Vibrational studies of the ferroelastic crystal—betaine borate. Part I. Vibrational investigation of the paraelastic phase

MOLSTR 11115

Journal of Molecular Structure 519 (2000) 257–274 www.elsevier.nl/locate/molstruc

Vibrational studies of the ferroelastic crystal—betaine borate. Part I. Vibrational investigation of the paraelastic phase M.M. Ilczyszyn* Faculty of Chemistry, Wrocław University, 50-383 Wrocław, Poland Received 19 May 1999; accepted 21 June 1999

Abstract Polarized vibrational spectra (infrared transmission and reflection and Raman) of betaine borate in paraelastic phase (room temperature) have been recorded and discussed in relation to X-ray crystal structure. The presented results confirmed that the betaine in the title crystal occurs in the zwitterion form and n OH modes of weak hydrogen bonds give broad band above 3000 cm 21. The good agreement between wavenumbers, polarization features and intensity of the corresponding bands apparent in the infrared transmission and reflection spectra were observed. The polarized infrared spectra did not confirm that the betaine is planar and BO32 3 ions lie in the bc-plane in paraelastic phase, however shown that deviation from the planarity of both molecules is rather small. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Infrared transmission spectra; Infrared reflection spectra; Raman spectra; Paraelastic phase; Betaine borate

1. Introduction An inner compound—betaine, (CH3)3N 1 –CH2 – COO 2, forms complexes with a variety of acids [1]. Many of these complexes display one or several phase transition [2]. The betaine borate belongs to this group and exhibits only one phase transition at about 142.5 K. This phase transition has been reported by Haussu¨hl [3] who investigated the temperature and phase dependence of the elastic constants and revealed an increasing softening of a c55 constant and instability of the lattice at ca. 142.5 K (c55 < 0). The presence of the phase transition has been also confirmed by an investigation of thermal expansion

* Fax: 1 48-71-222348. E-mail address: [email protected] (M.M. Ilczyszyn).

over the temperature range from 300 to ca. 100 K. It has been revealed that three principle coefficients of thermal expansion a 11, a 22 and a 33 show a discontinuity at ca. 142.5 K [3]. The lack of the distinct peak in DTA curve allows one to conclude that the transition in the title crystal is of second order type. Dielectric studies performed by Zimmer et al. [4] have confirmed that the phase transition in betaine borate is of second order type and have also revealed that a small and reproducible anomaly of e 2(T) appears at about 45 K. The Raman spectra recorded in the lattice vibrations region recently reported by Zimmer et al. [4] have shown softening some optical modes when the crystal was cooled down from room temperature to 9 K. This observation allowed to conclude that the ferroelastic transition in betaine borate is a pseudoproper transition, induced by a rather strong coupling between the strain es and at least two slightly softening optic modes of B2g-symmetry which leads to a

0022-2860/00/$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S0022-286 0(99)00308-7

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Fig. 1. Projection of the crystal structure of betaine borate on bc-plane in paraelastic phase (taken from Ref. [6]).

renormalization of the elastic modulus c55(T) in paraelastic phase. Although vibrational spectroscopy appears to be very helpful for determination of the nature and mechanism of the phase transitions [5] only Raman spectra of the title crystal in the lattice vibration region have been available so far [4]. Therefore the present studies were performed to provide (the internal vibrations region) and complete (the lattice vibrations region) detailed vibrational data on the betaine borate crystal. Our results are presented in two parts. In the first one the polarized vibrational spectra taken in the paraelastic phase are presented. Maximum attention is paid there to the correlation between X-ray data collected in the paraelastic phase [6] and polarization behaviour of bands arising from internal vibrations of borate anions, betaine and hydrogen bonds in order to give detailed assignment of the bands. However, in the second part of this work the polarized Raman and polarized transmission infrared spectra recorded at various temperatures are presented and discussed in relation to the crystal structure collected in the ferroelastic phase [6] and molecular mechanism of the ferroelastic phase transition.

2. Experimental The title compound ((CH3)3NCH2COO·H3BO3; abbreviated as Bet·H3BO3) was prepared by dissolving equimolar amounts of boric acid and betaine in water. The single crystals (suitable for infrared and Raman spectra measurement of dimension 10 mm × 10 mm × 12 mm) were obtained by a slow evaporation from a saturated aqueous solution at 300 K. The single crystal was oriented by means of the X-ray diffraction method and polarizing microscope. Two plates parallel to the (001) and (100) planes (ca. 4 mm thick), respectively, were cut out for both the infrared polarized transmission and reflection spectra measurements. The samples for infrared polarized reflection spectra measurements were only polished and fixed on to holder. The samples for the infrared polarized transmission spectra were stuck onto KBr windows and polished until the measurement of the infrared transmission spectra was possible. The polarized infrared spectra were recorded with the electric vector parallel to the crystallographic axes: a, b and c. Both polarized infrared transmission (4000–400 cm 21) and reflection (4000–80 cm 21)

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274 Table 1 Vibrational analysis of the unit cell vibrations in the Bet.H3BO3 crystal in the paraelastic phase (N: number of total modes; Ta: number of acoustic modes; T: number of translation modes; R: number of rotation modes; n: number of internal vibrations) D2h

N

Ta

T

R

n

Ag B1g B2g B3g Au B1u B2u B3u

46 32 32 46 32 46 46 32

0 0 0 0 0 1 1 1

4 2 2 4 2 3 3 1

2 4 4 2 4 2 2 4

40 26 26 40 26 40 40 26

IR

Raman

a xx, a yy, a zz a xy a xz a yz Z Y X

259

spectra were recorded using a Bruker IFS-88 FTIR spectrometer equipped with a wire grid polarizer on an AgBr (4000–400 cm 21) and on a polyethylene substrate (500–80 cm 21). A single crystal cubic shape sample was prepared for the Raman spectra. The edges of this sample were parallel to the X(a), Y(b) and Z(c) directions. The sample was set three times in Raman experiment in order to probe the six Raman spectra corresponding to six components of the polarizability tensor (xx, yy, zz, xy, xz, yz). The Raman spectra were recorded on the Jobin–Yvon Ramanor U 1000 spectrometer at a resolution 2 cm 21 using the 514.5 nm line of an argon ion laser for excitation and PMT and CCD detector.

