Electron diffraction study on the molecular structure of methane sulphonyl fluoride

399 Journal of Molecular Structure, 1.5 (1973) 399-408 @ Elsevier Scientific Publishing Company, Amsterdam

ELECTRON DIFFRACTION OF METHANE SULPHONYL

ISTVP;N HARGITTAI

- Printed in The Netherlands

STUDY ON THE MOLECULAR FLUORIDE

STRUCTURE

AND MAGDOLNA HARGITTAI

Centre for Studies on Chemical Structures, Hungarian Academy of Sciences, Budapest VIII, Puskin utca II-13 (Hungary) (Received

18 September

1972)

ABSTRACT

The molecular structure of methane sulphonyl fluoride in the vapour state was studied by electron diffraction. Assuming a value of 2.480 A for the distance between the oxygen atoms from a microwave determination, the following geometrical parameters (r, structure) have been obtained: r(C-H) = 1.093 fO.O1O A, r(S-0) = 1.410+0.003 A, r(S-F) = 1.561f0.004 A, r(S-C) = 1.759+0.006 A, LF-S-C = 98.2&l-5”, LO-S-F = 106.2 &0.4”, LO-S-O = 123.1+1.5” and LH-C-H = 112.9 -I_1.9”. All the observed variations in the molecular geometries of (CH,),SO,, CH$O,Cl, CH3S02F and SOzF2 may be accounted for by the valence shell electron pair repulsion theory. It is particularly advantageous to combine electron diffraction and microwave data in studying sulphone molecular geometries.

INTRODUCTION

The molecular geometry of methane sulphonyl fluoride, CH,SO,F, seems to have important features in discussing the sulphur bond configuration in sulphones as this configuration changes depending on the electronegativity of the substituents. For both S02Fz1 and S02(CH3)22m 3 microwave studies have yielded unambiguous results for the molecular geometry referring to the vanour phase. Jacob and Lide have also analysed the microwave spectra of CH3S02F and deduced a limited amount fo structural information’. As a continuation of our electron diffraction vapour phase studies on sulof methane sulphones, e.g. S02C124 and CH3S02C15 the present investigation phony1 fluoride was initiated aiming at extending structural information for this

molecule. In the light of the difficulties encountered in the electron diffraction study of CH$O,CI’ a unique determination of the molecular shape of CH3S0,F could not be expected from the electron diffraction data alone because of the large correlations among the parameters. In fact, CH,SO,F is an even more difficult case for electron diffraction than CH$SO&I because of smaller size i.e. more closely packed internuclear distances. Accordingly, it was decided that the value 0 distance available from Jacob and Lide’s microwave study* would fortheO--be used in the electron diffraction structural analysis_

EXPERIMENTAL

AND DATA REDUCTION

The electron diffraction patterns from the methane sulphonyl fluoride sample, an Eastman Kodak (U.S.A.) product, were taken with the Budapest apparatus whose nozzle6 and sector’ systems are described elsewhere. The nozzle temperature was about 105 “C during the experiments. 60 keV electrons were utilized. Three plates for each camera distances of 50 and 19 cm were chosen for analysis. A digital voltmeter attached to a Zeiss GIII photometer was used for reading off the optical density distributions_ The plates were oscillated around the centre of the diffraction pattern during the tracing_ The application of the digital voltmeter to the photometer and a least-squares procedure used for correcting the determination of the center of the diffraction pattern is described in more detail elsewhere’. and The ranges of intensity data used were 2.25 I s _5 12.25 A-’ 7.25 5 s s 31.00 A-i (s = 4x%-’ sin 30, where I, is the electron wave length and 6 is the scattering angle). The data interval was & = 0.25 A- ‘.

CH,S02F

o.!stJ 19cm CAMERA RANGE 0.424

8

12

Fig. 1. The total experimental

16

intensities

20

24

and the experimental

28 a&backgrounds

drawn in.

401

I

20

25

I

30 s.X’ Fig. 2. Experimental (dots) and theoretical (full line) molecular intensities and the difference curve. The theoretical curve was computed for the model whose parameters are presented in Table 1. 5

10

15

The experimental molecular intensities were obtained according to the expression sM”(s) = s[il(s) -B (s)]/B (s). H ere I(s) is the total experimental intensity and B(s) is the experimental background.The latter was drawn in through the oscillations of the total experimental intensity curve for both camera ranges as a smooth line. Theoretical molecular intensities calculated for preliminary models were also taken into consideration. The experimental backgrounds were modified during the structural analysis when better models became available in order to eliminate systematic trends in differences between the experimental and theoretical molecular intensities. The final versions of the experimental background are shown in Fig. 1. The experimental molecular intensities were scaled and averaged to form a single composite curve shown in Fig. 2.

