Vibrational spectra and vibrational analysis of acetonitrile-borane

448

J. Phys. Chem. 1980, 84, 448-452

appreciable perturbation in their binding states, since they are off the reaction coordinate. Short Grotthus chains involving one water molecule are common in crystals18and several involving more than one water molecule are also known.lg One referee suggested another possible mechanism in which the slow step involves the rotation of an H30+that comes "loose" from its solvation shell, followed by fast proton transfer. This idea is similar to the mechanism proposed by Conway, Bockris, and Linton,%opposed by Eigen21 because their treatment contained some questionable approximations, among which was the assumption that the normal rotation of water molecules in the absence of the electric field of the H30+ion was too slow to explain the high mobility of the hydrogen ion. Very rapid thermal orientation of the water molecules in liquid water ( 10" s-l) has been confirmed by NMR work on electrolyte so1utions.16f22

Downloaded by UNIV OF NEBRASKA-LINCOLN on September 11, 2015 | http://pubs.acs.org Publication Date: February 1, 1980 | doi: 10.1021/j100441a022

N

Acknowledgment. The author thanks Vicerrectoria de Investigacidn (UCR) for providing support through grant V.I. 02-09-46, and Professors M. M. Kreevoy and R. L. Schowen for their valuable suggestions. References a n d Notes (1) Presented at the Joint Biophysical Society-American Physical Society Meeting, Washington, D.C., March, 1978.

(2) Mata-Segreda, J. F. Rev. Coi. Quim. Ing. Quim. Costa Rica 1976, 6 , 26. (3) Mata-Segreda, J. F. Rev. Latinoam. Quim. Submitted for publication. (4) Mata-Segreda, J. F. Cienc. Tec. (Costa Rica) 1976, 2 , 149. (5) Stern, A. E.; Eyring, H. J . Phys. Chem. 1940, 44, 955. (6) &stone, S., Laiiler, K. J.; Eying, H. "The Theg,of Rate Processes"; McGraw-Hill: New York; 1941, (7) Baker, W. N.; La Mer, V. K. J . Chem. Phys. 1935, 3 , 406. (8) Kresge, A. J. Pure Appi. Chem. 1964, 8 , 243. (9) Gold, V. Adv. Phys. Org. Chem. 1969, 7, 259. (10) Albery, W. J. In "Proton Transfer Reaction"; Caldin, E.; Gold, V., Ed.; Chapman and Hall: London; 1975. (11) Schowen, K. B. J. In "Transition States of Biochemical Processes"; Gandour R. and Schowen, R. L., Ed.; Plenum Press: New Yo&; 1978. (12) Schowen, R. L. In "Isotope Effects in EnzymeCatalyzed Reaction"; Clealand, W. W.; O'Leary, M. H.; University Park Press: Baltimore; 1977. (13) Schowen, R. L. Prog. Phys. Org. Chem. 1972, 9 , 275. (14) A polynomial regression with the program SAS/REW is available from Centro de Informitica, UCR. (15) Janoschek, R.; Weidemann, E. G.; Pfeiffer, H.; Zundel, G. J . Am. Chem. SOC.1972, 94, 2387. (16) Roberts, N. K. J. Phys. Chem. 1976, 80,1117. (17) Kreevoy, M. M.; Liang, T.; Chang, K. C. J. Am. Chem. SOC. 1977, 99, 5207. (18) Lundgren, J. 0.Acta Oniv. Ups. 1974, No. 82, 40. (19) Grundwald, E.; Eustace, D., in ref 10. (20) Conway, B. E.; Bockris, J. O'M.; Linton, H. J . Chem. Phys. 1956, 24, 834. (21) See Egen, M.; De Maeyer, L. Proc. R . SOC.London, Ser. A, 1958, 247, 505; Angew. Chem., Inti. Ed. Engl. 1964, 3 , 1. (22) Hertz, H. G.; Zeidier, M. D. Ber. Bunsenges. Phys. Chem. 1963, 67, 774.

Vibrational Spectra and Vibrational Analysis of Acetonitrile-Borane Fumio Watari Depatfment of Applied Science, Faculty of Engineering, Tohoku University, Sendai, Japan (Received June 22, 1979) Publication costs assisted by Tohoku University

The infrared (4000-400 cm-') and Raman (3200-200 cm-'1 spectra of CH3CN.BH3,CH3CN.BD3,CD3CN-BH,, CD3CN.BD3,and the isotopic loBcompounds have been recorded. Fundamental vibrations except for the CNB bending and internal torsional modes have been assigned on the basis of CBUsymmetry. Normal coordinate analysis has been carried out in the staggered configuration. The N-B stretching force constant was found to have a value of 2.45 X lo2 N m-l, which is compared with the corresponding quantities of boron trihalide adducts of acetonitrile.

