Vibrational spectra of crystalline dimethylglyoxime, HONCCH3CH3CNOH

Spcarocbimii Acta,Vol.33A,pp.29 6a 36. Pergamen

Vibrational

Press

1977. Printed

in Northern

Irclsnd

spectra of crystalline dimethylglyoxime, HON=CCHr-CHX==NOH

GABOR KERESZTURY, SANDOR HOLLY Central Research Institute for Chemistry of the Hungarian Academy of Sciences, 1025 Budapest, Pusztaszeri ut 59/67, Hungary, and MARIO P. MARZCZCHI Istituto di Chimica Fisica, Universita di Firenze

Via G. Capponi 9,50121 Firenze, Italy. (Received 6 January 1976) of crystalline powders of dimethylglyoxime-de and -dz have of a single crystal specimen were recorded and used in the

Ah&met--Infrared and Raman spectra been investigated. Polarized i.r. spectra vibrational assignment. Small band shifts with the rotation hypothesis on occurrence of intermode

of the polarizer were observed in accord with a previous mixing in systems of low symmetry.

INTRODUCTION

E!KPEREWJWTAL

In a recent paper [l] we reported measurements on the

i.r.

spectra

of

oriented

crystalline

films

of

Commercial diiethylglyoxime (Reanal, Hungary) was purified before use by crystallization from water. The deuteratedcompound (DG-N=CCHa-CH3*N-OD) was prepared by repeated recrystallization from deuterium oxide (90% DaO).

thiosemicarbazide in polarized light. This paper was concerned with an interesting phenomenon,

a con-

tinuous frequency shift of some absorption bands with the rotation of the plane of polarization. In the discussion

various

possible

explanations

Preparation of the single crystal specimen

were

The usual procedure of growing an oriented crystalline film from melt under temperature gradient failed due to the rapid sublimation of DMG at the melting point (m.p. = 234”C, b.p. =245”C). Instead, a few grams of DMG have been melted in a porcelain cup, and the edge of a pair of compressed and heated KBr plates was dipped into the melt. The liquid spread between the two plates and solidified almost instantly. After several attempts a usable specimen (showing uniform extinction between crossed polaroids) was obtained. Removing one of the KBr plates the surface of the single crystal was polished with alcohol until a specimen of appropriate dimensions (2 X 5 X 0.04 mm3) was obtained.

suggested, but we believe that the effect originates from an intermode mixing between non-orthogonal fundamental

vibrational transitions in the triclinic

system. In order to support the suggestion that the observed effect might be a common orthogonal continued

(monoclinic

feature of non-

and triclinic) systems, we

the examination

of triclinic molecular

crystals by means of polarization i.r. spectroscopy. Dimethylglyoxime

(DMG)

proved to be a suitable

model for several reasons: (i) Its crystal structure is one of the simplest, with one molecule

per unit cell (no complications

Infrared and Raman spectra

in

band structure due to correlation field splitting). (ii) In crystalline state the molecule centrosymmetric trans-conformation, posed

to the

symmetry-tied

C,,

cis-conformation) orthogonal

itself has a

where (as op-

axes

the lack of makes

the

suggested type of interaction possible. (iii) The

vibrational

spectra of pure dimethyl-

glyoxime (unlike its complexes with various metal ions) have not been investigated extensively so far, the only report being that of MILONE and ISORELLO

l-21. 29

AU the infrared absorption spectra reported here were taken on a Perkin-Elmer Modei 225 graiing instrument in the region from 4000 to 300 cm-‘. KBr disc spectra were recorded for both DMG-de and -d2. The i.r. spectrum of the DMG single crystal specimen was investigated in linearly polarized radiation by using an AgBr wire grid polarizer unit placed into the common beam in front of the detector. Spectra were taken at every 30” of polarizer setting. In order to avoid distortion in the polarization character of absorption bands no beam condensing devine was used, which resulted in low enerev _conditions (8-10% transmittance). The Raman spectra of polycrystalline DMG-da and -dZ were recorded on a Cary 81 spectrometer modified for a