STRUCTURE ANALYSIS The geometry

of the models

As in case of CH$O,CI’, C, symmetry was assumed for the molecule as a whole. The CH, group had C,, symmetry and the pyramidal axis coincided with theextension of the S-C bond. The configuration of the methyl group was such that the bonds to the hydrogens staggered the bonds to the sulphur ligands as shown by the Newman projection of Fig. 3. In addition to the constraints imposed by the assumed symmetries, the value 2.480 A for the 0 - * - 0 non-bonded distance was used as a constraint taken from Jacob and Lide’s microwave study2. Thus, the independent parameters r(C-H), r(S-0), r(SC), r(S-F), LF-S-C, LFS-0 and LH-C-H were chosen.

402 F

H

0

H

0

*

H

Fig. 3. Newman projection S-C bond.

of the molecular model of CH3S02F

representing view along the

Experimental radial distribution

The experimental expression

radial distributions

were calculated according to the

31.00 f(r)

=

s=;25

sM(s)

exp (-as’)

sin (sr) AS

where a is an artificial damping constant. It is clearly observed on the experimental radia1 distributions, iIIustrated by curve E of Fig. 4, that there is strong overlap of the internucIear distances, stronger even, indeed, than for CH3S0,C15.

c

I

7

2

3

r.A

Fig. 4. Experimental (E) and theoretical (T) radial distributions and the difference curve. The artificial damping constant a = 0.002 AZ. Curve T was computed for the model whose parameters are presented in TabIe I. The individual interatomic distances and their relative weights are also

indicated. The number of dots sDecifies the number of bond angles separating the atoms_

403 The small maximum at 1.1 A is assigned to the C-H bond distance. All the other bond distances i.e. S-O, S-F and S-C appear under the maximum at 1.43 A having also a shoulder at about 1.8 A. The important non-bonded distances overlap particularly badly under the maximum at 2.44 A. Trial structures Due to the composite character of the maxima, the experimental radial distribution provided very little direct information for the trial structures. In most trial structures compiled for the least-squares refinement, the values for r(C-H), r(S-0), r(S-C), LF-S-C, LF-S-O and LH-C-H were taken from the results for analogous parameters of CH,SO,Cl’. In some refinements the starting value the microwave data on SO,F,‘_ In the early for r(S-F) was taken from stages of the structural analysis preliminary calculated mean amplitudes of vibration (I values) were used9 which were later refined”. For some of the parameters, e.g., LF-S-C and I(0 - - - 0) values in a wide range have been tried. Refinement The least-squares method was applied to the molecular intensities” form corresponding to the equation sM(s)

=

C C i j i#j

‘“(~[~‘“”COS

X exp (-&”

[~i(S)-yli(s)l

in the

x

s2) sin [s(r,-fc,s*)]

where the If(s)1 and v( s ) are the absolute values and phases of the complex electron scattering amplitudes12, the rfj, the internuclear distances, and the Zij and KU, the corresponding mean amplitudes of vibration and asymmetry constants respectively. The incoherent scattering factors for the B(s) theoretical background were taken from the tables of Tavard et al.’ 3_ Seip et aZ_‘s program14 with a diagonal weight matrix was utilized. At the beginning of the refinement, groups of parameters were formed and only those in the group were allowed to vary simultaneously. Typical groups comprised the bond distances, their Z values and the bond angles, or the bond angles and the Z values for non-bonded distances not involving hydrogen atom plus Z(S-H), etc. Later, all these parameters, except I(0 - - - 0), were allowed to vary simultaneously. The experimental backgrounds have been modified several times as mentioned in the previous section. Only the parameters involving hydrogen atom were observed to be sensitive to the changes in the experimental background. In several refinements asymmetry constants were also included for the bond

404 distances while those for the non-bonded distances were ignored throughout the analysis. The foIlowing values were tried, estimated on the basis of literature data for analogous parameters (x loo6 A”) C-H = 7.2, S-O = 0.8, S-F = 2.3 and S-C = 3.5. The introduction of the K values has not appreciably influenced the other parameters and, when alIowed to vary, the standard deviations obtained were much larger than the K values themselves. Therefore, all the values have been ignored in the final stages of analysis.

