Coordination Modes of Americium in the Am₂(C₂O₄)₃­(H₂O)₆·4H₂O Oxalate: Synthesis, Crystal Structure, Spectroscopic Characterizations and Comparison in the M₂(C₂O₄)₃­(H₂O)₆·<i>n</i>H₂O (M = Ln, An) Series

Americium oxalate single crystals, Am₂­(C₂O₄)₃­(H₂O)₆·​4H₂O, were prepared by <i>in situ</i> oxalic acid generation by slow hydrolysis of the diester. Their structure was determined by single-crystal X-ray diffraction and was solved by the direct methods and Fourier difference techniques. The structure (space group <i>P</i>2₁/<i>c</i>, <i>a</i> = 11.184(4) Å, <i>b</i> = 9.489(4) Å, <i>c</i> = 10.234(4) Å, β = 114.308(8)°, <i>Z</i> = 2) consists of layers formed by six-membered rings of actinide metals connected through oxalate ions. The americium atoms are nine-coordinated by six oxygen atoms from three bidentate oxalate ligands and three water molecules. The distances within the coordination sphere as well as infrared and Raman spectra of several isostructural lanthanide (Ce­(III), Pr­(III), Nd­(III), Sm­(III), Gd­(III)) and actinide (Pu­(III), Am­(III)) oxalates were compared to evaluate the similarities and the differences between the two series