Relativistic calculations of 2p and 3d excitation energies in the actinide metals

High pressure effects on U L3 x-ray absorption in partial fluorescence yield mode and single crystal x-ray diffraction in the heavy fermion compound UCd11

We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0–28.2 GPa) and single crystal x-ray diffraction (SXD) (0–20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K0 = 62(1) GPa and its pressure derivative, K0 = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

Comparative study of f-element electronic structure across a series of multimetallic actinide and lanthanoid-actinide complexes possessing redox-active bridging ligands

A comparative examination of the electronic interactions across a series of trimetallic actinide and mixed lanthanide-actinide and lanthanum-actinide complexes is presented. Using reduced, radical terpyridyl ligands as conduits in a bridging framework to promote intramolecular metal-metal communication, studies containing structural, electrochemical, and X-ray absorption spectroscopy are reported for (C(5)Me(5))(2)An[-N horizontal lineC(Bn)(tpy-M{C(5)Me(4)R}(2))](2) (where An = Th(IV), U(IV); Bn = CH(2)C(6)H(5); M = La(III), Sm(III), Yb(III), U(III); R = H, Me, Et) to reveal effects dependent on the identities of the metal ions and R-groups. The electrochemical results show differences in redox energetics at the peripheral "M" site between complexes and significant wave splitting of the metal- and ligand-based processes indicating substantial electronic interactions between multiple redox sites across the actinide-containing bridge. Most striking is the appearance of strong electronic coupling for the trimetallic Yb(III)-U(IV)-Yb(III), Sm(III)-U(IV)-Sm(III), and La(III)-U(IV)-La(III) complexes, [8](-), [9b](-), and [10b](-), respectively, whose calculated comproportionation constant K(c) is slightly larger than that reported for the benchmark Creutz-Taube ion. X-ray absorption studies for monometallic metallocene complexes of U(III), U(IV), and U(V) reveal small but detectable energy differences in the "white-line" feature of the uranium L(III)-edges consistent with these variations in nominal oxidation state. The sum of these data provides evidence of 5f/6d-orbital participation in bonding and electronic delocalization in these multimetallic f-element complexes. An improved, high-yielding synthesis of 4'-cyano-2,2':6',2''-terpyridine is also reported.