Introduction

Experimental Section

Vibrational spectra of acetonitrile-boron trihalide adducts have been analyzed by Swanson and and Devarajan and C y ~ i n .Schlesinger ~ and Burg4 have reported the formation of an adduct CH3CN.BH3 similar to the boron trihalide adducts from the reaction of diborane and acetonitrile. Although Emeleus and Wade5 have reported some features of the infrared spectrum of CH3CN-BH,, no detailed vibrational data are available for the acetonitrile-borane adduct. In particular, the stretching frequency of the N-B bond, which is of special interest for a vibrational study on such a complex, is not known yet. The present study was planned to observe and to analyze the infrared and Raman spectra of the acetonitrile-borane adduct and to compare the results with those of the boron trihalide adducts.

All preparative work was carried out in a conventional vacuum system. Commercially obtained acetonitrile and acetonitrile-d, were used without further purification. Diborane(6) was prepared according to the method of Shapiro et a1.6 Similarly, boron-10 enriched diborane(6) was prepared by using a 'O€3F3-ether complex provided by dissolving 1°BF3gas in diethyl ether. I0BF3was generated by thermal decomposition of KIOBF, (94 atom % boron-10) in a vacuum line a t 700-750 O C S 7 The infrared spectra (4000-400 cm-') were recorded on a Perkin-Elmer Model 337. The frequencies were read on a Hitachi QPD-33 recorder by abscissa expansion with a Perkin-Elmer expanded scale readout kit. The instrument was calibrated with indeneas The acetonitrile-borane adduct was prepzred by con-

0022-3654/80/2084-0448$01 .OO/O

0 1980 American Chemical Society

The Journal of Physical Chemistry, Vol. 84, No. 4, 1980 449

Vibrational Analysis of Acetonitrile-Borane

TABLE I: Description and Numbering of t h e Fundamental Vibrations of CH,CN,BH,a

E class

A, class v I CH, sym stretch

v 9 CH, deg stretch

v, BH, u , C-N u 4 CH, u s BH, v, C-C v 7 N-B

u l 0 BH, deg stretch

sym stretch stretch sym deformation sym deformation stretch stretch

-

v I 1 CH, deg deformation v I 2 BH, deg deformation

v , , CH, rock v I 4 BH, rock u I 5 CCN deformation

v,, CNB deformation

u8 a

A, class

-

torsion

Abbreviations used: sym, symmetric; deg, degenerate.


TABLE 11: Molecular Parameters and Coordinates for CH,CN,BH,

4000

1000

2000

1600

1200

1000

800

600

400

bond lengths, nm

bond angles, deg

r = C-H = 0.11025 R = B-H = 0.1211 d = C-C = 0.1439 D = C-N = 0.1135 L = N-B= 0.163

o = HCH = 109.47 p = HCC = 109.47 6 = HBH = 113.28 y = HBN = 105.32 e = CCN= 180.0

F R E O U E N C Y Icm-’)

IP

Figure 1. Infrared spectra of (A) CH3CN.”BH,, (B) CH3CN.”BD3, (C) CD3CN.’$H3, and (D) CD3CN.’OBD3 recorded in the solid state at -196

-

= CNB = 180.0

symmetry coordinatesa

+ Ar2 + Ar,) + AR, + A R ~ ) S, = A D s, = ( 1 / 4 ) ( A a 1 + A o , + A o , -

A, SI = ( l / f l ) ( A r ,

OC.

8,=

( I / ~ ) ( A R ,

S, = A d

s,= A L

A, S , = A r c E S , = (l/a ( A r , - Ar,) Sin = (I/ 2 ) ( A R , - A R , ) SI, = ( l / J Z ) ( A @ , - A a , ) SI, = (l/JZ)(A6 2 - A6 3 ) s,, = ( W m A P 2 - A O , ) = (1/fl)(Ar2 - ‘73) SI,= A e SI, = A p

2

The projections of R , and r l on a plane perpendicular to the threefold axis make an angle of 180” with each other. The anlge 01, lies between r, and r,, and the angle p, between r, and L , etc. m= cos y/cos (6 / 2 ) , n = 3(m2 -t 1). Torsion,

