Phase transition in malonic acid: An infrared study

CHEMICAL

Volume 69, number 2

PHYSICS

LETTERS

15 Janw

1980

PHASE TRANSITION IN MALONIC ACID: AN INFRAXED STUDY * Somnath

GANGULY,

Jacob

R. FERNANDES,

Solid Srare and Srruchtral Clremtstry

Recclved

8 November

Cautam

R. DESIRAJU

limt. Indron Dlsrzrute of Scwnce,

and C.N.R. RAO

Bangalore-560012.

lndra

1979

hlalomc acid is shown to undergo an mtcrestmg phase transrtlon at 360 K when bonded dimers present in the low-temperature phase become equivalent.

I_ Introduction At ordmary temperatures, malomc acrd (CH2(COOH)Z) possesses a triclimc structure (pi,C,) wrth two molecules per umt cell. The molecules are arranged m a zig-zag cham along the c-axrs with the carboxylic groups linked through hydrogen bonds [l] _The most Interesting feature is that the two cychc hydrogen-bonded dlmer uruts (rmgs I and II) are not coplanar, but are orthogonal as shown In fig. 1, the C-C, C=O and C-O distances in these umts are also different. Accordmgly, Prgenet et al. [2] fiid that the two drmers exhibit charactenstically different vibration frequencies, the Apmodes grvmg doublets in the Raman and the A, modes grvmg doublets in the infrared spectrum [2] _ hlusaev and hlnyukh [3] suggested a possrble hrgh-temperature transition in malonic acid. We considered It interesting to investigate the change in the nature of hydrogen bonding m malomc acid accompanymg such a phase transrtron, if rt does occur.

the two nontqurvalent cyclic

hydrogen-

spectrometer. i\ Specac variable temperature assembly was used to record the spectra through the phase transition.

b 2. Experimental Drfferential scannmg calonmetry of malonic acrd was carried out with a Perkm-Elmer (DSC-2) instrument. Infrared spectra were recorded with a PerkinElmer model 580 spectrometer and a Polytec FT * Commurucation tural Chemistry

No. 56 from the Sohd State and StrucUmt.

FIN..1. Two non+qulvalent hydrogen-bonded dimenc units (rings I and II) m the low-temperature phase OF matonic acid. (After Prgenet et al. 121.)

227

Volume 69. number 2

CHEMICAL PHYSICS LEl-fERS

3. Results and discussion Drfferentlal scanning calorimerry of dry, crystalLine malonic acrd showed a reversrble phase transrtion to occur at 360 K. The enthalpy change in the tran-

15 January

1980

sitron was 1.47 kJ mol-l , mdrcatmg the first-order nature of the transition. Infrared spectra of malomc acid through the phase transition are shown in figs. 2 and 3. Band assignments above and below the transition are m table 1. The most remarkable change m the mfrared spectrum above the phase transrtron 1s that there is only one set of vrbratronal frequencres due to the hydrogenbonded cychc dimer, rather than the two sets found below the transrtlon temperature_ Thus, the frequencies corresponding to ring II are missing m the spectrum of the high-temperature phase. It, therefore,

Table 1

I

1000

1500 WAVENUMBER

MO

Ct.?

I-If 1 IR spectra of lnalonlc acid m the 1800-400 gon throu_cb the phase rmnsltmn.

303

’

\

K

I

cm-’

I

I

\

rc-

Infrared bands (m cm-‘) of crystalhne malomc and belo& the phase transltion at 360 K

acrd above

303 K a)

368 K

posmon

assrgnment

3100 2900 3000 2960 1720 1690 1415 1425 1400 1315 1260 -

v(OH) dOH)

1225 1175 965 940 923 900 780 660 596 580 450 438 227 180 126 90 WAVENUMBER

IR spectra of malonrc acrd m the X0-50 through the phase mmsmon

FIN 3. gion

228

Ct.@

cm-’

re-

Ring

vasym(CH2) VsymKllz) u(C=O) vK=O) 6(CHz) 6(OH) 6(OH) ti(C-0) combmatron

w(CH2) WH2) -Y(OH)

posmon I II

II

3000 2960 1720 -

11

1445 -

I

I I 11

II

h(CH2)

I “s

,(C-Cl

6 ?COO)

YKCO) YKCO) 6 (CCO)

6 (CCO)

6KCC) v(OH 0) R’ R’

3100 -

II I II I

1400 1315 1240 1225 1175 -

b)

940 923 900 775 658 583 440 216 165 c) 90

a) The spectrum at 333 K gave the same bands as at 303 K. b) Combination band. c) There are two weaker bands on either srde at 174 and 158 cm-‘. These may be assgned to the T(C-C) modes

Volume

69, number

2

CHEMICAL

appears that the two hydrogen-bonded duneric units (rings I and II) become equivalent above the phase transition. We consider tlus to be a very interesting phase change indeed. A few details regarding the infrared band assignments for the two phases of malomc acid are m order. The assignments for the low-temperature phase

shown m table 1 are essentially the same as those of Plgenet et al. 121, except that we find two combmatlon bands characteristic of the low-temperature (ring II) and high-temperature phases at 1260 and 1240 cm-1 respectively_ The two bands due to ?(CCO) can also be assigned to the two nngs III the low-temperature phase. The 180 cm-t band which is mamly due to v(OH...O) (with some possible contnbutlon from the T(C-C) mode) in the low-temperature phase is shifted to 165 cm-l in the h&-ternperature phase, the latter showmg some structure (see table 1). The band due to the S(CCC) mode is also shifted to a lower frequency above the transitlon temperature_ It is interesting that one of the vlbrationrotation bands (13-6 cm-l) disappears above the phase transition. Smce the v(O-H) and v(C=O) frequencies are higher whale the 6(OH) and y(OH) frequencies are

Pl-iYSlCS

LI3TTIIRS

15 Janmry

1980

lower in the lugh-temperature

phase than in the lowtemperature phase, we expect the hydrogen bonding to be weaker in the high-temperature phase. Accordingly, the hydrogen-bond stretching frequency, v(OH...O), is also lower in the high-temperature phase. A comparison of the frequencies suggests that hydrogen bonding m the high-temperature phase would be simdar to th?t in ring I of the low-temperature phase.

Acknowledgement The authors thank the Uruversity sion for support of ths research.

Grants Commis-

References

[ I] J A. Goedkoop and C H. hlacGdlavry,

Acta Cryst. IO (1957) 125. [I] C. Plgcnet, G. Lucazea~ and A. Novak, J. Chum. Phys. 73 (1976) 141. [3] V-1 hlusaev and Yu V. hlnyukh. Soviet Phys. Cryst. 15 (1970) 468.