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

A hexanuclear Th(IV)-glycine complex was observed by Th L-3-edge EXAFS measurements in an aqueous solution. Within the stability range of this complex the positively charged hexanuclear species [Th-6(mu(3)-O)(4)(mu(3)-OH)(4)(H2O)(6)(Gly)(6)(HGly)(6)](6+) was preserved in a crystal with the composition [Th-6(mu(3)-O)(4)(mu(3)-OH)(4)(H2O)(6)(Gly)(6)(HGly)(6)]center dot(NO3)(3)(ClO4)(3)(H2O)(3). This complex appears as a 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)]center dot(ClO4)(4)H2O were obtained from the solution. Three water molecules in the thorium coordination sphere indicate that this complex occurs prior to the onset of Th(IV) hydrolysis.