Using Phosphonates to Probe Structural Differences Between Transuranium Elements and Their Proposed Surrogates

A variety of transuranium phosphonates have now been prepared and structurally characterized allowing for comparisons to be made with other metal ions that have been proposed to be surrogates for transuranics (e.g., Zr4+, Ce4+, Th4+, and U4+). The phosphonates that will be discussed in this work include Np(CH3PO3)(CH3PO3H)(NO3)(H2O)·H2O, Pu(CH3PO3)2, M[CH2(PO3)2](H2O)n (M=Ce, Th, U, Np, Pu; n = 0 − 2), and UO2An(H2O)2[CH2(PO3)(PO3H)]2 (An = Th, Np, Pu). Through the examination of these structures, rare coordination geometries for actinides have been uncovered. Simple periodic trends based solely on ionic radii are absent. However, there are examples where surrogate elements adopt the same composition and structure as transuranics, such as Pu(CH3PO3)2 versus Zr(CH3PO3)2.