RESULTS

Table 1 shows the results of the least-squares refinement. The total errors a, were estimated according to the formulae of Hedberg and Iwasaki15. Obtaining the standard deviations of the least-squares refinement, all geometrical parameters and 1values for non-hydrogen distances, except I(0 - - *0), plus I(C-H) and Z(S - - - H) were aIlowed to vary. These standard deviations were then multiplied by J2 to TABLE RESULTS

1 OF THE STRUCTURAL

Bond I

2 3 4 9 10 11 12 13

C-H s-0 S-F s-c F.--O” F---C” 0..-0b O*-*Cb S---Hb

Length, r 1.093 A 1.410 1.561 1.759 2.378 2.512 (2.480)= 2.604 2.309

ANALYSIS

Error, a, 0.010 0.003 0.004 0.006 0.007 0.029 0.014 0.03 1

A

OF

CHJSOzF= Anlplirrtde, I

0.063 A 0.039 0.052 0.057 0.054 0.056 (0.057) 0.077 0.149

Error, a, 0.009 0.002 0.003 0.004 0.006 0.024

A

Angle 5 6 7 8

F-S-C O-S-O 0-S-F H-C-H

a(deg) 98.2 123.1 106.2 112.9

c1 1.5 1.5 0.4 1.9

0.018 0.043

QThe explanation of obtaining the total errors G, is given in the text. b Dependent distances. c Assumed values. The standard deviations of the least-squares refinement changes in these values.

were insensitive

to

take account of possible correlation among the observations. The experimental error was estimated to be 0.2 per cent. The correlation coefficients between parameters were collected in Table 2. An additional error source is that the value for the 0 * - - 0 distance used as constraint from the microwave study2 is an r, parameter while the electron diffraction least-squares refinement was performed for the r, structure* corresponding to eqn. (1). A change of 0.01 A in the assumed value for r(0 - - - 0) corresponds * For a discussion see, for example,

ref. 16.

1000 too0 20 30 663 -6 360 -11 33 -168 -47 230 196 “-1 -111 105 104 58 33 ^..1 -261 II -194 -4 -191 7 -20 17 -330 49 170

r2

~OE~~l~l~NTS

(X

579 -7 -3t2 331 -55 393 280 -372 -216 -227 2 -300 479

1000

r3

we_

r4

27 17 253 -71 447 528 -80 -137 -150 33 -396 352

1000

1000)

746 84 -31 78 125 166 454 790 933 -523 41

1000

a5

-28 -60 -2’ 165 347 566 774 642 -561 -211

1000

a7

1000 -I 206 135 - 123 -217 - 96 119 -142 296

cd

* The numbering of p~r~rn~terscorresponds to that in Table 1.

112 113 k

110

19

14

ri r2 r3 r4 us u7 u8 II 12 I3

ri

CORRELATION

TABLE 2a

32

-28 -94 -54 -46 -39 -16 90

1000

II

7.55 204 192 131 139 -132 669

1000

I2

1000 246 200 114 152 -237 397

13

1000 324 336 160 -41 -14

14

472 -233 89

818

1000

19

1000 792 -322 38

110

1000 -364 138

112

1000 24

113

1000

k

406

to a change of 0.85” for the bond angle O-S-O. When performing refinements with assumed values of -2.470 A or 2.490 A for r(0 - - - 0), the only other parameter that changed appreciably was F-S-C becoming 98.4” and 97.3”, respectively. In estimating o, for O-S-O, o, of r(S-0) and the indeterminacy of the uncertainty ofr(0 - - -0) were taken into consideration. Besides, it was felt that Q, for O-S-O would not be more than that for F-!&C. AI1 the geometrical parameters determined seem to be reasonable. Achieving a more accurate determination is hindered mainly by the strong correlation between parameters, in particular between bond angles and I values for nonbonded distances. As for the mean amplitudes of vibration, I(S-0), Z(S-F) and I(S-C) seem to be reasonable, I(S-H) may be a little too large and the others are perhaps too small. Comparison with calculated values from spectroscopy data are presented in ref. 10.

DISCUSSION

The size of the methane sulphonyl fluoride molecule is intermediate between those of methyl sulphone and sulphuryl fluoride. The geometrical parameters of these molecules as well as those of methane sulphonyl chloride are collected in Table 3. Data referring to vapour phase studies are presented only, besides, the electron diffraction results reported for methyl suIphoner7 were omitted because of the ambiguity of the O-S-O parameter (cf. ref. 5). TABLE3 MOLECULAR

xso,

r&o),

GEOMETRIES

Y

cIi~so+3!f~

A

r(S-C).A r&Y), A LX-S-Y, deg LO-S-Y, deg LO-S-O, deg

1.429 1.775

1.431~0.004 1.777f0.006

103.1

103"17'~10'

121.4

121”1’&15’

CFf&iO~Cf’

C?i3SOz

Fd

l-424&-0.003 I.763f0.005

1.410~0.003 1.759f0.006

1.405*0.003

2.046f0.004 IOI.0f1.4 107.1f0.7 120.81t2.4

1.561&0.004 98.2f 1.5 106.2zkO.4 123.1115

1.530f0.003 96”7’f 10’

il Microwave spectroscopy, taken from ref. 2. In this table the mean values VII of ref. 2. B Microwave spectroscopy taken from ref. 3. e Electron diffraction taken from ref. 5. d Electron diffraction, present work. e Microwave spectroscopy taken from ref. 1.

