37Cl NMR chemical shifts and nuclear quadrupole couplings for some small chlorine compounds: experimental and theoretical study

16 August 1996

CHEMICAL PHYSICS LETTERS

ELSEVIER

Chemical Physics Letters 258 (1996) 330-335

35/37C1 NMR chemical shifts and nuclear quadrupole couplings

for some small chlorine compounds: experimental and theoretical study Martin A. Fedotov a, Olga L. Malkina b, Vladimir G. Malkin c,. a Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Science, 630090 Novosibirsk, Russia b Computer Center, Faculty of Natural Sciences, Comenius University, Mlynska Dolina CH-I, SK-84215 Bratislava, Slovakia c Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dubravska Cesta 9, SK-84236 Bratislava, Slovakia

Received 9 May 1996

Abstract An experimental study and quantum-chemical density functional theory calculations of 35/37C1NMR chemical shifts and nuclear quadrupole couplings for some small chlorine compounds were performed. The experimental and theoretical data are in good agreement. The results clearly demonstrate that high field chlorine NMR can be used for identification of small chloride molecules. Solvent effects on chlorine chemical shifts are estimated.

1. Introduction Due to the large NMR linewidth for most chlorine compounds, chlorine N M R is not widely used in chemistry. As a consequence chemical applications of chlorine NMR mostly consist of studies of C1and C10~- ions in solution [1]. Although chlorine NMR chemical shifts (CS) in some compounds have been known for a long time [2-4] the reliability of a major part of such data is questionable because of the large error bars. The situation is more favorable for high field chlorine NMR, as was indicated earlier [2]. In the

* Corresponding author.

present work, using this technique we found it possible to improve the accuracy of measurements and to obtain reliable results for a set of small molecules such as XC14 (for X = C, Si, Ge, Sn, and Ti) and chlorosubstituted methanes. This, in turn, gave us a good benchmark for theoretical quantum-chemical methods for calculations of chlorine NMR parameters. The recently developed sum-over-states density functional perturbation theory (SOS-DFPT) [5,6] with the individual gauge for localized orbitais (IGLO), was successfully applied to the calculation of NMR parameters for a wide range of compounds [5-12]. However, up to now the SOS-DFPT approach has been used mainly for calculations of the H - F atoms and only occasionally for other nuclei. In the present study, we show the results of experimental and theoretical (using the SOS-DFPT

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M.A. Fedotou et a l . / Chemical Physics Letters 258 (1996) 330-335

331

approach) studies of chlorine chemical shifts and electric field gradients.

3

2. Experimental

35"37C1 NMR spectra were recorded on a Bruker MSL-400 spectrometer at frequencies 39.20 MHz (35C1) and 32.63 MHz (37C1) in the frequency range 100 kHz at the room temperature. The pulse repetition frequency was 100 Hz at radiofrequency pulse duration of 12 p,s (~r/2). The accumulation number of free induction decay was about 20000. Chemical shifts (CS) were measured from 1 M NaCI solution as an external reference without a correction for magnetic susceptibility.

2 1 • ' ' '

i

oloo

, ,

i

500

. . . . . . . .

{,

o PPM

,

,

,

, ,

, r , , -500

, ....

i .... -%ooo

Fig. 1. NMR spectra of 10% volume solutions of chlorine compounds in ethyl ether at 293 K. (1) CH2CIz; (2) HCI2C-CHCI_~; (3) CHCI 3.

4. Results and discussion 3. Calculations

The calculations have been carried out using a modified version of the deMon-KS program [13-15] augmented by the deMon-NMR code. For all calculations the Perdew-Wang-91 exchange-correlation functional (PW91) [16] was employed. See Refs. [5,6] for further computational details. Unless otherwise indicated, the basis set BIII of Kutzelnigg et al. [17] (also called IGLO-III in some other publications) was used. Since BIII is not available for all nuclei the basis set of Schaefer et al. [18] with a modified contraction scheme (C: (5, 6 × 1/2, 4 × 1/1, 1); Na: (6 1, 2, 5 × 1 / 6 × 1/1, 1, 1); Si, CI: (6, 1 , 2 , 5 × 1 / 3 , 6 × l / l , 1, 1); Ge: (6, 1, 1 , 2 , 7 × 1/3, 9 × 1 / 6 × 1)) and polarisation functions (taken from BIII) was also employed. This basis set (denoted as TZV-2) was used for Na and for C, Si, Ge and Ti in a series XCI 4. For Sn, faute de mieux, the basis set BII of Kutzelnigg et al. [17] was employed. The experimental molecular geometries [19] t have been used throughout the paper.

i For NaCI, Ref. [23]; for XC14, Ref. [21]; for SnCl 4, Ref. [22].

