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Supramolecular chemistry of a series of organic zwitterions

Lombard, Jean (2017-12)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The aim of the work presented in this thesis was to investigate the various solid-state forms that can be adopted by a series of organic zwitterionic molecules, formed from reaction of acetylenedicarboxylic acid with pyridine derivatives. By carrying out a thorough and systematic study we were able to determine the usefulness of these molecules as supramolecular building blocks. The following zwitterions have been investigated: .(Z)-3-carboxy-2-(4-cyanopyridin-1-ium-1-yl)-acrylate .(Z)-1-(3-carboxy-1,1-dihydroxyprop-2-en-1-ide-2-yl)-pyridin-1-ium .(Z)-2-(3-carbamoylpyridin-1-ium-1-yl)-3-carboxyacrylate .(Z)-3-carboxy-2-(4-carboxypyridin-1-ium-1-yl)acrylate The first two zwitterions are formed from the reaction of acetylenedicarboxylic acid with 4-cyanopyridine and pyridine, respectively. Two conformational polymorphs of the first were identified: a kinetic and thermodynamic form. Three polymorphs of the second zwitterion were identified, their formation depending purely on the solvent choice. In each case the relationship between the polymorphs has been extensively studied – no interconversion between polymorphs is observed, which is unusual and rarely reported. The reaction between acetylenedicarboxylic acid and nicotinamide or isonicotinamide produces two new zwitterionic molecules (the third and fourth zwitterions in the list above), as well as a salt by-product. These zwitterions, as well as the 4-cyanopyridine zwitterion, were subsequently combined with various small organic co-formers in an attempt to form multi-component crystals. The structures of three new hydrated zwitterion-melamine salts have been identified, as well as the existence of six other salts which were identified based on NMR and IR data – all of which dissolve more easily compared to the zwitterions themselves. Considering the number of co-formers used, the discovery of so few salts is unusual – a search of the Cambridge Structural Database indicates that this may be due to a high propensity of charge-assisted hydrogen bonds that hold the zwitterions together to form homomeric molecular crystals. In addition, the structure-property relationships of a series of isostructural solvates have been investigated in order to gain further insight into the solid-state behaviour of organic molecules. The host framework, consisting of 1,10-phenanthrolinium and pamoate ions, is shown to selectivity include DMA and DMSO above DMF. This selectivity has additionally been demonstrated mechanochemically, which has not been reported before. Overall, the compounds investigated all show very interesting behaviour. Insight gained with respect to crystal packing, hydrogen- and charge-assisted hydrogen bonding, molecular shape, the inclusion of solvent into structures, the effect of temperature and solubility on crystallisation, and the usefulness of mechanochemistry, are discussed.

AFRIKAANSE OPSOMMING: Die doel van die werk uiteengesit in hierdie tesis was om die verskeie vastestof vorms, wat 'n reeks organiese zwitterioniese molekules kan aanneem, te ondersoek. Hierdie zwitterione word gevorm deur die reaksie van asetileendikarboksielsuur (ADC) met verskeie piridien-afgeleides. Dit was moontlik om die bruikbaarheid van hierdie molekules as supramolekulêre "boustene" te bepaal deur 'n deeglike en sistematiese studie uit te voer. Die volgende zwitterione is ondersoek: .(Z)-3-karboksie-2-(4-sianopiridien-1-ium-1-iel)-krilaat .(Z)-1-(3-karboksie-1,1-dihidroksieprop-2-en-1-ied-2-yl)-piridien-1-ium .(Z)-2-(3-karbamoielpiridien-1-ium-1-yl)-3-karboksiakrilaat .(Z)-3-karboksie-2-(4-karboksiepiridien-1-ium-1-yl)akrilaat Die eerste twee zwitterione word gevorm deur die reaksie van ADC met onderskeidelik 4-sianopiridien, en piridien. Twee konformasionele polimorfs van die eersgenoemde zwitterioon is geïdentifiseer: 'n kinetiese en termodinamiese vorm. Drie polimorfs van die tweede zwitterioon is geïdentifiseer, met die vorming van elk slegs afhanklik van die keuse van oplosmiddel. In elke geval is die verhouding tussen die verskillende vorms breedvoerig bestudeer – geen omskakeling tussen polimorfs is waargeneem nie, wat buitengewoon is. Die reaksie tussen ADC en nikotienamied of isonikotienamied produseer twee nuwe zwitterioniese molekules (die derde en vierde zwitterione in die lys hierbo), sowel as 'n sout neweproduk. Hierdie molekules, sowel as die 4-sianopiridien zwitterioon, is daarna gekombineer met verskeie klein organiese molekules (ko-vormers) in ʼn poging om multi-komponent kristalle te vorm. Drie nuwe gehidreerde zwitterioon-melamien soute is geïdentifiseer, sowel as 'n verdere ses potensiële soute – waarvan almal makliker oplos as die zwitterione self. In vergelyking met die groot aantal ko-vormers wat gebruik is, is die ontdekking van so min soute merkwaardig – 'n ondersoek van die 'Cambridge Structural Database' dui aan dat dit moontlik te doen het met die hoë geneigdheid van die lading-versterkte waterstofbindings wat die zwitterione verbind om molekulêre kristalle te vorm. Bykomend tot hierdie is die struktuur-eienskap verhouding van 'n reeks isostrukturele solvate ook ondersoek om verdere insig te kry oor die gedrag van organiese molekules in die vaste stof vorm. Die gasheer raamwerk, wat bestaan uit 1,10-phenanthrolinium en pamoaat ione, neem DMA en DMSO selektief bo DMF op. Hierdie selektiwiteit word boonop getoon selfs wanneer die eksperimente meganies uitgevoer word – iets wat nog nooit voorheen gerapporteer is nie. Oor die algemeen toon die bestudeerde molekules baie interessante gedrag. Insig is verkry (en bespreek) oor die rangskikking van organiese molekules in kristalle, waterstofbindings en lading-versterkte waterstofbindings, molekulêre vorm, die insluiting van oplosmiddels binne strukture, die effek van temperatuur en oplosbaarheid op kristallisasie, en die bruikbaarheid van meganiese chemie.

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