Vibrational spectra of adducts of acetonitrile with titanium and tin tetb achloride

Journal of Molecular Structure, o Elsevier Scientific Publishing

30 (1976) Company,

45-55

Amsterdam

-

Printed

in The Netherlands

VIBRATIONAL SPECTRA OF ADDUCTS OF ACETONITRILE TITANIUM AND TIN TETRACHLORIDE”

Y. KAWANO,

WITH

Y. HASE and 0. SALA

Instituto

de Quimica,

(Received

16 January

Universidade

de SCo Paulo, Stio Paul0 (Brazil)

1975)

ABSTRACT The IR and Raman spectra of the adducts of acetonitrile and acetonitrile-d, with titanium and tin tetrachloride have been measured in the solid state. The observed spectra suggest a cis-configuration for these adducts, and the vibrational assignments and the normal coordinate analyses have been performed on the basis of Czv symmetry.

INTRODUCTION

Previous papers on the IR [l-6] and Raman [ 6-81 spectra of SnC1,.2CH,Cn and SnC14.2CD3CN and the IR spectra [g-11] of TiC14.2CH3CN have already been published. However, a complete assignment has not been reported. The Raman spectra of TiC1+2CH3CN and the IR and Raman spectra of TiCI,. 2CDJCN have not yet been reported. For the adducts of the type MX4.2L, where L is a monodentate ligand, there are two probable configurations; one is &s-form with Cz,, symmetry for the skeleton and the other is trarzs-formwith Dgh symmetry presenting mutual exclusion. Therefore, vibrational spectroscopy can be used to differentiate between these two configurations. The present paper deals with the IR and Raman spectra and the vibrational assignment of the four adducts of acetonitrile, e.g., TiC14.2CH3CN, TiC14.2CD3CN, SnC14.2CH3CN and SnC14.2CD3CN. A normal coordinate analysis has been carried out to ascertain the assignment of the observed frequencies. EXPERIMENTAL

The adducts were prepared by the methods described in the literature [2,12]. Sample manipulations were carried out in a dry box. The IR spectra were recorded for nujol and fluorolube mulls, on a Perkin-Elmer

*Part of the doctoral

thesis of Y. K. presented

to the University

of Silo Paulo,

1973.

46

IR-180 (4000-180

cm-‘) IR spectrophotometer.

The Raman spectra were

recorded for the polycrystalline samples in sealed glass capillary tubes on a JarreWAsh Model 25-300 Raman laser spectrometer equipped with an argon ion (514.5 and 488.0 nm) and a krypton ion (647.1 nm) laser, for excitation. ASSIGNMENT

AND DISCUSSION

The IR and Raman spectral data of TiC14.2CH3CN and TiC14.2CD3CN are listed in Table 1, and those of SnC1+2CH&N and SnC14.2CD3CN in Table 2. The Raman spectra observed in the region of the =N stretching and of the skeletal vibrations for TiC14.2CH3CN and SnC1+2CH&N, together with the deuterated ones, are shown in the Figs. 1 and 2, respectively. For the c&configuration we can expect two C=N, two C-C, two M-N and four M-Cl stretching vibrations, coincident in both the IR and Raman spectra. For the trans-configuration, assuming a point mass model for the methyl groups, the mutual exclusion rule is expected to hold and we can expect one C-N, one C-C, one M-N and two M-Cl stretching vibrations in the Raman spectra and one CZN, one C-C, one M-N and one M-Cl stretching vibration in the IR spectrum. The observed coincidence in the IR and Raman spectra indicates a c&configuration, in agreement with the structure proposed from an IR study [ 3] for the titanium tetrachloride adduct and from the X-ray diffraction study [6] for the tin tetrachloride adduct. Accordingly, the observed frequencies have been assigned on the basis of CzVsymmetry and the expected forty-five fundamental vibrations are classified in the following representation: r = I~Q, (R,IR) + 8a,(R)

+ 9b, (R,IR) + 13b,(R,

IR)

