Bis(3-phenyl-1,2,4-thia­diazole-5-thiol­ato)mercury(II)

The title compound, [Hg(C₈H₅N₂S₂)₂], has crystallographic C₂ symmetry. The Hg—S distance is 2.353 (2) Å and the coordination geometry is linear, with an S—Hg—S angle of 179.77 (18)°. The exocyclic C—S single-bond distance is 1.749 (6) Å, and intra­molecular Hg...N distances of 2.857 (4) Å exist, as well as secondary Hg...C and S...S contacts.

S1. Comment

In recent years, there has been considerable interest in the complexes of heterocyclic thiones and oxadiazole, triazole and related ligands (Raper, 1997; Maravalli & Goudar, 1999; Bell et al., 2000, 2001, 2004). Aromatic nitrogen-containing heterocyclic molecules such as diazines and azolates have been increasingly used in a variety of bridging capacities (Steel, 1990). The fact that mercury(II) ions interact with many biological molecules through coordination with deprotonated thiol, imidazole, disulfide, thioether, amino or carboxylate groups is well known, and a great deal of effort has been devoted to the characterization of these interactions in model molecules and in proteins (Popović et al., 2000; Kajdan et al., 2000). Interest in the structural chemistry of mercury(II) halide complexes with ligands containing S donor atoms, such as heterocyclic thioamides, is related not only to the toxicological behaviour of the metal and to the detoxification of mercury, but also to their industrial applications, especially in semiconductors or in photovoltaic devices (Hadjikakou et al., 2003). Extensive use of heterocyclic thionates as bridging ligands stems from the presence of the thioamide N—C—S⁻ group. Parent ligands adopt the thione form in the solid but may exist, at least in part, as the thiol form in solution, particularly in non-polar solvents (Cotton & Walton, 1993).

Our previous reports (Ağırbaş et al., 1992; Dürüst et al., 1991) related to the synthesis of the various thiadiazole derivatives on the basis of thione–thiol rearrangement encouraged us to obtain the metal derivatives of the above-mentioned compounds. This work describes the synthesis and crystal structure of the first example, the title compound, (I).

The molecular structure of (I) is illustrated in Fig. 1. The molecule lies on a crystallographic twofold axis, and although this does not require the coordination geometry to be strictly linear, it is so within experimental error. No previous examples of complexes of 1,2,4-thiadiazol-5-ylthio ligands exist in the Cambridge Structural Database (CSD, Version 5.26, November 2004 release; Allen, 2002), but the Hg1—S1 distance agrees well with those in two recent determinations of bis(1,3-benzothiazole-2-thiolato-S)mercury(II) (CSD refcode METZUG), 2.344 (3)–2.351 (3) Å for three unique values (Bell et al., 2001) and 2.338 (3)–2.345 (3) Å (Popović et al., 2002). The mean value for Hg—S distances in Hg^II arenethionate complexes in the compilation of Orpen et al. (1989) is 2.362 Å.

The S1—C1 distance is indicative of a single bond, also in reasonable agreemement with the mean value of 1.761 Å reported for arenethiolates by Orpen et al. (1989) and with the values from the two determinations of METZUG [1.727 (10)–1.751 (9) Å]. Thus, the ligand is established to be a heterocyclic thiolate. Bond distances within the 1,2,4-thiadiazole ring are consisent with those of the only structure in the CSD having an S atom at C1 on this heterocycle, 3,5-bis(methylmercapto)-1,2,4-thiadiazole (BICJEC; Gattow et al., 1982), except that BICJEC has C2—N1 slightly longer [1.373 (6)] and N2—S2 slightly shorter [1.613 (5) Å]. The 1,2,4-thiadiazole and phenyl rings of (I) are coplanar, and the two thiadiazole rings related by the twofold axis are nearly orthogonal, forming a dihedral angle of 88.2 (1)°. The 1,2,4-thiadiazole ring is planar, with a maximum deviation 0.005 (4) Å (For which atom?), and the Hg atom lies 0.3179 (1) Å out of this plane, such that the Hg···N1 distance is 2.857 (4) Å. Similar, but slightly longer, such distances were found in the two determinations of METZUG, falling in the range 2.970 (8)–3.119 (8) Å, and intermolecular Hg···N contacts of average length 2.9 Å were found in the structure of a linear Hg^II aminothiolate complex (Almagro et al., 2001).

In similar linear Hg^II complexes with thiolate ligands, Block et al. (1990) and Casals et al. (1991) noted secondary Hg···S interactions shorter than the sum of the van der Waals radii, increasing the Hg coordination number. The title structure contains none of these, but has close contacts with the phenyl rings of the molecule related by y + 1, with the nearest distance being Hg···C4 = 3.289 (3) Å. Along with the aforementioned intramolecular Hg···N contacts, these secondary interactions complete the coordination sphere of Hg, which may be viewed as six-coordinate (Fig. 2). The figure also shows close S···S contacts along the c direction, S1···S1(−x, y, 1 − z) = 3.335 (1) Å, which are somewhat shorter than twice the van der Waals radius of S (1.8 Å; Bondi, 1964).

