3,3′-Dinitro-2,2′-dithio­dipyridine

In the title compound, C₁₀H₆N₄O₄S₂, (I), the mol­ecule has a centre of inversion. The structure is a positional isomer of 5,5′-dinitro-2,2′-dithio­dipyridine [Brito, Mundaca, Cárdenas, López-Rodríguez & Vargas (2007). Acta Cryst. E63, o3351–o3352], (II). The 3-nitro­pyridine fragment of (I) shows excellent agreement with the bonding geometries of (II). The most obvious differences between them are in the S—S bond length [2.1167 (12) Å in (I) and 2.0719 (11) Å in (II)], and in the C—C_ipso—N_ring [119.8 (2)° in (I) and 123.9 (3)° in (II)] and S—C—C [122.62 (18)° in (I) and 116.0 (2)° in (II)] angles. The crystal structure of (I) has an intra­molecular C—H...O inter­action, with an H...O distance of 2.40 (3) Å, whereas this kind of inter­action is not evident in (II). The mol­ecules of (I) are linked into centrosymmetric R⁴₄(30) motifs by a C—H...O inter­action. There are no aromatic π–π stacking and no C—H...π(arene) inter­actions. Compound (I) can be used as a nucleophilic tecton in self-assembly reactions with metal centres of varying lability.

S1. Comment

This paper forms part of our continuing study of the synthesis and structural characterization of divalent sulfur compounds (Brito et al., 2007, and references therein). We report here the structure of the title compound, (I), isolated during attempts to synthesize coordination polymers with 5,5'-dinitro-2,2'-dithiodipyridine, (II), and silver trifluoromethanesulfonate. Compound (II) was purchased from Aldrich (purity 96%, CAS No. 2127–10-8). Impurities are not identified in the technical information accompanying the compound, but we believe that (I) was probably an impurity in the commercial sample of (II). To our knowledge, compound (I) is not commercially available.

The molecular structure of (I) is shown in Fig. 1 and selected geometric parameters are given in Table 1. The asymmetric unit of (I) consists of one-half molecule on an inversion centre. A survey of C—S—S—C fragments (Allen et al., 1987) found that S—S bond distances are bimodally distributed: for torsion angles in the ranges 75–105 and 0–20°, the mean S—S bond distances are 2.031 (15) and 2.070 (22) Å, respectively. The corresponding value in (I) is 2.1166 (10) Å, placing it in the upper quartile for Allen's first set. In both isomers, the torsion angles X—C—S—S (where X = N or C) are close to 0 or 180° and within the range found in other substituted aromatic disulfides with an equatorial conformation according to the Shefter classification (Shefter, 1970).

A search of the Cambridge Structural Database (CSD, Version 5.29; Allen, 2002) for the pyridyl disulfide fragment yielded 15 structures, of which only two have an equatorial conformation and S—S and C—S bond lengths similar to those of (I), namely S,S'-bis[3-(ethoxycarbonyl)pyridin-2-yl]disulfide (CSD refcode TATPUA; Toma et al., 2004), and S,S'-bis[3-(n-butoxycarbonyl)pyridin-2-yl]disulfide (CSD refcode OCOYIO; Cindric et al., 2001). The C1—S1 bond length of 1.771 (2) Å in (I) is between the C—S single-bond distance of 1.81 (2) Å and the double-bond distance of 1.56 (4) Å (Etter et al., 1992) and is similar to those observed in organic disulfides with an equatorial conformation.

Also noteworthy are the C—C—C, C—C—S and C—C—N angles at the ipso positions (Table 1), where the C—C—C angles, in particular, are consistent with the electron-withdrawing properties of nitro substituents (Domenicano & Murray-Rust, 1979). The nitro group is rotated 11.0 (3)° out of the plane of the pyridine ring (Fig. 1). The molecular conformations are dominated by the near-orthogonality of the lone pairs on the two adjacent S atoms (Glidewell et al., 2000).

The molecular packing of (I) (Fig. 2) is completely different from that of the previous isomer. Only in the 3,3'-isomer, (I), does the nitropyridine ring participate in significant intramolecular C—H···O interactions, with an H···O distance of 2.40 (3) Å. These interactions may stabilize the conformation adopted by the molecule in the solid state (Fig. 1). The molecules are linked into centrosymmetric rings with an R⁴₄(30) motif (Bernstein et al., 1995) centred at (0,1/2,1/2) (Fig. 2, Table 2).

