Å] bond lengths are longer than those for C6—N5 and C3—N2 [1.2848 (17) Å, 1.2809 (18) Å], respectively. This is the result of the protonation of the N1 and N4 atoms. The C—N bond lengths in the B and C rings are comparable within 3σ, varying from 1.3384 (18) Å to 1.3416 (17) Å.

The central tetra­zine ring (A) shows a boat conformation with pseudo-symmetry mirror planes passing through bonds N2—C3 and N5—C6 [ΔCs = 1.30 (16)°] and atoms N1, N4 [ΔCs = 2.00 (14)°]. In this conformation, hydrogen atoms are located in the equatorial positions of the ring and the N—H bonds are directed to the bottom of the boat (compare torsion angles in Table 1 ▸). The planes of the aromatic pirydyl rings (B and C) are not to parallel to each other. The dihedral angles between these rings and central tetra­zine ring are 22.43 (7)° (A and B) and 25.71 (6)° (A and C). The dihedral angle between rings B and C is 27.13 (7)°. The overall mol­ecular structure could be recognized as a butterfly-like conformation as shown in Fig. 3 ▸.

Table 1

Selected torsion angles (°)

N2—C3—N4—H4	164.1 (13)	C3—N2—N1—H1	−168.4 (12)
C6—N5—N4—H4	−165.2 (14)	N5—C6—N1—H1	164.3 (13)

Figure 3

The butterfly-like mol­ecular conformation of (I).

Supra­molecular features

The crystal packing of (I) is mainly determined by inter­molecular hydrogen bonds of the N—H⋯N type (Table 2 ▸). Firstly, two similar hydrogen bonds (N1—H1⋯N5 and N4—H4⋯N2) between the 1,2,4,5-tetra­zine rings of neighbouring mol­ecules form a chain with an R 2 2(6) ring motif (Etter et al., 1990 ▸) (see Fig. 4 ▸). As a result, the mol­ecules are ordered into infinite ribbons extending along the [100] direction. This parallel arrangement of the ribbons is additionally stabilized by further inter­actions between adjacent mol­ecules [N5⋯C33(1 − x, 1 − y, 1 − z) = 3.2418 (18) Å and C34⋯C61(1 − x, 1 − y, 1 − z) = 3.3334 (19) Å], as shown in Fig. 5 ▸.

Table 2

Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N4—H4⋯N2i	0.89 (2)	2.56 (2)	3.3017 (16)	142.5 (17)
N1—H1⋯N5ii	0.880 (17)	2.415 (17)	3.1321 (16)	138.9 (15)

Symmetry codes: (i) ; (ii) .

Figure 4

N—H ⋯ N hydrogen bonds between rings of 1,2,4,5-tetra­zine of adjacent mol­ecules forming a chain of cyclic dimers.

Figure 5

A view of the unit-cell packing, showing the ribbon-like arrangement of mol­ecules. Short C⋯N and C⋯C inter­molecular contacts between adjacent mol­ecular ribbons are shown as dashed blue lines.

Database survey

A search of the Cambridge Structure Database (CSD version 5.39, update of February 2018; Groom et al., 2016 ▸) results in 76 deriv­atives of 3,6-bis­(pyridin-2-yl)-1,2,4,5-tetra­zine, among them compound (II) (refcode JUMXAQ; Klein et al., 1998 ▸), which is the oxidated form of (I). Even tought (II) crystallizes in the smae monoclinic space group as (I), its molecular and crystal structures show completely different features.

Synthesis and crystallization

Crystals suitable for X-ray measurements were obtained from a commercially available reagent (Aldrich Chemical Co.) and used without further purification. 0.5 mmol of 3,6-bis­(pyridin-2-yl)-1,2,4,5-tetra­zine and 0.5 mmol of 2-mercapto­pyridine N-oxide (in a 1:1 molar ratio) were mixed in ethanol (4 ml). The resulting solution was warmed to 343 K and then kept at room temperature. Within two weeks, after slow evaporation of the solvent, two kinds of crystal were obtained in a crystallizer. X-ray studies confirmed that the pink crystals were of the known structure (II), while the yellow crystals were identified as being of a previously unreported structure, i.e. (I).

