Applying Metalloligands, Postsynthetic Metalation and Direct Assembly to the Synthesis of Bimetallic Uranium Containing Hybrid Materials Open Access
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The primary focus of this dissertation has been the synthesis and study of bimetallic uranyl (UO22+) containing coordination polymers. These materials were synthesized under hydrothermal conditions, with various organic ligands, metalloligands, or coordination polymers as reagents. We have demonstrated that additional metal centers in uranyl containing materials may have an influence on both the architectures that are formed and the physical properties that are observed. These observations serve to broaden the fundamental understanding of the uranyl cation and its potential use in the synthesis of materials in the presence of a secondary metal center. Direct assembly, metalloligands, and postsynthetic metalation were individually employed to form the bimetallic uranyl containing coordination polymers in this dissertation. Direct assembly often requires the use of heterofunctional multitopic ligands that may bind two metal centers simultaneously. This method however, arguably offers little control over the resulting topologies. Metalloligands make use of a metal center that is pre-bound by a ligand that has additional coordinating sites for a secondary metal ion and offer some influence over how one metal center may be incorporated into the resulting topology. Postsynthetic metalation (PSMe) is often thought of as a method that starts with a coordination polymer that has free coordination sites that may bind a secondary metal center. This method arguably provides the most influence over the accessible topologies as one metal center is pre-bound and the other is likely to occupy the free binding sites without disrupting the starting topology. The PSMe of a coordination polymer however, may result in rearrangement to accommodate the secondary metal center as a consequence of metalation. We have proposed mechanisms for the rearrangements that were observed herein with a uranyl or copper(II) coordination polymer. The methods that were employed have proven to be useful in the synthesis of bimetallic coordination polymers. Further, the method chosen may provide varied degrees of influence over the resulting topologies, which may provide routes toward the targeted synthesis of architectures. Synthesis of bimetallic coordination polymers may permit us to target specific properties via the combination of the contributions from the ligand, the uranyl cation, and the secondary metal center selected. This dissertation was able to show that uranyl fluorescence is tunable in the presence of iron(II), silver(I), and copper(II). The extreme tuning of uranyl emission (no signal was observed) in the presence of iron(II) and silver(I) shows promise in the energy transfer from one metal center to another. The fluorescent properties of the U - Cu materials suggest that the uranyl cation may not only be tuned by the presence of the secondary metal center, but also by the local geometry of the organic ligands. This work (though admittedly focused on the exploration of the synthesis of bimetallic materials) forms the foundation for future endeavors in which we may synthesize materials that may be used with respect to ion exchange or luminescent and catalytic properties.
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