Structure and polarized infrared and Raman spectra of the solid complex of betaine and maleic acid (1:1)

Journal of

MOLECULAR STRUCTURE ELSEVIER

Journal of Molecular Structure 372 (1995) 9-27

Structure and polarized infrared and Raman spectra of the solid complex of betaine and maleic acid (1" 1) M.M.

I l c z y s z y n a, T. L i s a, H . R a t a j c z a k a'b'*

aDepartment of Chemistry, Wroctaw University, ul. Joliot-Curie 14, 50-383 Wroctaw, Poland blnstitute of Low Temperature and Structure Research of the Polish Academy of Sciences, ul. Ok61na2, 50-950 Wroctaw, Poland

Received 2 May 1995; accepted 12 May 1995

Abstract

Crystals of betaine maleic acid (BHM) of the formula [(CH3)3N + CH2COOH].[HCOO-CH=CH-COO- ] are monoclinic, space group PI/n, with a = 6.138(3), b = 10.831(4), c = 17.244(5) A, 3 = 92.85(4) ° and Z = 4. The betaine cation is linked to the maleic monoanion by a strong intermolecular O . . . O hydrogen bond of length 2.527(3) ,~ forming a "structure unit". The hydrogen maleate anion forms a ring structure containing a short, very asymmetric intramolecular hydrogen bond: O-.. O = 2.429(3), O - H = 1.04(4), H - . . O = 1.39(4) ,~. The polarized infrared and Raman spectra of the BHM single crystal have been measured at room temperature. The hydrogen bond modes and the internal vibrations of the maleate anion and betaine cation are discussed in relation to the crystal structure. A broad absorption was observed due to the antisymmetric stretching mode of both short hydrogen bonds, but it could not distinguish features pertaining to the intramolecular and intermolecular hydrogen bonds, respectively.

1. Introduction

Betaine is one of the simplest c~-aminocarboxylic acids forming a large number of complexes with different organic as well as inorganic compounds. Some of these complexes display different phase transitions [1]. Betaine maleic acid (1:1) complex (betaine maleate), [(CH3)3N+CH2 COOH]. [HCOO-CH=CH-COO-] (abbreviated as B H M ) belongs to this large betaine family. Very few reliable results concerning the title crystal have been reported in the literature [1,2]. There are neither spectroscopic nor full X-ray data for this compound. According to the available data * Corresponding author.

B H M forms orthorhombic crystals of space group P n m a with eight chemical formula units in the unit cell [2] and undergoes ferroelastic transition at about 194 K. However, a single crystal of the B H M obtained in our laboratory exhibits completely different features from those mentioned above [1,2]. It crystallizes in a monoclinic system in the P 2 1 / n space group with four formula units in the unit cell. X-ray diagrams obtained at 160, 180 and 190 K exhibit no changes. DSC measurement shows no phase transition in the 100-370 K temperature range. The discrepancies between our results and those found in the literature [1,2] indicates that the title compound crystallizes in two different forms. The present study was carried out to provide

0022-2860/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0022-2860(95)08940-3

10

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

30*

o3 _

0 ,,'o4

06

/

02

~'~-~E ,150' -

\

"" _.,'~,

¢3 C4

• %

x

x

j~S

-+/

Fig. 1. Projection of the crystal structure of BHM onto the ac plane. Notation: a and c are the crystallographic axes; X and Z are the main optical directions for the visible light on the ae plane. Upper part of the figure shows the relative orientation of the optical directions X and Z with respect to the crystallographic axes a and c. detailed structural and vibrational data for the B H M crystal.

2. Experimental

The B H M complex was obtained from an aqueous solution containing betaine and maleic acid in the ratio 1:1. Single crystals of B H M were grown from a saturated aqueous solution by slow evaporation at low temperature (283-288 K). The single crystal was oriented and relative orientations of the optical directions (X, Z ) with respect to the crystallographic axes (a, c) (Fig. 1) were determined with the aid of X-ray data and a polarizing microscope. Note that the twofold axis (C2) is parallel to the b crystallographic axis and to the Y

optical direction. However, neither X nor Z optical directions, which lie on the ac plane, coincide with the a or c crystallographic axes. The angle between the X direction and the a axis is equal to 57 °. Two samples (parallel to the a c ( X Z ) and ( Y Z ) faces, respectively) were cut for infrared polarized spectral measurements. They were stuck onto K B r windows by means of paraffin wax and polished until measurements of the transition infrared spectra were suitable. The infrared spectra parallel to the X, Z and b(Y) directions, respectively, were taken. In addition, the spectra on the ac plane with a number of other polarizations of the radiation (i.e. at every 15 ° with regard to the X direction) were measured. The polarized infrared spectra were recorded using a Bruker IFS-88 F T I R spectrometer equipped with wire grid polarizer on an

11

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

Table 1 Final positional and thermal parameters for BHM with esd values in parentheses Atom

x

y

z

ell

U22

U33

U23

UI3

UI2

N C1 C2 C3 C4 C5 C6 C7 C8 C9 O1 02 03 04 05 06

0.3107(3) 0.6044(4) 0.4058(4) 0.1260(5) 0.2217(6) 0.4738(6) 1.0446(4) 1.2670(4) 1.3270(4) 1.2000(4) 0.6665(3) 0.6914(3) 1.0360(3) 0.8773(3) 1.2945(4) 0.9869(3)

0.5608(2) 0.4012(3) 0.4363(3) 0.5788(4) 0.5659(4) 0.6610(4) 0.1872(2) 0.1606(3) 0.1184(3) 0.0846(3) 0.2902(2) 0.4662(2) 0.2335(2) 0.1640(2) 0.0495(3) 0.0932(2)

0.17140(10) 0.14560(13) 0.18875(14) 0.22443(20) 0.08897(17) 0.18766(26) 0.05196(14) 0.02536(15) -0.04202(15) -0.11440(15) 0.16606(10) 0.09959(10) 0.11830(10) 0.00932(9) -0.17020(11) -0.11658(10)

0.046(1) 0.045(2) 0.046(2) 0.052(2) 0.075(2) 0.078(2) 0.047(2) 0.038(2) 0.038(2) 0.055(2) 0.063(2) 0.063(1) 0.055(1) 0.040(1) 0.076(2) 0.051(2)

0.049(2) 0.054(2) 0.048(2) 0.086(3) 0.085(3) 0.055(2) 0.039(2) 0.053(2) 0.053(2) 0.056(2) 0.053(2) 0.073(2) 0.070(2) 0.066(2) 0.124(2) 0.088(2)

0.037(2) 0.035(2) 0.034(2) 0.065(2) 0.047(2) 0.093(3) 0.047(2) 0.052(2) 0.052(2) 0.046(2) 0.063(2) 0.060(2) 0.057(2) 0.051(1) 0.049(2) 0.045(1)