30

G.&BORKERESZTURY,SANDOR HOLLY and MARIO P. MARZOCCHI

Coherent Radiation model 52 Ar+ laser source. Normally the 488OA exciting line was used for the region of SO-4000 cm-‘, except for the 200&2600cn-’ region where the 5145 A line was used in order to avoid disturbance from a strong ghost. When recording the spectrum of DMG-d, a drop of silicon oil was placed on the surface of the sample to protect it from air humidity. RESULTS AND

DISCUSSION

Structure and vibrational selection rules The crystal and molecular structure of DMG was determined in a combined X-ray and neutron diffraction experiment by Hamilton [3], and earlier in an X-ray diffraction work by MERRITT and LANTERMAN

[4].

DMG

iS tridink,

SpaCe

group

ci’

= Pi

with Z = 1, i.e., the unit cell and the molecule have a common centre of symmetry. Neutron diffraction data reveal, however, that the eight heavy atoms of the molecule lie (within experimental error) in a common plane, which is approximately parallel to the (101) crystallographic face, and even the deviation of the O-H bond from this plane is negligible from spectroscopical point of view. Thus, accepting an additional symmetry plane, we arrive to a structure shown schematically in Fig. 1, and to a Czh site group instead of Ci. The structure of the reducible representation for internal vibrations in a C,,, basis is: 14A, (R)+13BU (i.r.)+7B,

(R)+8A,

(i.r.),

where the optical activity is given in brackets. The in-plane vibrational bands belong to species A, and B,, while A, and B, correspond to out-of-plane vibrations. The crystal structure described above gives rise to three rotational lattice modes, A, +2B,, which are observable in the Raman spectrum.

2.5

IOO-

0 4000

4

3

I

I

I 3000

6

5

I 1800

The i.r. spectra of crystalline DMG-d, and -d2 in KBr pellets are shown in Fig. 2. The effect of deuteration is clearly seen on all the three modes of the hydrogen-bonded OH group: the v(OH) at about 3200 cm-’ is replaced by v(OD) near 2400 cm-‘, and the in-plane and out-of-plane bendings are shifted from 1440 and 75Ocm-’ to 1100 and 560 cm-‘, respectively. In the Raman spectrum of DMG powder (Fig. 3(a)) the Y(OH) and P(OH) bands appear at 3300-3100 and 1505 cm-‘, respectively, and their deuterated counterparts can be found in Fig. 3(b) at 2385 and 1130 cm-‘. The most intense Raman bands at 1643 cm-l for DMG, and at 1625cm-’ for DMG-d, obviously correspond to the C--N stretching vibrations. It is interesting to note that the ungerade pair of this vibration does not appear in the i.r. spectrum of DMG due probably to a special type of coupling with @(OH). On dueteration the v(C=N) vibration

6

I

I 1600 v.

Internal vibrations

7

I

I

I 2000

Fig. 1. Molecular structure and hydrogen bonding in DMG crystal (x, y and z are the principal axes of inertia of the free molecule).

I

I

1400

I 1200

9

I

15

IO

I

I IO00

I

I 600

I 600

2Op2530 4op

IIll

I

I

400

cm-’

Fig. 2. Infrared absorption spectra of DMG-do (solid line) and DMG-d2 (broken line) in KBr pellets.

