5,5'-Di­methyl-2,2'-di­thio­di-1,3,4-thia­diazole

The title compound, C₆H₆N₄S₄, is formed through the thionato S-S bonding of parent 2-mercapto-5-methyl-1,3,4-thia­diazole mol­ecules, following the deprotonation of thiol groups in a mixed solvent. The title compound crystallizes in the monoclinic system, space group C2/c. The S-S distance is 2.028 (1) Å, typical of a single bond. The two 1,3,4-thia­diazo­le rings in the mol­ecule each remain planar, with a dihedral angle of 70.5 (1) Å, and are related by a twofold rotation axis through the middle of the S2-S2 bond. The geometric parameters for the parent ligand are also reported, to demonstrate the influence of deprotonation on the ligand dimensions.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.003 Å
• R factor = 0.035
• wR factor = 0.097
• Data-to-parameter ratio = 14.8

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



ABSTY_02  Alert C An _exptl_absorpt_correction_type has been given without
          a literature citation. This should be contained in the
          _exptl_absorpt_process_details field.
          Absorption correction given as empirical

General Notes



ABSTM_02  When printed, the submitted absorption T values will be replaced
          by the scaled T values. Since the ratio of scaled T's is
          identical to the ratio of reported T values, the scaling does
          not imply a change to the absorption corrections used in the
          study.
          Ratio of Tmax expected/reported      0.901
          Tmax scaled      0.815 Tmin scaled      0.725


 0 Alert Level A = Potentially serious problem

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S1. Comment

Triazole and its derivative ligands are versatile chelating ligands that can bridge a wide range of metal atoms into dimers, oligomers, and polymeric chains through multidendate donor atoms (Steel, 1990; Inoue & Kubo, 1976; Maekawa et al., 1999). The combined effects of deprotonation and coordination are found to cause significant changes to the bond lengths and angles in these ligands (Chen et al., 1993; Tandon et al., 1994). In a recent effort to investigate the dependence of optical properties of coinage metal complexes on the molecular structures and metal–metal interactions (Ford et al., 1999; Zhou et al.,2002), the title molecule, (I), was isolated as a dimerized structure of parent 1,3,4-triazole through S—S bonding (see Scheme). In this paper, we report the synthesis and crystal structure of (I).

As shown in Fig. 1, the dimerized structure is formed through the S—S connection of parent 2-mercapto-5-methyl-1,3,4-thiadiazole moieties following the deprotonation of thiol groups. The observed S2—S2' distance in the present disulfide structure is 2.028 (1) Å, very close to the sum of the atomic radius (1.035 Å) or single-bond covalent radius (1.04 Å) of the element. The S—S single-bond character is further confirmed by the associated S2—C3 distance of 1.764 (2) Å, which is only slightly smaller than the sum of single–bond radii (1.81 Å). The S1···S1' non-bonding distance is 3.666 Å. The torsion angle of C3—S2—S2'—C3' is −84.45 (16)°. The 2-mercapto-5-methyl-1,3,4-thiadiazole ring in the molecule remains planar, with an r.m.s deviation of 0.042 Å. The two ring planes make a dihedral angle of 70.5 (1) Å, related by a crystallographic twofold rotation symmetry through the middle of the S—S bond.

Table 1 lists important bond distances and angles for (I), as well as for the parent 2-mercapto-5-methyl-1,3,4-thiadiazole ligand, which has also been determined [C₃H₄N₂S₂, (II), space group Pbca, a = 10.5107 (6), b = 20.398 (1), c = 9.1157 (5) Å, V = 1121.6 (1) ų, R1/wR = 0.0383/0.1307, S = 1.152) (Song et al., 2002)]. To facilitate the comparison between dimerized (I) and parent (II), the molecular picture of the latter is also shown in Fig. 2. The bond distances in the structure are subjected to small variations upon the deprotonation and dimerization. Such effect was previously observed when the ligand is deprotonated and then coordinated to metal atoms (Chen et al., 1993; Tandon et al., 1994). The N—N distance is slightly lengthened, 1.382 (3) Å in (II) to 1.389 (3) Å in (I), in spite of an insignificant deviation within 3° σ, but both are comparable to the single-bond distance of 1.40 Å. Accordingly, the C—N bond distances are slightly shortened from 1.331 (3) Å in (II) to 1.286 (3) Å in (I), sufficiently short to suggest partial double-bond character (Senda et al., 1986; Mathew & Palenik, 1974). The cyclic C—S bond distances are also shortened from 1.742 (2) Å in (II) to 1.712 (2) Å in (I), both are slightly shorter than the value of 1.77 Å for a Csp²—S single bond (Mathew & Palenik, 1974). In contrast, the exocyclic C—S bond distances are significantly lengthened from 1.665 (2) Å in (II) with thiols, to 1.764 (2) Å in (I) with disulfur units. The structural effect of deprotonation is evident.

S2. Experimental

CuBr (0.5 mmol) and C₃H₄N₂S₂ (0.5 mmol) were stirred in a mixed solvent of alcohol (5 ml), acetonitrile (10 ml), and tetrahydropyran (5 ml) at room temperature. Yellow crystals of the title compound were obtained after a few days.