-0.002(1) -0.006(2) 0.004(2) -0.011(2) 0.015(2) -0.018(2) -0.002(2) -0.005(2) 0.003(2) 0.004(2) -0.001(2) 0.008(1) -0.024(1) -0.006(1) -0.015(2) -0.006(2)

0.003(1) -0.003(1) 0.000(1) 0.014(2) -0.007(2) 0.020(2) -0.006(2) -0.010(2) -0.002(2) 0.002(2) 0.006(1) 0.023(1) -0.004(1) -0.007(1) 0.010(1) -0.009(1)

-0.003(1) -0.002(2) -0.004(2) 0.005(2) 0.016(2) -0.021(2) 0.002(2) 0.000(2) 0.003(2) 0.002(2) 0.009(2) 0.002(2) 0.008(1) 0.003(1) 0.007(2) 0.003(1)

Atom

x

y

z

Uiso (.~2)

Atom

x

y

z

Uiso (,~2)

H1 H21 H31 H4 H42 H51 H6 H8

0.821(6) 0.292(5) 0.189(5) 0.343(5) 0.107(6) 0.519(6) 0.933(6) 1.483(5)

0.268(4) 0.376(3) 0.573(3) 0.555(3) 0.498(4) 0.649(4) 0.124(4) 0.105(3)

0.1408(18) 0.1758(15) 0.2774(18) 0.0580(16) 0.0833(19) 0.2399(21) -0.0636(21) -0.0486(13)

0.115(12) 0.060(7) 0.074(9) 0.063(9) 0.104(13) 0.098(13) 0.104(12) 0.058(7)

H2 H3 H32 H41 H5 H52 H7

0.441(4) 0.054(7) 0.023(6) 0.165(6) 0.589(5) 0.399(6) 1.383(5)

AgBr substrate. A single crystal cubic shape sample was prepared for the Raman spectral measurements. The edges of this cube were parallel to the X, Z and Y(b) directions. The cubic sample was set four times in the Raman experiment in order to record the six polarized Raman spectra corresponding to the six components of the polarizability tensor (xx, yy, zz, xy, xz, yz). The Raman spectra were recorded on a Ramanor U1000 spectrometer at a resolution 2 cm -1 using the 514.5 nm line of an argon ion laser (power 200 mW) for excitation. Polarized infrared and Raman spectra were taken at room temperature. The crystal density was measured pycnometrically by flotation in a CCI4/CH2C12 mixture. A specimen of size 0.4 × 0.4 × 0.2 mm was cut from a large crystal. A Kuma K M 4 diffractometer and M o K a radiation with a graphite monochromator were used for the lattice parameter and intensity measurements. Cell parameters were obtained

0.433(3) 0.654(4) 0.516(4) 0.645(4) 0.657(3) 0.741(4) 0.175(3)

0.2423(14) 0.2080(23) 0.2107(18) 0.0814(19) 0.1463(17) 0.1831(20) 0.0633(16)

0.051(7) 0.126(16) 0.087(11) 0.099(12) 0.080(10) 0.101(12) 0.067(8)

from a least-squares fit of the setting angles of 25 reflections in the range 9 < 0 < 11 o The crystal data are: (C5H12NO2) +. (C4H304)-, Mr = 233.22, monoclinic, a = 6.138(3), b = 10.831(4), c = 17.244(5) ,~, /3 = 92.85(4) °, V = 1145.0(8) ,~3, D m = 1 . 3 5 0 g c m -3, D e = 1.353(2) g cm -3, Z = 4, # ( M o K s ) = 0.11 mm -1, A = 0.71073 A, T = 296(2) K, space group P21/n. The data were collected with the 0/20 scan technique. Three check reflections, which were measured after each 100 reflections, showed + 3 % variation. The raw intensity data were corrected for Lorentz and polarization effects, but no absorption or extinction corrections were applied. A total of 3485 reflections were collected, of which 1471 had I > 2or(I). Symmetry related reflections were averaged to give a final set of 1124 reflections; Rmerg was 0.013. The structure was solved by direct methods and refined by full-matrix least-squares using

12

M.M. IIczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

C8

q

Cq~2 ~J

CI

~

Fig. 2. Overall view of the betaine cation and the maleate monoanion in BHM. Table 2 Principal bond lengths (,~), bond angles and torsion angles (deg) in the BHM crystal Parameter

Value

Parameter

Value

Bond lengths

N-C(2) N-C(4) C(1)-C(2) C(1)-O(2) C(7)-C(8) C(6)-O(3) C(9)-O(5)

1.494(3) 1.498(3) 1.508(3) 1.205(3) 1.318(3) 1.253(3) 1.210(3)

N-C(3) N-C(5) C(1)-O(1) C(6)-C(7) C(8)-C(9) C(6)-O(4) C(9)-O(6)

1.504(3) 1.493(3) 1.305(3) 1.490(3) 1.484(4) 1.258(3) 1.309(3)

Bond angles

C(2)-N-C(3) C(2)-N-C(5) C(3)-N-C(5) N-C(2)-C(1) C(2)-C( 1)-0(2) O(4)-C(6)-O(3) O(4)-C(6)-C(7) C(7)-C(8)-C(9) C(8)-C(9)-O(6)

107.1(2) 111.5(2) 108.1(2) 116.5(2) 125.0(2) 122.9(2) 121.0(2) 132.0(2) 119.3(2)

C(2)-N-C(4) C(3)-N-C(4) C(4)-N-C(5) C(2)-C(1)-O(1) O( 1)-C( 1)-0(2) O(3)-C(6)-C(7) C(6)-C(7)-C(8) C(8)-C(9)-O(5) O(5)-C(9)-O(6)

110.1(2) 108.8(2) 111.2(3) 109.3(2) 125.7(2) 116.1(2) 129.7(2) 119.6(2) 121.1(3)

O(2)-C(1)-C(2)-N C(1)-C(2)-N-C(4) O(4)-C(6)-C(7)-C(8) C(6)-C(7)-C(8)-C(9) C(7)-C(8)-C(9)-O(6)

0.9(3) 65.7(3) 3.7(4) 1.0(5) -1.5(5)

Torsion angles

O(I)-C(1)-C(2)-N C( 1)-C(2)-N-C(3) C(1)-C(2)-N-C(5) O(3)-C(6)-C(7)-C(8) C(7)-C(8)-C(9)-O(5)

- 179.2(2) - 176.2(2) -58.2(3) - 176.2(3) 178.7(3)

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

13

Fig. 3. The crystal packing in BHM.

the SHELXL93program [5], first with isotropic and then with anisotropic thermal parameters. The hydrogen atoms were found from the difference map and refined with isotropic thermal parameters. Neutral-atom scattering factors were taken from Ref. [6]. The final refinement resulted in R(F)= 0.0338 and wR(F2) = 0.0764, with

calculated weights w = 1/[cr2(F 2) + 0.0485PZ+ 0.185P], where P = (r~+2F~)/3. For the last cycle of refinement the maximal A/~r ratio was 0.05. The maximal peaks on the final difference map were 0.10 e ] k -3. The final atom parameters are given in Table 1. The overall view of both ions and numbering scheme are shown in Fig. 2.

