Synthesis, Structure, Magnetic, Luminescent and Photocatalytic Studies on Metal-Organic Framework (MOF) Compounds

Abstract

The research in the area of metal-organic frameworks (MOFs) continues to be interesting for their unique structures and tunable properties. In this thesis, the various aspects of metal-organic frameworks (MOFs) compounds are presented. As part of this study, preparation of MOFs of transition metals (Mn, Co, Ni, Zn), rare-earth metals (Y, La, Pr, Nd, Gd, Dy) and mixed metals (3d-4f) using aromatic carboxylates as linker ligands were accomplished. Structures of the synthesized compounds have been determined by single crystal X-ray diffraction technique. Magnetic properties of the transition metal based compounds have been studied by SQUID magnetometer and the magnetic behaviors have been correlated with their structures using suitable theoretical model. Photocatalytic properties on transition metal and mixed metal compounds have been investigated. Ligand-sensitized metal-center emission has been studied on the Eu3+ and Tb3+ doped MOF compounds of La and Y. Up-conversion luminescence properties of Nd based compounds have also been studied. To gain an insight into the possible mechanism of the formation of MOF compounds, a detailed study of the role of temperature and time during the synthesis has been undertaken. In addition, the transformations of low-dimensional structures to structures of higher dimensionality was also studied, both in the solid state as well as in the solution mediated processes. In Chapter 1 of the thesis an overview of framework compounds is presented. In Chapter 2, the synthesis, structure and magnetic properties of benzene tricaboxylate and 4,4’-oxybis(benzoate) compounds of 3d metals are presented. Some of these compounds show unusual structure and interesting magnetic properties. For example, three-dimensional MOF with -Mn-O-Mn- Kagome layer exhibits canted antiferromagntic behavior. Three-dimensional MOF based on body centered arrangement of Co4 clusters shows two-dimensional ferromagnetic behavior. In Chapter 3, the role of temperature and time of reaction in the formation of MOF compounds and the transformation studies are presented. These studies give a clue regarding the mechanism for the synthesis of MOF compound. In chapter 4, synthesis, structure and luminescent properties of rare-earth and 3d-4f mixed metal compounds are presented. The thermal decomposition of Gd-Co-pyridine carboxylate indicates the formation of nano-sized perovskite oxide at temperature ~ 700 °C. In chapter 5, the photocatalytic behavior for the decomposition of organic dyes using MOF compounds are presented.