For convenience, we will consider separately the assignment of the observed frequencies corresponding: (a) to the coordinated acetonitrile, (b) to the TX&N, skeleton, and (c) to the SnCl,N, skeleton. In the following discussion the Raman frequencies will be used. (a) Coordinated

acetonitrile

The fundamental vibrations of coordinated acetonitrile and acetonitrile-d3 are easily assigned by comparison with those reported for free acetonitrile [ 131, except for the C-C=N linear bending vibrations. The bands at 2997 and 2929 cm-’ of TiC14.2CH&N, and 2997 and 2928 cm-’ of SnCl,.2CH,CN are assigned to the C-H stretching vibrations. For the C-D stretching vibrations we assign the bands at 2248 and 2104 cm-’ of TiC1+2CD&N, and 2247 and 2101 cm-’ of SnC1,.2CD,CN. For TiC1+2CD3CN two bands at 2304 and 2300 cm-’ are assigned to the C-N stretching vibrations and are shifted 26 and 22 cm-‘, respectively, from the C=N stretching frequency of CD,CN, 2278 cm-’ [ 131. For SnCl, .2CD3 C:

47 TABLE

1

Infrared and Raman spectral data of TiCl,.BCH,CN TiC1,.2CD,CN

TiC1,.2CH,CN Infrared

Raman

2995 2927 2315 2310

2997

2288 2283

1405 1361

w m s s

m

s

s s

Infrared

Assignment Raman v

VW

1361 + 950 = 2311* 1361 + 939 = 2300* v(C=N) u(C=N) v(C=N)* u(C- N)*

2288 2282

1409 1361

m m 2305 2298

sh s

2304 2300

s s

2247 2200

s VW

2109 2106

VW w

2248 2200 2167 2107 2104 2030 1800

w w VW w s VW w

1093 1020

w VW

m m

VW m

1023~~ 950 w 939 w

775

370 318 280 244 233 219 192

sh m w VW VW VW m

m w

857 842

m VW

w

712 VW 462 VW 430 m 419 w 410 394 vs 390 sh 372 m 321 s 241 229 215 194 180 161 140

tasyrn (C-D) ? 1093

+ 1020

uwy,W-D) 2 x 1020

= 2113

= 2040

VW m

811 VW

390 vs, br

(C--H) (C--H)

2315 2308

w

420 sh

aSym

u .=,m

857 842 780

(cm-‘)

2929 m

1090 1018 10251x1 947 m 937 m

and TiC1,.2CD,CN

w w w w m w s

432 s

393 s 383 s, br

316 280 234 226 206

m w VW w w

396 m 387 vs 373 m 319 s 237 w 221 w 207 w 178 m 158 m 138s

4C--c) 4C-c) 4c-a 4C--C)

419 + 394 = 813 2 x 390 = 780 393 + 383 = 776 394 + 321 = 715 321 + 140 = 461 v(Ti-Cl) 6 (CCN) 6(CCN) 6 (CCN) v(Ti-Cl) d (CCN) v(Ti-CI) v(Ti-CI) 2 x 140 = 280 u(Ti-N) 2x 113=226 v(Ti-N), 6 (NTiN), 6 (CITiN) 6 (CITiN) 6 (CITiCI) 6 (ClTiCl)

6 (CITiN)

48 TABLE

1 (continued) TiCl,.BCD,CN

TiCl,.2CH,CN Raman

Infrared

Infrared

Assignment Raman

127 sh 112 s 71 63 57 44 28

113 106 68 62 54 44 30

w w m s m

s sh w w w s w

6 (CITiN) lattice mode lattice mode lattice mode 6 (TiNC) 6 (TiNC) 6 (TiNC) lattice mode -----

vs, very strong; s, strong; m, medium; w, weak; VW, very weak; sh, shoulder; asym, asymmetric; sym, symmetric; V, stretch; 6, bend; and p, rock. *See text. TABLE

2

Infrared

and Raman spectral

SnCl,.2CH,CN Raman

2993

2997 w 2935 m

w

2926 m 2313 s 2305 s

2286 s 2280 s

2928 2702 2313 2306

Infrared

790 w 408 w

(cm-‘)

Raman

s VW m m 2306 s 2285 w

2305 w 2298 m

2256 w 2198 w

2247 2195 2106 2101

2284 m 2278 m w w vw m

1401 VW 1357 m

1030 m

1090 w 1020 VW

855 s 845 s

855 s 850 s

1021 VW 942 w 933 w

410 sh

br, broad;

Assignment

1200 w

1022 s 942 s 933 s

?

u,,(C--HI usym (*W

2106 m 1400 m 1357 s

and SnCl,.2CD,CN

SnC1,.2CD,CN

Infrared

2933 m

data of SnCl,.2CH,CN

? ? ?