14

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

Table 3 Geometries of the hydrogenbonds and short C-H-. •O contacts in the BHM crystal X-H... Oa

O(1)-H(1)...0(3) O(6)-H(6).-. 0(4) C(2)-H(2)... 0(5') C(2)-H(2)... O(6i) C(2)-H(21)... O(3ii) C(3)-H(32)... O(5iii) C(4)-H(4)-.. 0(2) C(4)-H(41).-. O(4iv) C(4)-H(42)... O(2ii) C(5)-H(5)... O(2) C(5)-H(51)... 0(3 v) C(8)-H(8)... 0(4vi)

Distances (A)

Angles (deg)

X...O

X H

H...O

X-H...O

2.527(3) 2.429(3) 3.325(4) 3.384(4) 3.343(4) 3.121(5) 3.076(4) 3.421(5) 3.443(5) 2.957(5) 3.440(5) 3.484(4)

1.09(4) 1.04(4) 0.94(3) 0.94(3) 0.97(3) 0.95(4) 0.95(3) 0.93(4) 1.02(4) 1.03(3) 0.94(4) 0.98(3)

1.45(4) 1.39(4) 2.59(3) 2.45(3) 2.38(3) 2.64(4) 2.42(3) 2.60(4) 2.60(4) 2.31(3) 2.65(4) 2.65(3)

172(4) 176(4) 136(2) 172(2) 169(3) 112(3) 126(3) 147(3) 140(3) 119(3) 143(3) 143(2)

a Symmetrycodes: (i) x - 0.5, 0.5 - y, 0.5 + z; (ii) x - 1,y, z; (ii) x - 1.5, 0.5 - y, 0.5 + z; (iv) 1 - x, 1 - y, -z; (v) 1.5 - x, 0.5 + y, 0.5 - z; (vi) x + 1,y,z. The observed and calculated structure factors are deposited within the B.L.L.D. as Supplementary Publication No. SUP26540 (3 pages).

bond is almost linear ( O ( 1 ) - H ( 1 ) - O ( 3 ) = 172(4) °) and cry stallographically asymmetric ( O . . . H = 1.45(4) A, O - H = 1.09(4) A). 3.1.1. The hydrogen maleate anion

3. Results and discussion 3.1. Structure description

The principal bond distances and angles within the maleate monoanion and betaine cation are listed in Table 2. The crystal packing is illustrated in Fig. 3. The crystal consists of maleate monoanions [ H C O O - C H = C H - C O O ] - and betaine cations [(CH3)3N+COOH] which occupy general positions in the crystal (C1 symmetry). The hydrogen maleate anion forms a ring structure containing a short intramolecular hydrogen bond ( O . . . O = 2.429(3) ,~), as is normally found in acid maleates [7-11]. The hydrogen maleate anion so formed is linked by another hydrogen bond (an intermolecular one) ( O . . . O = 2.527(3) A) to the betaine cation forming a "structure unit" (Fig. 2 and Table 3). In the intermolecular hydrogen bond the maleate anion acts as a proton acceptor, the betaine cation as a proton donor. Thus one proton was transferred from one carboxylic group of maleic acid to the ionic carboxylate group of the betaine zwitterion. The intermolecular hydrogen

The seven-membered ring of the hydrogen maleate ion is approximately planar. The deviations of the atoms from the plane defined by all the heavy atoms are in the range 0.006(2)0.008(2) ,~ for C(6) and C(9), 0.022(1)-0.029(2) for C(7), C(8), 0(5) and 0(6) and 0.055(1)0.064(2) A for other oxygen atoms. The fragments C(8), C(9), O(5), 0(6) and C(6), C(7), O(3), 0(4) are individually very close to planar (theolargest deviations for both is equal to 0.001(2) A). The dihedral angle between the least-squares plane defined by the carbon skeleton and the carboxyl plane of C(9), O(5), 0(6) is 0.9(2) °. The corresponding twist of the carboxyl group C(6), O(3), 0(4) is 4.3(2) .~. Note that the deviation from planarity of the present hydrogen maleate anion is greater than in K H M [7,8] or N a H M . H 2 0 [9] and smaller than in M g ( H M ) z . 6 H 2 0 [11] or 1,8-bis(dimethylamino)naphthalene H M [10]. The bond distances in the C(6)O(3)O(4) group (,C(6)-O(3) = 1.253(3) ,~, C ( 6 ) - O ( 4 ) = 1.258(3) A and in the C(9)O(5)O(6) group o(C ( 9 ) - 0 ( 5 ) = 1.210(3) .~, C ( 9 ) - O ( 6 ) = 1.309(3)A) indicate that the former group appears as a carboxylate group,

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

- C O O - , the latter as a carboxylic group, -COOH [12]. Note that the C-O distances in the maleate anion are very close to those calculated for different forms of the carboxyl group, although the angles around the carbon atoms show a marked discrepancy from the calculated ones [12]. The angles in the - C O 0 - group are expected to be LOCO = 126° and LCCO = 117 °, and in the -COOH group, LOCO--- 125°, /CCO(H) = 112° and LCCO--- 123 ° [12]. The corresponding angles in the present case are as follows: for the carboxylate group LOCO = 122.9(2) °, L(CCO)' = 116.1(2) ° and LCCO= 121.0(2)°; for the carboxylic group LOCO=121.l(2) °, /CCO(H)-119.3(2) ° and LCCO= 119.6(2) °. Very similar relations of C-O distances and angles around carbon atoms in carboxyl groups, and their agreement and disagreement with respect to calculated values [12], have been found in N a H M . 3H20 [9]. The intramolecular O(4)...O(6) distance, 2.429(3) A, is within the range of potentially symmetric hydrogen bonds (2.40-2.50 A); however, the position of the proton here is highly asymmetrical: O ( 6 ) - H ( 6 ) = 1.09(4), H ( 6 ) . . . O ( 4 ) = 1.45(4) .~. An unusually asymmetrical position of the proton in the intramolecular hydrogen bond has been found in N a H M - 3 H 2 0 at low temperature [9] and has been explained by a different bonding situation around the oxygen atoms involved in this hydrogen bond. In the present case the bonding situation is the same around the 0(6) and 0(4) atoms engaged in the intramolecular hydrogen bond, but around the carboxylic group of the maleic residue it is completely different. This may cause the high asymmetry of the intramolecular hydrogen bond in BHM. The distances of the - C - C - and - C = C - bonds in the present ion depart slightly from the corresponding distances in other acid maleates [7-11]. The - C - C - bond lengths are equal to 1.490(3) and 1.484(4) .~, and the - C = C - bond length is equal to 1.318(3) .&. 3.1.2. The betaine cation