From the two stable magnetic isotopes (35C1, I - - - 3 / 2 and 37C1, I = 3 / 2 ) 35C1 is predominantly used in chlorine NMR because its natural abundance is three times higher than that of 37C1. Consequently, with 35C1 the appropriate signal-to-noise ratio ( S / N ) in NMR spectra can be obtained about ten times more rapidly than with 37C1. The chlorine NMR linewidth is determined by a quadrupolar mechanism of relaxation and is very broad for most chlorine compounds despite the small quadrupole moment of the nuclei ( - 0 . 0 8 2 barn for 35C1 and - 0 . 0 6 4 6 for 37C1 [23]). In a magnetic field of less than 2 T the chlorine linewidth almost surpasses chlorine CS ranges [1,2]. In the field of 9.4 T, the CS ranges exceed the linewidths of small molecules (Fig. 1). This decreases the error bar and gives us a better benchmark for theoretical calculations. The experimental and calculated data for chlorine chemical shifts and gradients of electric field are summarized in Tables 1 and 2. The agreement between the calculated and experimental chemical shifts is presented visually in Fig. 2. The quadrupole nucleus NMR linewidth for I = 3 / 2 and axial symmetry is given by

W1/2=

2~(e

2

qzza/h) 2 z¢/5

(1)

M.A. Fedotov et al./ Chemical Physics Letters 258 (1996) 330-335

332

Table 1 Experimental and calculated NMR and NQR parameters of some chlorine compounds Compound

CCI 4

Solvent

ether g

TiCI 4

benzene neat neat neat benzene neat

SiMe2CI2

ether

SiCI 4 GeCI 4 SnCI 4

Calculated NMR/NQR parameters a

Experimental data

~(35C1 ) b

WI/2 c

R(X-CI) d

,/ e

8(35C1) f

qzz

qyy

qxx

599 + 8 h 592 + 9 594 -I- 8 195 + 3 246 + 7 138 -1- 15 135 + 8 865 + 2 861 + 1 113 5:4

13 11 14.8 3.6 7.7 15.5 12.6 0.8 0.9 3.5

176.7

40.46

604

-- 83.5

41.8

41.8

201.8 211.3 231.0

20.3 25.27 23.72

182 262 111.2

-44.3 - 54.4 -49.3

22.1 27.2 24.7

22.1 27.2 24.7

217.0

5.98

871

- 13.6

6.8

6.8

103

-39.8

21.6

18.1

205.4

18.6

a qxx, qyy, and qzz are principal components of the quadrupole coupling tensor, in MHz. b In ppm with respect to 1M NaCI water solution; e The linewidth, in kHz. d Distances, in ppm. • The lowest NQR frequencies, in MHz, from Ref. [24]. f In ppm with respect to a single NaCI molecule; the calculated tr(35C1, NaCI) = 904.9 ppm; the following basis sets have been used: TZV-2 for Na, C, Si, and Ti, Bill for CI and H, and BII for Sn. s Diethyl ether, h The uncertainty is 3% of the linewidth.

and the N Q R f r e q u e n c y is d e f i n e d b y

v= e2qzzQ/2h,

m o l e c u l e s o f a c o m p o u n d a n d solvent. N e v e r t h e l e s s , (2)

l i n e w i d t h s correlate with v 2 v a l u e s i f the c o v a l e n t radii o f e l e m e n t s are taken into a c c o u n t . Surpris-

w h e r e qzz is the z - c o m p o n e n t o f the electric f i e l d

ingly, the d i f f e r e n c e b e t w e e n the c a l c u l a t e d values

g r a d i e n t tensor. F o r e s t i m a t i o n o f ¢c, the S t o k e s E i n s t e i n relation is c o m m o n l y used:

qzz and 2 v (relation (2)) a l m o s t w i t h i n 10% (see

~'c = 4"tr a 3 t l / 3 k T ,

(3)