2x 1357=2714 1357 + 942 = 2299* 1357 + 933 = 2290* v(C=N) u(C=N) u(C=N)* v(C=N)* zasyru(C-D) 1090 -I- 1020 = 2110 vsvm(C-D) s,,(CH,) ~,,@-I,) 845 + 360 = 1205 6 s&CD,) hasym(CD,) P(CH,) u(C-c) u(C-C) u(C-C) .(C-c) 394 + 401= 6 (CCN)

795

49

TABLE 2 (continued)

Infrared 398

w

390 w

364 356 336 303

sh w vs m

216 w 206 w

200 w

Assignment

SnC1,.2CD,CN

SnC1,.2CH,CN Raman 401 w 394 sh 358 348 336 302

w w vs m

Infrared 402 w 372 VW 360 w 343 s 305 s 230

m

212 VW 199 180 155 139 133 111 100

w VW m sh sh m m

65 m 48 w 36 m

Raman

196 w

190 m

6 (CCN)

381 372 357 346 336 301

VW w w w vs m

91 65 46 35

6

w VW m w m m

v(Sn-Cl) u(Sn-Cl) u(Sn-Cl) v(Sn-CI) ? u(Sn-N) 6 (NSnN) u( Sn-N) 6 (ClSnN) 6 (CISnCl) 6 (CISnCl) 6 (ClSnCl) 6 (CISnN)

m w w m

lattice mode ? 6 (SnNC) 6 (SnNC) 6 (SnNC)

205 VW 192 168 155 137 131 109

(CCN) (CCN) 6 (CCN)

6

lattice mode ?

vs, very strong; s, strong; m, medium; w, weak; VW, very weak; sh, shoulder; asymmetric; sym, symmetric; V, stretch; 6, bend; and p, rock. *See text.

asym,

the bands at 2305 and 2298 cm-‘, shifted 27 and 20 cm-‘, are also assigned stretching vibrations. Webster and Blayden [6] have observed only one band at 2300 cm -‘. For TiCld.2CHSCN Coerver and Curran 1141 observed a band at 2304 cm-’ and Rao [9] observed two bands at 2310 and 2290 cm-‘, for the CsN stretching vibrations. However, we observed four bands at 2315, 2308, 2288 and 2282 cm-’ in the C-N stretching frequency region. These bands can be explained in terms of a Fermi resonance. Considering the frequencies calculated for the combination bands 1361 + 950 = 2311 and 1361 + 939 = 2300 cm-‘, the corrected fundamental frequencies were 2292 and 2290 cm-‘. These frequencies are shifted 24 and 22 cm-’ from that of CH,CN, 2268 cm-’ [ 131, respectively, and are nearly the same as those from TiClJ.2CD3CN. For the SnC14.2CH3CN Webster and Blayden [6] observed two bands at 2307 and 2285 cm-‘, Farona and Grasselli [4] observed also two bands at 2300 and 2283 cm-’ and Coerver and Curran [ 141 observed only one band at 2303 cm-‘. We observed four bands, as in the case of TiC&.2CH&N at 2313,2306,2284 and 2278 cm-‘, in the C=N stretching region. Considering the frequencies calculated from

to the C=N

50

WAVEHUYBER,

CM-’

Fig. 1. The Raman spectra in the region of C=N stretching (a) TiCI,-.2CH,CN and (b) TiCl,.2CD,CN. *Spurious band.

and skeletal

vibrations

for:

the combination bands 1357 + 942 = 2299 and 1357 + 933 = 2290 cm-‘, the corrected fundamental frequencies were 2298 and 2294 cm-‘. These frequencies are shifted 30 and 26 cm-’ from that of CH$N, 2268 cm-’ 1131, respectively. The magnitude of these shifts are nearly the same as those in SnC14.2CD3CN. The shifts observed for the C=N stretching frequencies of the four adducts (20-30 cm-‘) are considerably less than those in the adducts of acetonitrile with boron trihalides (90-100 cm-‘) [ 15,161 or antimony pentafluoride (62 cm-‘) [17]. These shifts can be interpreted in terms of the Lewis acidities of these halides. Three bands at 1409,136l and 1023 cm-’ of TiC14.2CH&N and at 1401, 1357 and 1021 cm-’ of SnC14.2CH3CN are assigned to the deformation

WAVE#UMBER, Fig. 2. The Raman spectra in the region of C-N (a) SnC1,.2CH,CN and (b) SnCl,.ZCD,CN. *Spurious band.