As mentioned earlier, betaine in the title crystal appears as a cation. Hence its bond lengths and angles are very close to those found in the (Bet)2 .H2504 crystal [13] or in Bet. HC1 [14] in

15

which protons were transferred from sulphuric or hydrochloric acid, respectively, to the carboxylate group of the betaine zwitterion. At the same time, metric parameters are markedly different from those found in other betaine complexes (Bet. H3PO 4 [15], Bet. H3AsO4 [16], (Bet)2. Te(OH)6 [17]) in which proton transfer to the betaine zwitterion does not take place. The bond lengths and angles in the carboxylic group of the betaine cation (Table 2) are consistent with the geometrical parameters o f - C O O H [12]. In the present cation the C(1)-O(1)(H) distance is equal to 1.305(3) .~, and the C(1)-O(2) distance to 1.205(3) A. The former is slightly shorter but the latter is slightly longer than corresponding bonds in (Bet)2 .H2SO4 [13] and Bet. HC1 [14] crystals. The - C - C - bond appears to be the next bond sensitive to proton transfer. The - C - C - bond length (1.508(3) A) is shorter than in other complexes (1.529-1.537 A [15-17]) and close to the C C bond lengths in (Bet)2 • H2SO4 [13] and Bet. HC1 [14]. The C - N bond lengths lie in the range 1.494(3)-1.504(3) .~. They are shorter than in Bet-HaPO4 and Bet. H3AsO4 [15,16] complexes, but are very similar to those found in other betaine compounds [17,18]. 3.2. Vibrational spectra

The polarized infrared spectra of the BHM crystal are shown in Fig. 4, while Fig. 5 shows the polarized Raman spectra. The infrared powder spectrum of BHM is illustrated in Fig. 6. The wavenumbers, relative intensities and tentative assignments of the bands observed in the infrared and Raman spectra are collected in Tables 4 and 5, respectively. The bands observed in the studied region, i.e. in the range 4000-400 cm -~ of both infrared and Raman spectra, arise from vibrations of hydrogen maleate anions and betaine cations and in the first approximation may be divided into maleate and betaine skeleton internal vibrations and hydrogen bond vibrational modes. The bands were assigned with the help of the correlation diagram (Table 6) and the polarization properties of the bands compared with those predicted on the basis of the polar bond moment model [19] (Table 7).

M.M. Ilczyszyn et al.IJournal of Molecular Structure 372 (1995) 9-27

16

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Fig. 4(a). Polarizedinfrared spectra of BHM at room temperature(p-paraffinwax absorption), spectra recorded on the ac plane. 3.2.1. Hydrogen b o n d v i b r a t i o n s

There are two strong and different hydrogen bonds in the present crystal: an intramolecular one with O . . . O distances equal to 2.429(3) ,~ and an intermolecular one with O . . . O distances equal to 2.527(3) A. If one assumes that the transition dipole moments of the stretching uaOH modes of both hydrogen bonds are parallel to the O . - . O directions, the maximum absorption due to these vibrations is expected to appear in the spectra taken at 55 and 105 ° with respect to the X direction for intra and intermolecular hydrogen bonds, respectively (Table 7). Moreover, taking into account the O . . - O distances and the different types of hydrogen bonds, one should expect two different patterns of absorption. The broad absorption extending from 3000 to 400 cm -l with a broad and medium band in the 2500-2200 cm -1 region

arises from the uaOH mode of the intermolecular hydrogen bond [20]. The absorption similar to that observed in the spectra of K H M [22] or KHFur 3,4 [21] is assigned to the uaOH vibration of the intramolecular hydrogen bond. The infrared powder spectrum of BHM is dominated by strong asymmetric absorption with a maximum at about 1200 cm I and extending from 3000 to 800 cm -l (Fig. 6). On its highfrequency wing one can observe a broad and medium band at about 2470 cm -1. The polarized infrared spectra measured for the ac face reveal that this absorption manifests itself with different intensities in all components. In the spectra taken at 60, 75 and 90 ° with respect to the X direction, the absorption exhibits maximum intensity in the region 1800-800 cm -]. However, in the spectra recorded at 105, 120 and 135 ° with

M.M. llczyszyn et al./Journal 6 (Molecular Structure 372 (1995) 9-27

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"1)

o

0 IZI

<

2&o

i~

io~

~o

I

pl

I

;

WAVENUMBERS (cm-1)

O o9 ~o < ~

4000

I

3OOO

I 0 Z <

I I Z000 1500 WAVENUMBERS (cm-1) I I

io~o

5(Jo

!

=

0 co '<

4

4000

3&o

2ooo'

l~,o

~ooo

,~o

i

I

:

,"

I

I

WAVENUMBERS (cm-1) Fig. 4(a). Continued.

I cu

(100)

|

P

z < al 0 < WAVENUMBENS (em-1)

! °n,, 0m
~

I (t001

l= P

u'J <

4000

I 3000

I 2000

I 1500

F 1000

F 500

WAVENUMBERS (cm-1) Fig. 4(b). Polarized infrared spectra of BHM at room temperature (p-paraffin wax absorption), spectra recorded on the bZ( YZ) plane.

17

regard to the X direction, the absorption shows maximum intensity over the whole region, i.e. in the region 3 0 0 0 - 8 0 0 cm -]. A close examination of the polarized infrared spectra also indicated that it is impossible to distinguish two well-defined patterns of absorption which could be due to the uasOH stretching vibrations of the inter- and intramolecular hydrogen bonds. However, taking into account calculated values of the transition dipole moments of the uaOH modes one can say that the uaOH mode of the intramolecular hydrogen bond makes a marked contribution to the absorption observed in the spectra taken at 60, 75 and 90 ° . Simultaneously, the uaOH mode of the intermolecular hydrogen bond essentially contributes to the absorption in the spectra recorded at 105, 120 and 135 ° with respect to the X direction. The broad band at about 2470 cm ] overlapping the highfrequency part of the absorption is usually attributed to the overtone of an out-of-plane deformation mode (27OH) [23]. Unfortunately, no band in the 1 1 5 0 - 1 2 5 0 c m -I region is observed which would be good candidate for the 7OH mode. However, a broad and medium band at 1080 cm -I in some spectra taken in the a c face is observed. This was attributed to the 7OH mode of the intermolecular hydrogen bond. Thus the band at 2470 cm -1 does arise from 2-~OH which is in Fermi resonance with the uaOH and therefore the wavenumber of 2-~OH (2 × 1080 cm -1) is very close to the wavenumber of the minimum (2100 cm -1) between the band at2470 cm -1 and the remaining broad absorption. In the z z , z x and z y components of the Raman spectra some very weak and broad bands are observed (Table 5, Fig. 5). The origin of a band at 2472 cm -I may be the same as the band at 2470 cm 1 observed in the infrared spectra. However, the origin of other bands observed in this region is not yet clear. The bands due to the deformation modes 6OH and 7OH of both hydrogen bonds would be expected in the 1650-1500 and 1300-1100 cm l regions, respectively. The usually reliable attribution of the 6OH mode is somewhat problematic due to its low intensity and its position in the frequency region where strong u C = O , uaCOO and uaOH band occur [25-27]. Moreover, the vibrational analysis of the hydrogen maleate ion

