Di­iodo­bis(1-methyl-1,3-imidazolium-2-thiol­ato-S)­mercury(II)

The reaction of 1-methyl-1,3-imidazole-2-thione (meimtH) with mercury(II) iodide in methanol in a 2:1 molar ratio resulted in the formation of single crystals of the title compound, [HgI₂(C₄H₆N₂S)₂]. The Hg atom is coordinated by two I [2.7809 (9) and 2.7999 (8) Å] and two thione S atoms [2.520 (3) and 2.576 (3) Å] with irregular tetrahedral coordination geometry. The NH groups of the imidazole ring take part in intra- and intermolecular hydrogen bonds with I atoms [N...I 3.596 (8) and 3.611 (9) Å, respectively] joining mol­ecules into infinite chains parallel to the z axis.

S1. Comment

Heterocyclic thionates are electron-rich polyfunctional ligands (Raper, 1996). Whereas heterocyclic thionates are ambidentate ligands (S– or N-donor atoms), their monosubstituted analogues are S,N-bridging and/or chelating ligands. The N-disubstituted derivatives are exclusively monodentate S donors. Currently available X-ray structural data show that 1-methyl-1,3-imidazole-2-thione (meimtH) can act as a neutral S-donor ligand (Raper & Nowell, 1979, 1980; García-Martínez et al., 1993; Raper et al., 1980; Nowell et al., 1974; Raper & Brooks, 1977; Birker et al., 1982; O'Neill et al., 1982), as an S-bridging ligand (Creighton et al., 1985; Raper & Clegg, 1991) or as an anionic ligand (S-donor: Norris et al., 1983; N,S-bridging: Cooper et al., 1986; Raper et al., 1991; Agnus et al., 1980; Castro et al., 1995; Popović et al., 1999). The structure of the ligand itself, i.e. 1-methyl-1,3-imidazole-2-thione (meimtH), is known from two independent studies (Raper et al., 1983; Vampa et al., 1995). The C═S bond distances [1.686 (2) and 1.682 (2) Å in two crystallographically independent molecules; Vampa et al., 1995] and the protonation at N3 establish the presence of the thione tautomer in the solid state.

Mercury(II) halides form 1:1 and 1:2 complexes with 1-methyl-1,3-imidazole-2-thione, HgX₂(meimtH) and HgX₂(meimtH)₂, whereas mercury(II) acetate forms the complex Hg(meimt)₂. Two mercury(II) complexes with 1-methyl-1,3-imidazole-2-thione derived from HgBr₂ (Raper et al., 1998) and Hg(Oac)₂ (Popović et al., 1999) have been structurally examined. Firstly, HgBr₂(meimtH) (Raper et al., 1998), with a 4 + 1 trigonal-bipyramidal mercury coordination, contains bromo-bridged dimers that are further linked into weakly associated polymeric sheets via Hg···Br contacts of 3.587–3.791 Å. The monodentate meimtH ligand has thione–sulfur ligating character with Hg—S distances of 2.405 (4)–2.419 (4) Å. Secondly, Hg(meimt)₂ (Popović et al., 1999) possesses an Hg atom located on a twofold axis coordinated by two S [2.4305 (12) Å] and two N atoms [2.451 (4) Å] from four meimt ligands. The Hg—N bond is longer than the sum of the covalent radii for N and tetrahedral Hg (2.23 Å; Pauling, 1960; Grdenić, 1965). The Hg—S distance of 2.4305 (12) Å lies between expected values for linear and tetrahedral coordination. The meimt ligands bridge two Hg atoms forming endless chains parallel to the z axis.

The coordination of meimtH towards methylmercurio compounds appears to be dependent on pH and on the molar ratio of reactants. In complexes with a 1:1 mercury-to-meimtH ratio, Hg—S bonds are formed irrespective of the pH of the medium, whereas for the 2:1 ratio in basic conditions, both Hg—S and Hg—N bonds are expected to be formed (Buncel et al., 1982). There are two monomeric complexes containing the CH₃Hg^II unit, which is bonded to the exocyclic sulfur by Hg—S bonds of 2.382 (2) Å in CH₃Hg(meimtH)(NO₃) and 2.338 (7) Å in CH₃Hg(meimt) (Norris et al., 1983). Although the ligand in the latter contains an available electron lone pair at the deprotonated N atom, Hg does not form intermolecular contacts with the N atom of adjacent molecules, and the Hg—S bond distance is equal to the sum of Hg and S covalent radii of 2.34 Å (Grdenić, 1965; Pauling, 1960).

