1,2-Bis­(methylsulfanyl)-1,2-dicarba-closo-dodecaborane(12)

In the title compound, 1,2-(SCH₃)₂-1,2-closo-C₂B₁₀H₁₀ or C₄H₁₆B₁₀S₂, the methylsulfanyl groups are bonded to the C atoms of the 1,2-dicarba-closo-dodecaborane cage. The C_cage-C_cage distance is 1.8033 (18) Å and the S-C_cage-C_cage-S torsion angle is 1.07 (13)°. The C_cage-C_cage distance is compared with those in other 1,2-dicarba-closo-dodecaborane derivatives.

S1. Comment

The contribution of substituents at the cluster C atoms on the lengthening of the C_cage—C_cage or C1—C2 bond in 1,2-closo-C₂B₁₀H₁₂ or o-carborane derivatives is well known (Kivekäs, Sillanpää et al., 1995 Original citation ambiguous - please check; Sillanpää et al., 1996). Different C1—C2 distances in icosahedral o-carborane derivatives can be achieved by modifying the substituents at the C atoms of the cluster compound. This is important from the theoretical point of view, and in order to understand the isomerization process that takes place from ortho-, meta- and para-carborane isomers.

The C1—C2 distance is strongly dependent on the number of substituents and the atomic species of the substituents connected to the cluster C atoms. Accordingly, shortest distances of 1.629 (6) and 1.630 (6) Å have been reported for two crystallographically independent molecules of the unsubstituted parent compound 1,2-closo-C₂B₁₀H₁₂, carrying H atoms at both cluster C atoms (Davidson et al., 1996). Dealing with one atomic species, it is observed that a substituent at only one of the cluster C atoms does not increase the distance significantly, or affects the distance only slightly, but increased lengthening is observed if both cluster C atoms are substituted. Table 2 lists the C1—C2 bond lengths for a wide range of comparable compounds and the following observations have been noted. Firstly, the lengthening caused by aliphatic C substituents at both cluster C atoms is smaller than that of aromatic C. Secondly, in Si-substituted compounds, the C1—C2 distance is approximately comparable with that in the compound bearing two aliphatic C atoms at the cluster C atoms. Thirdly, the contribution of two P-substituents is comparable with that of two aryl groups. Finally, the longest C1—C2 distances (ca 1.80–1.86 Å) have been reported for 1,2-S₂-disubstituted o-carborane derivatives (Llop et al., 2002; Teixidor, Viñas et al., 1990; Teixidor, Romerosa et al., 1990). As far as we know, no crystallographic data are available for 1,2-N₂– and 1,2-O₂-disubstituted o-carborane compounds. However, a C1—C2 distance as long as 2.001 (3) Å has been reported for the [1-O-2-C₆H₅-1,2-closo-C₂B₁₀H₁₀]⁻ anion, containing a C═O bond (Brown et al., 1987).

We have suggested an empirically derived equation (Kivekäs, Sillanpää et al., 1994 Original citation ambiguous - please check; Kivekäs, Teixidor et al., 1995 Original citation ambiguous - please check) to calculate the C1—C2 distance, as well as carried out computational analyses to understand the nature of the bond (Llop et al., 2002; Paavola, 2002). As this kind of lengthening is exceptional and unique Or rare? in chemistry, we have continued our research on this topic and now report the crystal structure of the title compound, (I), the preparation of which has been previously reported by Llop et al. (2001). Please check added text. \sch

In compound (I), the SCH₃ groups are oriented in approximately the same direction from the cluster (Fig. 1). This is also indicated by the torsion angles of 101.13 (11) and −92.41 (11)° for C1—C2—S2—C14 and C2—C1—S1—C13, respectively. The molecule has approximately C_s symmetry, with the pseudo mirror plane passing through the midpoint of the C1—C2 bond and through atoms B3, B6, B8 and B10. The intramolecular S1···S2 distance of 3.4359 (6) Å is only 0.16 Å shorter than the sum of the corresponding van der Waals radii (Bondi, 1964), thus indicating only minor interaction between the atoms. The free electron pairs of the S atoms are oriented away from each other to avoid steric repulsion. The S1—C1—B6 and S2—C2—B6 angles of 112.05 (9) and 112.45 (9)°, respectively, are narrower than the mean S—C_cage—X (X is C_cage or B) angles of ca 119.5°, thus indicating that the S atoms are moved slightly from their ideal radial orientation towards atom B6.