Related literature

For related literature, see: Allen (2002); Allen et al. (1987); Bernstein et al. (1995); Brito et al. (2007); Cindric et al. (2001); Domenicano & Murray-Rust (1979); Etter et al. (1992); Glidewell et al. (2000); Shefter (1970); Toma et al. (2004).

S2. Experimental

All reactions were carried out under an atmosphere of purified nitrogen. Solvents were dried and distilled prior to use. 5,5'-dinitro-2,2'-dithiodipyridine and silver trifluoromethanesulfonate were purchased from Aldrich and were used without further purification. The title compound was obtained in an attempt to prepare coordination polymers with silver trifluoromethanesulfonate and the ligand. A mixture of 5,5'-dinitro-2,2'-dithiodipyridine (1 mmol, 310 mg) and silver trifluoromethanesulfonate (1 mmol, 256.9 mg) in methanol (20 ml) was refluxed for 8 h. After slow cooling of the reaction system to room temperature, pale-yellow prismatic crystals of (II) and colourless needle-shaped crystals of (I) were formed. Samples of the two isomers were isolated manually at ambient temperature. The spectroscopic properties of (I) were not determined due to the small amount of sample available.

S3. Refinement

All H atoms were located in a difference map and their positional and isotropic displacement parameters were refined.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN (Otwinowski & Minor, 1997); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997) and PLATON (Spek, 2003); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. A view of the molecular structure of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level and H atoms are shown as small spheres of arbitrary radii. Unlabelled atoms are related to labelled atoms by the symmetry code (-x, -y, -z + 1).
	Fig. 2. Part of the crystal structure of (I), showing the formation of a cyclic R^44(30) pattern. H atoms not involved in the motif shown have been omitted. [Symmetry code:(i) -x, -y + 1, -z + 1]

3,3'-Dinitro-2,2'-dithiodipyridine

Crystal data

C10H6N4O4S2	F(000) = 316
Mr = 310.31	Dx = 1.691 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1177 reflections
a = 3.8320 (17) Å	θ = 3.0–27.5°
b = 21.4002 (12) Å	µ = 0.46 mm^−1
c = 7.8301 (14) Å	T = 298 K
β = 108.339 (10)°	Needle, colourless
V = 609.5 (3) Å^3	0.20 × 0.05 × 0.02 mm
Z = 2

Data collection

Nonius KappaCCD area-detector diffractometer	1335 independent reflections
Radiation source: fine-focus sealed tube	1177 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.054
ϕ scans, and ω scans with κ offsets	θmax = 27.3°, θmin = 2.9°
Absorption correction: multi-scan (SORTAV; Blessing, 1995)	h = −4→4
Tmin = 0.970, Tmax = 0.987	k = −21→27
4650 measured reflections	l = −10→9

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	All H-atom parameters refined
R[F^2 > 2σ(F^2)] = 0.050	w = 1/[σ^2(Fo^2) + (0.0203P)^2 + 0.4035P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.100	(Δ/σ)max = 0.001
S = 1.22	Δρmax = 0.26 e Å^−3
1335 reflections	Δρmin = −0.22 e Å^−3
103 parameters

Special details

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.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