The molecule of the title compound HgI₂(meimtH)₂ is situated in a general position (Fig. 1). The Hg atom is tetrahedrally coordinated by two I atoms [Hg—I1 2.7809 (9) Å and Hg—I2 2.7999 (8) Å] and two thione S atoms [Hg—S1 2.520 (3) Å and Hg—S2 2.576 (3) Å]. The Hg—I distances are slightly shorter than the sum of covalent radii for I and Hg in tetrahedral coordination (2.81 Å; Pauling, 1960; Grdenić, 1965) and correspond well to the Hg—I distance in the red tetrahedral form of HgI₂ [2.783 (3) Å; Jeffrey & Vlasse, 1967]. In contrast, in the 1:1 complex with non-substituted 1,3-imidazole-2-thione, HgI₂(imtH₂), Hg displays a 3 + 1 coordination and the Hg—I bond values are markedly different [2.8187 (7) and 2.6518 (7) Å; Popović et al., 1999] because of participation of one of the I atoms in dimer formation.

The valence angles around The Hg atom of the title compound, (I), lie in the range 103.72 (6)–115.14 (6)°, corresponding to a somewhat distorted tetrahedral geometry at mercury. The Hg—S bond values are slightly longer than the sum of covalent radii for sulfur and tetrahedrally coordinated mercury (1.04 and 1.48 Å, respectively; Pauling, 1960; Grdenić, 1965). The Hg—S bond distance values are longer than in the above-mentioned mercury(II) complexes with meimt or meimtH ligands. Although the Hg atoms in these complexes have different coordination environments, the Hg—S bond values differ according to the nature of other donor atoms bound to mercury (C, Br or N). The tendency of mercury to form stronger Hg—I and weaker Hg—S bonds has been observed in the iodo complexes with other thiones, such as 3,4,5,6-tetrahydropyrimidine-2-thione (Popović et al., 2000).

The reduction in the π-electron density of the exocyclic C—S bond in the title complex relative to the average bond distance in the free ligand is accompanied by metal coordination. The extent of this reduction, as reflected in the the bond lengthening, differs between the title compound and the above-mentioned mercury complexes with meimtH. The lengthening is significant in the HgBr₂(meimtH) [1.73 (2)–1.74 (2) Å; Raper et al., 1998], Hg(meimt)₂ [1.747 (4) Å; Popović et al., 1999], CH₃Hg(meimtH)(NO₃) and CH₃Hg(meimt) complexes [1.741 (8) and 1.75 (2) Å, respectively; Norris et al., 1983], while in the title complex, the C—S bonds are marginally longer than in the free ligand [S1—C11 1.698 (9) Å and S2—C21 1.721 (9) Å versus 1.682 (2) and 1.686 (2) Å]. This is a consequence of the observed tendency of mercury to form stronger Hg—I and weaker Hg—S bonds. The lengthened C—S bond is invariably associated with an increase in the double bond character of the thioamide C—N bonds (Table 1), which are slightly shortened in comparison with the values in the free ligand [1.348 (3) and 1.344((3) Å; Vampa et al., 1995]. Although the major π-electron density appears to be concentrated in the thioamide fragment, all of the ring bond distances are affected by the extended conjugation, revealing the zwitterionic character of the coordinated ligand (C═S in X₂—C═S; X = any atom, 1.671 Å; C_ar—Nsp² 1.371 Å; Allen et al., 1987). The NH groups of the imidazole ring take part in intra- and intermolecular hydrogen bonds formation with I1 and I2 atoms (Table 2) joining molecules into endless chains parallel to the z axis.

S2. Experimental

The title compound was prepared as described by Popović et al. (1999). Crystals suitable for X-ray analysis were formed from a very dilute methanol solution at room temperature on standing for several days.