200

31

Vibrational spectra of crystalline dimethylglyoxime, HON==CCH3-CHJDNOH 2lxo

3600 90

I

Raman

shift

I800

A cd 1400 I

I

(O’

1200 I

1000 I

800 I

600 I

400 I

I 800

I 600

I 400

I

80

p 60 c5 E

40 3 :

3600

I 3400

I 3200

I 3000

I

281

I 2000

I 1800

I 1600

I 1400

I 1200

I 1000

9o-(b’ 8070-

d 0

2400

la00

I600

1400

I200

1000

800

400

Fig. 3. Raman spectra of polycrystalline DMG-do (above) and DMG-dl (below). appears as a band at 1614 cm-l with medium intensity. The N-O stretching is expected to give rise to a strong i.r. and a less intense Raman band. Consulting the i.r. spectra of similar molecules (e.g., acetone oxime [6], glyoxime, cyclopentanone oxime, cyclohexanone oxime), one can readily accept the assignment of the i.r. absorption band at 975 cm-’ to this vibration. It follows from the selection rules that in the Raman spectrum one more in-plane vibration is active than in the i.r. This additional vibration must involve the stretching of the C-C bond lying on the inversion centre. Considering that a conjugation may occur between the two C=N double bonds, thereby increasing the C-C bond order, the strong Raman line at 1338 cm-’ having no i.r. counterpart may be assigned to v(C-C). In this case, however, the C-C distance must be shorter than a normal single bond. The X-ray [4] and neutron diffraction results [3] (both of them based on a limited number of experimental data) are contradictory at this point, and spectroscopic evidence seems to confirm the former study. Apart from the vibration modes discussed above, and the vibrations of the methyl groups, which are

relatively easy to assign, there are some other in-plane and out-of-plane skeletal deformations. Owing to the complexity of these modes, their description and therefore their assignment is much more difficult in the absence of a reliable normal coordinate calculation. Some information in this respect can be gained by comparing the corresponding i.r. and Raman band intensities. More direct and useful data were expected from polarization i.r. measurements on the single crystal specimen. In Table 1 we have collected all the data obtained from i.r. and Raman measurements on the internal vibration bands. The proposed assignment is given in the last &unn. A summary of the fundamental vibrations is given in Table 2. Infrared polarization

measurements on single crystal

The most informative polarized i.r. spectra are shown in Fig. 4. It can be seen that the relative intensity of the 77Ocm-’ band is considerably lower than that in the KBr disc spectrum (Fig. 2). This intensity remains almost unchanged under the rotation of the polarizer, but increases rapidly on tilting the sample in any direction (see Fig. 4, dotted line). Since this band corresponds to the

32

GABOR KERESZTURY,SANDOR HOLLY and MARIO P.

MARZOCCHI

Table 1. Vibrational spectra of crystalline dimethylglyoxime-d, Dimethylglyoxime-do Infrared Raman Y (cm-‘)* v (cm-‘) W%

2960 sh 2920 w

2933 m

0 0

1440 s, br

90§

1362 s

901

1270 VW

v22; Vl

2973 w > 3024 2970 VW 2933 w

1645 vs 1584 w 1508 s 1437 w

1614 m

1386 m 1338 s

1364 s

1448 sh 1436 m

1270 w

0

1154m 1140 sh 1100s

85 1042 sh 1028 s

lQ25 w 975 vs

m w VW m, br

1625 vs 1555 w

903 vs

750 s, br 708 s 585 VW,br 530 wt 467 w 372 w 230 ?

90 90

485 m 432 m 354 w, br 173m

560 457 412 366 235

s, br m sh w ?

v2.5, v27, v36; v.5, VI6

v2s; v7

r7808+577) cm-’ (795 +432) cm-’

1024 m

VlO, VI7 v301 v37 v31 VII v32

(412+427) cm-’ VI2

v3.s v33

578 w

577 m

v2s; v.4

(2 X 795) cm-’

1132~

750 VW 695 s 652 sh

Ill 95

cm-’ cm-’ cm-’ cm-’

v29

783 m 710 w

795 m 715 VW

d V22d, Vl

(560+578) cm-’ V2.Sd (577 +485) cm-’

892 vs 840 sh

5

(2 x 1436) cm-’

V5

1440 w 1408 sh 1388 m 1356 s 1265 w

973 m

980 m

%5

v24; v3

(978 +980) (903 + 980) (978 + 795) (708 +980)

