Supramolecular assembly of [UO2X4]-2 (X = Cl, Br) with substituted methyl pyridinium cations: structure-property relationships
Join GW Chemistry Graduate Student Nicole Byrne for this edition of the Department of Chemistry seminar series.
Uranium-containing materials are of interest due to their relevance to the nuclear fuel cycle, especially when it comes to nuclear waste stewardship and non-proliferation efforts. When compared to the more common d-block metals, the behavior of those situated in the f-block (like uranium and the other actinides), is much less developed with respect to both fundamental chemistry and properties. As such, there remains a critical need to fully understand the chemistry of these elements, specifically in relation to the role of f-electrons in the chemical bonding of these materials (i.e. covalent nature of bonding or lack thereof).
To best explore the properties within families of materials, the approach is to perform a systematic study to establish modes of assembly and highlight trends throughout the series of materials. With these motivations in mind, a family of uranyl tetrahalides ([UO2X4]-2 where X= Cl- or Br-), paired with substituted methyl-pyridinium cations, has been prepared with aims to correlate trends in assembly to observed shifts in the Raman and luminescence spectra. Each of the compounds were prepared by slow evaporation of solutions from high halide media, to effectively shut down hydrolysis of the uranyl and promote discrete formation of uranyl tetrahalide building units. This particular family of organic ligands was chosen for their ability to provide non-covalent interactions, specifically charge-assisted hydrogen bonding, in the second coordination sphere. Shifts in both Raman and luminescence spectra have been proven to show sensitivity to the non-covalent interactions between the organic and the uranyl tetrahalide, as well as the equatorial ligand of the uranyl. The trends observed in the uranyl tetrahalide family will then be extended to other actinides, including the neptunyl, plutonyl, and americyl tetrahalides.