A new type of structural phase transition has been discovered recently in a class of hydrogen-bonded organic crystals

Chantrapromma, Asistant Professor Suchada

Fun, H.K.

How, P.T.

English

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fbil, frtn ,ttaat1 kun. f ' ? S ft ,;LvTHE NrNrH ASrA pAcrFrc pHysrcs coNFERENCES (eth Appc) )7311,y*:::"am- october 2s-s1, n04.FERROELASTIC PIIASE TRANSITION IN SOME PHENOLS-AMINES ADDUCTS.. DGERIMENTAL AND THEORETICAL FINDINGSH.-IC Fun t, B.-S. Lee 1, S. Chantrapromma', p.-T. How II School of Physics, Universiti Sains Malaysia11800 USM, Penang, Malaysia2 Deparfrnent of Chemistry, Faculty of Science, Prince of Songkla University,Hat-Yai, Songkla 90112, ThailandABSTRACTA new type of structural phase transition has been discovered recently in a class ofhydrogen-bonded organic crystals. The transition is ferroelastic, second order in nature, andassociated with the spontaneous breaking of a mirror symmetry in the crystal below thetransition temperature. The hansition has been analysed by a phenomenological expansion ofLandau free energy. We propose that the transition is induced by cooperative hydrogen bondinteractions indirectly coupled through the lattice phonons. A microscopic model isformulated according to this concept.INTRODUCTIONCrystalline solids containing phenols-amines adducts are widely used to studyhydrogen bonds. Phenols-amines adducts are produced by the interaction of phenols,compound having at least one hydroxyl group, and amines, compounds having at least oneamino group. The phenols and amines in the solid state are generally linked by intermolecularO-H...O, O-H...N or N-H...O types of hydrogen bonds which are among the most robust andversatile synthons in crystal engineering. Studies on the hydrogen bondings in these phenols-amines adducts can be used as models for the more complicated systems in biologicalsystems in which hydrogen bondings play a crucial and important role. Owing to our interestsin hydrogen bondings in such systems, we have investigated systematically in single crystalforms a class of phenols-amines adducts and their crystal structures were reportedt-u. Some ofthese single crystals of phenols-amines adducts undergo a reversible phase transition withvariation in temperature. For these samples, a hydrogen atom is transfened from the phenols(which then becomes as anion) to the amines (which then becomes a cation). Hydrogen bondsare then established between the donor/amines/cation and the acceptor/phenols/anion.Interestingly, these crystals undergo a temperature-dependent structural phase transition,which is second--order ferroelastic in its nature. These are the first reported cases of structuralphase transition induced by hydrogen bonding interactions.RESULTS AND DISCUSSIONThe phase transition that has been observed are classified into two categories (1)orthorhombic-to-monoclinic transition, and (2) monoclinic-to-triclinic fiansition. In boththese categories, the phase transitions are a result of the breaking of a mirror-plane symmetrywhen the temperature is lowered through the critical temperature, T" ; the lower symmetricX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia,11800 USM, Penang, Malaysia.Correspondence email : hkfu n@usm.my or hkfun@streamyx. comTHE NINTH ASrA PACIFIC PHYSICS CONFERENCES (9.h AppC)Hanoi, Vietnam - October 25-31. 2004phase being the low-temperature phase. The three crystal structures found to exhibit thesephase transitions are quinuclidiniam-2,4-dinitrophenolate (I), hexamethylenetetraminium-3,5-dinitrobenzoate-3,5-dinitobenzoic acid monohydrate(Il), and hexamethylenetetraminium2,4-dinitrophenolate monohydrate (III). Experimentally we have solved the 3-D structures ofboth the high and low temperature polymorphs of (I), (II), and (IIf, and have also measuredthe temperature dependence of these unit cell parameters through their transitiontemperaturesl '6 '7 'e.On the theoretical side, phenomenological expressions of Landau free energies havebeen formulated based on the assumption that these transitions are second order ferroelasticin nature. The temperature dependence of unit cell parameters predicted is consistent withexperimental findings and functional forms of temperature dependence of shear modulus andspecific heat of the bulk crystals were also derived'. Landau's theory, being macroscopic andphenomenological, however, cannot indicate the microscopic origin of these phasetransitions. We have formulated in parallel a microscopic theory, in which the proposed mainmechanism responsible for the phase transitions is the cooperative interactions of hydrogenbonds with the lattice vibrations, or phonons, of the crystalru. This findings of Landau andmicroscopic theories based on the experimental data were presented in this conference.ACKNOWLEDGEMENTThe authors thank the Malaysian government and Universiti Sains Malaysia for thefundamental research grant, No. 304lPFlZlW670011. SC thanks Prince of SongklaUniversity, Thailand for financial support.REFERENCESl. A. Usman, S. Chantrapromma, and H.-K. Fun, Acta Crstallogr. Sect. C 57, 1443 (2001).2. A. Usman, S. Chantrapromma, H.-K. Fun, B.-L. Poh, and C. Karulai,Acta CrstallogI.Sect. C 58,46 (2002).3. A. Usman, S. Chantrapromma, H.-K. Fun, B.-L. Poh, and C. Karalai, Acta Crstallogr.Sect. C 58, 136 (2002).4. S. Chanhapromma, A. Usman, H.-K. Fun, B.-L. Poh, and C. Karulai,Acta Crstallog.Sect. E58,102 (2002).5. S. Chantrapromma, A. Usman, H.-K. Fun, B.-L. Poh, and C. Karalai, Acta Crstallogr.Sect. E 58, 108 (2002).6. H.-K. Fun, S. Chantrapromma, and A. Usman, The Cambridge Crystallography DataCenter(2002), deposition numbers CCDC 177747 and 177748.7. H.-K. Fun, S. Chantrapromma,and A. Usman, The Cambridge Crystallography DataCenter(2002), deposition nurnbers CCDC 210835 and 210836.8. S. Chantrapromma, A.IJsman, H.-K. Fun, B. L. Poh, and C. Karalai, J. Mol. Struct. 688(2004).9. H.-K. Fun, A. Usman, S. Chanhapromma, J. Osman, L.-H. Ong, D. R. Tilley, andY. Ishibashi, Solid State Commun.127,677 (2003)10. P. T. How, B. S. Lee, H.-K. Fun, I.A. Razak and S. Chantrapromrna, (2004), submittedfor publication in Physical Review B (under review).

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Ferroelastic Phase Transition In Some Phenols-Amines  Adducts – Experimental And Theoretical Findings.

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Ferroelastic Phase Transition In Some Phenols-Amines Adducts – Experimental And Theoretical Findings.

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