Fig. 2. Polarized infrared transmission spectra of betaine borate recorded at room temperature on: ab-plane; EIIa, EIIb and bc-plane; EIIb, EIIc. p-paraffin wax absorption.

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Fig. 3. Polarized infrared reflection spectra of betaine borate recorded at room temperature on: ab-plane; EIIa, EIIb and bc-plane; EIIb, EIIc.

3. Crystal structure In the paraelastic phase (above 142.5 K) betaine borate belongs to the Pmcn ˆ D16 2h space group (Z ˆ 4) of the orthorhombic system [6]. The X-ray data reveal that boric acid as well as betaine molecule are planar (all heavy atoms of betaine frame; N, C(1), C(2), C(4), O(1) and O(2) lie in the one plane parallel to the (100) plane). Both molecules lose their planarity below 142.5 K. The crystal structure of the title crystal consists of chains running parallel to the z-axis and lying in the (100) plane. Each chain is composed of boric acid and betaine molecules which are alternately joined by hydrogen bonds with O…O distances of 2.700, ˚ [6]. All chains are associated to 2.716 and 2.656 A each other by van der Waals forces (Fig. 1).

The results of a group theoretical analysis of the fundamental modes (k ˆ 0) of betaine borate in paraelastic phase are presented in Table 1. According to this analysis, one should expect 6Ag 1 6B1g 1 6B2g 1 6B3g Raman active modes and 5B1u 1 5B2u 1 5B3u infrared active modes in the lattice vibrations region. However, in the internal vibrations region (above 200 cm 21) one should expect 40Ag 1 26B1g 1 26B2g 1 40B3g Raman active modes and 40B1u 1 40B2u 1 26B3u infrared active modes.

4. Results and discussion Polarized infrared transmission spectra of betaine borate taken at room temperature are shown in Fig. 2,

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

whereas the reflection spectra are presented in Figs. 3 and 6. Polarized Raman spectra are illustrated in Fig. 4. Moreover, infrared powder spectra of betaine borate and its deuterated analogue are shown in Fig. 5. The wavenumbers observed in the polarized infrared transmission, reflection and polarized Raman spectra and their proposed assignments are listed in Tables 2–4, respectively. The bands observed in the 4000–200 cm 21 region are due to hydrogen bond vibrations, internal vibrations of betaine and borate (BO32 3 ) anion. However, the bands apparent in the region below 200 cm 21 are derived from lattice vibrations. For conveniences, the vibrations of the hydrogen bond, the betaine and the borate moiety will be discussed separately. 4.1. Hydrogen bond vibrations As follows from X-ray data [6] three weak hydrogen bonds with O…O distances equal 2.700, ˚ there are in title crystal. Therefore 2.716 and 2.656 A one should expect broad absorption due to n OH modes above 2500 cm 21 [7] in the vibrational spectra. Moreover, considering the orientation of the transition dipole moments (t.d.m.) of the n OH vibrations it is readily noted that the bands of the n OH mode should appear in the spectra of the bc-plane (Table 5) only. Really, in the polarized infrared transmission spectra the broad band at 3145 cm 21 with the shoulders at 3210 and 3238 cm 21 is observed. It appears to be very intensive and broad in the spectra recorded in the b and c-direction. In the spectrum polarized parallel to the a-axis only a very weak and a very diffused band with maximum at ca. 3188 cm 21 is observed. Unfortunately, it is impossible to separate the n OH bands derived from different hydrogen bonds even by the polarized method. The bands due to the n OH vibrations are also observed in the polarized infrared reflection spectra. They are located at 3148 (IIb), 3146 (IIc) and 3169 cm 21 (IIa). Note that they appear to be very weak in all reflection spectra. Some differences in the position of the n OH bands observed in both infrared spectra (transmission and reflection) might be caused by the fact that they are broad and defused (particularly in the reflection spectra) and an unambiguous determination of their position is not easy. The Raman bands of the n OH modes are very weak