-a

TABLE 111: Observed and Calculated Frequencies (cm- I ) for CH,CN.”BH, and Potential Energy Distributionsa IR Raman calcd PED^ 2926 1OOSl 2392 98S, 2350 87S,, 9S, v4 1365 94s, v5 1167 96S5 67S,, 25S7 v, 977 v7 589 76S7,15S,, 75, ug 2985m 2992 99s, vIn 2383s 2394 99s,,. uI1 1445m 1440 uIz 1153s 1166 vI3 1032m 1034 vI4 926s 929 VIS 409 1’16 138 a Abbreviations used: w, weak; m, medium; s, strong. Raman intensities are not given since photomultiplier sensitivity varies in a wide ranee within the spectral region. The-potential energy dis6ibution is defrned as .xil:= 100. F i.i L I.j 2/~F..L..2.16 t i 11 v,

v, v,

IO 3000 2000 I500

1000

500

FREOUENCY I ~ r n ‘ ~ 1

Flgure 2. Raman spectra of (A) CH3CN.”BH3, (B) CH3CN.”BD3, (C) CD,CN.%H, and (D) CD,CN.”’BD, recorded in the solid state at ambient temperature.

densing acetonitrile and diborane in a 2 : l mole ratio into a small reaction tube with a stopcock at -196 “C. After closing the stopcock, the tube was allowed to warm slowly to room temperature. It was then opened to the vacuum

2920m 2383s 2345m 1364m 1153s 984w

2928 2393 2354 1363 1168 978 588 2993 2393 1445 1168 1034 929 404

450

The Journal of Physical Chemistv, Vol. 84, No. 4, 1980

TABLE IV: Observed and Calculated Frequencies (cm-I) for CH,CN."BD, and Potential Energy Distributionsa IR uI up

u3 u4 us

u6 u7 u)

uI0 uII

2925m 1720m 2356m 1368m 892s 980m 553w 2991m 1809s 1442m

VI2

uI3 vI4

1034 m 738 m

Vli

Raman calcd 2923 1708 2351 1358 884 972 546 2990 1808 1435 843 1031 734 390

'16


a,b

2926 1715 2351 1365 894 976 551 2992 1809 1440 844 1034 740 393 128

lOOS, 99S, 89S,,9S6 93S4 88S,, llS, 73S6,22S7 78S,,15S6,7S, 99S, 97S,, 90Sl,, 7S,, 98S,, 86S,,, 8S,, 88S,,, 6S,, 54S,,, 1 7 S I 6 ,14S,,, 14S,, 66S,,, 21S,,, l l S 1 4

TABLE V: Observed and Calculated Frequencies (cm-' ) for CD,CN."BH, and Potential Energy Distributionsa u, u2 u,

u4 us

v6

Raman

calcd

2104m 2393s 2339 w 11OOw 1162s 899m

2106 2393 2349 1100 1163 897 571 2245 2393 1032 1163 847 928 380

2105 2392 2353 1096 1167 896 570 2245 2394 1031 1166 845 929 378 132

u7

v, vIn ull u,, u,?

v,,

2245w 2393s 1024w 1162s 842 m 925 s

VI5 16

a,b

TABLE VI: Observed and Calculated Frequencies (cm-' ) for CD,CN."BD, and Potential Energy Distributionsa

PED^

See corresponding footnotes t o Table 111.

IR

Watari

IR

Raman

2100m 1706m 2341 m 1099w 877s 911 s 533w 2237m 1809s 1025w 841 m 841 m 735s

2107 1713 2353 1105 897 908 533 2246 1818 1031 846 846 739 370

2105 97S1 1715 99S2 u, 2353 87S,, 10S6 v, 1098 59S4,36S6 us 885 53S,,23S6,17S4 u6 902 50S,, 30S,, lOS,,lOS, u, 534 73S,,17S6,9S3 ug 2245 97S, uIO 1809 97S1, ull 1031 91S,,,6S9 uI2 842 63S,,, 27S1,, 5S1, u13 847 46S,,, 40S,,, BS,, uI4 736 90Sl, VIS 363 47S,,, 20S,,, 19S,,, 14S,, 'I6 122 64SI6,24S,,, 10Sl4 a , b See corresponding footnotes to Table 111. U,

u2

TABLE VII: Symmetry Force Constants for CH3CN,BH,a

PED^ 97Sl 98S, 86S,,10S6 57S,, 33S6 96Ss 34S6,32S,,31S4 70S,, 18S6,75, 97S, 99S,, 91S,,,6S, 94S,, 80S,,, 13S,, 9OS,,, 5S,, 46S,,, 23S16,24SI3,9SI4 62SI6,27S,,, 8S,,

