Date of Award

December 2014

Degree Type


Degree Name

Doctor of Philosophy (PhD)




Karin Ruhlandt-Senge

Subject Categories

Physical Sciences and Mathematics


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


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.


Open Access