The microwave and infrared spectra and structure of hydrothiophosphoryl difluoride

391 Journal of Molecular Structure, 15 (1973) 391-398 @ Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands

THE MICROWAVE AND INFRARED SPECTRA AND STRUCTURE HYDROTHIOPHOSPHORYL DIFLUORIDE

OF

CARL R. NAVE Department of Physics, Georgia State University, Atlanta, Ga. 30303 (U.S.A.) J. SHERIDAN Department of Chemistry, University CoIlege of North Wales, Bangor, Caerns. (Wales)

(Received 2 October 1972)

ABSTRACT

The microwave spectra of 32SPHF,, 34SPHF, and 32SPDF, have been analyzed. The structural parameters obtained from this analysis are: d(S-P) = 1.867+_0.005 A, d(P-F) = 1.551_+0.005 A, d(P-H) = 1.392&0.005 A, LSPF = 117.4+0.2 degrees, LSPH = 119.2kO.2 degrees, LFPF = 98.6kO.2 degrees. Centrifugal distortion coefficients were obtained for 32SPHFz. The spectra of two vibrational excited states of 32SPHF2 were observed. The two sets of rotational constants (A) 8336.72, 3726.70, 2807.56 MHz and (8) 8344.88, 3727.73, 2798.75 MHz were associated with the vibrational states with measured infrared frequencies 419 cm- ’ and 344 cm- ’ respectively. An analysis of the infrared spectrum is included. Dipole moment measurements yielded p = 1.87 f 0.03 D for 32SPHF2 and p = 1.86kO.03 D for 32SPDF2.

MICROWAVE SPECTRA

The spectra of 32SPHF2 and 32SPDF2 were assigned from the J = 1 3 2 and J = 2 + 3 transitions, based on the characteristic Stark patterns and the agreement with the calculated spectra. The low-J lines of 34SPHF2 were predicted and a detailed search was made using the experimental technique described below. This species was assigned on the basis of a detailed fit of three J = 1 4 2 and four J = 2 -+ 3 transitions along with an A-C versus K plot of the Q-branch series Also, the M = 0 Stark components could be observed for the J,,.J-3 * J2,3--1. J = 1 -P 2 transitions and the displacements were close to those observed for the other species. The inertial defect I, -I,-Zc aIso provided confirmation, as shown

392 TABLE

1

OBSERVE9

LOW-J

Transition

ROTATIONAL

TRANSITIONS

=+SPZiF2 Observed

‘+SPDFt LW

Obserued

12062.34 0.12 28735.12 -0.07 19513.49 -0.01 27939.30-0.04 12937.52 0.14 13982.14 -0.10 36 186.37 -0.01 27465.69 0.09 34033.37 -0_07 12533.04 -0.01 20076.10 -0.24 19 109.31 0.14 20 889.50 0.01 18 139.11 0.04 19592.70 -0.01

000-l 10 111-221

101-211 110-&o 10402 110411 &Z-&Z

202-3 1z 21I-311 211-303 22o-321 21x-303 ~~~-3~~ 212-313 2,,-3,2

FOR HYDROTHIOPHOSPHORYL

J4SPfiFz Al,

27571.30 -0.05 18901.25 0.07 26 840.06 0.04 12769.37 -0.13 13723.43 - 0.03 26642-10

0.04

12 756.69

0.07

18888.31

0.02 -0.02 -0.04

==SPfiFz,

(MHz) A”

“=SPHFz,

Bb

Observed

Av

Obsemed

As

Obserued

Au

28 597.02 19 124.02 27 840.11

-0.04 0.05 0.02

28 736.82 19516.88 27 942.06

- 0.05 0.06 0.1 I

28 762.40 19528.14 27 960.02

0.40 0.07 0.06

0.01 35 790.78 26 785.88 -00.02

19407.53

17991.73 19321.18

DIFLUORIDE

18 986.26

36 190.18 -0.09 0.04 27470.43

36217.69 -0.13 27489.38 0.04

19 120.25

19087.99

0.02

-0.02

19602.71

0.03

-0.06

19 579.39

0.03

-0.05

o Av

= z’~,,~- I’,.~,~. b A and B are vibrational

TABLE

excited states.

