Structure and properties of 2,2-dihydroxymalonates of trivalent Y, lanthanides, Pu and Am

The M-O bond lengths in the lanthanide series show a well-known behaviour due to lanthanide contraction, including so-called “gadolinium break”. All three bond lengths show a good linear correlation with Shannon ionic radii for Y³⁺ and Ln³⁺ ions with coordination number 9. Nevertheless, the slopes of these dependences are different (0.957(16) for OH-groups, 0.85(2) for carboxylate groups and 1.080(17) for water molecules) and differ from unity due to a layer nature of the structures. The ionic radii for Pu³⁺ and Am³⁺ with coordination number 9 are absent in the Shannon system of ionic radii. From our data, we can propose the values 1.172 and 1.156 Å for Pu³⁺, and Am³⁺, respectively. In all crystals the structure is stabilized through extensive hydrogen bonding involving carboxylic and hydroxyl groups and water molecules.