D. Zuccaro, J. Mccullough
Dec 1, 1959
Citations
0
Influential Citations
17
Citations
Journal
Zeitschrift für Kristallographie - Crystalline Materials
Abstract
Trimethylsul fonium iodide crystallizes in the monoclinic sys tem wi th t w o formula uni t s of (CH3)3SI in the unit cell. The space g roup is probably PZJm bu t a s t ruc tu re approaching closely to this symmet ry in t h e space group Ρ 21 is no t excluded. T h e t r imethylsul fonium ion approximates closely t o 3»» symmet ry wi th C—S = 1.83 A and t h e angle C—S—C = 103°. Pack ing distances a re normal a n d t h e s t ruc tu re may be described as a monoclinic dis tor t ion of t h a t of NaCl. T a b l e 1. Lattice parameters for trimethylaulfonium iodide Introduction Trimethylsulfonium iodide was reported by M U S S G N U G 1 to crystallize in the space group P2j/m with Ζ = 2 and with the lattice constants given in Table 1. The absence of a detectable pyroelectric effect was noted but no atomic positions were reported. 1 F. MUSSGNUG, Trimethvlammoniumjodid und Tr imethylsul foniumjodid . Naturwissensch. 29 (1941) 250. MUSSGNUG Present work a (A) 5 . 9 6 5 . 9 4 4 ± 0 . 0 1 0 b (A) 8 . 0 0 8 . 0 0 3 ± 0 . 0 1 0 c (A) 8 . 9 5 8 . 9 2 2 ± 0 . 0 1 0 β 1 2 6 ° 5 1 ' 1 2 6 ° 3 2 ' ± 20 ' d(obs.) g/cm 1.922 — d(calc. g/cm — 1.958 Ζ. Kjistallogr. Bd. 112 26 402 D . Ε . ZUCCARO a n d J . D . MCCTJLLOUGH The present study of trimethylsulfonium iodide was undertaken in order to determine the atomic positions and, from these, the structure of the trimethylsulfonium ion. Although the presence of the heavy iodide ion would be expected to cause high uncertainties in the carbon positions, the favorable space group and the presence of only two molecules in the unit cell made the investigation attractive. Crystallographic aud inteiisity data Trimethylsulfonium iodide was prepared by combination of approximately stoichiometric amounts of methyl sulfide and methyl iodide in ether solution. Crystals for use in the x-ray study were grown by slow evaporation of aqueous solutions of the salt. The selected crystals were in the common habit of needles along the b axis. The crystal used for the Wrissenberg photographs about the b axis was 0.10x0.15 mm in cross section while that used for the Buerger precession camera photographs was 0.14x0.22 mm in cross section. Moifa radiation was used for all of the intensity data. The multiplefilm technique was used in preparing the Weissenberg photographs while a series of timed exposures was used for the precession-camera data. The maximum difference in correction due to absorption of radiation in the specimen was computed to be 12°/0. Since this would cause no more than about 6°/0 difference in the corresponding \F\ values, no correction for absorption was applied in converting estimated intensities to |.F| values. The other usual corrections were applied, however. Lattice parameters based on MoKx = 0.7107 A are given in Table 1 where they are compared with those reported by MUSSGNUG. The only systematic absences noted were those for OkO with k odd. Thus the space group appears to be either P'21jm or P2V Determination and refinement of the structure By use of the 73 \F\ values for the observed hol reflections, a Patterson summation on (010) was computed. This indicated iodine positions near χ = 0.115,2 = 0.740 and sulfur positions near χ = 0.31, ζ = 0.33. With these positions as a partial trial structure, a Fourier summation on (010) was prepared. In addition to the iodine and sulfur maxima where expected, two maxima which could be at tr ibuted to carbon atoms appeared. These were consistent with a pyramidal (CH3)3S~ ion located in the mirror plane of P21/m. Four cycles of two-dimensional least-squares refinement were carried out on SWAC The crystal structure of trimethylsulfonium iodide 403 using the routines of SPARKS. PROSKN. KRUSE and TRUEBLOOD2 . The χ and ζ parameters resulting from this refinement are listed as Set 1 in Table 2. The y parameters for C2 and C3 in this set were computed to give the trimethylsulfonium ion the symmetry 3m. Table 2. Positional parameters in trimethylsulfonium iodide Atom Set 1 Set 2 a ( 2) Set 3 X 0.115 0.1144 0.0004 0.1144 y 0.250 0.2500 — 0.2500 ζ 0.740 0.7409 0.0003 0.7409 X 0.308 0.305 0.002 0.305 y 0.250 0.252 0.003 (0.250) ζ 0.327 0.332 0.001 0.332 jj X 0.953 0.926 0.007 0.926 y 0.250 0.243 0.009 (0.250) ζ 0.131 0.143 0.007 0.143 \ χ 0.429 0.430 0.019 (0.430) y (0.433) 0.419 0.010 (0.429) ζ 0.277 0.263 0.017 (0.265) '3 % 0.429 0.419 0.022 (0.430) y (0.067) 0.060 0.014 (0.071) ζ 0.277 0.280 0.018 (0.265) Sets 1 and 3 are based on P2Jm. Set 2 is based on P% }. Values in parenthesis were computed to give the trimethylsulfonium ion the symmetry 3wi, which it was found to have in Set 2. Further refinement was carried out by use of three-dimensional least-squares cycles based on the approximately 350 independent values for observed reflections listed in Table 4. Although incomplete, these data represent approximately two thirds of the observable data within range of Mo radiation at room temperature. Due to the relatively high temperature factors, nearly all of the observable reflections are within range of the Buerger precession camera. The starting positional parameters were those given in Set 1. Although anisotropic vibrational parameters were applied to each atom as described by TRUEBLOOD3, it was clear that those computed 2 R. A. SPARKS, R. J. PROSEN, F. H. KRUSE and Κ. N. TRUEBLOOD, Crystallographic calculations on the high-speed digital computer SWAC. Acta Crystallogr. 9 (1956) 350-358. 3 Κ . N. TRUEBLOOD, Symmetry transformations of general anisotropic temperature factors. Acta Crystallogr. !) (1956) 3,59—361.