261

and are only apparent in these components of Raman spectra which involved Y and Z-axis, e.g. yy, zz, yz. They are observed at 3261 (zz), 3249 (yy), 3165 (yz) and 3136 cm 21 (yy). Deuteration shifts the n OH band to lower frequency. New broad band appears at 2357 cm 21 with the shoulder at 2414 cm 21 (isotopic ratio 1.34). One should expect the d OH bands in the 1200– 1100 cm 21 region [7]. Unfortunately, in this region moiety vibrations intense bands due to the BO32 3 appear. So the assignments of the bands derived from the d OH modes are not straightforward. A weak band at 1172 cm 21 is observed in both the infrared (transmission and reflection) spectra polarized parallel to the b-axis. In the low temperature spectrum (see Part II) it becomes sharp and shifts to higher wavenumbers (appears at ca. 1191 cm 21). This band may arise from the d OH mode. Its polarization is consistent with the expected value for the d OH vibration (see Table 5). Besides in the IR powder spectrum of the Bet·D3BO3 new bands at 862, 832 and 810 cm 21 appear which were assigned to the d OD vibrations. One of them well corresponds to the band at (isotopic ratio is equal to 1172 cm 21 1172=862 ˆ 1:36). Moreover, detailed examination of the infrared powder spectra of Bet·H3BO3 and Bet·D3BO3 in the 1240–1130 cm 21 region shows also that deuteration leads to the reduction of intensity of the bands observed in this region (Fig. 5). This observation points out that the d OH vibrations give some contribution to the absorption apparent in the above region. One should expect the bands due to the g OH vibration of weak and intermediate hydrogen bonds below 1000 cm 21. In the powder infrared spectrum only a band at 793 cm 21 is identified with the g OH vibration. The polarized infrared spectra (transmission and reflection) show that this band is polarized along the a-axis direction (at 790 cm 21 in transmission spectra and at 785 cm 21 in reflection spectra). The second band arising from this mode was found at 905 cm 21 in the transmission spectrum polarized also in the a-axis direction. Note that polarization behaviour of both bands is consistent with the expected one for g OH modes of all hydrogen bonds (Table 5). On deuteration the g OH shifts to lower frequencies and one can observe its deuterated counterpart at 661 cm 21 (905=661 < 1:37) and 575 cm 21

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Fig. 4. Polarized Raman spectra of betaine borate recorded at room temperature: (a) spectra of Ag species (Z…xx†Y, Z…yy†X, X…zz†Y); (b) spectra of B1g species (Z…xy†X, Z…yx†Y, X…yx†Y†; (c) spectra of B3g species (X…yz†Y, Z…yz†Y, Z…yz†X); (d) spectra of B2g species (X…zx†Y, Z…xz†Y, Z…xz†X).

(790=575 < 1:37) in powder infrared spectrum of Bet·D3BO3. 4.2. The BO32 3 moiety vibrations The free BO32 3 ion of D3h symmetry should have four normal modes: two stretching (n 1(A1 0 ) and n 3(E 0 )) and two deformation (n 2(A2 00 ) and n 4(E 0 )) ones [8]. The n 2, n 3 and n 4 modes are infrared active,

the n 1, n 3 and n 4 are Raman active. Since BO32 3 anions occupy positions of Cs symmetry [6] in the title crystal, therefore all their modes become active in IR and Raman spectra and the degeneracy of the n 3 and n 4 is lifted (Table 6). Moreover, the correlation coupling leads to the additional splitting of each internal vibration into four components. In this approximation bands due to the n 1, n 3 and n 4 should be apparent in the infrared spectra recorded in the

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

263

Fig. 4. (continued)

b- and c-axis direction, whereas the bands due to n 2 should be only active in the infrared spectrum polarized parallel to the a-axis (Table 6). The discussion of the spectroscopic feature of BO32 3 is not easy due to two reasons. The very limited data concerning vibrations of this anion are available in literature so far. Moreover substantial discrepancy exists between attribution of the bands due to the internal vibrations of BO32 3 anion given by various

authors. The bands derived from internal vibrations of BO32 3 moieties in H3BO3 were found in the region of 1060 (n 1(n s)), 660–648 (n 2(g )), 1490–1428 (n 3(n as)) and 545 cm 21 (n 4(d )) [9]. However, Janda and Heller [10] have observed the bands of the internal vibrations of BO32 3 moieties in the following regions: 950–877 cm 21 (n 1(n s)), 750–720; 700– 620 cm 21 (n 2(g )), 1370–1193 cm 21 (n 3(n as)) and 550–520 cm 21 (n 4(d )).

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Fig. 5. Infrared powder spectra of betaine borate and its deuterated analogue recorded at room temperature as an emulsion in Nuloj and polychlorotrifluoroethylene oil.

Fig. 6. Polarized infrared reflection spectra of betaine borate recorded at room temperature in the 500–80 cm 21 region.

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

265

Table 2 The wavenumbers observed in the polarized infrared transmission spectra of Bet.H3BO3 (vs: very strong; s: strong; m: medium; w: weak; vw: very weak; sh: shoulder; n : stretching; d : deformation; v : wagging; t : twisting; r: rocking vibrations) Infrared polarized spectra ab-plane

Infrared powder spectra Bet·H3BO3

bc-plane

EIIa

EIIb

EIIb

EIIc

3604vw 3279sh

3604vw

3604vw

604vw

3236sh

3238sh

3210sh

3064w 3046w 3022w

3145s 3064s 3046s 3028s

3145vs 3064s 3046s 3028s

3145vs 3064s 3050s

3145vs 3062vs 3046vs

2657vw

2657w

2657vw

2726w 2663w

2477vw

2430vw

2657w 2562vw 2430vw

2431vw

2430w

Assignments

Bet·D3BO3

3235sh

n OH

3140w 3065w 3046w 3029m 3019w

n OH n asCH3 n asCH3 n asCH3 n asCH3

3188vw

2 × 1215 2418m 2357m

2337vw

2354sh 2325vw

2354sh 2325vw

2325vw

2 × 1162

2325w 2297sh 2213sh

2180vw 2096vw

2096vw

1968vw

1968vw

1803w 1737sh

1803vw 1737vw

1817vw 1803vw 1737sh

1806w 1730sh

1808w 1727sh

2 × 901 2 × 868

1636s 1490sh 1482vs

1636s 1490s

1633vs 1490vs

1633s 1491s

1635vs 1490vs 1480vs

n asCOO d asCH3 d asCH3

1453vs

1449vs

1453m 1447vs 1441sh

1447vs

1446s

d asCH3

1429vs 1419vs

1429vs 1419vs

1421vs

1423s

d CH2 n sCOO

1399vs 1387sh

1395vs

1397vs

d sCH3

2025vw

1895vw 1737sh 1687sh 1650sh 1627vw 1481vs

1443w

1400m

1327vw 1237vw 1218vw

1326vs 1286vw 1238s 1219s

1326s 1286vw 1238m 1219s

2 × 970 2 × 961

1940vw 1923vw

1416sh 1396vs 1385m 1370s 1336w 1326sh 1288vw 1214s 1186s

1355vs 1328vs

1327vs

v CH2

1237vs 1217s 1189s

1237w 1217m 1189w

tCH2 n 3BO3 n 3BO3?