S3. Refinement

The registered intensity data consisted of two octants and included a full set of Friedel opposites. Methyl H atoms were identified from difference syntheses, idealized and the rigid methyl groups allowed to rotate but not tip. Other H atoms were included at calculated positions and refined using a riding model; the H-atom isotropic displacement parameters were kept equal to 1.5U_eq for Csp³, and 1.2 for for Csp². The H atoms at N12 and N22 could be tentatively identified in the different Fourier map, but were not well defined. They were therefore generated assuming sp² hybridization at N and refined with a riding model. The polar axis direction was determined unambiguously by refining the Flack parameter. The maximum and minimum electron-density peaks in the final difference Fourier map are located 0.71 and 0.86 Å, respectively, from the Hg atom.

Computing details

Data collection: STADI4 (Stoe & Cie, 1995); cell refinement: STADI4; data reduction: X-RED (Stoe & Cie, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON98 (Spek, 1998); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure and the atom-numbering scheme of the bis[iodo(1-methyl-1,3-imidazolium-2-thiolato-S)]mercury(II) complex. Displacement ellipsoids are shown at the 50% probability level. The H atoms are drawn as small circles of arbitrary radii.
	Fig. 2. Packing diagram of the title complex. Hydrogen bonds are shown by dashed lines. The intermolecular N—H···Ihydrogen bond joins molecules into endless chain parallel to the z axis.

bis[iodo(1-methyl-1,3-imidazolium-2-thiolato-S)]mercury(II)

Crystal data

[HgI2(C4H6N2)2]	F(000) = 1224
Mr = 682.73	Dx = 2.830 Mg m^−3
Orthorhombic, Pca21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2ac	Cell parameters from 33 reflections
a = 11.543 (2) Å	θ = 10.0–18.6°
b = 13.996 (5) Å	µ = 13.71 mm^−1
c = 9.9180 (7) Å	T = 293 K
V = 1602.3 (7) Å^3	Plate, colourless
Z = 4	0.70 × 0.38 × 0.05 mm

Data collection

Philips PW1100 diffractometer updated by Stoe	3590 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.060
Graphite monochromator	θmax = 30.0°, θmin = 3.1°
ω scans	h = −16→16
Absorption correction: integration (X-RED; Stoe & Cie, 1995)	k = −19→19
Tmin = 0.074, Tmax = 0.505	l = −13→13
5113 measured reflections	5 standard reflections every 90 min
4575 independent reflections	intensity decay: 6.4%

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.043	H-atom parameters constrained
wR(F^2) = 0.116	Calculated w = 1/[σ^2(Fo^2) + (0.0793P)^2 + 0.3812P] where P = (Fo^2 + 2Fc^2)/3
S = 1.02	(Δ/σ)max < 0.001
4575 reflections	Δρmax = 0.99 e Å^−3
156 parameters	Δρmin = −1.45 e Å^−3
1 restraint	Absolute structure: Flack (1983)
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: −0.007 (8); 2110 Friedel pairs

Special details

Experimental. The Gaussian absorption correction was based on the following indexed crystal faces and distances in mm: 010 0.1349, 0–10 0.1349, 001 0.025, 00–1 0.025, 111 0.2475, −100 0.3479, 100 0.3479.