T a b l e 1). T h i s is e s p e c i a l l y r e m a r k a b l e s i n c e v valu e s h a v e b e e n m e a s u r e d f o r c o m p o u n d s in solution

and

qzz

values

have

been

calculated

for

free

w h e r e a is the h y d r o d y n a m i c radius o f the m o l e c u l e

molecules.

o f interest, r/ is the viscosity o f a solvent. R e l a t i o n (3) is o f l i m i t e d u s e f u l n e s s for c o m p a t i b l e s i z e d

g r a d i e n t s b y the D F T m e t h o d f o r d e u t e r i u m [26],

V e r y r e c e n t l y , the c a l c u l a t i o n s o f e l e c t r i c field

Table 2 Experimental NMR data of 10% volume solutions of chlorine compounds in comparison with calculated results. All chemical shifts are in ppm Compound

CC1a CHC13 CH2C12 tetrachloroethane dichloroethane MeCI

Solvent a

ether d benzene ether d MeCN c.f ether d ether d acetone f ether d.f MeCN ¢'f neat

Wb

13 14.8 7.7 7.2 7.8 18 21.5 6.5 7.5 22

8(0) Experimental

calculated g

599 + 8 594 + 9 401 + 8 411 + 7 226 -k 6 250 + 18 267 + 22 135 5:7 131 + 8 50 ¢

606.5 383.1 195.2

21.7

a Solvents for chlorine NMR. b Linewidth, in kHz. c From Ref. [25]. a Diethylether. e Acetonitrile. f 37C1 NMR data. g In ppm with respect to a single NaC1 molecule; the calculated o-(350, NaCI) ffi 904.9 ppm; TZV-2 basis set has been used for Na and Bill basis set has been used for other atoms.

M.A. Fedotov et al./ Chemical Physics Letters 258 (1996) 330-335 9OO A

700 --

I100

m te

_u

E e~

400

•o

300

m tl 0

100 0

.

; 100

I 200

300

400

500

I

I

I

600

700

800

900

Experimental chemical shifts (ppm) Fig. 2. Comparison between the calculated chlorine chemical shifts and experimental data for compounds presented in Tables 1 and 2.

nitrogen and oxygen [27] were performed. Usually, the calculated results are within 5-10% of experimental values depending on the nucleus under study. Judging by these results and the results for chlorine presented in Table 1 we conclude that the DFT method is able to reproduce the gradients of the electric field with reasonable accuracy for many nuclei and systems. We expect this method to yield systematically good results for nuclei at least up to transition metals. For the latter, more studies have certainly to be done before drawing any decisive conclusion. Starting with transition metals one probably has to take care of relativistic effects. However, our preliminary calculations of electric field gradients on iodine [28] demonstrate reasonable agreement with experimental data and thus indicate that

333

these additional problems are not of overriding importance. We have also found reasonably good agreement between the calculated and observed chlorine chemical shifts (see Fig. 2). For most of the compounds presented in Table 1, the difference between the calculated and experimental chlorine chemical shift is less than 16 ppm which is almost within the experimental error bar. As can be seen from Table 1, for these compounds the dissolution effect in nonpolar solvents is less than the experimental error. The largest deviation, about 25 ppm, found for SnCl 4 is probably due to a smaller basis set (BII) on tin. The calculated chlorine chemical shifts in chlorosubstituted methanes (except for CC14) do not agree so well with experiment (see Table 2). This is not surprising because they have dipole moments and therefore strongly interact with solvent molecules whereas the calculations have been carried out for free molecules. Therefore, we believe that the gasliquid shift is the major reason for the remaining discrepancy between our calculated and experimental data. A solvation effect is another possible source of the discrepancy. For the estimation of the solvent effect on chlorine CS we have used 37C1 NMR because 37C1 CS can be measured 1.3 times more precisely than 35C1 CS in spectra with the same S / N ratio. 37C1 chemical shifts in a set of solvents are presented in Table 3. Solvent effect can be estimated to be less than 18 ppm in the selected set of solvents although the dispersion of CS lies in the same range. Organic chloride NMR data (Tables 2 and 3) demonstrate the strong effect of chlorine substitution

Table 3 Chlorine NMR chemical shifts (~), in ppm, and the linewidths (W,/2), in kHz, in 10% solutions of some compounds together with their dielectric constants and viscosities. Solvent

e a

17 b

Et20 c CH 2 Br2 pyridine acetone methanol MeCN d

4.3 7.5 12.4 20.7 32.7 37.5

0.24 1.0 0.95 0.39 0.59 0.34

a Dielectric constants,

b Viscosities, in Cp.