18

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

(a)

(b) Betaine

Y(xX)Zx3

•

Y(xx)Z x2 5

Maleic acid

X(yy)Z

x5.5

X(yy)Zx6

" .

"

"

~

X z(z Y )x2 . ~ Y(Z~Xxl

_ ~

Z 111 I-

Z

--

Z

Z .< ,<

Y(xy)Z

I

,

I

z

Y(xY)Zx7

~ <

w

n," X(yx)Z X(yX)Zx9

L .,

X(zx)Y x45

.

..

.~

Y(zY)Xx20 54'00 32~00 30'00 28'00 26'00 2400 22'00 2000 WAVENUMBERS (cm-1)

x(zx)Y

I

l

x7.5

Yzy,×

I

II

2000 1800 1600 1400 1200 1000 800 WAVENUMBERS

600

400

200

(cm-1)

Fig. 5. Polarized R a m a n spectra of B H M at r o o m temperature. (a) 3600-2000 cm -l region; (b) 2000-200 cm -l region; (c) 2 0 0 - 1 0 cm -l region; (d) 2800-2000 cm -l region.

carried out by Avbelj et al. [28] shows that 6OH deformation of the intramolecular hydrogen bond is strongly mixed with u C = O , usC=O, u s C - O and 6sCH modes and contributes to three bands (at 1701, 1621 and 1572 cm -l) The assignment of the bands arising from the ",/OH modes is much easier. The characteristic 7OH vibrations usually do not couple with other vibrations of the molecule and the position of the "/OH bands is sensitive to temperature [29,30]. The weak band at 1655 cm -1 observed in the infrared spectra polarized at 120 and 150 ° with respect to the X direction was attributed to the 6OH mode of the intramolecular hydrogen bond. Polarization of this band agrees with the predicted one (Table 7). In the INS spectrum of K H M [31] the ~OH band of the intramolecular hydrogen bond was identified at 1621 cm -x. The broad and intense band at 1080 cm -1, well defined in the spectra recorded parallel to the X

direction and at 15, 150 and 165 ° with regard to this direction, was assigned to the ? O H vibration of the intermolecular hydrogen bond. The band at 1129 cm -1 was attributed to the "/OH intramolecular hydrogen bond. In the infrared [28] and INS [31] spectra of K H M the 7 O H mode has been detected at 1194 and 1209 cm -1, respectively. 3.2.2. Betaine cation and maleate acid anion skeleton internal vibrations Carboxyl group vibrations. The carboxyl groups in the BHM crystal were found in two forms: - C O O H (in the betaine cation and one carboxylic group in the maleate anion) and the anion C O O (one carboxylate group in the maleate anion). Hence in the 1750-1550 cm -l region one should expect bands due to both uC=O and uaCOOvibrations. Note that the geometrical parameters of both neutral carboxylic groups are very close

19

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

(c)

(d)

X(yy}Zx2

~

Y(xx)Z

Betaine•Maleic acid

_ X(zzlV

X(zZ)Yxl

_ ~ ~ _ Ylzz)x

Y(zZ)Xxl

o9 z I..u I-z

z tu I-z

Y(xy)Z x16

z <
z <

X(yx)Z x15.5

t~

X(Z.X)Yx6

~ ~ / ~

p

Y(zY)Xx25 180

160

140

120

10-0

B'O

6~0

40

2'0

2800 2700 2600 2500 2403 2300 2200 2100 2000

WAVENUMBERS (crn -1)

WAVENUMBERS (cm-.1) Fig. 5. Continued.

(Table 2). Moreover, if one assumes that the transition dipole moment of the u C = O mode is parallel to the C = O bond, the u C = O bands of both carboxylic groups should exhibit maximum intensity in the same spectrum recorded in the ac face. For that reason these two bands could not be distinguished in the infrared spectra. Fortunately, according to Table 7, the band due to u C = O of the carboxylic group in the betaine cation should be more intense in the spectrum recorded parallel to the Y ( b ) axis than the u C = O

I

I

4000

3000

I

2000

: -- I

1500

WAVENUMBERS(era -1)

1000

500

Fig. 6. Powder infrared spectrum of BHM in Nujol and poly(chlorotrifluoroethylene) emulsion.

band of the carboxylic group in the maleate anion. However, taking into account a correlation (Davydov) splitting, one can expect one band in the spectrum polarized parallel to the Y axis, one band in the spectra taken in the ac face and two bands in the Raman spectra. The infrared and Raman bands should appear at different frequencies. Three bands were observed in the polarized infrared spectra: the shoulder at 1728 cm -1 and bands at 1714 and 1691 cm -] could be assigned to the uC--O vibration. The shoulder is observed in the spectrum recorded parallel to the Z direction and appears as a band in other spectra taken in the ac face (at 1733 cm -1, 105°; at 1740 cm q , 120°). The second band (broad and intense) was found in the spectrum taken parallel to the b ( Y ) axis. The third band exhibits a change of shape and position (the lowest and the highest wavenumbers of this band are 1690 and 1705 cm -], respectively) in the spectra of the ac face with

M.M. Ilczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

20

Table 4 Wavenumbers observed in the polarized infrared spectra of the BHM single crystal

(OLO)

(lOO)

0°(11X)

30°

60°

3060w 3049w 3034w

3059w 3049w 3034m

3060w 3034m

90°([IZ)

120°

3283vw

3293vw

3034m 2991s

3049w 3034m 2997m

150°

3049w 3035w 2992m

Tentative assignmenta

lib(Y)

liE

3061m

3283vw 3061w t,'aCH3

3032w 2999m 2670w

3034m 2993s

vaCH2

2467sb

vOH (A)