See corresponding footnotes to Table 111.

line to remove volatile substances. Since preliminary infrared work on a sample sublimed onto a CsI plate a t -196 "C proved that the spectrum was just superposition of each spectrum of the two reactants, the infrared spectra were recorded by the KBr disk method. To reduce the reaction of the adduct with moisture, it was ground and mixed with KBr powder in a polyethylene bag filled with dry nitrogen gas. After placing the disk in a low-temperature cell and evacuating, the disk was immediately cooled by liquid nitrogen because the adduct sublimed under vacuum a t room temperature. If it occurs, the disk becomes opaque, and poor transparency results. In spite of caution taken against moisture, broad absorptions due to water were observed a t around 3300 and 1400 cm-', and the spectra showed some absorptions due to contamination from the reaction with the moisture. The infrared spectra of the 1°B compounds are shown in Figure 1. The Raman spectra (3200-200 cm-') were recorded on a JEOL JRS S-1 laser Raman spectrophotometer equipped with an NEC GLG 108 He-Ne laser. The spectrometer was calibrated with the emission lines of neon. The Raman sample was prepared in a capillary tube in a manner similar to that employed in the infrared work. The spectra were obtained a t ambient temperature in the solid state. The Raman spectra of the O ' B compounds are shown in Figure 2. Large scattering in the low-frequency region obscured bands below 250 cm-'. Assignments

Assignments were made on basis of CSusymmetry which is the presumed geometry for the isolated molecule. The

PED^

calcd

A, class F,,, F2,2 F3,3 F4,,

F,,, F6,6

F,?,

4.926 ( 1 3 ) 3.317 (11) 18.792 (65) 0.580 ( 5 ) 0.614 ( 5 ) 5'082 (59) 2.454 ( 8 0 )

E class F,,, F,,,," F,,,,, FI,,,,

4.659 2.959 0.557 0.396 0.606 0.597 0.364 0.2b

(34) (4) (8) (1) (13) (19) (17)

0.214 -0.047 -0.112 0.101

(51) (19) (14) (30)

F13,13 F14,14

F,,,,, F16,16

F4,6

F,,,

-0.383 ( 1 6 ) -0.443 ( 2 4 )

F,,,, F13,14

F13>15 F14?16

The subscripts identify F;,j with symmetry coordinates i and j as defined in Table 11. Stretching force constants N m rad-', in 10' N m-I, bending constants in N rad-', The dispersions stretch-bend interactions in of the force constants are given in parentheses. Force m i s t a n t taken from CH,CN.BF,' and constrained. a

+ +

fundamentals distribute as 7A1 A2 8E, where the Al and E modes are infrared and Raman active while the A2 mode is inactive in both. The designation of the fundamentals is given in Table I. The CH3 and CD, vibrations were found in the region of those of free acetonitrile and acetonitrile-d, with small frequency shift. The skeletal modes, C=N stretch, C-C stretch, and C-CEN bend, were observed shifted to higher frequency by about 100,50, and 20 cm-l, respectively, upon adduct formation. The BH, stretches u2 and ul0 and the BH, deformations v5 and v12 were observed as a single band in the infrared spectra around 2390 and 1160 cm-', respectively, because of the broadness of the absorptions and of a small frequency difference between the symmetric and degenerate vibrations. The corresponding modes of the BD, group were found splitting about 100 cm-' for the stretches around 1700 and 1800 cm-' and about 50 cm-' for the deformations around 890-880 and 840 cm-', though the degenerate BD, deformation of the CH3CN adduct was too weak to be observed. As Emeleus and Wade have r e p ~ r t e d ,the ~ N-B stretching mode of CH3CN.BH3was not found in the infrared spectrum, but it was in case of CD,CN*BH,. On the other hand, this mode was weakly but clearly found for the BD, adducts at 546 cm-' for CH3CN.'OBD3 and a t 533 cm-' for CD3CN.'OBD3. In the Raman spectra, all fundamentals except for the CNB bending and torsional modes were observed, though

The Journal of Physical Chemistry, Vol. 84, No. 4, 1980 451

Vibrational Analysis of Acetonitrile-Borane

TABLE VIII: Raman and Calculated Frequencies (cm-') for the "B Compoundsa _

_

_

-

CH,CN. l 1 BH, ~

~ 0 2

v5 '6

v7

v 10

v 12 v 14

-

~

Raman _

2383 1155 975 5'7 3 23133 1155 922

calcd

_

CH ,CN. 'I BD, _

2390 1162 973 572 2379 1164 922

CD,CN, l 1 13H,

CD,CN. "BD,

Raman

calcd

Raman

calcd

Raman

calcd

1705 877 975 539 1789 847 735

1710 879 975 541 1788 840 735

2387 1154 895 555 2387 1154 917

2390 1163 893 554 2379 1164 922

1705 871 898 523 1798 843 735

1710 879 892 525 1788 840 7 30

-

a Boron-11 represents the normal isotopic distribution. The frequencies for the other vibrational numbers not listed arle almost the same as those of the boron-10 compounds.

