Tuning Actinide Complexes Through Structure and Oxidation State

The properties of actinide materials have been explored by discriminate ligand selection based on hyperpolarizability and control of oxidation state. This has led to a number of interesting compounds that further the chemistry of the underexplored 5f series. This includes the synthesis and isolation of the surpisingly air stable U(III) and Np(III) sulfates along with the synthesis of Pu(III) molybdate and Pu(III) tungstate, which feature a metal to metal charge transfer.

There are two goals of this work. The first is to explore the bonding in trivalent 5f complexes with oxoanions. Oxoanion bonding to the 5f elements can range from completely ionic to partially covalent. However, there is little indication of which ligands will express covalent interactions and which will express ionic interactions. This work shows that the hyperpolarizability can be used as an indication of anion polarizability which heavily influences the type of bonding observed. Anions with low polarizability, such as phosphite, will participate in ionic bonding, and there will be little difference between the lanthanide and actinide compounds. Anions with high polarizability, such as molybdate or tungstate, will have partially covalent bonds to the actinide leading to unusual properties and distinct difference to the lanthanide analogues.

The second goal of this work is to access and stabilize unusually low oxidation states using hydrothermal techniques. As the electronic properties of actinides are dependent on oxidation state, the ability to access and stabilize different oxidation states is of utmost importance. Oxoanion complexes of U(III) and Np(III) are exceedingly rare, leaving many of their properties underexplored. It is shown that U(III) and Np(III) can be obtained hydrothermally from higher valent starting materials. These products are isolated using ZnHg amalgam hydrothermally, with no regards to O2 exclusion. This work also shows that this chemistry is useful outside of the actinides with the production of Eu(II), V(II), and Cr(II) compounds in a similar manner. This dissertation is focused on synthesis and characterization on a number of lanthanide, actinide, and transition metal complexes. Chapters 3 &8211; 6 focus on the bonding of ligands with low versus high hyperpolarizability when complexed with lanthanides and actinides. Chapters 7 &8211; 11 focus on the use of ZnHg as an in situ reductant. This work has implications for actinide chemistry through a method of ligand discrimination to affect actinide properties. This work also has general implications through the metal-to-metal charge transfer of f-elements which could impact the development of materials as well as the isolation of V(II) and Cr(II) through hydrothermal synthesis.