STUDY OF HYDROGEN BONDINGS IN PHENOL-AMINE ADDUCTS

Presenter	:	MOHD. MUSTAQIM ROSLI
E-mail	:	-
Date	:	14 / 5 / 2008
Time	:	3.00 PM
Venue	:	BILIK PERSIDANGAN SEMENTARA (CEMACS), ARAS 1, PUSAT PENGAJIAN SAINS FIZIK
Sypnosis	:	Five samples have been prepared to study the phase transition caused by hydrogen bonds in phenol-amine adducts. Those samples are (I) 2-Methylquinolinium 2,4-dinitrobenzoate, (II) the 1:1 adduct of 3,5-dinitrobenzoic acid and quinoline, (III) Hexamethylenetetraminium 2,4-dinitrobenzoate monohydrate, (IV) 4-Aza-1-azoniabicyclo[2.2.2]octane 2,4-dinitrobenzoate and (V) Hexamethylenetetraminium 3,5-dinitrobenzoate hemihydrate. Single crystal X-ray crystallography method has been used to determine whether there are any changes in lattice parameters at room temperature and 100K. A number of hydrogen bonds were observed in all the samples. However only sample (V) showed a phase transition phenomena in which different lattice parameter values were observed at room temperature and 100K (doubling the c-axis value). For sample (V), temperature dependence studies were done to find the critical temperature Tc. From the result, we know that this is a first order phase transition where the changes of the unit cell parameters occur discontinuously at the transition temperature Tc = 129K. This first order case is also explained macroscopically using Landau phenomenological theory. An alternative method of calculating the thermodynamic properties of a system with the second-order phase transition caused by interaction of hydrogen bonds and phonon of the crystal was also done in this study. This was carried out by separating out the pseudo-spin variables completely and using only pseudo-spin variables when calculating the free energy. The results agree with the previous published results.

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