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Ionic LiquidLiquid----SupportedSupported Schiff Bases and their Transition Metal Complexes: Synthesis, PhysicoPhysico----ChemicalChemical Characterization and Biological Activities A Thesis submitted to the UNIVERSITY OF NORTH BENGAL For the Award of DOCTOR OF PHILOSOPHY ininin CHEMISTRY ByByBy Mr. SANJOY SAHA M.Sc. in Chemistry Supervisor DR. BISWAJIT SINHA DEPARTMENT OF CHEMISTRY UNIVERSITY OF NORTH BENGAL OCTOBER-2018 Dedicated To My Beloved Parents Abstract Chapter I contains a brief overview on the ionic liquids (ILs), specially functionalized ionic liquids (FILs) along with the properties of the ionic liquids consisting of different cations and anions, their applications and the advantages of using ILs over conventional organic solvents. Chemistry of Schiff bases and their transition metal complexes as well as their applications in different fields were also briefly discussed. This chapter also contains a brief literature survey on related works as well as the object and application of the research works embodied in this dissertation. Chapter II briefly describes the spectroscopic and analytical techniques employed for the physico-chemical characterization of the synthesized compounds. This chapter also contains sources of the different chemicals used and describes the syntheses and physicochemical characterization of some amine functionalized ionic liquids required for the syntheses of various ionic liquid-supported Schiff bases used as ligands in subsequent chapters of this thesis. In chapter III Mn(II) and Co(II) complexes synthesized from the ionic liquid- supported Schiff base, 1-{2-(2-hydroxybenzylideneamino)ethyl}-3-methyl imidazolium bromide have been presented. Their structural characterization by various analytical and spectroscopic methods was described. Their antibacterial activities were tested by in vitro disc diffusion method against Escherichia coli and Bacillus subtilis to assess their minimum inhibition concentrations. Chapter IV describes syntheses of the ionic liquid supported Schiff base, 1-{2- [(2-hydroxybenzylidene)amino]ethyl}-3-methylimidazolium hexafluorophosphate and its Mn(II), Co(II) and Cu(II) complexes. Their physico-chemical characterizations by various spectroscopic (ESI-MS, 1H-NMR, 13 C-NMR, FT-IR and UV-Visible) and analytical (elemental analysis and magnetic susceptibility measurements) techniques were presented. Antibacterial activities against gram positive and negative bacteria by in vitro disc diffusion methods have been discussed. In chapter V, the syntheses of an air and moisture stable ionic liquid- supported Schiff base, 1-{2-(2-hydroxy-5-nitrobenzylideneamino)ethyl}-3- ethylimidazolium tetrafluoroborate and its Co(II), Ni(II) and Cu(II) complexes have been described. These compounds were characterized by different spectroscopic i (powder X-ray diffraction, ESI-MS, UV-Visible, FT-IR, 1 H-NMR and 13 C-NMR) methods and analytical (elemental analysis, molar conductance and magnetic susceptibility measurements) techniques. The antibacterial studies of the synthesized compounds were explored and the metal complexes exhibited significant activities against the selected gram negative bacteria ( Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris and Enterobacter aerogenes ) and gram positive bacteria (Staphylococcus aureus and Bacillus cereus ). In Chapter VI the syntheses of the Co(II), Ni(II) and Cu(II) complexes of the Schiff base, 1-{2-[(2-hydroxy-5-bromobenzylidene)amino]ethyl}-3-ethylimidazolium tetrafluoroborate have been described. These complexes were characterized by various analytical and spectroscopic methods. The antibacterial activities ( in vitro ) of the Schiff base and its complexes have been performed by disc diffusion method. The complexes showed reasonable antibacterial activities against the selected four gram negative bacteria ( E. coli, P. aeruginosa, P. vulgaris and E. aerogenes ) and two gram positive bacteria ( S. aureus and B. cereus ). Chapter VII describes the syntheses and physico-chemical characterization of the Schiff base, 1-{2-(2-hydroxy-5-bromobenzylideneamino)ethyl}-3- ethylimidazolium tetrafluoborate and its Fe(III) and Cr(III) complexes. Their physico- chemical characterization by various analytical and spectroscopic methods such as elemental analysis, UV-Visible, FT-IR, 1 H NMR, ESI MS, TGA/DTG, molar conductance and magnetic susceptibility measurements have been illustrated. Antibacterial activities of these compounds against Escherichia coli and Staphylococcus aureus were also perfomed. Chapter VIII describes the synthesis, physico-chemical characterization and potential biological applications of some transition metal complexes of the ionic liquid-supported Schiff base, 1-{2-(2-hydroxy-5-chloro-benzylideneamino)ethyl}-3- methylimidazolium