2632w 2623w 2582w 2559wb 2510w 2428w 2009w 1929w 1897w 1883w 1834w 1815w

2471w 2423w 2353w 1993w 1921w

2471m 2424m

2479mb 2423m

2470sb

2000w 1929m

1993m 1930s 1897s

1990s 1933sh 1890vs

1884w 1841w

1884m 1834m

2464mb 2426m

2423sh

2009sh

2001w

1897s

1896w 1885s

1817s 1728sh

1807s 1781vs 1740sh

1818m 1740s 1716vs

1709sh 1691vs 1655sh 1613sh 1563vs

1711sh 1690vs 1660sh 1617vs

1705vs 1652 1623s

1551vs

1553vs

1704vs 1652" 1620vs 1565vsb

1701vs 1652w 1618vs 1577vs

1698vs 1657m 1614vs 1570vs

1411vs 1396vs

1392vs

1993sh

1391vs

1399vs

different p o l a r i z a t i o n s o f the r a d i a t i o n a n d is well defined in the spectra r e c o r d e d at 60, 75 a n d 90 ° with respect to the X direction. The p o l a r i z a t i o n s o f two b a n d s (a s h o u l d e r at 1728 cm -1 a n d a b a n d 1716 cm -1) are p a r t l y in a g r e e m e n t with those expected for the v C = O v i b r a t i o n in the b e t a i n e c a t i o n a n d were assigned to this vibration. T h e third b a n d was a t t r i b u t e d to the v C = O m o d e in m a l e a t e anion. T h e b a n d due to the uaCOO m o d e was identified at 1575 c m -1 in the s p e c t r u m t a k e n p a r a l l e l to the

vOH(B)

1728vs }

vC=Ob

1701vs

vC=O 6OHIA vC=C vaCOO

1620s 1575s

1619s 1579vs

1484vs 1422vs 1410sh

1426sh 1413sh

1395vs 1385vs

1367"

1818s 1779s

1385vs 1367"

6CH2 6sCH3 vsCOO

Y(b) axis and in the spectra measured in the ac face in the range 1550-1571 cm -l. In the spectra of the ac face the uaCOO band shows dependence of shape and position on polarization of the radiation. However, in the spectra measured at 60 and 75 ° it is hidden by absorption arising from the uaOH of the hydrogen bond. In some R a m a n spectra one can observe the

b a n d s at 1726 c m -a (xx, 1731 c m -1 (zz, xy) a n d

yx, zy),

1718 c m - l (zx), 1705 c m -1 (yy) which

are due to vC=O modes. Except for the band

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

21

Table 4 continued

(OLO) O°QIX)

(lOO) 30°

1358s 1331s 1288w

1331vs

60°

90°(Ill)

120°

150°

1350vs

1352vs

1354vs

1357s

1331vs

1332vs 1290"

1333vs

1332s

1270vs 1253m 1229s 1216s

1230vs 1215s

1233vs 1213vs

1238vs 1218vs

1225s

1274s 1257m 1227vs

l196vs

l197vs

l198vs l146vs

l198vs

l195vs

l197vs

1129m

lib(Y)

[IZ

1348vs

1348vs

1270vs

1290" 1270vs

1229vs

1231" }

1209vs

1203vs

1127vs lll2vsb 1096vs

1079s 1013m 994w 954w 933vs 892m 880m 803vw 778m 693w

1083s 1013s 987m 957w 933vs 894vw 879m 802vw 777m 694vw

650vw

651vw 599vw 588w 539vw 448w

590vw 541vw 449m

Tentative assignmenta

1013s 986s 957s 932vs 890w 878vs 802w 776vs 690w 667w 647m 599vw 588m 539m 446w

1091sb

vCCm 6CHIn wCH2 vC-OHm vC-OH b tCH2 6sCHm

7OHIA lll0vsb

1014sh 985vs 956vs 932s 890s 878vs 801vw 778vs 689m 667sh 648vs

1065vs 1013s 984s 955s 933s 893s 879sh 802w 778vs 691s 668w 648vs

589m 539s 443s

589m 539s 442vs

1073s 1013m 982w 956m 933s 893s

7OHIE 1013m 988vs 953w 890vs 872vs

986vs 955vs

778m 692w

777s 691w

891vs 877vs 801w 778vs 691s

650w

652m

) 649vw I

592vw 539w 448m

587vw 539w 443m 425w

t,'aC3N vCC rCH2 vCN 6COO(H) /,,CCm ~'sC3N 6COO

wCOO(H) wCO0

589m 539s 443vw

7CHIn or rCOO(H) rCO0 6aC3N

a Abbreviations: vs, very strong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder; v, stretching mode; 6, in-plane mode; 3', out-of-plane mode; a;, wagging mode; t, twisting mode; r, rocking mode; subscript m means maleate ion; subscript b means betaine cation; subscripts a and s mean asymmetric and symmetric modes, respectively; subscripts IA and IE mean intra- and intermolecular, respectively; *, transmission window. at 1713 c m -1 they are very weak. T h e shoulder at 1597 c m -1 m a y arise f r o m the v a C O O m o d e . T h e b a n d due to v s C O O was identified at 1411 c m -1 in the infrared s p e c t r u m p o la r iz e d parallel to the Y direction a n d in some (zz, zx, yx, zy) R a m a n spectra at 1413 c m -1. T h e s t r o n g b a n d at a b o u t 1270 c m -1 (120 °, 150 °, IIb) a n d the w e a k b a n d at 1288 c m -1 ([[X) in the p o l a r i z e d infrared spectra were a t t r i b u t e d to the v C - O ( H ) modes. O n l y one b a n d at 1261 c m -1 was f o u n d in the R a m a n s p e c t r u m (zx) wh i ch co u l d arise f r o m v C - O ( H ) vibration.

T h e d e f o r m a t i o n an d l i b r at i o n m o d e s o f an an i o n i c c a r b o x y l a t e g r o u p were identified at a b o u t 691 cm -1 (6COO; d e p o l a r i z e d b a n d s h o w i n g m a x i m u m intensity in the s p e c t r u m m e a s u r e d at 120 ° with regard to the X direction), 599 c m - j (a;COO) an d 539 c m -1 ( r C O O ; also depolarized, exhibiting m a x i m u m intensity in infrared spectra r e c o r d e d at 90 an d 120 ° with respect to the X direction). T h e i r R a m a n c o u n t e r p a r t s can be f o u n d at 699, 6 9 4 c m - l (6COO), 6 0 9 c m -1 (coCOO) an d 539 c m -1 ( r C O O ) . N o t e that the p o s i t i o n o f the b an d s o f the l i b r at i o n m o d e s are

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

22

Table 5 Wavenumbers observed in the polarized Raman spectra of the BHM single crystal Wavenumber