2

ROTATIONAL

A (MHz)

CONSTANTS

32SPHFz

32SPDF2

3JSPHF2

“SPHF2,

8336.572&0.006=

7976.61 f0.03

8333.40&0.03

8336.72&0.03

Ab

32SPHF2, Bb 8344.88f0.03

B (MHz)

3725.667&0.003=

364l.52+0.03

3596.86&-0.03

3726.70f0.03

3727.73&-to.03

C (MHz)

2805.302~0.002”

2798.88f0.03

2731.91 f0.03

2807.56f0.03

2798.75f0.03

&--I,-& (amu At)

- 105.1249

-105.1395

- 105.1305

- 105.0169

- 105.5616

d(F-F)

2.352

2.352

2.352

2.351

2.357

A

a Standard deviation from fit of 71 transitions b A and B are excited vibrational states_

with centrifugal

distortion

included.

in Table 1. The spectra of two excited vibrational states of 32SPHFz were observed. Rough measurements of the relative intensities of excited state Iines indicated that vibrational states A and B as noted in Tables 1 and 2 correspond to the measured infrared absorption frequencies 419 cm-l and 344 cm-l respectively, which were the only infrared absorptions observed in this region, The observed frequencies for the J = 1 -_* 2 and J = 2 + 3 transitions are listed in Table 1, and the corresponding rotational constants are listed in Table 2. Centrifugal distortion effects were relatively small, causing about 3 MHz deviation from the rigid rotor frequency at J = 10. A centrifugal distortion calculation was

393

carried out using 71 measured transitions of the normal species 32SPHF,. The computer program developed by W_ H. Kirchhoff’ was used for this calculation. ,411transitions were fit to the order of experimental error with an overall root mean square deviation of 0.06 MHz for the 71 transitions. The calculation confirmed that the centrifugal distortion corrections were essentially negligible for the J = 1 -+ 2 and J = 2 + 3 transitions so the frequencies of these transitions for the other species were used without corrections to obtain the rotational constants. The rotational constants and centrifugal distortion constants for 32SPHF2 with their standard deviations obtained from the least square fit are listed in Table 3. TABLE

3

MOLECULAR

Rotational

PARAMETERS

constants

FOR

32SPHF2

(MHz)

A = 8336.572f0.006 B = 3725.667&0.003 C = 2805.302&0.002 Centrifugal

distortion

coefficients

(MHz)

TX T2 tga L.r

= -0.0232&0.0004 = -0.0052~0.0001 = 0.129 fO.003 *0.001 = -0.039 7 bbbb= -0.0041 fO.OOO1

7cccc =

-0.00135f0.00007

JJtl is a calculated parameter based on the values of the other parameters*. It is not determinable as an independent parameter.

INFRARED

SPECTRA

SPHF, belongs to the symmetry point group C, and the nine normal vibrations may be classified into six A’ (parallel to the molecuIar plane) and three A” (perpendicular to the molecular plane) modes. The molecular plane is defined by the A and C inertial axes. For a small molecule such as SPHF, it is not possible to give precise descriptions of the normal modes in terms of localized bond movements, but the presence of certain bonds with very different stretching force constants from the others enables several characteristic absorption peaks to be identified. Most of the fundamentals give rise to very intense absorptions as compared to the many combination bands and overtones observed. The highest frequency fundamental at 2458 cm-’ is associated largely with the stretching of the P-H bond, while the absorption at 710 cm-’ is typical of the P=S grouping 2* 3 . Both these absorptions give rise to “A-type” band contours with strong central Q branches. The P-R separation predicted by Seth Paul and Dijkstra (ref. 4) for such parallel bands agrees well with the measured splittings (Table 4).

394 TABLE 4 INFRARED

Relatiue intensify

W W W W VW S VW W VW W W W W

ABSORPTION

Absorption band centres (cm-‘)

Rotational band contour

P-Rb separation (cm-‘)

Assignment

3466 3405 3382 3167 2878 2458 2030 1941

A B c c C? A ? A

16 12

VI+Q(= 3477) ? v1 +a~~(= 3381) v1 +vo(= 3168) v, +v&= 2877) fundamental vl

1860 1823 1798 1727 1631

? ? ? A

W

1416 1341 1243 1128

m

1054

W W W

S

1019

S

923 901 760

m vs W s

m m

BANDS*

963

710 419 344

A A A ? C A A B A B A A

C? A

18

17

17 18 18 16

18

17 15 16

11 18 18 17

2x+(= 2038) va-!-v&= 1942) *‘T+Yg(= 1864) 2 XY~(= 1846) 2 xvs(= 1802) Yztv.&= 1729) Y~+v.&= 1633)

