A new allotrope of elemental sulfur: Convenient preparation of cyclo-S14 from S8

Article abstract of DOI:10.1002/(SICI)1521-3773(19980918)37:17<2377::AID-ANIE2377>3.0.CO;2-O

Three simple steps lead from S₈ to cyclo-S₁₄, which is stable at 20°C. The final synthetic step [Eq. (a)] provides the title compound, which was characterized spectroscopically and by X-ray structure analysis. Formally, the structure of S₁₄ is derived by insertion of an S₂ unit into S₁₂. tmeda = N,N,N',N'-tetramethylethyl-enediamine.

Full text of DOI:10.1002/(SICI)1521-3773(19980918)37:17<2377::AID-ANIE2377>3.0.CO;2-O

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[(tmeda)ZnS6] ‡ S8Cl2 !cyclo-S14 ‡ [(tmeda)ZnCl2]
2
(2)
A New Allotrope of Elemental Sulfur:
Convenient Preparation of cyclo-S14 from S8**
However, on attempting to isolate S14 from the mixture,
decomposition to S8 occured regularly. This may be due to the
presence of the strong nucleophile tmeda (pKa ˆ 5.85/8.97),[10]
which is only partly removed by the insoluble zinc complex 2.
Strong nucleophiles are known to catalyze the decomposition
of thermodynamically unstable sulfur homocycles.[11] After
addition of P4O10 to the reaction mixture to remove the
remaining amine, pure S14 could be isolated in 11% yield
(based on 1). As side product S12 was isolated, which
apparently originates from the reaction of 1 with the S6Cl2
that was present in S8Cl2 as another chlorination product.
S14 forms intense yellow rodlike crystals, which intergrow to
form bundles and melt at 1178C with decomposition. The
primary decomposition products are S7 and S8, but not S6;
therefore, a reaction sequence S14 !2S7 ! !S8 is likely. At
208C S14 is stable for days in the crystalline state and as a
solution in CS2. The solubility in CS2 is greater than that in
CHCl3.The EI mass spectrum (70 eV) exhibits only peaks for
Ralf Steudel,* Oliver Schumann, Jürgen Buschmann,
and Peter Luger
Sulfur forms far more allotropes than any other element. At
present, at least 21 sulfur allotropes are known to exist at
ambient pressure, 17 of which have been characterized by X-
ray crystallography.[1] They all contain sulfur atoms with a
coordination number (CN) of 2. The densities of these
3
compounds range between 1.9 and 2.2 gcm , and the
internuclear distances between 200 and 218 pm.[2] All inves-
tigated low-pressure allotropes are excellent electrical insu-
lators (band gap ca. 2.9 eV). At high pressures, at least four
additional allotropes have been obtained, three of which have
been studied by X-ray diffraction. At 33 GPa sulfur becomes a
semiconductor (of unknown structure), and at 83 GPa a
metallic conductor. This ªsulfur metalº crystallizes in an
orthorhombic layer structure with CN ˆ 4, but at 162 GPa the
structure transforms into that of b-polonium with CN ˆ 6. At
206 GPa the density reaches 6.6 gcm 3; however, the inter-
nuclear distances of 207.9 pm are ªnormalº[3] (a-S8: 205 pm[4]).
The two metallic sulfur modifications become superconduc-
tors below 10 and 17 K, respectively.[5]
‡
the sulfur ions Sn (n ˆ 1 ± 9). It contains no other elements,
and the molecular ion was not observed. The Raman
spectrum at 1008C (Table 1)[12] differs from those of all
Table 1. Wavenumbers [cm 1] of the Raman bands of crystalline S14 at
1008C (krypton laser, 674 nm; relative intensities in parentheses).
Here we report on a new monotropic low-pressure allo-
trope of sulfur which can be prepared in three steps from the
thermodynamically stable form a-S8. The starting material is
the hexasulfido complex 1, which was prepared by Rauchfuss
et al.[6] from zinc powder, orthorhombic a-S8, and N,N,N',N'-
tetramethylethylenediamine (tmeda) at 908C in 75% yield
[Eq. (1)].