TABLE IX: Comparison of Product Rule Ratios for the Various Isotopic Combinations of the CH,CN.BH, Moleculec' A, class E class _______


theor calcd theor calcdb CH,CN~'oBH,/CD,CN~'o~D,3.78 CH,CN~'oBD,/CD,CN~loBD, 1.94 CD,CN~'oBH,/CD,CN~'oBD, 1.94 CH,CN~loBH,/CD,CN~loBH,1.94 CH,CN~'oBD,/CD,CN~'oBH, 1.00 CH,CN~loBH,/CH,CN~'oBD, 1.94

3.71 1.83 1.90 1.95 0.96 2.02

6.70 2.60 2.58 2.59 1.00 2.57

6.44 2.46 2.53 2.55 0.97 2.62

The product rule is expressed as n j v i / ~ ~ p=i '(lGl/ Th'e Raman frequencies were used t o evaluate the calculated values. The calculated frequencies for the CNB bending mode were used. a

IG'

I)"~."

the degenerate BD3 deformation of CD3CNJoBD3 was assigned to the same frequency as that of the CD3 rock. An attempt t o observe the CNB bending mode changing condition for preparation of the adduct was unsuccessful because of larger scattering in the low-frequency region. The assignments of the fundamentals for the loB adducts are givien in Tables 111-VI.

Normal Coordinate Analysis Normal coordinate analysis was carried out in order to confirm the assignments and to derive the N-B force constant. The analysis was made by using the matrix method of Wilsong on an ACOS 77/700 computer a t the Computer Center, Tohoku University. Structural parameters were taken from CH3CN.BF310 for the CH3C)N.Bpert and from (CH3)3N-BH311 for the BH3 part. The methyl group was assumed to be tetrahedral and the C-C=N-B skeleton to be linear. The C-H bond length was taken to be the same as that found in acetonitri1e.l:' The molecule was assumed to be in a staggered configuratnon of CBLsymmetry. The molecular parameters and symmetry coordinates are presented in Table 11. The G maixix was calculated from a matrix B which relates the Cartesian displacement coordinates to the internal coordinates and the masses of the atoms. The G matrix was symmetrized from a transformation matrix U between the internal coordinates and the symmetry coordinat es.13 The actual calculation of the normal frequencies was

done in terms of the symmetry force constants by ming the program designed on the basis of the weighted leastsquares metl10d.l~ Hence no unique force field was necessary to be specified as the valence force field or others. The least-squares solution is given as J'PAX = J'PJAF. The Raman frequencies were used for the calculation and the individual eigenvalues were weighted as w ,= l / X , . Initial force constants for the CH3CN.B part were taken from the values of CH3CN.BF3,1and those for the BH3 part from the values of (CH3),As.BH3.15 Since the CNB bending frequencies were not observed, the force constant for this mode was assumed to be the same as that for Nm and not included in CH3CN.BF3 (0.2 X refinement. The least-squares refinement was carried out to fit the calculated frequencies to the observed for the four loB compounds simultaneously. An interaction constant between two vibrational moldes not having a t least one atom in common (a corresponding G matrix element is zero) was constrained to zero. Other interaction constants were added one by one in the calculation, and any constant, which was smaller in magnitude than its dispersion or smaller than 0.02 in magnitude, or whose inclusion caused the secular equation to be illconditioned, was omitted in the least-squares adjustment procedure. This produced a fit between the calculated and observed frequencies with the average deviation of 0.31 % for both the Al and the E class vibrations from the observed valuers. Since the torsional mode was not observed, no calculation was performed for it. The calculated frequencies are given in Tables 111-VI, together with the potential energy distributions expressed as 1 0 0 ~ l l ~ l ~ 2 / ~ ~ The F , , 1symmetry ~ ~ ~ . ' 6 force constants

Vibrational spectra and vibrational analysis of acetonitrile-borane

Recommend Documents