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3 ▸. Hydrogen atoms of aromatic rings were introduced in calculated positions with idealized geometry and constrained using a rigid body model with isotropic displacement parameters equal to 1.2 the equivalent displacement parameters of the parent atoms. The H atoms of the NH groups, in 1,2,4,5-tetra­zine ring, were located in a difference Fourier map and freely refined.

Table 3

Experimental details

Crystal data
Chemical formula	C12H10N6
M r	238.26
Crystal system, space group	Monoclinic, P21/n
Temperature (K)	100
a, b, c (Å)	5.4603 (1), 12.7845 (3), 15.6474 (4)
β (°)	97.281 (2)
V (Å3)	1083.49 (4)
Z	4
Radiation type	Cu Kα
μ (mm−1)	0.78
Crystal size (mm)	0.11 × 0.10 × 0.08
Data collection
Diffractometer	Rigaku Oxford Diffraction SuperNova, Dual, Cu at zero, Atlas
Absorption correction	Multi-scan (CrysAlis PRO; Rigaku OD, 2015 ▸)
T min, T max	0.958, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections	8686, 2004, 1767
R int	0.027
(sin θ/λ)max (Å−1)	0.603
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S	0.035, 0.095, 1.12
No. of reflections	2004
No. of parameters	171
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å−3)	0.14, −0.24

Computer programs: CrysAlis PRO (Rigaku OD, 2015 ▸), SHELXT2014 (Sheldrick, 2015a ▸), SHELXL2014 (Sheldrick, 2015b ▸), WinGX (Farrugia, 2012 ▸), PLATON (Spek, 2009 ▸) and publCIF (Westrip, 2010 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S205698901801753X/ff2157sup1.cif

Structure factors: contains datablock(s) I. DOI: 10.1107/S205698901801753X/ff2157Isup2.hkl

Click here for additional data file.

Supporting information file. DOI: 10.1107/S205698901801753X/ff2157Isup3.cml

CCDC reference: 1884403

Additional supporting information: crystallographic information; 3D view; checkCIF report

C12H10N6	F(000) = 496
Mr = 238.26	Dx = 1.461 Mg m−3
Monoclinic, P21/n	Cu Kα radiation, λ = 1.54184 Å
a = 5.4603 (1) Å	Cell parameters from 3734 reflections
b = 12.7845 (3) Å	θ = 4.5–76.4°
c = 15.6474 (4) Å	µ = 0.78 mm−1
β = 97.281 (2)°	T = 100 K
V = 1083.49 (4) Å3	Plate, yellow
Z = 4	0.11 × 0.10 × 0.08 mm

Rigaku Oxford Diffraction SuperNova, Dual, Cu at zero, Atlas diffractometer	2004 independent reflections
Radiation source: micro-focus sealed X-ray tube, SuperNova (Cu) X-ray Source	1767 reflections with I > 2σ(I)
Detector resolution: 10.4052 pixels mm-1	Rint = 0.027
ω scans	θmax = 68.5°, θmin = 4.5°
Absorption correction: multi-scan (CrysAlisPRO; Rigaku OD, 2015)	h = −6→6
Tmin = 0.958, Tmax = 1.000	k = −15→14
8686 measured reflections	l = −18→17

Refinement on F2	0 restraints
Least-squares matrix: full	Hydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.035	H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.095	w = 1/[σ2(Fo2) + (0.051P)2 + 0.2596P] where P = (Fo2 + 2Fc2)/3
S = 1.12	(Δ/σ)max < 0.001
2004 reflections	Δρmax = 0.14 e Å−3
171 parameters	Δρmin = −0.24 e Å−3

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.