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Table 2 (continued) Infrared polarized spectra ab-plane EIIa

1150vw 1132vw 1066vw 985vw 953sh 921vs 905vs

Infrared powder spectra bc-plane

Bet·H3BO3

Bet·D3BO3

1151s 1126sh 1076sh 985m

1152w 1126w

EIIb

EIIb

1172sh 1150s

1172w 1150m

985m

985w

985m

957m

957w

958vw

958m 919s

990w 970w 957w 925m

902vs

902m

902s

909s

876sh

876sh

900vw 889sh 876vw

EIIc

1151s 1126w

714s 687vs

795vw 780vw

727m 716sh 694m 661w

g OD

575vw 552vw

g OD n 4BO3 rCOO d asC3N 1

793w 780vw 726m 715m 688m

688vw

d OH n 3BO3 rCH3 d NCH n asC3N 1 n asC3N 1 n CC rCH2 g OH n CN n 1BO3 d OD d OD d OD g OH n sC3N 1 d COO n 2BO3 v COO

878sh 862w 832vw 810vw

790m

Assignments

668vw 597vw 548vw 522vw

548vw 522vw

548vw 523vw 436vw

Detailed examination of the polarized infrared spectra of betaine monohydrate [11] and the title crystal in the 1220–1150 cm 21 region provides conclusive evidence that the numerous absorption features observed in this region should be assigned to the n3 BO32 3 modes. Three bands are observed in this region in the polarized infrared spectra: at ca. 1214, 1186 and ca. 1150 cm 21. The first one appears in all polarized infrared transmission spectra at slightly different wavenumbers (at 1218 (IIa), 1219 (IIb) and 1214 cm 21 (IIc)) and in reflection spectra (at 1220 (IIa), 1219 (IIb) and 1214 cm 21 (IIc)). The maximum intensity is observed in the IR transmission spectra polarized parallel to the b- and c-direction. However, only in the reflection spectrum polarized parallel to the c-direction the intensity is very strong. vibrations are The Raman counterparts of n3 BO32 3

559vw 523vw

very weak and are apparent at 1209 and 1206 cm 21 in xx, xy and xz components. The second band of strong intensity is observed in the transmission and reflection spectra polarized in the c-axis direction at 1186 and 1184 cm 21, respectively, and of very weak intensity at 1196 cm 21 in the spectra recorded along the a-axis. Surprisingly, there are no bands in Raman spectra in this region. The third band is observed at ca. 1150 cm 21 in all polarized infrared transmission and reflection spectra, however it exhibits maximum intensity in the b- and c-direction in the former spectra and in the c-direction in the latter one. Its Raman counterpart is apparent at 1154 cm 21 only in the yz spectrum. The very weak absorption observed at 876 cm 21 in the polarized infrared transmission spectrum polarized parallel to the c-direction and a shoulder at the

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274 Table 3 The wavenumbers observed in the polarized infrared reflection spectra of Bet·H3BO3 single crystal at room temperature (vs: very strong; s: strong; m: medium; w: weak; vw: very weak; sh: shoulder; n : stretching; d : deformation; v : wagging; t: twisting; r: rocking vibrations) ab-plane

bc-plane

Assignments

EIIa

EIIb

EIIb

EIIc

3234vwsh 3169vw

3236vwsh 3150vw 3066vw

3216vwsh 3148vw

3228vwsh 3146w

3039vw

3048vw

2429vw 2342vw 2316vw 1807vw 1636vw 1491vw 1481sh 1450vw

2431vw 2318vw

2 × 1153

1650vw 1504vw 1480w 1450vw

3029vw 2433vw 2352vw 2326vw 1802vw 1636vw 1491vw 1482sh 1450w

n OH n OH n asCH3 n asCH3 n asCH3 2 × 1221

1626vw 1490vs 1475m 1446s 1442sh

n asCOO d asCH3 d asCH3 d asCH3

1434vw 1424vw 1399vw

1428m 1421m 1394vs

1428sh 1420vs 1392vs

1374vw

1378vw

1378vw

1395s 1385m

d CH2 n sCOO d sCH3 d sCH3

1368s 1336w 1322vw 1220vw 1196vw 1156vw 1126vw 1074vw 986vw

1327m 1237w 1219w

1327s 1237w 1219w

1172sh 1150w

1173sh 1149w

986vw 957vw

986vw 957vw

985m 958vw

902m

902w

901vw

727vw

727vw

727m

551vw 522vw

548vw

1214s 1184vs 1151vs 1126w

431s 384s 344s

n asC3N 1 n CC rCH2 n CN n sC3N 1, g OH d COO n 2BO3 v COO n 4BO3 rCOO d asC3N 1 d sC3N 1 d CCN