CM-I stretching

and skeletal

vibrations

for:

vibrations of the CH3 groups. Two bands at 1020 and I.093 cm-’ of TiC1,.2CD,CN and at 1020 and 1090 cm-’ of SnCL,.ZCD$N are assigned to the CD3 deformation vibrations. The bands at 950 and 939 cm-’ of T~Cl~.ZC~~C~ and at 942 and 933 cm-” of SnCX+2CH,CN are easily assigned to the C-C stretching vibrations. Two bands at 857 and 842 cm-’ of TiC1+2CD&N and at 855 and 850 cm-’ of SnC1,.2CD,CN are also assigned to the C-C stretching vibrations. The C-C=N linear bending vibrations are observed at 419,410 and 390 cm-’ for Ti~~~.2C~~~N and at 396 and 387 cm-’ for the deuterated one, The band at 38’7 cm-’ is assumed accidentally degenerated with one of the Ti-Cl stretching vibrations. Clark 1111 assigned a band at 422 cm-’ to one of these vibrations. The bands at 410,401 and 394 cm-’ of SnCIJ,2CH3CN are assigned to the C-C=N linear bending vibrations. Farona and Grasselli 143

52

and Webster and Blayden [6] assigned the bands at 410,400 and 392 cm-’ observed in the IR spectrum of SnC1+2CH&N to these vibrations. For SnCl,.2CD,CN the observed bands at 381 and 372 cm-’ are assigned to these linear bending vibrations. (b) TiCI,N,

Skeleton

The ‘I-Cl stretching frequencies have been predicted in the 400-280 cm-’ region by Beattie and Webster [lo] and Clark [ 181. However, for other six-coordinated adducts of titanium tetrachloride [ 19-221 they have been assigned in the region 450-280 cm-‘. The four Ti-Cl stretching vibrations of TiCl+ZCD&N should appear in the same region as for TiC14.2CH3CN. Therefore, comparing the observed frequencies for both the adducts and considering the Ti-Cl stretching frequencies assigned to other six-coordinated adducts of titanium tetrachloride we assign the bands at 430, 394, 372 and 321 cm-’ of TiC14.2CH3CN and at 432,387,373 and 319 cm-’ of TiCl.+2CD&fi to the Ti-Cl stretching vibrations. The bands at 241 and 215 cm-’ of TiC14.2CH&N and at 237 and 207 cm-’ of TiC1+2CD&N are tentatively assigned to the Ti-N stretching vibrations. These frequencies are comparable with the Ti-N stretching frequencies of TiC14.2C2H&N (226 and 212 cm-‘) or of TiC14.2C2HJCN (229 and 218 cm-‘) 1231. The assignment of the bands below 220 cm-’ is rather tentative. However, additional support in this assignment was obtained from the results of the normal coordinate analysis and from the bending vibrations of TiC14 and (TiCI&)‘- 1241. The assignment of the observed bands is summarized in Table 1. (c) SnCl, N2 Skeleton

‘The Sn-Cl stretching frequencies have been predicted in the 360-300 cm- ’ region by several authors [4, 6, 25]_ Comparing the observed frequencies for both the adducts_ and the Sri-Cl stretching frequencies assigned for the six-coordinated adducts of tin tetrachloride, we assign the bands at 358, 348, 336 and 302 cm-’ of SnC14.2CH3CN and at 357,346, 336 and 301 cm-’ of SnC14.2CD3CN to the Sn-Cl stretching vibrations. These frequencies agree with those observed by Webster and Blayden [6] , in the Raman spectrum of SnC14.2CH3CN. Two bands at 212 and 199 cm-’ were observed for SnC1+2CH&N and at 205 and 192 cm-’ for SnC14.2CD3CN. These bands are assigned to the Sn-N stretching vibrations. Farona and Grasselli [4] have assigned the IR bands at 222 and 207 cm-’ to these vibrations. Ohkaku and Nakamoto [25] have also assigned, based on metal isotope data, the bands at 210-150 cm-’ to the Sn-N stretching vibrations of the bipy and phen complexes. The assignment of the remaining bands in the low frequency region is, as

53

already mentioned for TiClQNs, rather tentative. Additional information was obtained from the results of normal coordinate analysis and from the bending vibrations of SnCL, and (SnC16 )*- [24]. The assignment of the observed bands is summarized in Table 2. NORMAL