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

	x	y	z	Uiso*/Ueq
S1	0.12815 (15)	0.04092 (3)	0.56682 (7)	0.0276 (2)
O1	0.4423 (6)	0.14861 (10)	0.6805 (2)	0.0495 (5)
O2	0.6756 (6)	0.21671 (10)	0.5420 (3)	0.0586 (6)
N1	−0.0227 (6)	0.05151 (10)	0.2104 (3)	0.0338 (5)
N2	0.4861 (6)	0.17034 (10)	0.5429 (3)	0.0357 (5)
C1	0.1373 (6)	0.08007 (11)	0.3691 (3)	0.0259 (5)
C2	0.3044 (6)	0.13896 (11)	0.3727 (3)	0.0282 (5)
C3	0.3017 (8)	0.16864 (14)	0.2147 (4)	0.0379 (6)
C4	0.1319 (8)	0.13897 (15)	0.0545 (4)	0.0445 (7)
C5	−0.0226 (8)	0.08091 (14)	0.0589 (4)	0.0413 (7)
H3	0.414 (8)	0.2052 (14)	0.222 (4)	0.039 (8)*
H4	0.122 (8)	0.1571 (15)	−0.049 (4)	0.051 (9)*
H5	−0.152 (7)	0.0574 (15)	−0.049 (4)	0.046 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0318 (3)	0.0282 (3)	0.0236 (3)	−0.0021 (2)	0.0097 (2)	0.0014 (2)
O1	0.0642 (14)	0.0512 (13)	0.0335 (10)	−0.0113 (10)	0.0158 (10)	−0.0057 (9)
O2	0.0698 (15)	0.0427 (13)	0.0672 (15)	−0.0241 (11)	0.0269 (12)	−0.0123 (11)
N1	0.0420 (12)	0.0316 (12)	0.0269 (11)	0.0025 (9)	0.0096 (9)	0.0023 (8)
N2	0.0353 (12)	0.0289 (12)	0.0434 (13)	0.0009 (9)	0.0129 (10)	−0.0056 (10)
C1	0.0270 (12)	0.0260 (13)	0.0262 (11)	0.0053 (9)	0.0104 (9)	0.0030 (9)
C2	0.0280 (12)	0.0279 (13)	0.0301 (12)	0.0041 (10)	0.0112 (10)	0.0016 (10)
C3	0.0396 (15)	0.0317 (16)	0.0457 (16)	0.0018 (12)	0.0180 (12)	0.0095 (12)
C4	0.0561 (19)	0.0457 (18)	0.0358 (15)	0.0080 (14)	0.0201 (14)	0.0156 (13)
C5	0.0539 (17)	0.0427 (17)	0.0253 (13)	0.0069 (13)	0.0098 (12)	0.0011 (12)

Geometric parameters (Å, º)

S1—C1	1.771 (2)	C1—C2	1.410 (3)
S1—S1^i	2.1167 (12)	C2—C3	1.388 (4)
O1—N2	1.233 (3)	C3—C4	1.373 (4)
O2—N2	1.231 (3)	C3—H3	0.89 (3)
N1—C5	1.343 (3)	C4—C5	1.382 (4)
N1—C1	1.347 (3)	C4—H4	0.89 (3)
N2—C2	1.458 (3)	C5—H5	0.97 (3)
C1—S1—S1^i	95.34 (9)	C1—C2—N2	120.9 (2)
C5—N1—C1	118.4 (2)	C4—C3—C2	118.1 (3)
O2—N2—O1	123.5 (2)	C4—C3—H3	123.4 (19)
O2—N2—C2	118.6 (2)	C2—C3—H3	118.4 (19)
O1—N2—C2	117.9 (2)	C3—C4—C5	118.4 (3)
N1—C1—C2	119.8 (2)	C3—C4—H4	120 (2)
N1—C1—S1	117.62 (18)	C5—C4—H4	121 (2)
C2—C1—S1	122.62 (18)	N1—C5—C4	124.3 (3)
C3—C2—C1	121.0 (2)	N1—C5—H5	112.4 (18)
C3—C2—N2	118.1 (2)	C4—C5—H5	123.3 (18)
C5—N1—C1—C2	−1.0 (3)	O1—N2—C2—C3	169.6 (2)
C5—N1—C1—S1	179.12 (19)	O2—N2—C2—C1	169.1 (2)
S1^i—S1—C1—N1	3.70 (19)	O1—N2—C2—C1	−10.6 (3)
S1^i—S1—C1—C2	−176.16 (18)	C1—C2—C3—C4	−0.1 (4)
N1—C1—C2—C3	1.1 (4)	N2—C2—C3—C4	179.7 (2)
S1—C1—C2—C3	−179.09 (19)	C2—C3—C4—C5	−0.9 (4)
N1—C1—C2—N2	−178.7 (2)	C1—N1—C5—C4	0.0 (4)
S1—C1—C2—N2	1.1 (3)	C3—C4—C5—N1	1.0 (5)
O2—N2—C2—C3	−10.8 (4)

Symmetry code: (i) −x, −y, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C3—H3···O2	0.89 (3)	2.40 (3)	2.714 (4)	101 (2)
C3—H3···O2^ii	0.89 (3)	2.58 (3)	3.335 (4)	143 (2)

Symmetry code: (ii) x, −y+1/2, z−1/2.