251m 191vs 169s 148m

tCOO (?) Lattice Vibration

913m 785w 732sh 712w 686vs 548w 438w 389w 350w

193w 149s 130m

383w 348vw 273vw 247w

v CH2 tCH2 n 3BO3 n 3BO3? d OH n 3BO3 rCH3

267

same wavenumber in the spectrum polarized along the b-axis is assigned to the n1 BO32 3 mode. No bands near this frequency were found in the reflection spectra. Its Raman counterpart was detected at 879 cm 21. It appears in all Raman spectra, however maximum intensity it shows in the spectra corresponding to xx, yy and zz componets of the polarizability tensor. Note that the band attributed to the n1 BO32 3 mode appears to be the most intensive band in these Raman spectra. The strong band observed at 714 cm 21 in the transmission spectrum recorded in the a-axis direction and weak band located at 712 cm 21 in the reflection spectrum measured also along the a-axis were attributed to the n2 BO32 3 vibration. No band corresponding to this mode is observed in the Raman spectra. The absorption arising from the n4 BO32 3 vibration was identified at ca. 548 cm 21 in transmission spectra polarized along the b- and c-axes and at 548 and 551 cm 21 in the reflection spectra recorded along bands the a-, b- and c-axes direction. The n4 BO32 3 are very weak in these infrared spectra. The corresponding bands were observed in the Raman spectra at 524 cm 21 (xx, yy, zz and yz) and 508 cm 21 (xx, yy and zz). The former band exhibits medium intensity in the yz spectrum, the latter is very weak. Note that our assignment of the bands due to internal vibrations of BO32 3 ion is closer to that given by Janda and Heller [10] than by Bethell and Sheppard [9]. As follows from Table 6 that a good agreement exists between spectroscopic features of the n 1 and n 2 vibration observed in the polarized infrared spectra and predicted in the site symmetry approximation. However, the number of the bands due to n3 BO32 3 vibration and their polarization are difficult to explain even in the factor group approximation. According to this approximation two bands due to n3 BO32 3 mode should appear in the spectrum polarized parallel to the c-axis (B1u) and two bands in the spectrum taken along the b-axis (B2u). However, three strong bands are in the spectra polarized parallel to the c-axis, two bands are in the spectrum recorded along the b-axis and additionally two very weak bands in the spectrum probed in the a-axis direction. This observation (the in the presence of the bands derived from n3 BO32 3 spectrum polarized parallel to the a-axis) indicates that the BO32 3 ion is not planar (it does not lie in the bc-plane as it results from X-ray data [6]). As the absorption arising from the n3 BO32 3 and observed in

Dn (cm 21)

X…ZZ†Y

Z…YY†X

Z…YX†Y

Z…XY†X

X…YX†Y

Z…XZ†Y

X…ZX†Y

Z…XZ†X

Z…YZ†Y

Z…YZ†X

X…YZ†Y

1371 433

1413

1488

638 730

5138 2065

1042 1049

2091 7330

363 338 247

5036

2819

7277 1280sh 1318

3630

435 689

1283

2067 2067

1449

5084

1191

1042

4147

995

4234

12528

3604

3084

9275

2515

486(b)

318

2117

1319 1209

1349 1229

6195 5667

662

630

3681

459

244

1867

171

3396 2783sh 2783 809sh 824 641sh

409

1592

275

169

n asCOO n asCOO

1744

416

2498sh

1412

6270

1201sh

3301

2344

2639

2344

9608

376

160

1571

410 608 184 410

1678 4493

2139

375 439 601

1529 445 369

499

909

256 386

1715

385

244

1396

574

370

1959

668 712

495

2217

504

2362

843 140 209

3572 734 1107

274

1032 1278

464

6898 365

2242 550sh

n asCH2 n sCH3 n asCH3 n asCH3 n asCH2

983

888 698

2911

n OH n OH n OH n OH n asCH3 n asCH3 n asCH3 n asCH3 n asCH3 n asCH2

222

527 175

748

Assignments

4141

408

839

1453

2977

937

519

3002

1779

695

359

1119 189 310

d asCH3 d asCH3 d asCH3 d asCH3 d asCH3 d asCH3 d asCH3 d asCH3 d asCH3 d CH2 n sCOO d sCH3 d sCH3 d sCH3 v CH2 tCH2

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

3261 3249 3165 3136 3067 3051 3049 3032 3025 2989 2985 2981 2978 2958 2948 2918 2886 2871 2839 2810 2801 1640 1621 1510 1492 1482 1477 1467 1460 1456 1451 1446 1438 1420 1409 1401 1398 1377 1325 1284 1241

Z…XX†Y

268

Table 4 The wavenumbers (cm 21) and intensities of bands observed in the polarized Raman spectra of Bet·H3BO3 crystal at room temperature (sh: shoulder; v: stretching d : deformation; v : wagging; t: twisting; r: rocking vibration)

Table 4 (continued) Dn (cm 21)

X…ZZ†Y

Z…YY†X

Z…YX†Y

241

756

1327

4471 459

2811 8654

1148 703

311 6947 18313 509

2526 25451 30994 1082

2841 6076 2390 855

1499 657 238

1429 1305 991

2742 309 779

2314

2438

873 2548

311

874 3769 1151 3023

914

157 198 157 164 225 211 259 252 786 159

Z…XY†X

X…YX†Y

Z…XZ†Y

1437

5520

299

165 169

885 858

219

858 957

158 172 157 673

539

Z…XZ†X

1154

217

437 1598

1753 4356

384 1235

1614

1024 4121

164 1256

907 924 825

233 343

489 1387

341 492

2143

673

2170

533

1262

751

X…ZX†Y

3341

Z…YZ†X

X…YZ†Y

207

195

985

145

134

310 1877

235 1874

1000 8077

1009

606

2894

662 371 332

219 150 204

1337 821 981

607 2665

712 1800

1427 7790

195 321

115

566 566

1091

749

3213

965

2176 174

618

164

1324 533

292 1752

628

Z…YZ†Y

704

604

1712

1272

4128

3872

3965

598

1199

2143

1669

6919 1029

1254

16146

405

1810

646 1864

455 1278

1810 5238

889

528

2400 1937

529

517

5005

11353

1271sh 2220

7475

18567

5362

8641

18799

5838

38664

89725

28577

6965 16180

13301

45115

2341 3000

3309 21273

17148

59806

n 3BO3 n 3BO3 n 3BO3 rCH3 n asC3N n asC3N n CC rCH2 n CN n CN n 1BO3 n sC3N d COO rCOO n 4BO3 n 4BO3 d asC3N d asC3N

