Synthesis and characterization of mixed An(IV)An(III) oxalates (An(IV) = Th, Np, U or Pu and An(III) = Pu or Am)

International audienceReaction of a solution containing a tetravalent actinide An(IV), a trivalent actinide An(III) and a single-charged cation such as hydrazinium in presence of oxalic acid in acidic medium under controlled conditions, leads to the precipitation of mixed An(IV)-An(III) oxalate compounds never reported before. By varying the (An$^{IV}$,An$^{III}$) pair and depending on the An$^{IV}$-An$^{III}$ ratio, two original series were obtained (N$_2$H$_5$,H$_3$O)$_{2+x}$An$^{IV}$$_{2-x}$An${III}$$_x$(C$_2$O$_4$)$_5$.4H$_2$O (1) and (N$_2$H$_5$,H$_3$O)$_{1-x}$(An$^{III}$$_{1-x}$An$^{IV}$$_x$(C$_2$O$_4$)$_2$.H$_2$O).4H$_2$O (2). The crystal structures were identified from powder diffraction patterns by analogy to hydrazinium uranium (IV) lanthanide (III) oxalates whose structures were solved recently by single-crystal X-ray diffraction. Complementary investigations by UV-visible and Infra-Red spectroscopies and thermogravimetric analysis confirm the presence of both tetravalent and trivalent states of actinides in structures (1) and (2) and the role of single-charged cation and water molecules.The originality of both structures is the existence of a mixed crystallographic site for the tetravalent actinide and the trivalent one, the charge balance being ensured by the adjustment of the single-charged ions within the structure. The main difference is that actinides are ten-coordinated in (1) and nine-coordinated in (2).This is the first evidence of a mixed actinide(IV)-actinide(III) site in an oxalate structure

Neodymium(III) Complexes with Bulky ansa-Bis(cyclopentadienyl) Ligands: Synthesis and Use in Olefin Oligomerization

The trivalent neodymium complexes [rac-{Me2Si(η5-2-SiMe3-4-t-Bu-C5H2)2}Nd(μ-Cl)2Li(THF)2] (rac-3), [rac-{Me2Si(η5-2,4-(SiMe3)2C5H2)2}Nd(μ-Cl)2Li(THF)2] (rac-5), and [{Me2Si(η5-2,4-(SiMe3)2C5H2)(η5-3,4-(SiMe3)2C5H2)}Nd(μ-Cl)2Li(THF)2] (C1-6) have been prepared and their structures investigated by NMR and X-ray crystallography. These new chlorolanthanocenes, when combined in situ with a dialkylmagnesium cocatalyst, initiate the polymerization of ethylene and 1-octene to yield di(oligoalkyl)magnesium species, which can be finally hydrolyzed to oligomers. Bulky bridged complexes rac-3, rac-5, and C1-6 gave significantly more active catalysts for 1-octene oligomerization (Mn = 400−1300, Mw/Mn = 1.11−1.65) than systems based on nonbridged complexes [(η5-C5Me5)2Nd(μ-Cl)2Li(Et2O)2] (1) and [(η5-1,3-(SiMe3)2C5H3)2Nd(μ-Cl)2Li(THF)2] (7). Ethylene oligomerization (Mn = 400−5000) was best achieved with complexes 1 and rac-3, as important catalyst decay occurred with bridged bis(trimethylsilyl) systems rac-5 and C1-6