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

	x	y	z	Uiso*/Ueq
Hg	−0.05011 (3)	0.26093 (3)	0.85625 (7)	0.04622 (11)
I1	−0.15470 (5)	0.16607 (5)	0.64205 (6)	0.04358 (15)
I2	0.16215 (5)	0.34169 (5)	0.78087 (6)	0.04754 (17)
S1	−0.16820 (19)	0.3940 (2)	0.9583 (3)	0.0466 (6)
N11	−0.4003 (6)	0.4140 (6)	0.9777 (7)	0.0375 (15)
N12	−0.3524 (6)	0.3223 (6)	0.8150 (8)	0.0437 (19)
H12N	−0.3123	0.2905	0.7573	0.052*
C11	−0.3090 (7)	0.3749 (6)	0.9167 (9)	0.0345 (16)
C12	−0.5028 (8)	0.3865 (8)	0.9161 (11)	0.047 (2)
H12	−0.5774	0.4058	0.9391	0.057*
C13	−0.4734 (9)	0.3277 (9)	0.8185 (11)	0.052 (3)
H13	−0.5241	0.2954	0.7617	0.063*
C14	−0.3928 (9)	0.4802 (8)	1.0916 (10)	0.048 (2)
H14A	−0.3328	0.4596	1.1520	0.072*
H14B	−0.4655	0.4814	1.1385	0.072*
H14C	−0.3751	0.5432	1.0590	0.072*
S2	0.0049 (2)	0.14267 (19)	1.0447 (3)	0.0444 (5)
N21	0.1810 (6)	0.0621 (6)	0.8988 (8)	0.0406 (17)
N22	0.2403 (7)	0.1622 (6)	1.0452 (9)	0.049 (2)
H22N	0.2414	0.2040	1.1088	0.058*
C21	0.1458 (7)	0.1213 (7)	0.9962 (9)	0.0358 (16)
C22	0.2987 (8)	0.0658 (9)	0.8913 (11)	0.055 (3)
H22	0.3442	0.0297	0.8331	0.066*
C23	0.3377 (9)	0.1276 (10)	0.9784 (16)	0.068 (4)
H23	0.4144	0.1450	0.9929	0.081*
C24	0.1079 (8)	0.0009 (10)	0.8170 (13)	0.061 (3)
H24A	0.0287	0.0210	0.8253	0.091*
H24B	0.1151	−0.0640	0.8472	0.091*
H24C	0.1314	0.0052	0.7243	0.091*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Hg	0.03560 (16)	0.0487 (2)	0.0544 (2)	0.00502 (13)	0.00110 (18)	0.0010 (2)
I1	0.0407 (3)	0.0457 (3)	0.0444 (3)	0.0018 (2)	0.0026 (2)	−0.0027 (3)
I2	0.0361 (3)	0.0533 (4)	0.0533 (4)	−0.0048 (2)	0.0075 (3)	−0.0049 (3)
S1	0.0317 (10)	0.0465 (14)	0.0615 (15)	−0.0013 (9)	0.0007 (9)	−0.0093 (11)
N11	0.040 (4)	0.041 (4)	0.032 (3)	0.005 (3)	0.008 (3)	0.000 (3)
N12	0.043 (4)	0.048 (5)	0.040 (4)	0.006 (3)	0.003 (3)	−0.021 (3)
C11	0.036 (4)	0.031 (4)	0.036 (4)	0.009 (3)	−0.002 (3)	0.001 (3)
C12	0.033 (4)	0.049 (5)	0.059 (5)	0.020 (4)	0.000 (4)	−0.001 (5)
C13	0.037 (4)	0.071 (8)	0.049 (6)	0.000 (4)	−0.007 (4)	−0.013 (5)
C14	0.052 (5)	0.052 (6)	0.040 (5)	0.006 (4)	0.008 (4)	−0.005 (4)
S2	0.0427 (11)	0.0500 (13)	0.0406 (11)	0.0046 (10)	0.0088 (10)	0.0046 (10)
N21	0.026 (3)	0.046 (4)	0.050 (4)	0.005 (3)	−0.003 (3)	−0.008 (3)
N22	0.040 (4)	0.056 (5)	0.050 (5)	0.006 (4)	−0.009 (4)	−0.011 (4)
C21	0.035 (4)	0.037 (4)	0.035 (4)	0.005 (3)	−0.002 (3)	−0.003 (3)
C22	0.026 (4)	0.078 (8)	0.061 (7)	0.009 (4)	−0.012 (4)	−0.016 (5)
C23	0.040 (5)	0.064 (8)	0.098 (11)	0.008 (5)	−0.016 (6)	−0.020 (8)
C24	0.041 (5)	0.070 (7)	0.071 (7)	0.002 (5)	0.007 (5)	−0.028 (6)

Geometric parameters (Å, º)