1023 w 976

90 -5

(1645 + 1508) cm-’ (1338 + 1645) cm-’ in Fermi I res. with v2 and vt5 q3,

2935 2907 2860 2385

1228 w 1140m

Assignment** (2 x 1645) cm-’

2860 VW 2390 vs 1930 w, br 1870 w, br 1755 VW

2880 sh 1935 w, br 1880 w 1770 VW 1680 w -1620 VW,br

Dimethylglyoxime-d, Raman Infrared v (cm-‘)* Y (cm-‘)

3300-3280 VW,sh -3200 VW,br 3130-3125 VW,br 3022 w 2974 w

-3300 sh -3200 br, s 3100 sh

and -d2

V13 v3sd

483 m 427 w 348 w, br

v34Cv39); v14 v19 v3dv34);

v20?

v40

170m

VZl?

* Observed in KBr-pellet spectra. t Found in the single crystal only. $ Angles of polarization (max. intensity) measured from an arbitrary direction in the single crystal. 5 Partial polarization. TTransition moment perpendicular to the plane of the sample. ** For notation of fundamentals see Table 2.

Vibrational spectra of crystalline diiethylglyoxime,

33

HON==CCH~-CH3~NOH

Table 2. Summary of the fundamental vibrations of dimethylglyoxime Y

lJ

No.

Approx. description

O-H stretch CH3 asymm. stretch CH3 symm. stretch C=N stretch O-H bend CH3 asymm. def. CH3 symm. def. C-C stretch C-Cmethyl stretch CH3 rock N-O stretch skeletal def. skel. def. (CNO bend) skel. def.

2 7 8 9 10 11 12 13 14

22 23 24 25 26 27 28 29 30 31 32 33 34

2974 2933 1645 1508 1437 1386 1338 ? 1028 980 795 577 485

B, species (Raman) 15 16 17 18 19 20 21

(cm-‘)

B, species (i.r.)

A, species (Raman) ; 3 4

Approx. description

No.

(cm-‘)

2960 2920 -1620 1440 -1440 1362 1140 1025 975 903 708 467(372)

A,, species (i.r.) 35 CH3 asymm. stretch 36 CH3 asymm. def. 37 CH3 rock 38 O-H def. (torsion) 39 skel. def. 40 CH, torsion 41 C==N torsion 42 C-C torsion

2974 1437 1028 ? 432 354? 173?

CH3 asymm. stretch CH3 asymm. def. CHj rock O-H def. (torsion) skel. def. CH3 torsion C==N torsion

O-H stretch CH3 asymm. stretch CH, symm. stretch C+N stretch O-H bend CH3 asymm. def. CH3 symm. def. C--C&,,,,, stretch CH3 rock N-O stretch skql. def. skel. def. (CNO bend) skel. def.

2960 -1440 1025 750 372(467) 230? ? ?

x 2.5 100

0 4coo

3

4

5

6

7

6

9

IO

15

I

I

I

I

I

I

I

I

I

I 3000

I 2000

I 1600

I 1600

I 1400

I 1200

I 1000

I 600

20@ /III /,

I 600

25 30

4050 I-

1

I 400

i

Fig. 4. Polarized i.r. absorption spectra of a DMG single crystal plate grown parallel to the (101) face: 90”, - - - - 0” from an arbitrary direction, at normal incidence; . . . . . 0”, sample tilted by about 30”.

