Synthesis and comparative structural analysis of metal diphosphonates
Date of Award
Doctor of Philosophy (PhD)
Physical Sciences and Mathematics
The work presented herein describes the synthetic methodologies to prepare novel metal phosphonates as well as their structural studies. These compounds fall into the category of metal-organic frameworks, which is traditionally dominated by transition metals, leaving behind the earth abundant alkaline earth metals, which could lead to interesting applications. The main goal of this work is to find the synthetic pathway towards novel alkaline earth metal phosphonates by varying reaction conditions such as; pH, temperature, solvent, metal influence, and stoichiometry. In addition, by varying ligand geometry this work is geared in order to establish a relationship between the ligand topology and the overall geometry of the resulting metal-organic framework.
To systematically study the relationship between the ligand topology and the geometry of the resulting MOF, a series of ligands were selected; [1-2-phenylenebis(methylene)]bisphosphonic acid, [1,3-phenylenebis(methylene)]bisphosphonic acid, and [1,4-phenylenebis(methylene)]bisphosphonic acid. These ligands allow a systematic study of the structural effect of the ligand geometry, while maintaining chemical identity.
The first part of this thesis is dealing with the synthesis of novel magnesium, calcium, strontium, and barium phosphonate metal-organic frameworks. For alkaline earth metals synthetic challenges are manifested in the large diameters of the metals and the absence of energetically favorable d-orbitals which lead to weak metal-ligand bonds. This leads to a range of possible coordination patterns, and consequent difficulties in obtaining crystalline materials suitable for single crystal X-ray crystallography. In the last part of this thesis a novel iron (III) phosphonate was synthesized and analyzed structurally.
In expanding our knowledge of the phosphonate ligand in the metal-organic frameworks, we have discovered that the topology of the ligand not only dictates the dimensionality of the resulting compound, but also affects the coordination of the metal. For the [1,4-phenylenebis(methylene)]bisphosphonic acid ligand a three-dimensional framework was obtained, while the 1,3 and 1,2 substituted ligands yielded sheet like two-dimensional materials. The metal size plays a substantial role as well, with higher metal coordination numbers, often achieved by additional water coordination
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Lopez, Valerie, "Synthesis and comparative structural analysis of metal diphosphonates" (2019). Dissertations - ALL. 1007.