	x	y	z	Uiso*/Ueq
N5	0.3304 (2)	0.59460 (9)	0.30162 (7)	0.0159 (3)
N1	0.7587 (2)	0.61063 (9)	0.30346 (7)	0.0167 (3)
N66	0.7195 (2)	0.45247 (9)	0.18218 (7)	0.0178 (3)
N4	0.3800 (2)	0.66133 (9)	0.37517 (7)	0.0162 (3)
N2	0.7969 (2)	0.61146 (9)	0.39548 (7)	0.0166 (3)
N36	0.4117 (2)	0.70258 (9)	0.54575 (7)	0.0196 (3)
C3	0.6017 (2)	0.63816 (10)	0.42759 (9)	0.0151 (3)
C31	0.6094 (2)	0.65389 (10)	0.52161 (8)	0.0159 (3)
C6	0.5274 (2)	0.57389 (10)	0.26787 (8)	0.0150 (3)
C61	0.5133 (2)	0.50651 (10)	0.19059 (8)	0.0153 (3)
C62	0.2981 (2)	0.49884 (11)	0.13279 (8)	0.0183 (3)
H62	0.1608	0.5397	0.1394	0.022*
C65	0.7096 (2)	0.38393 (10)	0.11717 (9)	0.0191 (3)
H65	0.8497	0.3444	0.1116	0.023*
C64	0.5020 (3)	0.36871 (11)	0.05778 (9)	0.0194 (3)
H64	0.5020	0.3195	0.0140	0.023*
C34	0.6135 (3)	0.69920 (11)	0.69170 (9)	0.0201 (3)
H34	0.6106	0.7167	0.7493	0.024*
C32	0.8134 (3)	0.62397 (11)	0.57895 (9)	0.0196 (3)
H32	0.9460	0.5895	0.5596	0.024*
C63	0.2943 (3)	0.42869 (11)	0.06517 (9)	0.0201 (3)
H63	0.1539	0.4219	0.0252	0.024*
C33	0.8137 (3)	0.64675 (11)	0.66537 (9)	0.0215 (3)
H33	0.9465	0.6272	0.7054	0.026*
C35	0.4179 (3)	0.72475 (11)	0.62978 (9)	0.0211 (3)
H35	0.2832	0.7593	0.6476	0.025*
H1	0.886 (3)	0.5796 (14)	0.2850 (11)	0.022 (4)*
H4	0.253 (4)	0.6611 (15)	0.4051 (13)	0.030 (5)*

	U11	U22	U33	U12	U13	U23
N5	0.0158 (5)	0.0169 (5)	0.0144 (5)	0.0008 (4)	−0.0001 (4)	−0.0012 (4)
N1	0.0134 (5)	0.0221 (6)	0.0148 (5)	−0.0014 (5)	0.0020 (4)	−0.0020 (4)
N66	0.0154 (5)	0.0182 (6)	0.0198 (6)	0.0000 (4)	0.0025 (4)	−0.0009 (4)
N4	0.0138 (5)	0.0196 (6)	0.0150 (6)	0.0025 (4)	0.0007 (4)	−0.0025 (4)
N2	0.0159 (5)	0.0191 (6)	0.0145 (5)	−0.0009 (4)	0.0003 (4)	−0.0013 (4)
N36	0.0174 (6)	0.0229 (6)	0.0181 (6)	0.0010 (4)	0.0009 (4)	−0.0024 (4)
C3	0.0138 (6)	0.0136 (6)	0.0173 (7)	−0.0002 (5)	−0.0001 (5)	0.0003 (5)
C31	0.0161 (6)	0.0144 (6)	0.0170 (7)	−0.0025 (5)	0.0015 (5)	0.0009 (5)
C6	0.0137 (6)	0.0149 (6)	0.0162 (6)	0.0006 (5)	0.0007 (5)	0.0022 (5)
C61	0.0151 (6)	0.0144 (6)	0.0166 (6)	−0.0010 (5)	0.0032 (5)	0.0015 (5)
C62	0.0153 (6)	0.0211 (7)	0.0185 (7)	0.0017 (5)	0.0018 (5)	0.0005 (5)
C65	0.0168 (6)	0.0175 (6)	0.0236 (7)	0.0007 (5)	0.0055 (5)	−0.0018 (5)
C64	0.0223 (7)	0.0183 (6)	0.0181 (7)	−0.0027 (5)	0.0049 (5)	−0.0025 (5)
C34	0.0253 (7)	0.0193 (7)	0.0155 (6)	−0.0053 (5)	0.0017 (5)	−0.0006 (5)
C32	0.0180 (7)	0.0204 (7)	0.0203 (7)	0.0013 (5)	0.0019 (5)	0.0023 (5)
C63	0.0175 (6)	0.0237 (7)	0.0183 (7)	−0.0024 (5)	−0.0005 (5)	0.0002 (5)
C33	0.0212 (7)	0.0231 (7)	0.0190 (7)	−0.0019 (5)	−0.0024 (5)	0.0038 (5)
C35	0.0209 (7)	0.0226 (7)	0.0202 (7)	0.0000 (5)	0.0040 (5)	−0.0033 (5)