~(Wi/2

)

CHCI 3

1,1,2,2-(CHC12)2

1,2-(CH2C1)2

401 412 419 409 403 411

250 + 18(18)

135 + 7(6.5)

+ 8(7.7) + 10(10) 5: 14(14) + 7(6.8) + 8(8.2) at- 7(7.2)

c Diethyl ether,

a Acetonilrile.

267 -t- 22(21.5) 131 + 8(7.5)

334

M~A. Fedotov et al. / Chemical Physics Letters 258 (1996) 330-335 p.p.m.

1000 t

,

o

500 ,

,

~

[

J

I I SiClz

X:

CCI 4

-CCI 3

I

I

Ti

C

I

..I ..............

] ...........

6 siCI3

•-•tt 2

Ge

V

~

3

Si Sn

l=l .........

clo5 clo~ I

4

~CCI

z

CI-

..... ~.... ~. I

I ~-SiCI I ~"SiCI 2

I I

I

I

I

I

I

I

I

[

i

1 I

Fig. 3. Chlorine chemical shift ranges for different chemical environments. (1) Ions in water solution. A linewidth is shown for a field of 9.4 T and 293 K. (2) XCI 4, for various X elements. (3) Chloroorganics, a linewidth is shown. (4) Chlorosilanes.

in the second coordination sphere of the chlorine atom, of interest in its chemical shift. Proton substitution by an organic ligand in the second coordination sphere moderately affects the chlorine CS. It looks like the chemical shifts of fragments - C C 1 3 , o r =CCI 2, or -=CC1 cover quite compact and almost separated areas and therefore they might be used for identification of the fragments by the CS. The effect of substitution in silicon fragments SiCI3, SiCI 2, SiCI is less pronounced than in the corresponding carbon fragments. Unfortunately the linewidth grows rapidly with increase of the molecular size (see Tables 2 and 3). However, additional data can be provided by quantum-chemical calculations with reasonable accuracy, as shown in this paper. The chlorine chemical shift ranges based on the data from Tables 1-3 are presented in Fig. 3.

5. Conclusions The present joint experimental and theoretical study demonstrates that high field chlorine NMR can be used for chlorine fragment identification of relatively small molecules. The results of the chlorine chemical shift calculations using sum-over-states density functional perturbation method (SOS-DFPT) are in good agreement with experimental data. Discrepancies between theoretical and experimental data (less than 16 ppm for tetrahedral chlorine compounds, except for SnCI a, and up to 30 ppm for other compounds where gas-liquid shifts and solva-

tion effects are likely larger due to relatively large dipole moments) are comparable with deviations of chemical shifts due to different solvents (less than 18 ppm). The results of electric field gradient calculations by density functional theory are also in good agreement with experimental data (usually, the error is less than 10%). These data, together with the results of other studies, show that density functional theory based approaches for NMR chemical shift and gradient of electric field calculations are important practical tools for nuclei at least up to the transition metals.

Acknowledgement

The authors are grateful to the Computational Center of the Slovak Academy of the Science and the Computational Center of the Faculty of the Natural Sciences of the Comenius University for providing us with computational resources. Financial support from the Slovak Grant Agency for Science (grant No. 2 / 1 1 7 2 / 9 6 ) is gratefully acknowledged. This work has also benefited from the earlier Alexander von Humboldt Fellowship of VGM at the Ruhr-Universif~t Bochum.

References [1] B. Lindman and S. Forsen, in: NMR-basic principles and progress, Vol. 12. Chlorine, bromine and iodine NMR, eds. P. Diehl and R. Kosfeld (Springer, Berlin, 1976).