S2. Experimental

A warm solution of HgCl₂ (0.5 mmol, 135.7 mg) in aqueous ethanol (10 ml) was added dropwise to a solution of 3-phenyl-1,2,4-thiadiazol-5-thione (Ağırbaş et al., 1992) (1 mmol, 194 mg) in ethanol (10 ml). A white precipitate formed immediately. The reaction mixture was refluxed for 2 h. The solvent was evaporated under reduced pressure, and the crude product was recrystallized from ethyl acetate as colourless needles (m.p. 489–492 K). Spectroscopic analysis: R_f: (EtOAc–light petroleum, 1:1): 0.68; ¹H NMR (Solvent?, δ, p.p.m.): 7.27–7.35 (m, 6H), 7.95–7.98 (m, 4H); ¹³C NMR (Solvent?, δ, p.p.m.): 127.8, 128.6,129.2,130.4,131.4; IR (Medium?, ν, cm⁻¹): 1463, 1432, 1319, 1279, 1113, 1039, 898, 781, 704. Analysis, calculated: C 32.73, H 1.72, N 9.54, S 21.85%; found: C 33.20, H 2.21, N 9.53, S 21.66%. MS (EI, 70 eV): 592 (M⁺, 2), 386 (15), 283 (2), 225 (17), 219 (23), 135 (100), 122 (26), 103 (65), 77 (20).

S3. Refinement

The absolute structure was determined by refinement of the Flack (1983) parameter, using 746 Friedel pairs. H atoms were placed in idealized positions, with C—H distances of 0.95 Å and displacement parameters assigned as U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: COLLECT (Nonius, 2000); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The structure of (I), viewed normal to the twofold axis, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A stereoview, illustrating the secondary interactions in (I). The b axis is vertical and the S···S contact lies approximately along c.

Bis(3-phenyl-1,2,4-thiadiazole-5-thiolato)mercury(II)

Crystal data

[Hg(C8H5N2S2)2]	F(000) = 556
Mr = 587.11	Dx = 2.226 Mg m^−3
Monoclinic, C2	Melting point: 489-492 K K
Hall symbol: C 2y	Mo Kα radiation, λ = 0.71073 Å
a = 23.066 (2) Å	Cell parameters from 1083 reflections
b = 5.0026 (4) Å	θ = 2.5–28.3°
c = 8.0220 (7) Å	µ = 9.27 mm^−1
β = 108.871 (9)°	T = 105 K
V = 875.90 (14) Å^3	Lath, colourless
Z = 2	0.17 × 0.05 × 0.03 mm

Data collection

Nonius KappaCCD (with Oxford Cryostream) diffractometer	1960 independent reflections
Radiation source: fine-focus sealed tube	1959 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.053
ω scans with κ offsets	θmax = 28.3°, θmin = 2.6°
Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997)	h = −29→30
Tmin = 0.355, Tmax = 0.757	k = −5→6
4345 measured reflections	l = −10→10

Refinement

Refinement on F^2	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F^2 > 2σ(F^2)] = 0.023	w = 1/[σ^2(Fo^2) + 4.7102P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.050	(Δ/σ)max = 0.001
S = 1.04	Δρmax = 0.75 e Å^−3
1960 reflections	Δρmin = −0.84 e Å^−3
115 parameters	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
1 restraint	Extinction coefficient: 0.0030 (3)
Primary atom site location: structure-invariant direct methods	Absolute structure: Flack, (1983), with 746 Friedel pairs
Secondary atom site location: difference Fourier map	Absolute structure parameter: −0.005 (9)