d sC3N d asC3N d CCN tCOO 1 a t t i c e v i b r a t i o n

269

728

Assignments

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

1226 1209 1206 1154 1136 1006 983 958 931 906 902 879 782 729 595 550 524 508 446 434 391 373 354 250 191 171 156 150 132 130 118 104 101 93 72 69 57 53 50 49 46 38 35

Z…XX†Y

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M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

Table 5 The values of the directional cos 2 of the transition dipole moments (t.d.m.) of some betaine vibrations, BO32 ion vibrations and 3 hydrogen bond vibrations calculated in the polar bond approximation (using the data involved in Ref. [6]) in paraelastic phase (abbreviations as in Table 2) Type of vibration

X…a†

Y…b†

Z…c†

n C(3)–O(2) n C(3)–O(1) n sCOO n asCOO d COO rCOO v COO tCOO n C(2)–C(3) n C(2)–N n C(1)–N n C(4)–N n C(5)–N n sC3N n asCH2 n sCH2 d CH2 rCH2 tCH2 v CH2 n BO(3) n BO(4) n BO(5) n 1BO3 n 2BO3 a ˚ O(2)…O(4) Roo ˆ 2.716 A n OH d OH g OH ˚ O(1)…O(3) Roo ˆ 2.700 A n OH d OH g OH ˚ O(5)…O(2) Roo ˆ 2.656 A n OH d OH g OH

0 0 0 0 0 0 1 0 0 0 0 0.6622 0.6621 0 1 0 0 1 0 0 0 0 0 0 1

0.0071 0.7276 0.724 0.1669 0.724 0.1669 0 0.724 0.6393 0.8065 0.4707 0.0143 0.0143 0.8359 0 0.0087 0.0087 0 0.0087 0.9912 0.7347 0.7747 0.0023 0.9852 0

0.9932 0.2722 0.276 0.8326 0.276 0.8326 0 0.276 0.3603 0.1932 0.5291 0.3235 0.3235 0.1639 0 0.991 0.991 0 0.991 0.0087 0.2655 0.2252 0.9974 0.0147 0

0 0 1

0 1 0

1 0 0

0 0 1

0.7135 0.2867 0

0.2865 0.7133 0

0 0 1

0.7659 0.9974 0

0.2341 0.0024 0

It was assumed that the t.d.m. of n 2BO3 vibration is perpendicular to the plane created by the BO32 3 ion (see Ref. [8, p.123]). a

the spectrum polarized in the a-axis appears to be very weak and very defused one may admit that the deviafrom the planarity is rather very tion of the BO32 3 small. However, an excess of the bands due to the n3 BO32 3 may be caused by the presence of the two boron isotopes 11B and 10B [12] and consequently two

10 borate moieties: 11 BO32 BO32 3 and 3 (natural abundance of boron isotopes is equal ca. 80% ( 11B) and 20% ( 10B)).

4.3. The betaine internal vibrations The absorption pattern due to internal vibrations of betaine in the title crystal is very close to that observed in the vibrational spectra of betaine monohydrate [11], because the structures of betaine in both complexes [6,13] are very similar. Carboxyl ion vibrations. The betaine occurs in zwitterion form [6]. The absorption arising from the n asCOO mode appears in all polarized infrared transmission spectra (1627 (IIa), 1636 (IIb), 1633 cm 21 (IIc)) and reflection spectra (1650 (IIa), 1636 (IIb) and 1626 cm 21 (IIc)). It exhibits the strongest intensity in the transmission spectra taken along b- and caxes and in the reflection spectrum recorded in the cdirection. In the Raman spectra the bands due to the n asCOO mode are found at 1640 cm 21 (yy) and at 1621 cm 21 (zz) of very weak intensity. Note that the squared directional cosines of the t.d.m. of n asCOO mode (Table 5) does not reproduce either intensity or polarization of the bands due to this vibration. According to this approximation the n asCOO band should only appear in the spectra recorded for the bc-plane and should exhibit the strongest intensity in the spectrum polarized parallel to the c-axis. In reality, the bands due to n asCOO are observed in all polarized infrared spectra (transmission and reflection). Moreover, in the transmission spectra recorded for the bc sample it exhibits the same (strong) intensity for the b and c polarization. The second mode of the carboxylic group (n sCOO) appears as a very intense band at 1419 cm 21 in the polarized infrared transmission and reflection spectra polarized parallel to the b-axis and as a very weak band at 1409 cm 21 in some components of Raman spectra. The polarization of this band is consistent with expected one in the polar bond approximation (Table 5). A very weak band observed at 728 cm 21 in the reflection spectrum polarized parallel to the b-axis and medium band at 727 cm 21 in the spectrum polarized parallel to the c-axis were attributed to the d COO mode what is confirmed by the expected polarization for this band. Detection of the corresponding band in