FS02F'

123”58’&12

are givenfrom Table

407 Comparison of the geometries has certain limitations because of the relatively large uncertainties of some parameters and also because the microwave data refer to r0 structures and the electron diffraction data to r, structures’6. Nevertheless, the observed variations in the geometries of the molecules discussed seem to show definite trends which may be summarized as follows: passing from methyl sulphone to sulphuryl fluoride in the series of CH3S0,CH3, CH$O&I, CH,S02F, FS02F, (1) al1 the S-O, S-C and S-F bonds become shorter, (2) the values of bond angles X-S-Y (X = C or F and Y = C, Cl or F) and O-S-Y (Y = Cl or F) decrease, and (3) the value of bond angle O-S-O

increases. All the trends observed may be

accounted for in terms of Gillespie’s valence shell electron pair repulsion (VSEPR) theory”. (A) According to the VSEPR model, coordination of a more electronegative l&and makes the bonding electron pair draw away from the sulphur atom toward the Iigand and the electron pair orbita is contracted. From this, the sulphur bonds shorten, and the bond angle, in whose formation the sulphur-ligand bond is taking part, decreases. Hence the explanation for trends (1) and (2)_ (B) There is an other rule then in the VSEPR theory that multiple bond orbitals repel other orbitals more strongly because of their size than single bond orbitals. AccordingIy, the shortening of the S-O bonds i.e. the increase of the double bond character is accompanied by the opening of the O-S-O angle and this accounts for trend (3). We can note, however, that as more electronegative ligands are attached to

the sulphone group, all the sulphur bonds get shorter. Thus, according to rule (B) all the other bond angles could also be expected to open which is not observed and which would, besides, contradict rule (A). In the case of the bond angles X-S-Y and O-S-Y, therefore, there are two competing effects according to the VSEPR theory and the one summarized in (A) prevails. As for the utilization of microwave datum in this study, it can be stated that an unambiguous determination of the O-S-0

angle was possible, although, only

one of the three experimental constraints produced by the microwave study of Jacob and Lide2 was used. If comparing the determination of the value for the O-S-O angle in CH,S02F with that in the electron diffraction investigations on P33)2S02”

and CH,SOzC15

as discussed in ref. 5, the merits of combining

the data from the two techniques are obvious. In addition to the geometry presented for CH,SO,Cl in Table 3 two other models were also found to produce excellent agreement with the experiment differing from the data of Table 3 in the value for the O-S-O angle. It was then concluded that the geometry with a 127.1(42.4)” O-S-O bond angle reported for (CH3),S02 as a result of Oberhammer and Zeil’s electron diffraction studyI may be only one of the possible models producing the same agreement with the experiment. The extremely strong correlation between parameters does not make a unique determination possible from electron diffraction data alone. As a test of our results for CH,SO,F, a

408 refinement schemewasconstructed in which thevalue of 127”was usedasaconstraint for the bond angle O-S-O. In this refinement the same agreement between theoretical and experimental data could be produced as that demonstrated by Fig. 2 for the structure of Table 1. The combination of electron diffraction and microwave spectroscopy seems promising indeed for the accurate determination of the molecular geometries of XSOtY sulphones, preferably in a more complete way than done in the present study, i.e. utilizing all the direct information coming from the microwave studies. The tetrahedral bond configuration of the sulphur atom in sulphones usually produces cIosely packed internuclear distances and thus strong correlation between parameters for the electron diffraction analysis. This situation can be changed by involving data from rotational spectra mainly because of the different correlation pattern. NeedIess to say, more accurate geometric parameters are certainly needed forestablishing a little more quantitative correlations of bonding and structure for the sulphone molecules.

REFERENCES I 2 3 4 5

6 7 8 9 IO

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be submitted. 11 K. HEDBERG AND M. IWASAKI, Acta Crysrallogr.,

17 (1964) 529. 12 T. G. STRAND, Program for Calcalarionof Partial Waves Electron Scattering Factors ofAtoms, Oslo, 1968. 13 C. TAVARD, D. NICOLA~ AND M. ROUAULT, J. Chim. Phys., 64 (1967) 540. 14 B. ANDERSEN, H. M. SEIP, T. G. STRAND AND R. STBLEVIK, Acta C/tern. Stand-, 23 (1969) 322415 K. HEDBERG AND M. IWASAKI, J. C/rem Plrys_, 36 (1962) 589. 16 K. KUCHIT~U AND S. J. CYVIN, in S. J. CYVIN (editor), Molecrdar Stractares and Vibrations Elsevier,

Amsterdam,

1972.

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