Temperature-Dependent Phase Transition Studies And Influence Of Hydrogen Bonding Interactions On The Structural And Packing Modes Of Organic Molecules In Single Crystalline State

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dc.contributor.authorQuah, Ching Kheng
dc.date.accessioned2018-08-30T02:17:36Z
dc.date.available2018-08-30T02:17:36Z
dc.date.issued2011-04
dc.description.abstractIn this research, owing to the interests in phase transitions due to hydrogen bonds, fifteen samples with crystal structures and crystal networks that are utilizing the hydrogen bonding were prepared in single crystal form for X-ray structure determination. Temperature-dependent phase transitions studies by single crystal X-ray diffraction is the main experimental method used to study the hydrogen bonding interactions in this research. Fifteen crystal structures were determined and their crystal packing modes were also studied. Only two out of fifteen samples showed phase-transition which were explained macroscopically by Landau theory. The phase transition behaviour of three temperature polymorphs of hexamethylenetetraminium p-nitrobenzoate co-crystal has been investigated by single crystal X-ray diffraction experiment at three different temperatures using the same crystal. The co-crystal undergoes multiple phase transitions from monoclinic Cm to Cc (first transition) and Cc to Cc (second transition). These transitions are reversible. Both of the phase transitions are of first order, involving the discontinuity and doubling of the c- and a-, b- axes at critical temperatures (TC) 259.5 and 182.5 K, respectively. The p-nitrobenzoate anions are disordered except for the low temperature phase (100 K), displaying order-disorder phase transformation at transition temperature 182.5 K. The crystal structure analyses for data collected at 290 K show that there is only one intermolecular N—H···O hydrogen bond whereas there are three and fourteen unique intermolecular N—H···O and C—H···O hydrogen bonds at temperatures 195 and 100 K, respectively. The crystal of 2,4,4’-trimethoxybenzophenone undergoes a reversible temperature-dependent isomorphous phase transition from monoclinic P21 at temperature higher than the critical temperature (TC) 154.5 K to another monoclinic P21 at temperature lower than TC. The phase transition is of first order, involving the discontinuity and almost doubling of the c-axis at TC. The crystal structure analyses for data collected at 297 K show that there is one intermolecular C—H···O hydrogen bond whereas there are four intermolecular C—H···O hydrogen bonds at the temperature 100 K. The hydrogen bonding plays the pivotal role in these phase transitions as shown by the decrease of hydrogen bonding as the temperature is raised.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/6476
dc.language.isoenen_US
dc.publisherUniversiti Sains Malaysiaen_US
dc.subjectInfluence of hydrogen bonding interactions on the structuralen_US
dc.subjectpacking modes of organic molecules in single crystalline stateen_US
dc.titleTemperature-Dependent Phase Transition Studies And Influence Of Hydrogen Bonding Interactions On The Structural And Packing Modes Of Organic Molecules In Single Crystalline Stateen_US
dc.typeThesisen_US
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