Table 6 Correlation diagram for the internal vibrations of BO32 3 moiety in Bet·H3BO3 complex in paraelastic phase Site symmetry Cs

Free ion D3h

Factor group D2h

Infrared

n 1(A1 )

1060

a

0

A (y,z;R)

950–877 b

n 2(A2 00 )

668–648 a

A 00 (x;R)

750–720, 700–620 b

n 1(E 0 )

1490–1428 a

2A 0 (y,z;R)

1370–1193 b

n 4(E 0 )

545 a 550–520 b

a b

2A 0 (y,z;R)

Ag (xx,yy,zz) B3g (yz) B1u (z) B2u (y)

876sh (z) 876sh (y)

B1g (xy) B2g (xz) Au B3u (x)

714s (x)

2Ag (xx,yy,zz) 2B3g (yz) 2B1u (z) 2B2u (y)

2Ag (xx,yy,zz) 2B3g (yz) 2B1u (z) 2B2u (y)

Reflection 879 879

712w (x) 1209,1206 1154

1214s (z) 1186s (z) 1151s (z) 1219s (y) 1150s (y) 1218vw (x) 1150vw (x)

1214s (z) 1184vs (x) 1151vs (z) 1219w (y) 1149w (y) 1220vw (x) 1196wv (x) 1156vw (x) 524,508 524

548vw (z) 548vw (y)

548vw (z) 551vw (y) 548w (x)

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

Transmission 0

Raman

Wavenumbers taken from Ref. [9]. Wavenumbers taken from Ref. [10].

271

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M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

the transmission spectra is not easy because of absorption of a paraffin wax by means of which crystal was stuck into KBr window. However, detailed examination of the low temperature spectra shows that the band due to d COO at ca. 728 cm 21 is apparent in spectra polarized along the b- and c-axis (see Part II). Its Raman counterpart was found at 729 cm 21 in the xx, yy, zz, xy and yz spectra. The absorption arising from the v COO vibration was found in both infrared spectra polarized along the a-axis at 687 cm 21 (transmission spectra) and 686 cm 21 (reflection spectra). In both spectra, they appear to be very strong. Additionally, a very weak band is observed at 688 cm 21 in the transmission spectrum polarized parallel to the b-axis. Note that according to the polar bond approximation, a band due to v COO is expected only in the spectrum polarized in the a-direction. A corresponding band in Raman spectra was not identified. The band arising from v COO mode in trichloroacetate ions at the same wavenumber was observed by Soliman [14]. The rCOO mode gives rise to the weak absorption apparent at 522 cm 21 in the infrared transmission spectra polarized parallel to the b- and c-axes, at 522 cm 21 in the infrared reflection spectrum taken along the b-axis and the medium absorption at 550 cm 21 in the five componets (xx, yy, zz, xy and yz) of Raman spectra. The polarization of this band is consistent with the expected one (Table 5). The C–N bond vibrations. Two types of the C–N bonds are present in betaine. The first type is involved in the (CH3)3N 1 group, the second connects this group to the acidic part of betaine. Similar to the betaine monohydrate [11] and contrary to the data reported in literature and concerning a tertiary amine [15,16] the absorption derived from internal vibrations of (CH3)3N 1 group are well defined in both infrared and Raman spectra. The band observed in the polarized infrared transmission and reflection spectra at 985 cm 21 was assigned to the n asC3N vibration. It appears in all transmission and reflection spectra. It exhibits the medium intensity in the former spectra recorded in the b- and c-directions and in the latter in the c-direction. Its Raman counterpart is observed at 1006 and 983 cm 21. The n sC3N mode appears at 780 cm 21 as a very weak band only in the infrared transmission spectrum polarized parallel to the bdirection and at 782 cm 21 in all Raman spectra.

Note that the n sC3N band is the most intensive in xx, yy and zz Raman spectra. Similar observation was reported for the vibrational spectra of betaine monohydrate [11]. The weak band observed at 438 cm 21 (IIa) and strong band at 431 cm 21 (IIc) in the reflection spectra were assigned to the d asC3N mode. In the Raman spectra the bands due to this mode are apparent at 446 and 434 cm 21. The d sC3N mode gives rise to the absorption observed at 389 cm 21 (IIa) and 384 cm 21 (IIb and IIc) in reflection spectra and at 373 and 354 cm 21 in some components of polarized Raman spectra. The strong and sharp band observed at 902 cm 21 (IIb) and a weak band at 900 cm 21 (IIc) in polarized infrared transmission spectra and a medium band observed at 903 cm 21 (IIb) and at 901 cm 21 (IIc) in polarized infrared reflection spectra were attributed to the n CN vibration. In some polarized Raman spectra this vibration appears at 904 cm 21. Note that polarization of the n CN band is as expected (Table 5). The band due to n CN vibration in vibrational spectra of betaine monohydrate [11] was observed at little lower wavenumber (at ca. 895 cm 21) than in the title crystal. The –CH3, –CH2 and –CC– group vibrations. The absorption pattern due to internal vibrations of –CH3 and –CH2 groups are very close to that observed in the vibrational spectra of betaine monohydrate [11]. Their detailed assignments are given in Tables 2–4. The n CC vibration gives rise to a medium (IIb) and very weak (IIc) band at ca. 957 cm 21 in polarized infrared transmission spectra and very weak band at ca. 958 cm 21 (IIb, IIc) in the polarized infrared reflection spectra as is expected in the polar bond approximation. In both spectra, the bands appear to be sharp. Its Raman counterpart was found at 958 cm 21 and exhibits a medium intensity. This observation points out that in the title crystal the n CC mode exhibits spectroscopic features expected for this type of vibration [15] and is not coupled with internal vibrations of the COO 2 group. Such coupling has been found for glycine. The normal coordinate analysis for this compound has shown that the n CC mode is not pure and is coupled with n sCOO, g wCH2, p COO and d COO [17,18]. The detailed examination of the polarized infrared spectra show that in some cases the polarization behaviour of the bands due to the internal and vibration modes of betaine observed in spectra do not coincide