3332 3067 3062 3056 3052 3043 3035 2992 2982 2972 2969 2940 2897 2889 2884 2877 2872 2840 2815 2809 2777 2764 2566 2551 2501 2489 2472 2422 2365 2272 2228 2067 1726 1718 1713 1705 1619 1616 1597 1478 1459 1454 1450 1445 1413 1392 1356 1335 1261 1237 1231 1221 1215

Y(xx)Z

Y(zz)X

X(zz) Y

X(yy)Z

X(zx) Y

Y(xy)Z

X(yx)Z

Y(zy)X

Tentative assignment~

270 sh 47936

22627

1826

13235

1267

1826

8658

4699

3488

4360

8031 sh

7453 2342

5725 1810

sh 15787 6458 11359 sh

sh 24514 sh 37646

10221 11470 16561 sh

8310

vaCH2 sh

sh 7090

19516

9006

4913

2174

2195 777 1412 738

vaCH3 vCH vaCH3 vaCH3 vaCH3 vaCH3

677

1547 4135 1286

vsCH3

2031 4227 1252 1525

2953

1320

1841

5305

2075

459 1353 294 471 2210(b)

997

vOH 566

2130(b)

329(b)

vOH

886 518 518 2001(b) 1866(b)

830 759

1571

628

vOH

sh 1327

1039

4997 }

3205 39058

37683

50371

48035

vC=Ob 1098

1712 4042

200t

4008

3120 2492 5021

sh sh 7853

14442 26874 19415

967

sh

vaCOO 2455

1449 1654

1751 2618

1540 1563 1426

2618 2985 2353 sh 970 988 2366

2736 } 4432

7488 7344

sh 2586 2481 2819

vC=O vC=C

sh 25317 17984

992

1591

14652

1162

2830 3254 2642

6aCH 3

1432

sh

g~COO 6~CH3 vCCm taCH2 uC-OH tCH 2

1133 sh 3658

2599 1768

2418

1920

1605

6sCHm

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

23

Table 5 continued Wavenumber

1201 1195 1126 1016 1009 990 956 941 936 891 879 800 780 699 694 649 609 591 545 539 450 442 428 377 368 344 332 317 314 300 270 247 160 157 147 140 131 124 117 114 99 97 94 87 77 70 60 56 44 40 33 31 27

Y(xx)Z

Y(zz)X

X(zz) Y

2527 1455

5575 3805 3067 1887 1445 22984

5331 3820 2685 1891 1438 21855

2477

2459

12214

11306 5521 49306

X(yy)Z

X(zx) Y

Y(xy)Z

X(yx)Z

1466

1956

1791 1243

Y(zy)X

Tentative assignmenta

sh

1026

1057

1714 1017

1488 1708

942 1072 1419 1157

2568

3080 2053 1503

2379 2106 1191

735

2723

1947 629

rCH 3 7CH

952 [ 589

4956

1390 2684 7292 20347 1093(b)

53567

1797 9332 2217 1516 9121 2112

1804

4294 3247 539 2788

1587

712 831 1143 1158

595 777 731

2635 2904

1248 1441

719 1185

2042 2172 6633

2493 1690

sh 6088

3918 3819

3366 3366

sh

J

1501 1700 ~

999 3918

3139

995

2389 3387 4783

1938 1585 1175 999

1419 1697 5057

3330

2751

2184

853

889

2792

5515 11300

4256

6911 1558

853 861

1024

sh 17238

2176 3918 5081 5081

2355

1972

3709 5922

1047

813

15942

3919 7656 6911

10196

15361

4305

7992

16912

16224

12760

12341

7160 16490 15618

14820 13011

18061 20156

14867 15628

15792 9596

12869

11046

6539

4993

12760

12760

10337

9830

9076

85317

87289

28372 52811 58393

40217

54662

21683

9491 23384

14396

20577

11668 8181

139628 126883

363554 9695

a Abbreviations as in Table 4.

349698

177817

61742

I 6aC3N

sh sh

6c00 ~COO(H) wCOO rCOO(H) 7CH rCOO 6aC3N

2147

841 4306

vaC3N vCCb rCH2 7CHm vCN vCC m 6COO(H) ~C3N

sh

~sC3N 6CCN 7CH

24

M . M . llczyszyn et al./Journal o f Molecular Structure 372 (1995) 9 - 2 7

Table 6 Vibrational analysis of the unit cell vibrations of the BHM crystala Unit cell group symmetry

Activity

Lattice vibrations

Internal vibrations

(C2h) Ag

IR

Raman

A

T

R

B

M

HB

ia

xx, yy, zz

0

6

6

51

24

6

0 1 2

6 5 4

6 6 6

51 51 51

24 24 24

6 6 6

XZ

Bg Au Bu

ia Y X, Z

zy, x y ia ia

a A = number of acoustic vibrations; T =number of translational vibrations; R = number of rotational vibrations; B = betaine ion; M = maleate anion; HB = hydrogen bond; ia = inactive.

very close to these found in the vibrational spectra of the betaine monohydrate crystal [32]. The strong band at 880 cm -t in the infrared spectra and an intense band at 879 cm -l in the

Raman spectra were assigned to the 6COO(H) mode. Note that the bands due to 6COO(H) are located higher than in other carboxylic acids [25-27] and much higher than the 6COO band of

Table 7 Values of the directional cosine of the transition dipole moments (t.d.m.s) of some betaine cation, maleate anion and hydrogen bond vibrations calculated using the polar bond approximation model Type of vibration

X

Y[]b

Z

0a

Betaine cation uC(1)-O(I)(H) uC(1)=O(2) wfOO(H) 6COO(H) rCOO(H) tCOO(H) uC(2)-N uC(2)-C(1) uN-C(3) uN-C(4) 7CNC 6CNC uN-C(5) u~C3N

0.3824 -0.2679 0.9223 0.1261 0.3649 0.9223 -0.3827 0.0709 0.0460 -0.9581 -0.0808 0.9957 0.5381 -0.3709

-0.9211 0.5859 0.3852 -0.3687 -0.8460 0.3852 0.9030 -0.2498 0.1313 0.0396 0.9876 -0.0961 0.7265 0.8868

-0.0727 -0.7670 -0.0278 -0.9211 0.3885 -0.0278 0.1946 -0.9658 0.9902 -0.2840 0.1346 -0.0340 -0.4275 0.2754

169.4 70.7 178.3 97.7 46.7 178.3 153.1 94.2 87.4 16.5 120.9 178.0 141.5 143.4

Maleate anion uC(6)-O(3) uC(6)-O(4) usCOO uaCOO 6COO tCOO wCOO rCOO vC(9)=O(5) ~,C(9)-O(6)H wCOO(H)

0.6980 -0.9282 -0.2405 0.9261 -0.2405 0.2907 0.2907 0.9261 -0.3502 -0.5933 -0.2176

0.3983 -0.2012 0.2061 0.3412 0.2061 -0.9171 -0.9171 0.3412 -0.3152 0.0758 0.9433

0.5948 0.3131 0.9481 0.1603 0.9481 0.2729 0.2729 0.1603 -0.8823 0.8008 -0.2507

40.4 161.4 104.2 9.8 104.2 43.2 43.2 9.8 68.3 126.6 49.0

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

the carboxylate group in the present crystal. The aJCOO(H) vibrations give rise to a strong infrared band at 647 cm I (][Z) and a shoulder at 667 cm -1 (llZ) and a weak R a m a n band at 649 cm -1 (xx, zx, xy, yx). The weak, depolarized infrared band at about 590 cm -l and two weak R a m a n bands at 591 and 545 cm -l were assigned to the rCOO(H) vibrations.