N5—C6	1.2848 (17)	C61—C62	1.3926 (18)
N5—N4	1.4306 (16)	C62—C63	1.385 (2)
N1—C6	1.3953 (17)	C62—H62	0.9300
N1—N2	1.4285 (15)	C65—C64	1.386 (2)
N1—H1	0.880 (19)	C65—H65	0.9300
N66—C65	1.3384 (18)	C64—C63	1.386 (2)
N66—C61	1.3416 (17)	C64—H64	0.9300
N4—C3	1.4051 (17)	C34—C35	1.387 (2)
N4—H4	0.88 (2)	C34—C33	1.389 (2)
N2—C3	1.2809 (18)	C34—H34	0.9300
N36—C35	1.3412 (18)	C32—C33	1.383 (2)
N36—C31	1.3415 (18)	C32—H32	0.9300
C3—C31	1.4800 (18)	C63—H63	0.9300
C31—C32	1.3922 (19)	C33—H33	0.9300
C6—C61	1.4786 (18)	C35—H35	0.9300
C6—N5—N4	111.75 (11)	C63—C62—H62	120.9
C6—N1—N2	114.45 (10)	C61—C62—H62	120.9
C6—N1—H1	115.4 (12)	N66—C65—C64	123.53 (12)
N2—N1—H1	108.3 (12)	N66—C65—H65	118.2
C65—N66—C61	117.28 (12)	C64—C65—H65	118.2
C3—N4—N5	113.90 (10)	C65—C64—C63	118.36 (13)
C3—N4—H4	111.4 (13)	C65—C64—H64	120.8
N5—N4—H4	110.1 (13)	C63—C64—H64	120.8
C3—N2—N1	112.02 (11)	C35—C34—C33	118.16 (13)
C35—N36—C31	116.93 (12)	C35—C34—H34	120.9
N2—C3—N4	121.69 (12)	C33—C34—H34	120.9
N2—C3—C31	120.37 (12)	C33—C32—C31	118.30 (13)
N4—C3—C31	117.75 (12)	C33—C32—H32	120.9
N36—C31—C32	123.55 (12)	C31—C32—H32	120.9
N36—C31—C3	114.85 (12)	C62—C63—C64	119.26 (13)
C32—C31—C3	121.54 (12)	C62—C63—H63	120.4
N5—C6—N1	121.95 (12)	C64—C63—H63	120.4
N5—C6—C61	119.77 (12)	C32—C33—C34	119.21 (13)
N1—C6—C61	118.25 (11)	C32—C33—H33	120.4
N66—C61—C62	123.33 (12)	C34—C33—H33	120.4
N66—C61—C6	115.02 (11)	N36—C35—C34	123.82 (13)
C62—C61—C6	121.63 (12)	N36—C35—H35	118.1
C63—C62—C61	118.13 (12)	C34—C35—H35	118.1
N2—C3—N4—H4	164.1 (13)	C3—N2—N1—H1	−168.4 (12)
C6—N5—N4—H4	−165.2 (14)	N5—C6—N1—H1	164.3 (13)

D—H···A	D—H	H···A	D···A	D—H···A
N4—H4···N2i	0.89 (2)	2.56 (2)	3.3017 (16)	142.5 (17)
N1—H1···N5ii	0.880 (17)	2.415 (17)	3.1321 (16)	138.9 (15)