Stretching
modes
Bending
modes
Torsional and
lattice modes
483 (7)
474 (5)
468 (25)
462 sh
460 (59)
453 sh
270 (7)
252 (2)
243 (5)
234 (23)
212 (2)
198 (18)
189 (7)
177 (11)
163 (25)
153 (16)
128 (48)
122 (7)
90 (23)
79 (14)
69 (59)
61 (41)
57 (36)
47 (100)
34 (23)
Zn ‡ 3/4S8 ‡ tmeda ![(tmeda)ZnS6]
1
(1)
447 (11)
444 (11)
Complex 1 forms yellow air-stable crystals, and its mole-
cules contain a seven-membered metallacycle with the
chelating ligand S62 . Like [(C5H5)2TiS5] the zinc complex acts
as a sulfur-transfer reagent. For instance, treating a suspension
of 1 in CS2 with Se2Cl2 at 608C afforded the heterocycle 1,2-
Se2S6.[7] We studied the reaction of a solution of 1 in CS2 at
08C with dichlorooctasulfane S8Cl2 [Eq. (2)], which is acces-
sible by careful chlorination of cyclo-S8 with elemental
chlorine.[8] The HPLC analysis[9] of the mixture indicated the
formation of cyclo-tetradecasulfur in high concentration.
other cyclic sulfur allotropes, but is consistent with expect-
ations. Besides eight lines, two of which are shoulders, in the
1
S ± S stretching region (440 ± 485 cm ), several bands for the
deformation, torsion, and lattice vibrations are present in the
1
region below 290 cm . Signals due to S8 and S12 are not
detectable.
The reversed-phase HPLC chromatogram of pure S14 shows
only one large peak, the retention time of which lies between
those of S13[8] and S15.[14] With this technique S14 was identified
previously as a trace component in quenched sulfur melts and
in synthetic sulfur mixtures.[9, 15]
The cyclic structure of S14 was confirmed by a single-crystal
X-ray structure analysis.[16] At 208C the crystals decomposed
rapidly in the X-ray beam. Therefore, the sample was cooled
to 1008C, and at this temperature the reflection intensities
remained constant. The structure is triclinic with two mole-
cules in the unit cell and a density of 2.045 gcm 1 at 1008C.
The S14 molecules occupy general sites but have approxi-
mately CS molecular symmetry (Figure 1). The noncrystallo-
[*] Prof. Dr. R. Steudel, Dipl.-Chem. O. Schumann
Institut für Anorganische und Analytische Chemie
der Technischen Universität
Sekr. C2, Strasse des 17. Juni 135, D-10623 Berlin (Germany)
Fax : (‡ 49)30-314-26519
E-mail: steudel@schwefel.chem.tu-berlin.de.
Dr. J. Buschmann, Prof. Dr. P. Luger
Institut für Kristallographie der Freien Universität
Takustrasse 6, D-14195 Berlin (Germany)
[**] Sulfur Compounds, part 206. This work was supported by the
Deutsche Forschungsgemeinschaft, the Deutschen Akademischen
Austauschdienst, and the Verband der Chemischen Industrie.
Part 205: R. Steudel, O. Schumann, J. Buschmann, P. Luger, Angew.
Chem. 1998, 110, 515; Angew. Chem. Int. Ed. 1998, 37, 492.
Angew. Chem. Int. Ed. 1998, 37, No. 17
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[1] The following phases consist of cyclic molecules: S6, S7 (a ± d), S8 (a ±
g), S9 (a, b), S10, S11, S12, S13, S15, S18 (a, b), S20, S6 ´ S10. In addition, two
polymeric allotropes S1 are known (also termed Sm or Sw).
[2] a) R. Steudel, Chemie der Nichtmetalle, 2nd ed., de Gruyter, Berlin,
1998; b) R. Steudel, K. Bergemann, J. Buschmann, P. Luger, Inorg.