COORDINATE

TREATMENT

The normal coordinate analysis was carried out assuming a modified Urey-Bradley force field. The geometrical parameters for SnC14.2CH3CN were taken from the average values of the X-ray diffraction data [6] except for the C-H bond distance, obtained from the rotational constants for CH$N [26]. In the absence of structural data for TiC&.2CH&N the parameters were assumed to be the same as for SnCL,.ZCH&N except for the Ti-Cl bond distance, transferred from the X-ray data of (TiCl,.POCl,), [27], and the Ti-N bond distance, calculated from the covalent radii. The bond distances used were: r(Sn-Cl) = 2.35, r(Ti-Cl) = 2.23, r(Sn-N) = 2.33, r(Ti-N) = 2.21, L(C=N) = 1.10, D(C-C) = 1.44 and d(C-H) = 1.10 8, and the valence angles were: L(a = CIMCI) = 103”) L(fi = NMN) = 77”, L(6 = CIMCl) = 94”, L(y = NMCl) = 90”, L(Q = NMCl) = 85”, L(p = CCH) = 109” 28’, L(E = HCH) = 109” 28’, L(B = MNC) = 180” and L(8 = CCN) = 180”. The internal coordinates are shown in Fig. 3. The numerical calculations were carried out with a set of computer programs [28] using an IBM 360/44 computer.

Fig. 3. Structure and internal coordinates of MCI,.BCH,CN

(M = Ti, Sn).

54

In addition to the seventeen force constants ordinarily introduced for the adducts on the simplified Urey-Bradley force field, two stretchingstretching truns-interaction force constants I(M-N, M-Cl) and I(M-Cl, M-Cl) were considered. Using this set of the force constants, the calculations were also carried out for TiC14.2CD3CN and SnC14.2CD3CN. The final sets of the force constants gave satisfactory agreements between the calculated and observed frequencies for TiC1+2CH3CN (average error l-l%), for SnC142CH3CN (average error 1.6%) and for both the deuterated adducts (average error 2.0%). The symmetry coordinates, the force constants and the calculated and observed frequencies with the potential energy distribution data are available on request from the British Library Lending Division, Boston Spa, Yorkshire LS23 7BQ as SUP. PUB. No. 26013 (11 pages). The force constant K(C=N) = 17.965 mdyn 8-l for TiC1+2CH,CN and 18.100 mdyn 8-l for SnC14.2CH3CN are a little larger than that for CH&N, 17.488 mdyn 8-l [29]. This increase in K(C-N) upon adduct formation has been attributed to the increase of the C-N bond strength [16, 20, 30, 311. The force constants K(Ti-Cl) = 1.403 (axial) and 1.620 (equatorial) mdyn a-* for TiC14.2CH&N are smaller than that for TiCh,, 2.471 mdyn a-’ [32] and larger than that for (TiCI )2-, 1.093 mdyn A-’ 1331, in agreement with the bond lengths for these compounds 2.23,2.17 1341 and 2.33 K [35], respectively. The same is true for K(Sn-Cl) = 1.497 (axial) and 1.707 (equatorial) mdyn 8-l for SnC1,.2CH3CN. 2.326 mdyn A-’ for SnCl, [32] and 1.00 mdyn A-’ for (SnC1,)2- [36], being the bond lengths 2.35, 2.281 [ 371 and 2.42 A [ 351, respectively. The force constant K(Ti-N) = 0.794 mdyn A-’ for TiC1,.2CH,CN and K(Sn-N) = 0.668 mdyn A-’ for SnCll. BCH$N are comparable in agreement with the fact that the observed shifts of the C-N stretching vibrations are nearly the same for both the adducts. The normal coordinate treatment confirms our tentative assignments_ In the high frequency region the potential energy distribution shows that C-H (C-D) stretching and CH, (CD,) deformation vibrations are approximately independent while there is some coupling between t?le C=N and C-C stretching vibrations. In the low frequency region the vibrational modes are rather coupled. ACKNOWLEDGEMENTS We wish to thank Prof. Kiyoyasu Kawai of Toyama University, Japan, for his valuable discussions and suggestions. This work was supported by Fundacao de Amparo 5 Pesquisa do Estado de Sao Paulo (FAPESP) and Conselho National de Pesquisas. One of us (Y. H.) thanks FAPESP for a fellowship grant.

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