A comparative study of the extraction, transport and coordination chemistry of novel monotopic and ditopic salen-type ligands

Hensberg, Joshua Craig (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: This dissertation reports the synthesis and full characterisation of a series of novel monotopic and ditopic Schiff base salen-type ligands. The monotopic and ditopic ligands were assessed in competitive extraction and competitive bulk liquid membrane transport experiments for the recovery of the metal ions; Cu(II), Ni(II), Co(II), Zn(II), Cd(II) and Pb(II). Additionally, the ditopic ligands were assessed in competitive extraction and competitive bulk liquid membrane transport experiments involving anions; Cl-, NO3- and SO42-. Monotopic ligands, L1-L6, were designed with varying structural modifications focused on affecting the disposition of the donor atoms in these ligands. This was accomplished by reacting two equivalents of 5-tert-butyl-2-hydroxybenzaldehyde with one equivalent of different diamines. L1-L6 were successfully synthesised and fully characterised using 1H and 13C NMR spectroscopy, FT-IR (ATR) spectroscopy, melting point determination, mass spectrometry, micro-elemental analysis as well as SCD analysis (in all cases except L5). Single crystals of two complexes were attained, Ni[L4-2H] and Cu[L6-2H], respectively. The solid-state structures of the free ligand and corresponding metal complex were compared and it was observed that ensuing conformational changes are evident upon coordination to the metal ion. Ditopic ligands L7-L10 were designed with varying structural modifications to the diamine group and to the incorporated dialkylamino methyl pendant arms. They were synthesised by way of a four-step convergent synthesis and fully characterised using a range of analytical techniques including FT-IR (ATR) spectroscopy, 1H and 13C NMR spectroscopy, mass spectrometry, melting point determination (in the cases of L7 and L9) and elemental analysis. In the competitive metal ion extraction experiments, all ligands displayed an exceptional selectivity towards Cu(II) over the other metal ions. There was a slight increase in the uptake of Cu(II) by the ditopic ligands in comparison to the corresponding monotopic ligands and was justified by the incorporation of the dialkylaminomethyl groups which promoted their solubility in the organic phase. In the competitive bulk liquid membrane transport studies, all ligands continued their preference for Cu(II) ions. The cation flux rates (molh-1) for Cu(II) under the experimental conditions employed, was low despite being transported effectively into the organic membrane phase. This suggested a high formation constant for Cu(II). Ditopic ligands showed a surprising potential for the transport of Zn(II) under the experimental conditions employed. The ditopic ligands presented herein show potential to effectively separate Cu(II) ions from Zn(II) ions. Lastly, “copper-only” complexes of ditopic ligands L7-L10 were subjected to competitive anion extraction and bulk liquid membrane transport tests with the anions Cl-, NO3- and SO4-. In both tests, the ligands showed selectivity in the increasing order: SO42- < Cl- < NO3-, indicating the prevalence of the Hoffmeister bias.

AFRIKAANSE OPSOMMING: Hierdie werkstuk handel oor die sintese en volle karakterisering van ‘n reeks nuwe monotopiese en ditopiese Schiff basis salen-tipe ligande. Die monotopiese en ditopiese ligande was geevalueer in mededingende ontginning en mededingende vloeistof membraan vervoer eksperimente vir die isolering van metaalione; Cu(II), Ni(II), Zn(II), Co(II), Cd(II) en Pb(II). Die ditopiese ligande was ook geevalueer in mededingende ontginning en mededingende vloeistof membraan vervoer experimente van verskeie anione; Cl-, NO3- en SO42-. Tydens die ontwerp van die monotopiese ligande L1-L6, word daar ondersoek ingestel oor hoe die skenker atome beinvloed word deur spesifieke strukturele eienskappe. Dit word bewerkstellig deur verskillende diamine groepe te inkorporeer met 5-tersiêre-butyl-2-hydroxybenzaldehyde in ‘n 1:2 mol verhouding. L1-L6 is suksesvol gesintetiseer en ten volle gekarakteriseer met behulp van 1H en 13C-KMR-spektroskopie, FT-IR (ATR) spektroskopie, smeltpunt bepaling, massaspektrometrie, elementele analise asook SCD analise (in alle gevalle behalwe L5). Enkelkristalle van twee komplekse was geisoleer, Ni[L4-2H] en Cu[L6-2H], onderskeidelik. Die vaste-toestand strukture van die vrye ligand en ooreenstemmende metaal komplekse dui aan dat ‘n konformasie verandering wel plaasvind tydens koördinasie vam die metaalioon aan die onderskeilike ligand. Die variasie van die oorbrugende diamine groepe geinkorporeer by die monotopiese ligande was weereens gebruik vir die ditopiese ligande L7-L10, asook die ïnkorporeering van dialkielamino metiel arms. Die ligande is gesintetiseer deur middel van 'n vier-stap konvergente sintese en ten volle gekarakteriseer deur 'n verskeidenheid analitiese tegnieke, insluitende FT-IR (ATR) spektroskopie, 1H en 13C-KMR-spektroskopie, massaspektrometrie, smeltpunt bepaling (in die geval van L7 en L9) en elementele analise. Na aanleiding van die mededingende metaalioon onttrekking eksperimente, was dit duidelik dat beide reekse ligande 'n uitsonderlike selektiwiteit vir Cu(II) vertoon teenoor die ander metaalione. Daar was 'n effense toename in die opname van Cu(II) vir die ditopiese ligande in vergelyking met die ooreenstemmende monotopiese ligande. Hierdie was geregverdig deur die ïnkorporeering van die dialkielamino metiel groepe wat die oplosbaarheid van die ligande/komplekse in die organiese fase bevorder. Tydens die mededingende vloeistof membraan vervoer studies het beide reekse ligande weereens ‘n voorkeur vir Cu(II) ione getoon. Die katioon vloed tempo (molh-1) vir Cu(II) onder die eksperimentele toestande was laag ten spyte van die effektiewe vervoer na die organiese membraan fase. Dit voorspel dat die ligande 'n hoë vorming konstante vir Cu(II) toon. Verbasend genoeg toon die ditopiese ligande potensiaal om Zn(II) ook te vervoer onder die eksperimentele toestande. Dus, die ditopiese ligande bied potensiaal om Cu(II) ione van Zn(II) ione selektief te skei. Laastens, slegs die Cu(II) komplekse van ditopiese ligande L7-L10 was ondersoek vir die mededingende ontginning en mededingende vloeistof membraan vervoer toetse met die anione Cl-, NO3- en SO42-. In beide toetse het die ligande selektiwiteit vir die anione in die toenemende volgorde van SO42- < Cl < NO3- getoon wat aandui die Hoffmeister bias word volhou.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101384
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