The main interest of (I) is in its C1—C2 bond. The bond length of 1.8033 (18) Å is in line with the earlier observed distances in 1,2-disubstituted o-carborane derivatives. The bond is clearly longer than the relevant bond in the C–, Si- and P-1,2-disubstituted compounds and is comparable with the distances in the 1,2-S₂-disubstituted compounds. Thus, the C1—C2 distance in (I) is equal to the distance of 1.799 (3) Å in 1,2-(SC₆H₅)₂-1,2-closo-C₂B₁₀H₁₀ (Llop et al., 2002), and is equal to or slightly shorter than the distances of 1.816 (6), 1.826 (5) and 1.858 (5) Å in 1,2-µ-SCH₂CH₂OCH₂CH₂S-1,2-closo-C₂B₁₀H₁₀ (Teixidor, Romerosa et al., 1990) and 1,2-µ-SCH₂(CH₂OCH₂)₂CH₂S-1,2-closo-C₂B₁₀H₁₀ (Teixidor, Viñas et al., 1990). The C1—C2 distance in (I) also equals the distance of 1.792 (5) Å observed in the [2-CH₃-1-S-1,2-closo-C₂B₁₀H₁₀]⁻ anion (Kivekäs et al., 1999), thus indicating that the contribution of methyl and sulfide groups is comparable with that of two SCH₃ groups. The C1—C2 distance found in (I) is a further confirmation that the S atoms in 1,2-disubstituted o-carborane derivatives lengthen the C1—C2 distance considerably.

In the [2-CH₃-1-S-closo-C₂B₁₀H₁₀]⁻ anion there is a short intramolecular distance of 2.68 Å between a methyl H atom and the sulfide group, indicating a hydrogen bond between the atoms (Kivekäs et al., 1999). In (I), containing neutral SCH₃ substituents at the cluster C atoms, the shortest S···H(CH₃) distance between different SCH₃ substituents is intermolecular and as long as 3.24 Å, ca 0.2 Å longer than the sum of the corresponding van der Waals radii (Bondi, 1964). The shortest intermolecular (S2···H12) contact is 2.95 Å. These distances indicate that there are only weak van der Waals packing forces between the molecules.

Please check that all references have been correctly cited. There are, for instance, 4 separate Kivekäs et al. (1994) references but only two apparent citations (and only two of these have the correct page ranges in the list below). Each reference must be uniquely cited.

S2. Experimental

Please provide brief details of the source of the compound and the crystallization process.

S3. Refinement

Methyl groups were refined as rotating groups, with C—H = 0.98 Å and U_iso(H) = 1.5U_eq(C). The other H atoms were refined using a riding model, with B—H = 1.12 Å and U_iso(H) = 1.2U_eq(B), starting from idealized positions.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990a); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL/PC (Sheldrick, 1990b); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. A view of (I), showing the atom-numbering scheme and with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radii.

1,2-Bis(thiomethyl)-1,2-dicarba-closo-dodecaborane(12)

Crystal data

C4H16B10S2	F(000) = 488
Mr = 236.39	Dx = 1.216 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 2472 reflections
a = 7.1667 (1) Å	θ = 2.9–25.7°
b = 15.1733 (2) Å	µ = 0.37 mm^−1
c = 11.8894 (2) Å	T = 173 K
β = 92.976 (1)°	Prism, colourless
V = 1291.14 (3) Å^3	0.22 × 0.20 × 0.10 mm
Z = 4

Data collection

Nonius KappaCCD area-detector diffractometer	2208 reflections with I > 2σ(I)
Radiation source: Enraf Nonius FR590	Rint = 0.013
Horizonally mounted graphite crystal monochromator	θmax = 25.7°, θmin = 3.2°
Detector resolution: 9 pixels mm^-1	h = −8→8
ϕ scans, and ω scans with κ offsets	k = −18→16
4565 measured reflections	l = −14→14
2397 independent reflections

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)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.086	H-atom parameters constrained
S = 1.07	w = 1/[σ^2(Fo^2) + (0.0386P)^2 + 0.5289P] where P = (Fo^2 + 2Fc^2)/3
2397 reflections	(Δ/σ)max = 0.001
147 parameters	Δρmax = 0.20 e Å^−3
0 restraints	Δρmin = −0.24 e Å^−3

