Coordination polymers of the alkaline earth metals for applications in synthesis and gas storage

The work presented in this thesis outlines our efforts to synthesize alkaline earth metal coordination complexes that could potentially serve as gas storage and synthetic precursor materials. The properties of these complexes are heavily influenced by factors such as the propensity to aggregate and the absence of energetically available d-orbitals which provide directionality. These often pose a challenge in obtaining suitable, stable compounds. Some challenges in the crystallization of alkaline earth coordination complexes involve the precipitation of insoluble aggregates. Thus, a great part of the work focused on studying suitable reaction conditions towards the formation of X-ray quality crystals for structural elucidation. Slow concentration and hydro/solvothermal techniques, among others, were prime crystallization methods in this work. The bulk of this thesis is divided in two parts. The first part details our attempts to synthesize metal organic frameworks (MOFs) of Mg, Ca, Sr and Ba. Our ligands of choice were the p, m, o-pyridinecarboxylic acids which provide two different binding sites. These consist of an N-donor and an anionic carboxylic acid, the N-donor located at different positions in the pyridyl ring depending on the isomer. These are also of low cost and soluble in different organic solvents. The use of pyridinecarboxylic acids resulted in the systematic isolation of five magnesium coordination complexes, three of which exhibit open-framework character and remain stable after removal of guests, and two of which are hydrogen bonded networks. Further, systematic work with the heavier metals resulted in three fully 3-dimensional complexes based on Ca, Sr and Ba and one hydrogen-bonded Ca complex. A pattern is observed when using the linear p or angular m-pyridinecarboxylic acid in the presence of MeOH/DMF mixtures, in which 3-dimensional motifs with open-framework (p) and dense (m) character (Mg, Ca and Sr) are displayed. The dimensionality decreases in the presence of water or strongly coordinating donors, leading to the formation of hydrogen bound or 2-dimensional complexes. The second part of this thesis involves the isolation of crown stabilized alkaline earth tosylates. The work resulted in the isolation of four new crown stabilized alkaline earth tosylates. Trends observed include an increase in coordination number as the size of the metal increases. Variation of crown:metal stoichiometry was also studied and resulted in two different calcium species displaying fully separated (1:1) and contact separated (1:2) ion association modes. For Sr and Ba, (1:1) stoichiometries resulted in hydrogen bound contact species. This thesis provides a selection of alkaline earth metal coordination complexes. The preparation of these complexes has led to the elucidation of their synthetic routes. Full characterization of the complexes is also provided