The other betaine cation skeleton internal vibrations. Apart from internal vibrations of the carboxyl group, the bands due to other internal vibrations of betaine in B H M appear to be located at very similar wavenumbers to the vibrational spectra of betaine monohydrate [32]. The band due to the uCN mode can be observed at about 890 cm -l in the polarized infrared spectra and at 891 cm -1 in the R a m a n spectra.

25

The bands derived from the stretching vibrations of the C3N group were identified as follows: the depolarized bands at 986 and 1013 cm -z showing different intensities in the spectra taken in the ac face were attributed to the t~asC3N mode. Their R a m a n counterparts were found at 990 and 1009 cm -1. The intense, narrow and depolarized band observed in the infrared spectra at 778 cm l and the narrow R a m a n band at 780 cm -I (the most intense in all the R a m a n spectra) were assigned to the usC3N mode. Two weak bands at 450 and 428 cm -l in some (zz, zx, yx) R a m a n spectra and the weak band at 425 cm -1, appearing only in the spectrum recorded parallel to the Y(b) axis, arise from the 6asf3N vibration. However, the weak bands at 377 and 368 cm -1 in the R a m a n spectra could be derived from the t~sf3N mode. The band due to the L,C-C mode was found at

Table 7 continued Type of vibration

X

Y[lb

Z

0a

6COO(H) tCOO(H) rCOO(H) uC(7)-C(7) vC(7)=C(8) •C(8)-C(9) uC(6)-C(7)

-0.9661 -0.2176 0.1396 0.9809 -0.5357 -0.9644 -0.2875

-0.2449 0.9433 -0.2242 0.1660 -0.3483 -0.2503 0.1917

-0.0831 -0.2507 -0.9646 -0.2209 -0.7695 -0.0875 0.9383

4.9 49.0 98.2 167.3 55.7 5.2 107.0

Intermolecular hydrogen bond t.d.m, of uOH I10(1)-H(I) uOH 6OH 3,OH

0.2086 -0.9614 -0.1797

-0.2350 0.1290 -0.9635

-0.9495 0.2433 0.1989

102.4 168.7 132.1

t.d.m, of L,OH II o(1).. ,o(3) vOH 6OH 3'OH

0.2574 -0.9495 -0.1797

-0.2413 0.1168 -0.9635

-0.9358 -0.2915 0.1989

105.4 170.6 132.1

lntramolecular hydrogen bond t.d.m, of uOH II H(6)-H(6) uOH 6OH ~on

-0.4086 -0.9076 0.0981

-0.3265 0.0447 -0.9442

-0.8526 0.4176 0.3145

64.4 155.3 72.7

t.d.m, of L,OH 110 ( 6 ) . . . 0(4) vOH 6OH ")'OH

0.5468 -0.8314 -0.0981

0.3157 0.0959 -0.9442

0.7754 0.5473 -0.3146

54.8 146.6 72.7

a The angle between the projection of the transition dipole moment (t.d.m.) onto the ac plane and the X direction (in degrees).

26

M.M. llczyszyn et al./Journal of Molecular Structure 372 (1995) 9-27

955 cm -1 in the infrared spectra. It exhibits the strongest intensity in the spectrum polarized parallel to the Z optical direction which exactly corresponds to the crystal structure (Fig. 1 and Table 7). In the R a m a n spectra the uCC band was identified at 956 cm -1 .

The other maleate anion skeleton internal vibrations. The bands due to the u C H vibrations can be expected above 3000cm -1 [28]. Unfortunately, the bands due to the uasCH 3 vibrations also appear in this region. Hence our assignments listed in Tables 4 and 5 may be uncertain. The bands arising from the 6CH mode was found at 1348 cm -1 (lib) and 1216 cm -1 (llX, 30 °, 60 °, [[Z) in the infrared and at 1215 cm -1 in the R a m a n spectra. This mode has been identified at 1347 cm -l in INS [31] and at 1362 and 1218 cm -I in the vibrational [28] spectra of K H M . The 7 C H mode essentially contributes to the bands at 1005, 867, 600 and 325 cm -1 in the infrared spectra of K H M . Taking this into account one can assume that the 7 O H mode in the present spectra contributes markedly to the bands at 1016, 936, 591 and 332 cm -l in the R a m a n spectra and to the band at 590 cm -1 in the infrared spectra. The bands due to the u C = C mode were identified in the spectrum taken parallel to the Z(b) axis at 1620 cm -1 and in all the spectra recorded in the ac face in the 1623-1614 cm -~ region. The u C = C band appears at 1619 cm -1 in the R a m a n spectra. l h e u C - C modes may contribute to two depolarized infrared bands: a strong band at about 1350 cm -1 and a weak band at 802 cm -1. Their R a m a n counterpart were found at 1356 and 800 cm -l, respectively.

4. Conclusion X-ray studies of the title crystal show that the maleate monoanion forms a ring structure containing ao very short intramolecular ( O . . . O - 2.429(3) A) hydrogen bond which is often found in other hydrogen maleate salts. In spite of a very short O . . . O distance, the intramolecular

hydrogen bond in the present crystal is asymmetric. A m o n g short intramolecular hydrogen bonds found in other maleate acid salts so far, the one in B H M appears to be the most asymmetric. The second intermolecular, hydrogen bond was detected between the maleate monoanion and the betaine cation. In this hydrogen bond a proton was transferred from maleic acid to betaine so that the former appears as an anion and the latter as a cation. The polarized infrared spectra of the B H M crystal reveal a broad absorption due to the uaOH vibrations of the strong hydrogen bonds. However, it is not possible to distinguish between the absorption arising from the uaOH of the intramolecular and intermolecular hydrogen bonds. The spectra confirm the existence of carboxyl groups in two forms: - C O O H and - C O O - . In spite of the carboxylic group the betaine exhibits very similar spectroscopic features to those in the betaine monohydrate crystal.

Acknowledgements This research was supported by the National Committee for Scientific Research ( K B N grant No. 20799101).

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