Chem. 1996, 35, 2184; c) R. Steudel in SulfurÐIts Significance for
Chemistry, for the Geo-, Bio- and Cosmosphere and Technology (Eds.:
A. Müller, B. Krebs), Elsevier, Amsterdam 1984, p. 3.
[3] H. Luo, S. Desgreniers, Y. K. Vohra, A. L. Ruoff, Phys. Rev. Lett. 1991,
67, 2998; Y. Akahama, M. Kobayashi, H. Kawamura, Phys. Rev. B
1993, 48, 6862; H. Luo, R. G. Greene, A. L. Ruoff, Phys. Rev. Lett.
1993, 71, 2943.
[4] P. Coppens, Y. W. Yang, R. H. Blessing, W. F. Cooper, F. K. Larsen, J.
Am. Chem. Soc. 1977, 99, 760.
Figure 1. Structure of cyclo-S14 in the crystal. Bond lengths [pm], an-
gles [8], and torsional angles [8]: S1 ± S2 205.5(4), S2 ± S3 205.1(3), S3 ± S4
205.4(3), S4 ± S5 206.1(4), S5 ± S6 205.0(4), S6 ± S7 204.7(4), S7 ± S8 205.6(4),
S8 ± S9 204.7(3), S9 ± S10 204.9(3), S10 ± S11 206.0(3), S11 ± S12 205.5(4),
S12 ± S13 205.2(4), S13 ± S14 205.9(3), S14 ± S1 205.1(4); S1-S2-S3 108.4(2),
S2-S3-S4 107.8(2), S3-S4-S5 104.4(2), S4-S5-S6 104.0(2), S5-S6-S7
104.95(14), S6-S7-S8 108.3(2), S7-S8-S9 106.95(13), S8-S9-S10 109.32(14),
S9-S10-S11 106.0(2), S10-S11-S12 107.1(2), S11-S12-S13 105.0(2), S12-S13-
S14 104.5(2), S13-S14-S1 105.1(2); S1-S2-S3-S4 ‡96.0(2), S2-S3-S4-S5
[5] V. V. Struzkhin, R. J. Hemley, H. Mao, Y. A. Timofeev, Nature 1997,
390, 382.
[6] A. K. Verma, T. B. Rauchfuss, S. R. Wilson, Inorg. Chem. 1995, 34,
3072.
[7] A. K. Verma, T. B. Rauchfuss, Inorg. Chem. 1995, 34, 6199.
[8] R. Steudel, J. Steidel, T. Sandow, Z. Naturforsch. B 1986, 41, 958.
[9] R. Strauss, R. Steudel, Fresenius Z. Anal. Chem. 1987, 326, 543.
[10] L. Spialter, R. W. Moshier, J. Am. Chem. Soc. 1957, 79, 5955.
[11] R. E. Davis in Inorganic Sulphur Chemistry (Ed.: G. Nickless),
Elsevier, Amsterdam, 1968, p. 85.
[12] Investigating unstable sulfur allotropes by Raman spectroscopy
requires the use of a laser beam with low-energy radiation (red or
infrared); otherwise, photochemical conversion into S8 may occur. For
experimental details, see ref. [8].
‡72.5(2), S3-S4-S5-S6
100.8(2), S4-S5-S6-S7
94.9(2), S5-S6-S7-S8
‡82.7(2), S6-S7-S8-S9 ‡107.1(2), S7-S8-S9-S10 100.7(2), S8-S9-S10-S11
‡95.9(2), S9-S10-S11-S12 100.7(2), S10-S11-S12-S13 75.9(2), S11-S12-
S13-S14 ‡101.7(2), S12-S13-S14-S1 ‡101.5(2), S13-S14-S1-S2 77.9(2),
S14-S1-S2-S3 94.7(2).
[13] R. Steudel, H.-J. Mäusle, Z. Naturforsch. A 1978, 33, 951.
[14] R. Strauss, R. Steudel, Z. Naturforsch. B 1988, 43, 1151.
[15] R.Steudel, H.-J. Mäusle, D. Rosenbauer, H. Möckel, T. Freyholdt,
Angew. Chem. 1981, 93, 402; Angew. Chem. Int. Ed. Engl. 1981.
[16] Crystal structure analysis of S14: 0.55 Â 0.16 Â 0.15 mm, triclinic, space
graphic mirror plane contains S2 and S9. The internuclear
distances vary from 204.7 to 206.1 pm; the arithmetic mean of
205.3 pm is only insignificantly larger than that of ortho-
rhombic a-S8.