2 x v~(= 1420) Y,+Y,(= 1342) v3 Y&= 1267) v.$_tvg(= 1129) Qfz’s(= 1054)

fundamental 1~~ fundamental fundamental tundamental

Y~ r3 us

I’~+v&= 763) fundamental a.4 fundamental v5 fundamental iv6

vs, very strong; s, strong; m, medium; w, weak; VW, very weak. a All absorption bands were measured for vapour phase. t. Using the observed rotational constants, the calculated5 P-R separations

bands for “3*SPHF2” measured values.

are 17, I3 and 26 cm-’

respectively.These

for type A, B and C are in good agreement with the

The two lowest frequency modes observed at 419 and 344 cm-’ can be identified with the two vibrational satellite spectra seen in the microwave spectrum. The lowest of these is associated with considerable movement of the F-F distance as shown from the observed changes in the rotational constants. Consequently the 344 cm-l absorption is assigned to the A’ vibration where the F-P-F angle is deformed. Since the combination band of the 344 and 419 cm-’ bands is clearly seen at 760 cm-‘, the 419 cm-’ absorption must also arise from an A’ mode and it is tentatively assigned to a wagging motion of the PF2 group in the molecular plane. The strong “type A” band seen at 1019 cm-l is sensitive to deuteration6, and thus-.it is probably associated with the P-H in-plane deformation vibration.

395 TABLE

5

STRUCTURAL

PA-

d(P-H) &P-F) d(S-P) LSPF iSPH LFPF

= = = = = =

TABLE

6

TENTA-I-WE

Vibration =Jl VZ V3 VS

VS Vti V-I VS

5'9

RS

FOR

SPHF,

1.392f0.005 A 1.551f0.005 A 1.867&0.005 A 117.4&0.2O 119.2*0.2” 98.6&-0.2”

ASSlGNMENT

OF

NORMAL

VIBRATIONS

Wauemrmbtv

Symmetry class Approximate description

2458 1019 923 710 419 344 963 901 ?

A’ A’ A’ A’ A’ A’ A” A” A”

stretch P-H in-plane deformation P-H symmetric stretch P-F2 stretch P-S in-plane wag PFz deformation FPF out-of-plane wag P-H asymmetric stretch PFz rock PFt

The PF2 group would be expected to give rise to two very strong absorptions corresponding to symmetric and antisymmetric stretching vibrations of the P-F bonds. These two modes are assigned to the bands at 923 and 901 cm-‘; the higher frequency absorption having a central Q branch corresponding to the A’ mode. One of the two remaining A” fundamentals, the out-of-plane wagging motion of the P-H bond, is assigned to the type B contour seen at 963 cm-‘. There is no obvious candidate to be seen for the ninth fundamental. This vibration would largely be associated with the rocking of the PF2 group and should give rise to a type B band contour. With the exception of one weak absorption, all observed lines can confidently be accounted for in terms of overtones and combination bands of the assigned fundamentals.

EXPERIMENTAL

Samples of SPHFz and SPDF2 were obtained from Cavell, who reported the preparation of this substance7*5. The 34S species was observed in natural abundance.

396

The microwave spectra were measured with a conventional 100 kc squarewave Stark modulated spectrometer. To obtain the sensitivity necessary for observation of the 34S species, p hase sensitive detection was used and the klystron was phase-locked with a Shomandl Model FDS 30 Syncriminator. Using detector bandwidths in the range 0.25-1.0 cycles/set, the low-J lines were recorded in both directions along with frequency markers from a Schlumberger Precision Signal Generator Type DO 1001 and Synchronous Oscillator Type 0 1500. The Schlumberger frequency chain was locked to a stabilized crystal oscillator which was calibrated against the 100 kc standard frequency from Droitwich. With repeated measurements, reproducibility within less than 0.05 Mc/sec was obtainable. All measurements were made near -78 “C. Infrared spectra in the range 4000-200 cm-l were recorded using a PerkinElmer 225 spectrometer. The instrument was calibrated using absorption peaks of ammonia and water vapour. Spectra below 400 cm-l were obtained using a cell with polythene windows. The effective resolution was 4 1 cm-’ throughout the whole range.