M.A. Fedotov et a l . / Chemical Physics Letters 258 (1996) 330-335

[2] Ya. Sayto, Can. J. Chem. 43 (1965) 2530. [3] K.J. Johnson, J.P. Hunt and H.W. Dodgen, J. Chem. Phys. 51 (1969) 4493. [4] A.P. Kreshkov, V.F. Andropov and V.A. Drozdov, Russian J. Phys. Chem. 46 (1972) 309. [5] V.G. Malkin, O.L. Malkina, M.E. Casida and D.R. Salahub, J. Am. Chem. Soc. 116 (1994)5898. [6] V.G. Malkin, O.L. Malkina, L.A. Eriksson and D.R. Salahub, in: Modern density functional theory: a tool for chemistry, theoretical and computational chemistry, Vol. 2, eds. J.M. Seminario and P. Politzer (Elsevier, Amsterdam, 1995). [7] Chr. Maerker, P. von R. Schleyer, D.R. Salahub, O.L. Malkina and V.G. Malkin, J. Am. Chem. Soc., submitted for publication. [8] M. Kaupp, V.G. Malkin, O.L. Malkina and D.R. Salahub, Chem. Phys. Lett. 235 (1995) 382. [9] M. Kaupp, V.G. Malkin, O.L. Malkina and D.R. Salahub, J. Am. Chem. Soc. 117 (1995) 185l; Erratum t 17 (1995) 8492. [10] M. Kaupp, V.G. Malkin. O.L. Malkina and D.R. Salahub, Chem. Eur. J. 2 (1996) 24. [11] V.G. Malkin, O.L. Malkina and D.R. Salahub, J. Am. Chem. Soc. 117 (1995) 3294. [12] T.B. Woolf, V.G. Malkin, O.L. Malkina, D.R. Salahub and B. Roux, Chem. Phys. Lett. 239 (1995) 186. [13] D.R. Salahub, R. Fournier, P. Mlynarski, I. Papai, A. StAmant and J. Ushio, in: Density functional methods in chemistry, eds. J.K. Labanowski and J.W. Andzelm (Springer, Berlin, 1991) p. 77. [14] A. St-Amant and D.R. Salahub, Chem. Phys. Lett. 169 (199O) 387. [15] A. St-Amant, Thesis, Universit6 de Montrral (1992). [16] J.P. Perdew and Y. Wang, Phys. Rev. B 45 (1992) 13244;

[17]

[18] [19]

[20]

[21]

[22]

[23]

[24] [25]

335

J.P. Perdew, in: Electronic structure of solids, eds. P. Ziesche and H. Eischrig (Akademie Verlag, Berlin, 1991); J.P. Perdew, J.A. Chevary, S.H. Vosko, K.A. Jackson, M.R. Pederson, D.J. Singh and C. Fiolhais, Phys. Rev. B 46 (1992) 6671. W. Kutzelnigg, U. Fleischer and M. Schindler, in: NMRbasic principles and progress, Vol. 23 (Springer, Berlin, 199O) p. 165. A. Sch~ifer, C. Huber and R. Ahlrichs, J. Chem. Phys. 100 (1994) 5829. Landolt-Bbrnstein, Numerical data and functional relationships in science and technology, Vol. 7 (Springer, Berlin, 1979); K.P. Huber and G. Herzberg, Molecular spectra and molecular structure, Vol. 4. Constants of diatomic molecules (Van Nostrand-Reinhold, New York, 1979). A.I. Efimov et al., eds., Svoistva neorganicheskich soedinenii, Spravochnik, (Khimiya, Leningrad, 1983) p. 392, in Russian. A.F. Wells, Structural inorganic chemistry (Oxford Univ. Press, London 1962); N. Godbout, V.G. Malkin, O.L. Malkina and D.R. Salahub, J. Chem. Phys., submitted for publication; N. Godbout and D.R. Salahub, work in progress. P. Pyykkb, Z. Naturforsch. 47a (1992) 189; L.A. Eriksson, O.L. Malkina, V.G. Malkin and D.R. Salahub, Intern. J. Quantum Chem., submitted for publication. N.P. Biryukov, M.G. Voronov and I.A. Safin, Tablitzy chastot YaKR (Khimiya, Leningrad, 1968), in Russian. T. Onak, M. Diaz and M. Barfield, J. Am. Chem. Soc. 117 (1995) 1403.