M.M. Ilczyszyn / Journal of Molecular Structure 519 (2000) 257–274

with the expected one in the polar bond approximation. This disagreement relates to the internal and liberation modes of carboxylic group (n asCOO and v COO). Simultaneously, the perfect accordance exists between observed and expected polarization of the bands derived from n CC and n CN mode. Moreover, one has to admit that the “forbbiden” in the polar bond approximation bands appear to be very weak and defused in the spectra. These observations point out that the betaine is not as planar as it is follows from Xray data [6], e.g. only four heavy atoms of betaine frame; N, C(1), C(2) and C(3) lie in the plane parallel to the (100), however O(1) and O(2) of the carboxyl group are out of this plane. Simultaneously, taking into account the intensity of the “forbbiden” bands one can reasonably conclude that the deviation from the planarity is rather small. 4.4. The lattice vibrations The lattice vibrations have been studied in the Raman experiment (in the region of 300–10 cm 21, see Fig. 4) and by the far infrared reflection spectroscopy (in the region of 500–80 cm 21, see Fig. 6). Detailed examination of all Raman spectra shows that the strongest bands are apparent in the spectrum X…zx†Y (Table 4). In the spectrum Z…xx†Y one can easily notice the broadening of the exciting line. It starts at ca. 200 cm 21. The broad wing of the Rayleigh line is also apparent in the spectra Z…yz†X, Z…yy†X and X…zz†Y however, its intensity is much lower. Similar observation has been made for betaine phosphite crystal [19]. Such a feature is usually associated with strong overdamped low frequency mode [5] or is characteristic for the crystal with disorder in structure. According to the selection rules (Table 1) one should expect 6Ag 1 6B1g 1 6B2g 1 6B3g 1 6Au 1 5B1u 1 5B2u 1 5B3u modes in the vibrational spectra in the lattice vibrations region but in each Raman spectra six lattice modes should be apparent. Detailed examination of the polarized Raman spectra in the 300–10 cm 21 region (Fig. 4) has shown that only the B3g spectrum exhibits six modes as it was expected. There are five bands in the B1g and B2g species and till ten bands in the Ag spectra. Our observation differs from that of Zimmer et al. [4]. The main discrepancy relates to the number of bands observed in the Ag species. Three components of polarizability

273

tensor (xx, yy and zz) and three components of Raman spectra belong to the Ag symmetry. However Zimmer et al. [4] have shown and discussed only one Raman spectrum of Ag symmetry (yy). 5. Conclusion The polarized infrared and Raman spectra show that the betaine occurs in the zwitterion form in betaine borate crystal. The polarized infrared spectra indicate that the strong absorption due to asymmetric stretching vibrations of weak hydrogen bonds are apparent above 3000 cm 21 mainly in the spectra taken for the bc-plane, in accordance with expectation. It is noteworthy that the wavenumbers, polarization features and intensity of the corresponding bands observed in the transmission and reflection infrared spectra are very similar. The polarized infrared spectra show that the BO32 3 ion and the betaine are not planar as it follows from Xray studies [6]. Detailed examination of the absorption derived from internal vibration of betaine allows to conclude that only the four atoms of betaine frame; N, C(1), C(2) and C(3) lie in the plane parallel to the (100); the O(1) and O(2) atoms of the carboxyl group are beyond this plane. However, it is clearly seen from presented spectra that the mention above deviation from the planarity is not large. The comparision of the wavenumbers of the corresponding bands observed in polarized infrared and Raman spectra show that the correlation couplings exist for the most modes in the title crystal. Such interaction relates to the BO32 3 anion vibration (e.g. n3 BO32 3 ), betaine vibrations (e.g. n asCOO, n sCOO, n asC3N, n sC3N, d asC3N) and n OH mode. Note that the largest Davydov splitting is observed for the last mode. The broadening of the exciting line in the spectrum Z…xx†Y has been observed. It may be due to disordering in the crystal in the paraelastic phase or it may indicate the presence of low wavenumber strongly damped mode. Acknowledgements Dr J. Baran is thanked for critical reading of the manuscript and helpful discussion.

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[10] R. Janda, G. Heller, Spectrochim. Acta A 36 (1980) 997. [11] M.M. Ilczyszyn, H. Ratajczak, Vibr. Spectrosc. 10 (1996) 177. [12] P. Ney, M.D. Fontana, A. Maillard, K. Polgar, J. Phys.: Condens. Matter 10 (1998) 673. [13] T.C.W. Mak, J. Mol. Struct. 220 (1990) 13. [14] M.S. Soliman, Spectrochim. Acta A 49 (1993) 183. [15] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Chapman and Hall, London, 1975. [16] B. Wojtkowiak, M. Chabanel, Spectrochimie Moleculaire, Technique et Documentation, Paris, 1977. [17] M. Kakihana, M. Akiyama, T. Nagumo, M. Okamoto, Z. Naturforsch A 43 (1988) 774. [18] Ch. Destrade, Ch. Garrigon-Lagrange, M.T. Forel, J. Mol. Struct. 10 (1971) 203. [19] J. Baran, Z. Czapla, M.K. Drozd, M.M. Ilczyszyn, M. Marchewka, H. Ratajczak, J. Mol. Struct. 403 (1997) 17.