STRUCTURE

Six structural parameters are required to specify the geometry of the molecule SPHF2. These parameters can be obtained in a straightforward manner from the equations for the inertial dyadic in the principal frame of 32SPHF, plus the center of mass equations_ The coordinates of S and H in this frame were obtained from Kraitchman’s equations’. The F-F distance was obtained from the inertia1 defect I,, -1, -I,. This reduced the set of equations to five equations with four undetermined parameters. One of these equations contained the distance of S from the A axis, a small and relatively poorly determined quantity from Kraitchman’s equations, in a product and thus had a larger uncertainty than the other equations. The remaining four equations were solved for the four undetermined parameters in terms of I. and I, of 32SPHF2. The resulting structural parameters are listed in Table 5. From this model the rotational constants were recalculated. The calculated constants were in agreement with each of the nine observed constants within 0.2 Mc/sec, or within less than 0.006 %_

The dipole moments of 32SPHF2 and 32SPDF2 were determined from Stark effect measurements on the three ,Y,, J = 1 -V 2 transitions. The Stark displacements for these molecules and for OCS at identical electric field settings were measured and the Stark coefficients were determined from their ratios. The dipole

397

Fig.

1. Structure

and orientation

of dipole

moment

of SPHFz

_

moment of 32SPHF2 was calculated as 1.87_tO.O3 D with ,u= = 1.53 D and pa = 1.08 D. The dipole moment of 32SPDF, was calculated to be 1.86+0.03 with p, = 1.51 D and pu,= 1.09 D.

The direction of the dipole moment was calculated to be 22.8 degrees away from the bisector of the PF2 triangle, as illustrated in Fig. 1. In this calculation fluorine was assumed to be negative and hydrogen positive with respect to the phosphorus.

DISCUSSION

The calculated

P-S bond length is in agreement with that in PSF, (ref. 9)

within experimental error. However the P-F distance is 0.04 A greater than the electron diffraction result for PSF, (ref. 10) and 0.02 A greater than the value assumed for the best fit of the microwave datag. The P-F and P-H bond lengths are less by 0.03 A and 0.02 A respectively than the results obtained by Kuczkowski (ref. 11) in the case of PHF, . The P-H bond length is in agreement, within experimental error, with that obtained for OPHF, by Centofanti and Kuczkowski12. The P-F bond length is 0.01 A greater than the result for OPHF, , which is slightly greater than the quoted experimental error.

ACKNOWLEDGEMENTS

The authors wish to express their appreciation to R. G. Cave11for providing

the sampIes of SPHF, and SPDF2, and to N. L. Owen for his work in the collection and analysis of the infrared data. mnks are also due to the Science Research Council for a research grant to assist this work.

398 REFERENCES 1 W. H. KIRCHHOFF, J. Mol. Spectrosc., 41 (1972) 333. 2 L. J. BELLAMY, The Infrared Spectra of Complex Molecules, Methuen, London, 1958, p. 321. 3 N. B. COLTHRUP, L. H. DALY AND S. E. WIBERLY, Introduction to Infraredand Raman Spectroscopy, Academic Press, New York, 1964, p. 302. 4 W. A. SETH PAUL AND G. DIJK~TRA, Spectrochim. Acta, 23A (1967) 2861. 5 T. L. CHARLTON AND R. G. CAVELL, Inorg. Chem., 6 (1967) 2204. 6 R. G. CAVELL, personal communication. 7 T. L. CHARLTON AND R. G. CAVELL, Chem. Cornman., (1966) 763. 8 J. KRAITCHMAN, Amer. J. Phys., 21 (1953) 17. 9 Q_ WILLIAMS, J. SHERIDAN AND W. GORDY, J. Chem. Phys-, 20 (1952) 164. 10 D. P. STEVENSONAND H. RUSSELL, J. Amer. Chem. Sot., 61 (1939) 3264. 11 R. L. KUCZKOWSKI, J. Amer. Chem. Sot., 90 (1968) 1705. 12 L. F. CENTOFANTIAND R. L. KUCZKOWSKI, Inorg. Chem., 7 (1968) 2582.