Department of Chemistry

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Browsing Department of Chemistry by Author "Batisai, E."

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    The design and synthesis of mixed ligand metal organic frameworks for xylene inclusion
    (2022-11-10) Dlamini, Nonhlahla Fortunate; Batisai, E.; Barbour, L. J.
    Host-guest chemistry, also known as inclusion chemistry, is an important subfield of supramolecular chemistry where there is great current interest owing to its great promise in the areas of separation of small molecules, sensors, and chiral separation. The term ‘inclusion compounds’ refers to the association between large compounds (host) that is able to enclose a smaller molecule (guest). This association utilizes non-covalent interactions, and the supramolecular entity is known as a “host-guest complex” or supermolecule. The aim of the study is to design and synthesize mixed ligands metal organic frameworks (MOFs) for xylene inclusion. The first part of the study involves the synthesis and characterisation of five pyridine N-donor and O-donor ligands, namely: 2,7-di(pyridin-4-yl)benzo[lmn][3,8]phenthroline-1,3,6,8(2H,7H)tetraone(Lig1), 2,7-bis(pyridin-3-ylmethyl)benzo[lmn][3,8]phenthroline-1,3,6,8(2H,7H)tetraone(Lig2), 2-(pyridin-4-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Lig3), 2-(pyridin-4-ylmethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Lig4) and N,N'-bis(glycinyl)pyromellitic diimide (Lig5). The second part involves the synthesis and characterization of MOFs. The MOFs will be synthesized by reacting the pyridine N-donor ligands, carboxylate O-donor co-ligands (fumaric acid; 2.2-bipyridine; 2.2-bipyridine-4.4’-dicarboxylic acid, 4.4’-oxybis(benzoic acid) and 2.6-naphthalenedicarboxylic acid) and transition metal salts in DMF under solvothermal conditions. The synthesized MOFs were characterized using thermogravimetric analysis (TGA), single crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD). Xylene inclusion experiments were performed on the MOFs and the resulting inclusion compounds were characterized using TGA, SCXRD and PXRD.
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    Separation of Isomers Using Host-Guest Methods
    (2026-05-19) Rambevha, Lesedi; Batisai, E.
    Selective separation of positional isomers remains difficult due to their nearly identical physical and chemical properties. This study synthesized a new host molecule, 2-(1, 3- dioxo- 1 H- benzo [de] isoquinolin- 2 (3 H)-yl) acetic acid (H) and tested its ability to discriminate picoline isomers (2-, 3-, and 4-) and lutidine isomers (2,2-, 2,4-, 2,2-, 2,6-, and 3,5-). The approach involved crystallizing the host in the individual isomers and evaluating its potential as a supramolecular host for isomer separation. Single crystal X-ray diffraction (SCXRD) confirmed the formation of discrete 1:1 host–guest complexes with all isomers and revealed that the host-guest complexes primarily rely on a strong, directional hydrogen bond between the host's carboxylic acid group and the pyridyl nitrogen of the guest. The host and the guest further interact via C–H ··· O interactions. Hirshfeld surface analysis revealed that O ··· H/H ··· O and H ··· H contacts dominate intermolecular interactions, emphasizing the cooperative role of hydrogen bonds and van der Waals forces in stabilizing the complexes. Differential Scanning Calorimetry (DSC) analysis revealed unique thermal behaviors for each inclusion complex: H·2PIC releases the guest between 124 °C and 178 °C, H·3PIC at 129 °C and 186 °C, and H·4PIC between 170 °C and 198 °C. Thermogravimetric analysis (TGA) confirmed lutidine guest inclusion by showing distinct mass-loss steps: 3,5LUT is released from 137 to 191 °C, 2,6LUT from 117 to 146 °C, and 2,4LUT from 138 to 216 °C. The host framework remained stable up to around 351 °C, indicating structural stability after guest removal. Competition experiments were conducted by exposing the host to binary mixtures of picoline and lutidine isomers of varying ratios, and the results were analyzed using GC–MS and GC–FID. The selectivity coefficient (K) was calculated to determine the host's selectivity towards different mixtures of the guest. For picoline isomers, selectivity followed the order 4PIC > 3PIC > 2PIC, with the highest selectivity coefficient observed in the 3PIC: 2PIC mixture at an equimolar ratio of 1:1 (K = 14.43), surpassing the value of 10 typically associated with strong, practically useful selectivity. For lutidine isomers, the order was 3,5LUT > 2,4LUT > 2,6LUT. The most effective discrimination was observed in the 3,5LUT: 2,6LUT pair, with a K value of 39.82 at an equimolar ratio. This indicates a highly efficient molecular recognition process and potential for crystallization-based separation.