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	1.09815 (5)	0.10846 (3)	0.48976 (3)	0.03685 (14)
S2	0.81334 (6)	0.09893 (3)	0.71317 (3)	0.04101 (15)
C1	1.06957 (18)	0.20545 (9)	0.56839 (11)	0.0238 (3)
C2	0.91855 (18)	0.20105 (9)	0.68494 (11)	0.0247 (3)
B3	1.1564 (2)	0.21644 (10)	0.70533 (12)	0.0251 (3)
H3	1.2500	0.1657	0.7471	0.030*
B4	1.2316 (2)	0.28472 (11)	0.59328 (13)	0.0298 (3)
H4	1.3769	0.2816	0.5631	0.036*
B5	1.0332 (2)	0.30198 (11)	0.49946 (13)	0.0314 (4)
H5	1.0457	0.3104	0.4066	0.038*
B6	0.8429 (2)	0.24366 (11)	0.55724 (12)	0.0263 (3)
H6	0.7324	0.2103	0.5025	0.032*
B7	0.9887 (2)	0.27737 (11)	0.78095 (13)	0.0283 (3)
H7	0.9752	0.2693	0.8738	0.034*
B8	1.1838 (2)	0.33137 (11)	0.72558 (13)	0.0294 (3)
H8	1.2989	0.3588	0.7825	0.035*
B9	1.1045 (3)	0.38500 (11)	0.59791 (15)	0.0370 (4)
H9	1.1655	0.4490	0.5705	0.044*
B10	0.8619 (3)	0.35929 (12)	0.57317 (14)	0.0355 (4)
H10	0.7616	0.4054	0.5279	0.043*
B11	0.7912 (2)	0.29513 (11)	0.68763 (14)	0.0316 (4)
H11	0.6460	0.2992	0.7177	0.038*
B12	0.9568 (3)	0.38048 (11)	0.71272 (15)	0.0354 (4)
H12	0.9219	0.4415	0.7602	0.043*
C13	1.2998 (3)	0.05695 (13)	0.55561 (19)	0.0581 (6)
H13A	1.4030	0.0994	0.5613	0.087*
H13B	1.3359	0.0063	0.5104	0.087*
H13C	1.2711	0.0370	0.6312	0.087*
C14	0.9520 (3)	0.05539 (14)	0.83013 (17)	0.0604 (6)
H14A	1.0752	0.0384	0.8051	0.091*
H14B	0.8898	0.0036	0.8601	0.091*
H14C	0.9669	0.1004	0.8891	0.091*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
S1	0.0346 (2)	0.0362 (2)	0.0391 (2)	0.00712 (15)	−0.00376 (16)	−0.01648 (15)
S2	0.0414 (2)	0.0428 (3)	0.0380 (2)	−0.01989 (17)	−0.00580 (17)	0.00984 (16)
C1	0.0224 (6)	0.0265 (7)	0.0225 (6)	0.0008 (5)	0.0017 (5)	−0.0021 (5)
C2	0.0217 (6)	0.0307 (7)	0.0215 (6)	−0.0020 (5)	−0.0004 (5)	0.0009 (5)
B3	0.0220 (7)	0.0287 (8)	0.0242 (7)	−0.0015 (6)	−0.0022 (6)	−0.0008 (6)
B4	0.0281 (8)	0.0348 (8)	0.0267 (8)	−0.0072 (7)	0.0034 (6)	−0.0016 (6)
B5	0.0375 (9)	0.0324 (9)	0.0241 (7)	−0.0021 (7)	0.0001 (6)	0.0047 (6)
B6	0.0238 (7)	0.0325 (8)	0.0222 (7)	0.0041 (6)	−0.0031 (6)	−0.0009 (6)
B7	0.0259 (7)	0.0372 (9)	0.0215 (7)	−0.0008 (6)	−0.0001 (6)	−0.0044 (6)
B8	0.0306 (8)	0.0296 (8)	0.0278 (8)	−0.0052 (6)	−0.0010 (6)	−0.0048 (6)
B9	0.0487 (11)	0.0266 (8)	0.0353 (9)	−0.0060 (7)	−0.0017 (8)	0.0027 (7)
B10	0.0431 (9)	0.0304 (9)	0.0322 (8)	0.0097 (7)	−0.0073 (7)	0.0002 (7)
B11	0.0257 (7)	0.0411 (9)	0.0278 (8)	0.0080 (7)	−0.0008 (6)	−0.0080 (7)
B12	0.0413 (9)	0.0296 (8)	0.0348 (9)	0.0068 (7)	−0.0037 (7)	−0.0089 (7)
C13	0.0395 (9)	0.0535 (11)	0.0799 (14)	0.0236 (8)	−0.0123 (9)	−0.0305 (10)
C14	0.0630 (12)	0.0551 (12)	0.0614 (12)	−0.0202 (10)	−0.0132 (10)	0.0331 (10)

Geometric parameters (Å, º)

