Understanding the Structural Chemistry of Heterobimetallic Uranyl Transition Metal Phosphonoacetates

The solid-state chemistry of uranium has greatly advanced over the past few decades because of improvements in instrumentation, new synthetic methods, and recognition of the importance of correlating structural features with physicochemical properties for elements involved in the nuclear fuel cycle. In particular, uranium(VI) forms many compounds with all known oxoanions. There are many uranium(VI) families, such as borates, iodates, tellurites, phosphates, germanates, chromates, and phosphonates. By using single crystal X-ray diffraction, the structures of these types of novel compounds can be examined and studied. With our research, we strive to design and investigate materials that will sequester radioactive elements.

In this doctoral thesis, the reader will find a collection of published results that are focused on synthesizing novel heterobimetallic (mixed-metal) transition metal uranyl phosphonates. To prepare these compounds, the moderate-pressure and temperature process of hydrothermal synthesis was used. The key step of achieving these mixed crystals was the slow hydrolysis of triethyl phosphonoacetate, which allows the gradual introduction of this ligand. The phosphonoacetate ligand was used to bridge between various early transition metals and uranium(VI). The most important method used to analyze these structures was single crystal X-ray diffraction. Additional methods used for characterization were UV-vis spectroscopy, Raman spectroscopy, thermogravimetric analysis, and BET. These compounds have unexpected structures, unusually high-symmetry, and uncommon features in the family of carboxyphosphonates. With these types of behaviors, we demonstrated the unpredictable and diverse nature of uranyl phosphonates.