Phosphonoacetate as a Ligand for Constructing Layered and Framework Alkali Metal Uranyl Compounds

Abstract

The hydrothermal reactions of KCl, RbCl, CsOH, and CsCl with phosphonoacetic acid and uranium trioxide at 180 degrees C for three to five days results in the formation of five different crystalline uranyl carboxyphosphonates, K[(UO(2))(2)(PO(3)CH(2)CO(2))(PO(3)CH(2)CO(2)H)(H(2)O)] x H(2)O, Rb[(UO(2))(2)(PO(3)CH(2)CO(2))(PO(3)CH(2)CO(2)H)(H(2)O)] x H(2)O, Cs[(UO(2))(2)(PO(3)CH(2)CO(2))(PO(3)CH(2)CO(2)H)(H(2)O)] x H(2)O, Cs[(UO(2))(PO(3)CH(2)CO(2))], and Cs(3)[(UO(2))(4)(PO(3)CH(2)O(2))(2)(PO(3)CH(2)CO(2)H(0.5))(2)] x nH(2)O, respectively. In all compounds, the UO(2)(2+) moieties are bound by phosphonate and carboxylate forming pentagonal bipyramidal environments around the uranium centers. At low pH, some of the carboxylate portions of the phosphonoacetate are protonated. The addition of hydroxide removes these protons, and a different structure is adopted. In contrast to all other uranyl carboxyphosphonates, Cs(3)[(UO(2))(4)(PO(3)CH(2)O(2))(2)(PO(3)CH(2)CO(2)H(0.5))(2)] x nH(2)O adopts a three-dimensional network structure with large channels along the c axis that house the Cs(+) cations.