34

GABOR KERESZTURY,S~D~R HOLLY and MARIO P.MAR~~~~HI

out-of-plane O-H deformation, we concluded that the sample face is perpendicular to the transition moment of the y(OH) vibration, i.e., the molecules lie nearly parallel to the sample surface. The crystallographic orientation of the sample was corroborated by X-ray diffractometry. The reflection intensity vs 20 Bragg angle is illustrated in Fig. 5. As expected, no other reflections of DMG than those of (101) (20 =26.72”) and (202) (28 = 55.04”) can be observed in addition to those of the KBr support (28=27.03 and 55.69). The clearly observable splitting of all peaks is due to the K_ (A = 1.5443 A) (A = 1.5405 A) and %, wavelengths in the nickel-filtered Cu K, radiation, which indicates the high uniformity of the single crystal specimen. Once the crystal orientation is known, the measured polarization angles yield direct information on the relative directions of transition moments, inasmuch as they are close to one of the dielectric axes of the crystal [6, 71. This condition holds for the completely polarized fundamentals at 708, 905, 980 and 1140 cm-‘, belonging to in-plane vibrations. An interesting observation is that the transition moments associated with these bands scatter around two perpendicular directions (see Table l), although the directions of the in-plane transition

moments are not fixed by symmetry. We should expect here different polarization directions for almost every in-plane vibration (like in thiosemicarbazide [l]); the observed situation must be an occasional consequence of the particular modes of vibrations. At any rate, the usefulness of polarization data is strongly reduced by this effect, which requires further investigations.* Another problem in the analysis of the polarization data is that the characteristic vibrational bands which could fix reference directions are not completely polarized. In the case of P(OH) this is caused by an overlap with &,(CH,), and for &(CH,) at 1360 cm-” it may be due to dielectric anisotropy [6]. In the absence of a more or less accurate reference line in the molecular plane, the application of the polarization data in the assignment leads only to rough approximations. Furthermore, the directions of transition moments for the strongly coupled skeletal vibrations can not be related directly to bond directions or other structural characteristics. We must be satisfied therefore with the fact that, presuming the polarization direction of the N-O stretching band at 98Ocm-’ to be approximately parallel to the N-O bond, the polarization data do not contradict the assignment presented in Tables 1 and 2. External modes According to the selection rules, three rotational lattice modes are expected to be Raman-active in the crystalline state. The detection of the weaker lines in the Raman spectra was seriously hampered by the high stray light in the region below 200 cm-‘. None the less, four bands were observed

at 88 (s), 103 (VW), 112 (w) and 173 (m) cm-’ for DMG-do, and at 87 (m), 100 (VW), 111 (VW) and 170 (w) cm-’ for DMG-d2, respectively. The corresponding frequency pairs, and the principal inertia moments (in a.m.u. A’) of the two isotopic molecules are listed in Table 3. The agreement between (I&“‘/I,)“’ ((u = x, y, z) and the frequency ratios is in general very good, but unfortunately they are of little help in the assignment owing to the closeness of all values. The highest intensity v1 bands correspond probably to the libration around the out-of-plane z-axis (R,, which is the stretching of N. . . H hydrogen bond; see Fig. l), and v2 and vj should correspond to the R, and R, lattice modes, respectively. In

Fig. 5. Parts of the X-ray ditiactogramme of the single crystal plate: reflection intensity vs 20 Bragg angle (the region above 54” is presented at four-fold ordinate expansion).

*As an extension of this work a normal coordinate analysis and computation of the directions of transition moments are under development.

Vibrational spectra of crystalline dimethylglyoxime, HON=CCI&-CHs(%NOH Table 3. Low-frequency Raman bands and principal moments of inertia* (see Fig. 1)

DMG-do DI$G-dl

88 87

$$J1’~

103 100

1.01 -

112 111

To3

-1.01

173 170 -1.02

115.96 118.41 -1.01

402.90 429.07 1.031 -

512.47 541.08 1.027 -

*Frequencies are given in cm-l, and the Z, values in amu A’ units.

spite of the fact that IY and I, are much greater

than I,, this assignment may be correct, because the frequencies of R, and R, modes should, in fact, be increased relative to Rx owing to the intermolecular hydrogen bonding. The band with the highest frequency ( v4 in Table 3) may then be the overtone of the A, lattice mode, or more likely, due to an out-of-plane internal vibration (z+ in Table 2). Results of frequency shift measurements