The conformation of sulfur homocycles is best described by
the ªmotifº, which is the order of the signs of the torsional
Å
group P1 (no. 2), Z ˆ 2, a ˆ 5.469(3), b ˆ 9.662(5), c ˆ 14.331(7) Š,
a ˆ 95.97(4), b ˆ 98.96(4), g ˆ 100.43(4)8, Vˆ 728.8(7) Š3, m ˆ
2.044 mm 1, MoKa radiation, l ˆ 0.71068 Š. Of 4440 measured reflec-
tions (2.16 ꢀ q ꢀ 30.008), 54% with I ꢀ 2s(I), 4270 were independent;
Rint ˆ 0.051. Due to the large width (1.78, w scan) and irregular form of
the reflection profiles the w scan mode was used, the background on
both sides of the reflections was measured point by point. Initial
coordinates of the sulfur atoms from direct methods with SIR92.
Refinement on F 2 (SHELXL93), 127 refined parameters, R1 ˆ 0.084,
R1 ˆ SH j jFo j j Fc j j/SH j Fo j , wR2 ˆ 0.25 with all independent
angles around the ring. The motif of S14 is ‡‡
‡‡
‡‡
‡
. Since the first 12 signs are the same as those of
the S12 molecule,[17] the structure of S14 can be generated from
that of cyclo-S12 by opening any bond and inserting an S2
fragment (S9 and S10). The absolute values of the torsional
angles in S14 are in the range of 72.5 ± 101.78; the arithmetic
mean of 93.18 is also close to the corresponding value of S12
(898). The mean bond energy of S12 is only 1 kJmol 1 smaller
than that of S8. Therefore, S12 is only second to S8 in
thermodynamic stability. The difference between the mean
reflections,
wR2 ˆ {SH[w(F2o Fc2)2]/SHwF4o}1/2
,
w ˆ [s2(F2o) ‡
(0.1542P)2] with P ˆ [max(F2o,0) ‡ 2F2c]/3; max./min. residual elec-
tron density 1.51/ 1.13 eŠ 3. Further details of the crystal structure
investigation may be obtained from the Fachinformationszentrum
Karlsruhe, D-76344 Eggenstein-Leopoldshafen, Germany (fax:
(‡49)7247-808-666; e-mail: crysdata@fiz-karlsruhe.de), on quoting
the depository number CSD-408504.
1
1 [18]
bond energy of S14 and that of S8 is 2 kJmol .
[17] J. Steidel, R. Steudel, A. Kutoglu, Z. Anorg. Allg. Chem. 1981, 476,
171.
[18] R. Steudel, R. Strauss, L. Koch, Angew. Chem. 1985, 97, 58; Angew.
Chem. Int. Ed. Engl. 1985, 24, 59.
Experimental Section
cyclo-S14
: Solvents were dried over P4O10 and distilled. Under an
atmosphere of dry nitrogen, S8Cl2 (4.2 g, 12.8 mmol) in CS2 (17.5 mL) was
added dropwise over 1 h to 1 (4.8 g, 12.8 mmol) in CS2 (70 mL) at 08C. The
temperature was then allowed to rise to 208C over 1 h. The colorless
precipitate of 2 was collected by filtration and washed with 50 mL of CS2;
the filtrate and wash solutions were combined. To remove dissolved tmeda
P4O10 (ca. 0.4 g) was added to the clear yellow solution (the hygroscopic
P4O10 contains strongly acidic POH groups which protonate the amine).
CHCl3 (10 mL) was added to precipitate sparingly soluble S12. After
cooling to 358C the mixture of S12 and P4O10 was filtered off. Addition of
a further 10 mL of CHCl3 to the filtrate and cooling to 358C for several
days afforded yellow bundles of S14 (yield 650 mg).
Received: April 6, 1998 [Z11685IE]
German version: Angew. Chem. 1998, 110, 2502 ± 2504
Keywords: allotropy ´ sulfur ´ zinc
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Angew. Chem. Int. Ed. 1998, 37, No. 17