Crystal Growth and First Crystallographic Characterization of Mixed Uranium(IV)–Plutonium(III) Oxalates

The mixed-actinide uranium­(IV)–plutonium­(III)
oxalate single crystals (NH4)0.5[PuIII0.5UIV0.5(C2O4)2·H2O]·nH2O (1) and (NH4)2.7PuIII0.7UIV1.3(C2O4)5·nH2O (2) have been prepared by the diffusion of different ions through membranes
separating compartments of a triple cell. UV–vis, Raman, and
thermal ionization mass spectrometry analyses demonstrate the presence
of both uranium and plutonium metal cations with conservation of the
initial oxidation state, UIV and PuIII, and
the formation of mixed-valence, mixed-actinide oxalate compounds.
The structure of 1 and an average structure of 2 were determined by single-crystal X-ray diffraction and
were solved by direct methods and Fourier difference techniques. Compounds 1 and 2 are the first mixed uranium­(IV)–plutonium­(III)
compounds to be structurally characterized by single-crystal X-ray
diffraction. The structure of 1, space group P4/n, a = 8.8558(3) Å, b = 7.8963(2) Å, Z = 2, consists of
layers formed by four-membered rings of the two actinide metals occupying
the same crystallographic site connected through oxalate ions. The
actinide atoms are nine-coordinated by oxygen atoms from four bidentate
oxalate ligands and one water molecule, which alternates up and down
the layer. The single-charged cations and nonbonded water molecules
are disordered in the same crystallographic site. For compound 2, an average structure has been determined in space group P6/mmm with a = 11.158(2)
Å and c = 6.400(1) Å. The honeycomb-like
framework [PuIII0.7UIV1.3(C2O4)5]2.7‑ results
from a three-dimensional arrangement of mixed (U0.65Pu0.35)­O10 polyhedra connected by five bis-bidentate
μ2-oxalate ions in a trigonal-bipyramidal configuration.