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
Hg1	0.0000	0.00000 (2)	0.0000	0.01570 (10)
S1	0.00604 (5)	−0.0010 (7)	0.29842 (12)	0.0177 (2)
S2	0.10139 (7)	0.3598 (3)	0.55952 (17)	0.0253 (3)
N1	0.0790 (2)	0.3789 (9)	0.2311 (5)	0.0156 (9)
N2	0.1417 (2)	0.5766 (8)	0.4869 (6)	0.0240 (12)
C1	0.0619 (2)	0.2499 (10)	0.3498 (6)	0.0164 (10)
C2	0.1238 (2)	0.5585 (9)	0.3124 (6)	0.0180 (15)
C3	0.1498 (2)	0.7291 (10)	0.2051 (7)	0.0166 (10)
C4	0.1296 (2)	0.7040 (10)	0.0220 (7)	0.0174 (10)
H4	0.1002	0.5712	−0.0332	0.021*
C5	0.1525 (3)	0.8728 (11)	−0.0802 (7)	0.0191 (11)
H5	0.1387	0.8547	−0.2048	0.023*
C6	0.1953 (2)	1.0677 (9)	0.0002 (7)	0.0197 (13)
H6	0.2102	1.1852	−0.0697	0.024*
C7	0.2165 (3)	1.0912 (10)	0.1838 (7)	0.0200 (11)
H7	0.2467	1.2209	0.2389	0.024*
C8	0.1935 (2)	0.9258 (10)	0.2845 (7)	0.0198 (12)
H8	0.2073	0.9449	0.4090	0.024*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg1	0.01764 (13)	0.01780 (13)	0.01175 (12)	0.000	0.00489 (8)	0.000
S1	0.0212 (5)	0.0207 (5)	0.0120 (4)	−0.0003 (15)	0.0063 (4)	−0.0007 (13)
S2	0.0311 (8)	0.0279 (7)	0.0125 (6)	−0.0100 (6)	0.0011 (5)	0.0011 (5)
N1	0.014 (2)	0.0166 (19)	0.016 (2)	−0.0018 (17)	0.0047 (17)	−0.0024 (16)
N2	0.032 (3)	0.020 (3)	0.017 (2)	−0.0060 (17)	0.0034 (18)	0.0017 (15)
C1	0.019 (3)	0.015 (2)	0.014 (2)	0.0018 (19)	0.0042 (19)	−0.0001 (18)
C2	0.016 (2)	0.021 (5)	0.016 (2)	0.0020 (19)	0.0040 (17)	−0.0002 (18)
C3	0.014 (2)	0.017 (3)	0.019 (2)	0.0049 (19)	0.006 (2)	0.0015 (19)
C4	0.018 (3)	0.016 (2)	0.016 (2)	0.000 (2)	0.0022 (19)	−0.0014 (19)
C5	0.018 (3)	0.021 (3)	0.018 (2)	0.002 (2)	0.004 (2)	0.001 (2)
C6	0.023 (3)	0.017 (4)	0.022 (2)	0.0006 (18)	0.010 (2)	0.0022 (17)
C7	0.016 (2)	0.016 (2)	0.027 (3)	−0.0012 (17)	0.005 (2)	−0.0011 (18)
C8	0.018 (2)	0.019 (3)	0.019 (2)	−0.0009 (18)	0.003 (2)	−0.0010 (17)

Geometric parameters (Å, º)

Hg1—S1	2.353 (2)	C3—C8	1.405 (7)
Hg1—S1^i	2.353 (2)	C4—C5	1.393 (8)
S1—C1	1.749 (6)	C4—H4	0.9500
S2—N2	1.653 (5)	C5—C6	1.390 (7)
S2—C1	1.724 (5)	C5—H5	0.9500
N1—C1	1.312 (7)	C6—C7	1.399 (8)
N1—C2	1.365 (6)	C6—H6	0.9500
N2—C2	1.328 (7)	C7—C8	1.377 (8)
C2—C3	1.471 (7)	C7—H7	0.9500
C3—C4	1.396 (7)	C8—H8	0.9500
S1—Hg1—S1^i	179.77 (18)	C5—C4—H4	119.9
C1—S1—Hg1	92.00 (18)	C3—C4—H4	119.9
N2—S2—C1	92.6 (2)	C6—C5—C4	120.0 (5)
C1—N1—C2	109.6 (4)	C6—C5—H5	120.0
C2—N2—S2	107.9 (4)	C4—C5—H5	120.0
N1—C1—S2	111.3 (4)	C5—C6—C7	120.1 (5)
N1—C1—S1	123.6 (4)	C5—C6—H6	119.9
S2—C1—S1	125.1 (3)	C7—C6—H6	119.9
N2—C2—N1	118.6 (5)	C8—C7—C6	119.8 (5)
N2—C2—C3	122.0 (4)	C8—C7—H7	120.1
N1—C2—C3	119.4 (4)	C6—C7—H7	120.1
C4—C3—C8	119.1 (5)	C7—C8—C3	120.8 (5)
C4—C3—C2	120.2 (5)	C7—C8—H8	119.6
C8—C3—C2	120.7 (5)	C3—C8—H8	119.6
C5—C4—C3	120.3 (5)
C1—S2—N2—C2	0.4 (4)	N1—C2—C3—C4	−1.2 (7)
C2—N1—C1—S2	0.8 (5)	N2—C2—C3—C8	−2.3 (8)
C2—N1—C1—S1	−179.1 (4)	N1—C2—C3—C8	176.5 (5)
N2—S2—C1—N1	−0.8 (4)	C8—C3—C4—C5	−0.3 (8)
N2—S2—C1—S1	179.2 (4)	C2—C3—C4—C5	177.4 (5)
Hg1—S1—C1—N1	7.1 (5)	C3—C4—C5—C6	−0.2 (8)
Hg1—S1—C1—S2	−172.8 (3)	C4—C5—C6—C7	1.3 (8)
S2—N2—C2—N1	0.0 (6)	C5—C6—C7—C8	−1.9 (8)
S2—N2—C2—C3	178.7 (4)	C6—C7—C8—C3	1.4 (8)
C1—N1—C2—N2	−0.5 (7)	C4—C3—C8—C7	−0.3 (8)
C1—N1—C2—C3	−179.3 (5)	C2—C3—C8—C7	−178.0 (5)
N2—C2—C3—C4	−179.9 (5)

Symmetry code: (i) −x, y, −z.