tetrafluoroborate. The geometrical structures of the complexes were established by different spectroscopic and analytical data. Their potential biological applications against gram positive ( Staphylococcus aureus and Bacillus cereus ) and gram negative ( Escherichia coli and Klebsiella pneumoniae ) bacteria were explored and discussed accordingly. Finally in chapter IX the concluding remarks on the research works embodied in this thesis were made. ii PREFACE I started the research work presented in this thesis entitled “ Ionic Liquid-Supported Schiff Bases and their Transition Metal Complexes: Synthesis, Physico-Chemical Characterization and Biological Activities ” in 2011 under the supervision of Dr. Biswajit Sinha, Professor, Department of Chemistry, University of North Bengal, India with an aim to synthesize the imidazolium based ionic liquid-supported Schiff bases and their transition metal complexes, their physico-chemical characterization and exploration of their biological activities, specially antibacterial and antimicrobial activities against naturally available bacteria. It is well known that metal ions play vital roles in a number of biological processes. The metal ions with biologically active ligands are a subject of considerable interest; therefore much attention was paid due to their numerous applications as antitumor, antibacterial and antifungal agents. Schiff bases have been studied extensively over the years due to their selectivity and sensitivity towards various transition metal ions. They may act as polydentate ligands for the complexation with different transition metal ions like Mn(II), Co(II), Ni(II), Cu(II), Mn(III), Fe(III), Cr(III), etc . Of late ionic liquids have drawn much interest in the context of green synthesis and catalysis, etc . Their merit lies in the ease with which their properties can be tuned by varying either the anion or the cation or the substitutions on the cation. The study of ionic liquids that are air and moisture stable has become a subject of extensive scientific investigations well documented in the literature. Catalytic utilization of the transition metal complexes prepared by these tunable ligands is very promising. Suitable changes of the steric or electronic environment about the metal complexes can have a dramatic influence on their physico-chemical properties. The functionalized ionic liquids (FILs) are favorite as ligands for the recovery of metal catalysts used in a series of chemical transformations such as olefin metathesis, hydrogenation, hydroformylation, Negishi cross-coupling reaction, Heck reaction, Suzuki and Stille coupling reactions, etc . Therefore studies on the ionic liquid (imidazolium based)-supported Schiff bases and their transition metal complexes would be quite interesting from the point of view: their stability, geometry, biological activity and potential applications in many fields. iii Acknowledgement Words fall short to express my sincere gratitude and indebtedness to my supervisor, Dr. Biswajit Sinha, Professor, Department of Chemistry, University of North Bengal for his untiring guidance and valuable suggestions during the course of research work. His support and valuable suggestions were truly incomparable, encouraging and motivational. I am profoundly obliged to Prof. P. Ghosh, HEAD, Department of Chemistry, N.B.U and Prof. M. N. Roy, Coordinator, SAP-DRS-III, N.B.U for their constant touch, constructive criticism and valuable advices during the period of my research work. I also wish to express my deep sense of gratitude to the other faculty members of the Department of Chemistry, N.B.U for their cordial support. I am also thankful to all the non-teaching staff of this department for their helps. I sincerely thank my lab mates Dr. Dhiraj Brahmin, Dr. Abhijit Sarkar, Dr. Rajendra Pradhan, Mr. Bijan Kumar Pandit, Mr. Amarjit Kamath, Mr. Koushik Acharjee, Mr. Dipu Kumar Mishra, Mrs. Annaya Das and Mr. Uttam Kumar Singha for their helping hands during different stages of my research work in spite of their busy academic schedule and involvements. I am highly grateful to my colleagues especially Dr. R.P. Dhakal, Principal, Kalimpong College, Kalimpong for helping me in some or the other way. Special thanks are due to Dr. Malay Bhattachariya, Department of Tea Science, N.B.U & Sri. Goutam Basak, Raiganj University for their help and cordial cooperation. I also acknowledge the services of USIC (NBU), SAIF-NEHU (SHILONG), CDRI, (Lucknow), IIT (Chennai) in accomplishing various analytical and spectroscopic analyses. I am highly obliged to the Departmental Special Assistance Scheme under the University Grants Commission, New Delhi, India (SAP-DRS-III, NO.540/12/DRS/2013) for providing financial and instrumental assistance.

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