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Dissertation
Linker design for f-Element hybrid materials chemistry
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
DOI: 10.25820/etd.008451
Abstract
Coordination polymers (CPs) and metal-organic frameworks (MOFs) are diverse classes of hybrid materials with tunable structures and properties. Compared to transition metal-based systems, rare earth element (REE) and uranyl-based CPs and MOFs remain underexplored yet represent an intriguing class of materials owing to the unique properties associated with f-electrons. Delineating parameters for the rational design of REE and uranyl CPs and MOFs remains challenging, particularly in controlling and predicting metal-ion assembly and material dimensionality, and reticular chemistry design principles have not been realized in f-element systems.The research presented herein aimed to fill knowledge gaps within the f-element hybrid material literature and involved the synthesis and characterization a series of REE and uranyl CPs using a family of pyridinone-based dicarboxylate (PODC) ligands to realize the role of linker engineering in controlling the structural assembly and properties of the resulting networks. Organic linkers play a decisive role in the synthesis of CP materials, serving as tunable components and often requiring tailoring to enable the formation of unique structures with desired properties. PODC linkers feature both oxygen and nitrogen donor atoms have not been previously used in inorganic hybrid materials. The multiple donor sites on these ligands provides opportunities for diverse coordination and chelation modes, making PODC linkers promising candidates for constructing robust CP frameworks, and in addition, they can promote secondary intermolecular interactions that are important in the crystal engineering of CPs and MOFs. Four structurally related PODC organic linkers were employed to systematically evaluate how the arrangement of donor atoms influences CP network structure and properties. PODC linkers were synthesized in-house, and optimized synthetic pathways were developed to obtain the ligands in high purity and yield. Complete characterization, including 1H and 13C NMR spectroscopy, mass spectrometry, and single-crystal X-ray crystallography (when suitable crystals were obtained), was performed. In chapters 3-5, three isomers (2,5-, 3,4-, and 3,5-dicarboxylates) were investigated for complexation with trivalent REE cations under hydro- or solvothermal conditions. Structural features of each compound were determined via single-crystal X-ray diffraction, which showed that positional variation of donor atoms within the PODC linkers significantly influences coordination behavior and directs the formation of distinct framework topologies. Additionally, hydrogen-bonding interactions involving the ligand functional groups were consistently observed and contribute to the supramolecular organization of the CPs and MOFs.
The coordination behavior of the three isomers, along with one structurally related linker, was further explored with the uranyl cation (UO22+) in chapter 6, whose linear geometry introduces additional constraints on framework assembly. Structural analysis of the resulting uranyl coordination polymers revealed diverse coordination modes and structural motifs, highlighting the significant influence of ligand donor arrangement on uranyl framework assembly. Positional and functional group variation within the PODC ligands resulted in distinct architectures, ranging from discrete and 1D assemblies (2,5-isomers) to two-dimensional networks (3,5-isomer) and 3D frameworks for the more flexible 3,4-PODC isomer.
To understand PODC linker coordination behavior in mixed-metal environments, 3,4-PODC was employed in systems containing uranyl cations in the presence of Nd3+ and Sr2+. Preliminary results are described in chapter 7, and Nd3+ and Sr2+ were selected based on their relevance in spent nuclear fuel where U(VI) is often found in the presence of a range of metallic fission products. A pronounced preference for uranyl binding by 3,4-PODC was observed, leading to selective crystallization of uranyl-containing crystalline phases in mixed-metal systems. Such selective crystallization behavior highlights the potential of these ligand systems for metal-selective solid-state assembly and may provide insights relevant to the separation of uranium in competitive environments. Chapter 8 of this thesis presents the conclusions, summarizing the key accomplishments of the preceding experimental chapters. Overall, this thesis demonstrates that linker engineering using PODC ligands provides a platform for controlling the structural assembly of REE and uranyl CPs, while offering insights into crystal engineering concepts and separation applications.
Details
- Title: Subtitle
- Linker design for f-Element hybrid materials chemistry
- Creators
- Ashanthi Kumari Katuwana Arachchige
- Contributors
- Korey P. Carter (Advisor)Tori Z. Forbes (Committee Member)Edward G. Gillan (Committee Member)David B. Martin (Committee Member)Scott R. Daly (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2026
- DOI
- 10.25820/etd.008451
- Publisher
- University of Iowa
- Number of pages
- xxi, 429 pages
- Copyright
- Copyright 2026 Ashanthi Kumari Katuwana Arachchige
- Language
- English
- Date submitted
- 04/17/2026
- Description illustrations
- Illustrations, graphs, charts, tables
- Description bibliographic
- Includes bibliographical references (pages 203-235).
- Public Abstract (ETD)
The development of novel materials with useful chemical and physical properties is an important goal in materials chemistry. One class of materials that has attracted significant attention is coordination polymers (CPs), which are extended networks formed when metal ions connect with organic molecules. The assembly of these materials is often compared to building with LEGOs, in which metal ions and organic molecules serve as the building blocks. Metal ions act as connection points, and organic molecules function as linkers that allow for material assembly. In this thesis, I explore how “molecular building blocks” can be used to construct new CPs containing rare earth elements (REE) or uranium as metal ions. A family of organic molecules known as pyridinone-based ligands was used as linkers to connect metal ions into extended networks. The research described herein shows that diverse CPs with unique structural features and properties could be constructed, and that small changes in the structure of the organic linkers influence how the metal ions connect and assemble in the solid-state. The findings provide insights that can guide the design of future advanced CP materials with tailored structures and properties.
- Academic Unit
- Chemistry
- Record Identifier
- 9985177376402771
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