Polymeric Structure of Oxalato-Bridged Complexes of Tetravalent Actinides Th, U, Np and Pu

A series of isostructural oxalates of Th, U, Np, and
Pu have been
synthesized. The crystal structure of {C­(NH2)3}4[An­(C2O4)4]·2H2O comprises infinite [An­(C2O4)4]4n− chains, guanidinium cations
and water molecules. Each An atom is connected to five oxalate anions,
two of which act as bridging tetradentate ligands, while the other
three function as terminating bidentate ligands. Electron and IR spectra
of the compounds as well as the results of thermal analysis correlate
with their structure. An actinide contraction effect is demonstrated
by a decrease in the An–O interatomic distances and the volumes
of An atom coordination polyhedra and Voronoi–Dirichlet polyhedra.
Ten-coordinate An oxalates are discussed in terms of continuous shape
measures approach.