S3. Refinement

The H atoms on the ligands were located at geometrically calculated positions with H-atom parameters constrained.

Computing details

Data collection: SMART (Siemens, 1995); cell refinement: SMART; data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1996); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the molecule of (I), shown with 50% probability displacement ellipsoids.
	Fig. 2. A view of the molecule of (II), shown with 50% probability displacement ellipsoids.

(I)

Crystal data

C6H6N4S4	F(000) = 536
Mr = 262.39	Dx = 1.625 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.5647 (6) Å	Cell parameters from 1505 reflections
b = 6.9212 (6) Å	θ = 3.8–25.0°
c = 18.2692 (15) Å	µ = 0.85 mm^−1
β = 98.074 (1)°	T = 293 K
V = 1072.23 (15) Å^3	Cube, yellow
Z = 4	0.40 × 0.40 × 0.24 mm

Data collection

Siemens SMART CCD diffractometer	948 independent reflections
Radiation source: fine-focus sealed tube	807 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
ω scans	θmax = 25.0°, θmin = 3.8°
Absorption correction: empirical (using intensity measurements) ?	h = −10→7
Tmin = 0.805, Tmax = 0.905	k = −8→4
1847 measured reflections	l = −21→18

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.035	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.097	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0581P)^2 + 0.4258P] where P = (Fo^2 + 2Fc^2)/3
948 reflections	(Δ/σ)max = 0.001
64 parameters	Δρmax = 0.32 e Å^−3
0 restraints	Δρmin = −0.28 e Å^−3

Special details

Geometry. Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

3.1535 (0.0073) x + 3.9961 (0.0033) y + 12.2368 (0.0083) z = 11.4708 (0.0030)

* 0.0494 (0.0016) C1 * −0.0061 (0.0021) C2 * −0.0488 (0.0018) C3 * 0.0038 (0.0017) N1 * −0.0251 (0.0016) N2 * −0.0422 (0.0012) S1 * 0.0689 (0.0011) S2

Rms deviation of fitted atoms = 0.0415

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
S2	0.60982 (8)	0.15497 (9)	0.73527 (4)	0.0511 (3)
S1	0.45955 (8)	0.51058 (9)	0.64879 (4)	0.0525 (3)
N2	0.7220 (3)	0.3574 (3)	0.63259 (12)	0.0527 (6)
N1	0.7063 (3)	0.5180 (3)	0.58654 (13)	0.0534 (6)
C3	0.6028 (3)	0.3380 (3)	0.66769 (12)	0.0394 (5)
C2	0.5768 (3)	0.6104 (3)	0.58890 (12)	0.0418 (6)
C1	0.5333 (3)	0.7907 (4)	0.54579 (15)	0.0544 (7)
H1A	0.6142	0.8213	0.5163	0.082*
H1B	0.5225	0.8953	0.5792	0.082*
H1C	0.4351	0.7714	0.5142	0.082*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S2	0.0579 (5)	0.0462 (4)	0.0536 (4)	0.0147 (3)	0.0228 (3)	0.0122 (3)
S1	0.0449 (4)	0.0562 (5)	0.0616 (5)	0.0183 (3)	0.0259 (3)	0.0189 (3)
N2	0.0516 (13)	0.0536 (12)	0.0578 (13)	0.0174 (10)	0.0243 (10)	0.0134 (10)
N1	0.0531 (14)	0.0568 (13)	0.0556 (13)	0.0173 (10)	0.0267 (10)	0.0161 (10)
C3	0.0406 (12)	0.0395 (12)	0.0398 (12)	0.0070 (9)	0.0122 (9)	−0.0003 (9)
C2	0.0439 (13)	0.0447 (13)	0.0395 (12)	0.0069 (10)	0.0157 (10)	0.0028 (10)
C1	0.0591 (16)	0.0528 (14)	0.0559 (15)	0.0132 (13)	0.0243 (12)	0.0135 (13)

Geometric parameters (Å, º)

S2—C3	1.764 (2)	N1—C2	1.286 (3)
S2—S2^i	2.0280 (13)	C2—C1	1.495 (3)
S1—C3	1.712 (2)	C1—H1A	0.9600
S1—C2	1.730 (2)	C1—H1B	0.9600
N2—C3	1.287 (3)	C1—H1C	0.9600
N2—N1	1.389 (3)
C3—S2—S2^i	104.11 (8)	N1—C2—S1	113.74 (18)
C3—S1—C2	86.73 (11)	C1—C2—S1	122.86 (17)
C3—N2—N1	111.64 (19)	C2—C1—H1A	109.5
C2—N1—N2	112.9 (2)	C2—C1—H1B	109.5
N2—C3—S1	115.04 (17)	H1A—C1—H1B	109.5
N2—C3—S2	118.15 (17)	C2—C1—H1C	109.5
S1—C3—S2	126.53 (14)	H1A—C1—H1C	109.5
N1—C2—C1	123.4 (2)	H1B—C1—H1C	109.5

Symmetry code: (i) −x+1, y, −z+3/2.