As mentioned in the Introduction, we attempted to find continuous frequency shifts with the change of the polarizer angle, a phenomenon observed by triclinic us in another molecular crystal, thiosemicarbazide [l]. Some small effects could indeed be observed for the in-plane vibration bands of DMG (see Table 4), and they had similar nature as those in the former case. In systems of low symmetry fundamental vibrational transitions of the same symmetry species may have different directions of transition moments. According to the qualitative explanation given in Ref. [l], if two broad bands belonging to such transitions overlap, they perturb each other, and the perturbed vibrational states will have mixed eigenfunctions and polarization characters with mixing coefficients varying with frequency inside the bands. If the angle /3 between the unperturbed transition moments of the different bands is zero, the Table 4. Band shifts with the angle of polarization for some vibrations in the polarized ix. spectra of DMG single crystal Angle* (“) 0

30 60 90 120 150

interaction may be very strong (depending upon the interaction energy), but the polarization character will not change inside the bands, because the interacting transition moments are parallel. A good example for this case is the triclinic modification of p-dichlorobenzene, single crystals of which (like those in Ref. [8]) exhibit bands polarized in directions practically coincident with the orthogonal molecular symmetry axes. The peaks do not shift in this crystal while rotating the plane of polarization. The interaction energy decreases while p is increasing, but now the polarization character will change throughout the bands according to the mixing coefficients. This type of mixing appears as continuous frequency shift of absorption maxima in the polarized spectra recorded at different angles of polarization (this has been observed in thiosemicarbazide [l]). At 0 = 90” we have no interaction, and simple summation of the bands is observed without frequency shifts. In DMG the transition moments are close to orthogonal (see Table l), and values of /3 near O-10” and 80-90” are obtained. This means, according to our theory, that only small frequency changes are expected in both cases. The magnitudes of observed frequency shifts presented in Table 4 are, with one exception, in accord with the hypothesis of intermode mixing.* The exception is the very broad v(OH) band, for which the frequency of the maximum absorption is shifted considerably with the rotation of the polarizer. However, this cannot be a phenomenon due to intermode mixing between fundamentals. More work is needed for elucidation of this feature.

Band centres (cm-‘) % -

709 708 707 706 704

y32

v31

V28

906 908 910 900 905

980 976 974 (992) 987 985

1356 1358 1360 1361 1362 1360

* Measured from an arbitrary direction.

??_2

2900-3100 320&3320 3330 3370 3350 3280

Acknowledgements-We wish to thank Mr. Cs. KERTI%Z for the X-ray measurement and Dr. A. K&MAN for his help in its interpretation. This work was supported in part by the Italian Cons&&o Nazionale delle Ricerche. * Similar interference effects, observed in the polarized ix. spectra of some monoclinic crystals, due to interactions between a continuum and a sharp line are treated quantitatively by MARZOCCHI et al. [9].

36

G&OR

KEREZTURY, SANDOR HOLLY and MARIO

RWERENCFS [l]

G. KERESZTURYand M. P. MARZOCCHI, Chem Phys. 6, 117 (1974). [2] ;45M;;roNE and E. BORELLO, Nuouo Cimento 5, 562 [3] W. C. -HAMILTON,Acta Cryst. 14, 95 (1961). [4] L. L. MEW and E. L. LANTERMAN, Acta Cryst. 5, 811 (1952).

P. MARZ~CCHI

[S]W. C. HARRIS and S. F. BUSH, J. Chem. Phys. !%,

6147 (1972). [6] H. Sus, Spectrochim. Acta 17, 1257 (1961). [7] J. HERRANZ and J. M. DELGADO, Spectrochim Acra 314 1255 (1975). [S] :gyi) M. KRUSE, Spectrochim. Acta 26A, 1603

[9] M. P. 'MARZOCCHI,L. ANGELONI and G. SBRANA, Chem Phys. 12,349 (1976).