S1—C1	1.7610 (13)	B6—B10	1.769 (2)
S1—C13	1.7876 (18)	B6—B11	1.792 (2)
S2—C2	1.7630 (14)	B6—H6	1.1200
S2—C14	1.7929 (18)	B7—B12	1.772 (2)
C1—B4	1.687 (2)	B7—B11	1.773 (2)
C1—B5	1.692 (2)	B7—B8	1.776 (2)
C1—B3	1.7208 (19)	B7—H7	1.1200
C1—B6	1.7233 (19)	B8—B12	1.789 (2)
C1—C2	1.8033 (18)	B8—B9	1.789 (2)
C2—B7	1.684 (2)	B8—H8	1.1200
C2—B11	1.695 (2)	B9—B12	1.772 (3)
C2—B6	1.7121 (19)	B9—B10	1.792 (3)
C2—B3	1.7255 (19)	B9—H9	1.1200
B3—B8	1.770 (2)	B10—B11	1.769 (3)
B3—B4	1.792 (2)	B10—B12	1.789 (2)
B3—B7	1.795 (2)	B10—H10	1.1200
B3—H3	1.1200	B11—B12	1.771 (2)
B4—B8	1.774 (2)	B11—H11	1.1200
B4—B9	1.775 (2)	B12—H12	1.1200
B4—B5	1.780 (2)	C13—H13A	0.9800
B4—H4	1.1200	C13—H13B	0.9800
B5—B10	1.773 (2)	C13—H13C	0.9800
B5—B9	1.776 (2)	C14—H14A	0.9800
B5—B6	1.792 (2)	C14—H14B	0.9800
B5—H5	1.1200	C14—H14C	0.9800
C1—S1—C13	104.27 (7)	B11—B7—B8	108.43 (11)
C2—S2—C14	104.25 (8)	C2—B7—B3	59.37 (8)
B4—C1—B5	63.57 (9)	B12—B7—B3	107.42 (11)
B4—C1—B3	63.45 (9)	B11—B7—B3	107.37 (10)
B5—C1—B3	114.42 (11)	B8—B7—B3	59.42 (9)
B4—C1—B6	114.26 (11)	C2—B7—H7	123.7
B5—C1—B6	63.31 (9)	B12—B7—H7	122.2
B3—C1—B6	109.48 (10)	B11—B7—H7	121.8
B4—C1—S1	126.22 (9)	B8—B7—H7	121.7
B5—C1—S1	119.05 (9)	B3—B7—H7	122.1
B3—C1—S1	122.47 (9)	B3—B8—B4	60.76 (9)
B6—C1—S1	112.05 (9)	B3—B8—B7	60.80 (9)
B4—C1—C2	109.06 (10)	B4—B8—B7	109.65 (11)
B5—C1—C2	108.71 (10)	B3—B8—B12	107.75 (11)
B3—C1—C2	58.57 (7)	B4—B8—B12	107.87 (11)
B6—C1—C2	58.04 (7)	B7—B8—B12	59.59 (9)
S1—C1—C2	117.90 (8)	B3—B8—B9	107.74 (11)
B7—C2—B11	63.28 (9)	B4—B8—B9	59.77 (9)
B7—C2—B6	114.26 (11)	B7—B8—B9	107.63 (12)
B11—C2—B6	63.44 (9)	B12—B8—B9	59.37 (10)
B7—C2—B3	63.50 (9)	B3—B8—H8	121.4
B11—C2—B3	114.35 (11)	B4—B8—H8	120.9
B6—C2—B3	109.78 (10)	B7—B8—H8	121.1
B7—C2—S2	126.21 (9)	B12—B8—H8	122.4
B11—C2—S2	120.03 (10)	B9—B8—H8	122.4
B6—C2—S2	112.45 (9)	B12—B9—B4	108.58 (12)
B3—C2—S2	121.43 (9)	B12—B9—B5	108.50 (12)
B7—C2—C1	108.99 (10)	B4—B9—B5	60.16 (9)
B11—C2—C1	109.17 (10)	B12—B9—B8	60.31 (10)
B6—C2—C1	58.64 (7)	B4—B9—B8	59.71 (9)
B3—C2—C1	58.32 (7)	B5—B9—B8	107.72 (11)
S2—C2—C1	117.29 (9)	B12—B9—B10	60.28 (10)
C1—B3—C2	63.11 (8)	B4—B9—B10	107.66 (12)
C1—B3—B8	104.85 (10)	B5—B9—B10	59.60 (10)
C2—B3—B8	104.72 (11)	B8—B9—B10	107.65 (12)
C1—B3—B4	57.36 (8)	B12—B9—H9	121.0
C2—B3—B4	107.85 (10)	B4—B9—H9	121.7
B8—B3—B4	59.74 (9)	B5—B9—H9	121.7
C1—B3—B7	107.76 (10)	B8—B9—H9	122.0
