Advances in Chemistry of the Actinide Elements

Abstract

Recent research accomplishments that elucidate the bonding and reactivity of the actinides are highlighted in this review. Improved syntheses of protactinium and transplutonium metals and Compounds have led to determination of physical properties that reveal effects of 5f interactions. Theimodynamic measurements on metals, aqueous ions, and oxides have yielded more systematic understanding of the chemistry of the entire actinide series. Advances in bonding include the preparation of new organoactinide Compounds with strong a and TT metal-carbon and metal-hydrogen bonds; the development of new actinide complexing, sequestering, and extracting agents; and the study of chemical consequences of radioactive decay on oxides and halides. New techniques that impact actinide chemistry are laser fluorescence and photochemistry, radiocoulometry, and pulse radiolysis. Progress has also been made in outlining the basic chemical behavior of the heaviest actinides and the transactinides.Two isomorphs of ThBr4 are known, the well-known /3-ThBr4 and a low-temperature, poorly-characterized a-ThBr4. Below 92 K, j3-ThBr4 displays Splitting of a Raman Vibration and of a bromine nuclear quadrupole resonance line, and new X-ray and neutron diffraction lines appear [2,7]. These observations are not consistent with any conventional superlattice of the tetragonal unit cell, and are caused by a second-order phase transition in which bromine atoms along the c ciystallographic axis are displaced sinusoidally from their sites with a repeating distance of 3.201 c. This phenomenon is a subject of intense investigation and illustrates how careful measurements on pure, Single ciystals can reveal new scientific ideas.

Molar enthalpies of formation of BaCmO3 and BaCfO3

“…With rcf,+=0.0821 nm, t=0.876 and AfH~(complex) = -(76.0 + 8.5) kJ mol-1, we obtain AfHm(CfO2, cr)= -(854 + 10) kJ mo1-1. This value is in very good agreement with that of -858 kJ mo1-1, estimated by Morss [29] based on the empirical interrelationship between the molar volumes of the lanthanide and actinide dioxides and their standard molar enthalpies of solution.…”

“…Finally, using the entropy values listed by this latter author, namely, S°(CP +, aq)=-412 J K -1 mo1-1, S~(Cf 3+, aq)=-197 J K -1 mo1-1, accepting an uncertainty of +20 J K -1 tool -1 for the difference {S°(Cf 4+, aq) -S°(Cf 3, aq)}, and S°(H2, g) = 130.571 + 0.005 J K-1 mol-1 [11], we obtain E°(Cfa+/cf 3 ÷) = 3.28 + 0.14 V for the standard potential of the cfa+/cf 3+ couple. Our value is virtually identical to that of 3.2 V given by Morss [29], but is based on the first experimental thermochemical data from a solid tetravalent californium compound.…”

“…An extrapolation to californium of the plot {AfH°(M'O2, cr)-Afn°(M '4+, aq)} versus M '4+ ionic radius [25] leads to {AfH~(CfO2, cr)-AfHo(CP +, aq)}=-(549+5) kJ mo1-1 and yields AfH°(Cf 4+, aq)=-(305+ 11) kJ mo1-1, which compare favorably with -313 kJ tool -1 estimated by Morss [29]. Finally, using the entropy values listed by this latter author, namely, S°(CP +, aq)=-412 J K -1 mo1-1, S~(Cf 3+, aq)=-197 J K -1 mo1-1, accepting an uncertainty of +20 J K -1 tool -1 for the difference {S°(Cf 4+, aq) -S°(Cf 3, aq)}, and S°(H2, g) = 130.571 + 0.005 J K-1 mol-1 [11], we obtain E°(Cfa+/cf 3 ÷) = 3.28 + 0.14 V for the standard potential of the cfa+/cf 3+ couple.…”

Empirical Evaluation of the Thermodynamic and Magnetic Properties from the Atomic Distances of NaCl-type Actinide Compounds

“…The measured values of SO(298)rep in the first column are cited mostly from ref. (5), and in this column of SO(298)rep, the estimated values for some thorium and uranium' chalcogenides shown in ref. (6) are also included.…”