Hg—S1	2.520 (3)	N22—C21	1.325 (12)
Hg—S2	2.576 (3)	N22—C23	1.391 (15)
Hg—I1	2.7809 (9)	C22—C23	1.302 (17)
Hg—I2	2.7999 (8)	N12—H12N	0.86
S1—C11	1.698 (9)	C12—H12	0.93
N11—C11	1.333 (11)	C13—H13	0.93
N11—C12	1.387 (13)	C14—H14A	0.96
N11—C14	1.463 (12)	C14—H14B	0.96
N12—C11	1.345 (12)	C14—H14C	0.96
N12—C13	1.399 (12)	N22—H22N	0.86
C12—C13	1.316 (15)	C22—H22	0.93
S2—C21	1.721 (9)	C23—H23	0.93
N21—C21	1.335 (12)	C24—H24A	0.96
N21—C22	1.361 (10)	C24—H24B	0.96
N21—C24	1.452 (13)	C24—H24C	0.96
S1—Hg—S2	108.49 (9)	C22—C23—N22	105.5 (10)
S1—Hg—I1	115.14 (6)	C11—N12—H12N	125.6
S2—Hg—I1	110.76 (7)	C13—N12—H12N	125.6
S1—Hg—I2	106.39 (6)	C13—C12—H12	126.9
S2—Hg—I2	103.72 (6)	N11—C12—H12	126.9
I1—Hg—I2	111.63 (3)	C12—C13—H13	126.0
C11—S1—Hg	107.7 (3)	N12—C13—H13	126.0
C11—N11—C12	111.1 (8)	N11—C14—H14A	109.5
C11—N11—C14	124.3 (8)	N11—C14—H14B	109.5
C12—N11—C14	124.5 (8)	H14A—C14—H14B	109.5
C11—N12—C13	108.9 (8)	N11—C14—H14C	109.5
N11—C11—N12	105.7 (8)	H14A—C14—H14C	109.5
N11—C11—S1	125.6 (7)	H14B—C14—H14C	109.5
N12—C11—S1	128.7 (7)	C21—N22—H22N	125.1
C13—C12—N11	106.1 (8)	C23—N22—H22N	125.1
C12—C13—N12	108.1 (9)	C23—C22—H22	125.3
C21—S2—Hg	98.2 (3)	N21—C22—H22	125.3
C21—N21—C22	108.7 (8)	C22—C23—H23	127.2
C21—N21—C24	126.4 (7)	N22—C23—H23	127.2
C22—N21—C24	124.9 (9)	N21—C24—H24A	109.5
C21—N22—C23	109.9 (9)	N21—C24—H24B	109.5
N22—C21—N21	106.4 (8)	H24A—C24—H24B	109.5
N22—C21—S2	126.9 (7)	N21—C24—H24C	109.5
N21—C21—S2	126.7 (7)	H24A—C24—H24C	109.5
C23—C22—N21	109.5 (10)	H24B—C24—H24C	109.5
S2—Hg—S1—C11	−103.7 (3)	S1—Hg—S2—C21	−138.8 (3)
I1—Hg—S1—C11	21.0 (4)	I1—Hg—S2—C21	93.9 (3)
I2—Hg—S1—C11	145.2 (3)	I2—Hg—S2—C21	−26.0 (3)
C12—N11—C11—N12	0.3 (10)	C23—N22—C21—N21	−0.6 (12)
C14—N11—C11—N12	−177.5 (9)	C23—N22—C21—S2	−178.8 (10)
C12—N11—C11—S1	177.7 (7)	C22—N21—C21—N22	1.5 (12)
C14—N11—C11—S1	−0.1 (13)	C24—N21—C21—N22	179.3 (11)
C13—N12—C11—N11	−2.1 (11)	C22—N21—C21—S2	179.7 (8)
C13—N12—C11—S1	−179.4 (8)	C24—N21—C21—S2	−2.5 (16)
Hg—S1—C11—N11	162.0 (7)	Hg—S2—C21—N22	97.7 (9)
Hg—S1—C11—N12	−21.2 (10)	Hg—S2—C21—N21	−80.1 (9)
C11—N11—C12—C13	1.7 (12)	C21—N21—C22—C23	−1.9 (16)
C14—N11—C12—C13	179.5 (10)	C24—N21—C22—C23	−179.8 (12)
N11—C12—C13—N12	−2.9 (14)	N21—C22—C23—N22	1.5 (16)
C11—N12—C13—C12	3.2 (14)	C21—N22—C23—C22	−0.5 (15)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N12—H12N···I1	0.86	2.77	3.596 (8)	163
N22—H22N···I2^i	0.86	2.80	3.611 (9)	157

Symmetry code: (i) −x+1/2, y, z+1/2.