Structure and stability range of a hexanuclear Th(IV) – glycine complex

A hexanuclear Th(IV) glycine complex was observed by Th L3-edge EXAFS measurements in aqueous solution. Within the stability range of this complex the positively charged hexanuclear species [Th6(µ3-O)4(µ3-OH)4(H2O)6(Gly)6(HGly)6]6+ was preserved in a crystal with the composition [Th6(µ3-O)4(µ3-OH)4(H2O)6(Gly)6(HGly)6]•(NO3)3(ClO4)3(H2O)3. This complex appears as result of a competing reaction between hydrolysis and ligation by glycine. At a pH value below the stability range of the hexanuclear complex, crystals with the composition [Th(H2O)3(HGly)3]•(ClO4)4H2O were obtained from the solution. Three water molecules in the thorium coordination sphere indicate that this complex occurs below the onset of Th(IV) hydrolysis.