C2—B3—B7	57.13 (8)	B10—B9—H9	122.1
B8—B3—B7	59.78 (9)	B11—B10—B6	60.85 (9)
B4—B3—B7	108.03 (11)	B11—B10—B5	110.10 (12)
C1—B3—H3	122.2	B6—B10—B5	60.79 (9)
C2—B3—H3	122.3	B11—B10—B12	59.71 (10)
B8—B3—H3	123.9	B6—B10—B12	107.50 (11)
B4—B3—H3	122.1	B5—B10—B12	107.86 (12)
B7—B3—H3	122.2	B11—B10—B9	107.93 (12)
C1—B4—B8	106.09 (11)	B6—B10—B9	107.57 (11)
C1—B4—B9	105.49 (11)	B5—B10—B9	59.77 (10)
B8—B4—B9	60.52 (9)	B12—B10—B9	59.31 (10)
C1—B4—B5	58.34 (8)	B11—B10—H10	120.8
B8—B4—B5	108.20 (12)	B6—B10—H10	121.6
B9—B4—B5	59.95 (10)	B5—B10—H10	120.8
C1—B4—B3	59.18 (8)	B12—B10—H10	122.5
B8—B4—B3	59.50 (9)	B9—B10—H10	122.4
B9—B4—B3	107.34 (11)	C2—B11—B10	105.85 (11)
B5—B4—B3	106.85 (11)	C2—B11—B12	105.20 (11)
C1—B4—H4	123.8	B10—B11—B12	60.73 (10)
B8—B4—H4	121.7	C2—B11—B7	58.05 (8)
B9—B4—H4	122.2	B10—B11—B7	108.30 (12)
B5—B4—H4	122.1	B12—B11—B7	59.98 (9)
B3—B4—H4	122.3	C2—B11—B6	58.73 (8)
C1—B5—B10	106.16 (11)	B10—B11—B6	59.59 (9)
C1—B5—B9	105.24 (11)	B12—B11—B6	107.31 (12)
B10—B5—B9	60.63 (10)	B7—B11—B6	106.32 (11)
C1—B5—B4	58.08 (8)	C2—B11—H11	124.2
B10—B5—B4	108.27 (11)	B10—B11—H11	121.6
B9—B5—B4	59.90 (10)	B12—B11—H11	122.1
C1—B5—B6	59.20 (8)	B7—B11—H11	122.2
B10—B5—B6	59.49 (10)	B6—B11—H11	122.5
B9—B5—B6	107.22 (12)	B9—B12—B11	108.69 (12)
B4—B5—B6	106.61 (11)	B9—B12—B7	108.60 (12)
C1—B5—H5	124.0	B11—B12—B7	60.06 (9)
B10—B5—H5	121.6	B9—B12—B8	60.32 (10)
B9—B5—H5	122.3	B11—B12—B8	107.95 (11)
B4—B5—H5	122.2	B7—B12—B8	59.85 (9)
B6—B5—H5	122.4	B9—B12—B10	60.41 (10)
C2—B6—C1	63.33 (8)	B11—B12—B10	59.56 (10)
C2—B6—B10	105.10 (11)	B7—B12—B10	107.44 (11)
C1—B6—B10	104.99 (11)	B8—B12—B10	107.75 (12)
C2—B6—B11	57.82 (8)	B9—B12—H12	120.9
C1—B6—B11	108.46 (10)	B11—B12—H12	121.6
B10—B6—B11	59.56 (9)	B7—B12—H12	121.8
C2—B6—B5	108.31 (10)	B8—B12—H12	121.8
C1—B6—B5	57.50 (8)	B10—B12—H12	122.1
B10—B6—B5	59.71 (10)	S1—C13—H13A	109.5
B11—B6—B5	108.19 (11)	S1—C13—H13B	109.5
C2—B6—H6	121.8	H13A—C13—H13B	109.5
C1—B6—H6	121.9	S1—C13—H13C	109.5
B10—B6—H6	124.0	H13A—C13—H13C	109.5
B11—B6—H6	121.9	H13B—C13—H13C	109.5
B5—B6—H6	122.0	S2—C14—H14A	109.5
C2—B7—B12	105.66 (11)	S2—C14—H14B	109.5
C2—B7—B11	58.66 (8)	H14A—C14—H14B	109.5
B12—B7—B11	59.96 (10)	S2—C14—H14C	109.5
C2—B7—B8	106.20 (10)	H14A—C14—H14C	109.5
B12—B7—B8	60.55 (10)	H14B—C14—H14C	109.5
S1—C1—C2—S2	1.07 (13)	C2—C1—S1—C13	−92.40 (12)
C1—C2—S2—C14	101.12 (11)