Investigations Of Open–framework Structures Based On Main Group, Transition Metal And Actinide Elements

Abstract

Open–framework inorganic materials are an important class of compounds because of their many applications in the areas of ion–exchange, separation and catalysis. Ever since the discovery of microporous aluminophosphates by Flanigen and co–workers in the early 80’s, the field of open–framework compounds has witnessed explosive growth. It is now established that the open–framework compounds comprise of almost all the elements of the periodic table. In addition, it has been shown that the inorganic anions in the open–framework compounds can be partially substituted by rigid organic linkers such as the oxalate. The resulting inorganic–organic hybrid structures are interesting due to the variable nature of the binding properties of the organic and inorganic moieties. The present thesis consists of systematic studies on the formation of amine–templated inorganic open–framework structures and inorganic–organic hybrid compounds based on the main group, transition metal and actinide elements. In Chapter 1 of the thesis an overview of inorganic open-framework materials is presented, with an emphasis on the elements that have been employed in the present study. Chapter 2 has two parts (Parts A and B) describing the synthesis and structure of open-framework tin(II) containing compounds. In Part A, the syntheses and structures of amine–templated tin(II) phosphates are presented, and in Part B, the syntheses and structures of a family of tin(II) oxalate compounds are discussed. Weak intermolecular forces such as hydrogen-bond interactions, π•••π interactions, and lone-pair–π interactions have been observed in these compounds, and appear to lend structural stability. As part of this study, efforts have been made to evaluate the energies associated with the π•••π interactions and the lone-pair–π interactions using suitable theoretical models. In Chapter 3, a new family of organically templated hybrid materials based on indium, synthesized by partially substituting the inorganic anion (phosphite/phosphate/suphate) by the oxalate group, is presented. These compounds exhibit a wide range of structures in which the oxalates play a variety of roles. The observation of the first zero-dimensional molecular hybrid structure and the isolation of concomitant polymorphic compounds is noteworthy. The molecular hybrid structure is reactive and undergoes transformation reactions under both acidic and basic conditions. In Chapter 4, the synthesis and structural studies of five new open–framework phosphate and phosphite compounds of gallium are presented. All the compounds have three-dimensional structures, and the formation of a gallium phosphate based on only one type of building unit (spiro–5) is noteworthy. While a large number of organically templated transition metal phosphates have been synthesized, studies on transition metal phosphites are not many. In Chapter 5, the synthesis, structure and magnetic properties of a family of transition metal (cobalt, vanadium, manganese) phosphite structures templated by the organic amines are presented. A previously known vanadyl phosphite has also been isolated and investigated by temperature dependent ESR and magnetic susceptibility studies. All the transition metal compounds exhibit antiferromagnetic behavior. In Chapter 6, the synthesis, structure, and transformation reactions in amine-templated actinide phosphonoacetates are presented. The compounds, which are based on uranium and thorium, are built up from the connectivity between the metal polyhedra and the phosphonoacetate/oxalate units, forming two– and three–dimensional structures. It has been shown that the two–dimensional uranyl phosphonoacetate–oxalate compound can be prepared by two different synthetic approaches: (i) solvent–free solid state reaction at 150˚C and (ii) room temperature mechanochemical (grinding) route. The formation of oxalate hybrids using the phosphonocarboxylate ligand is a new approach in the synthesis of multi-component hybrid compounds.