Reaction of (CpSiMe(3))(3)U or (CpSiMe(3))(3)Nd with (Cp*Al)(4) or Cp*Ga (Cp* = C(5)Me(5)) afforded the isostructural complexes (CpSiMe(3))(3)M-ECp* (M = U, E = Al (1); M = U, E = Ga (2); M = Nd, E = Al (3); M = Nd, E = Ga (4)). In the case of 1 and 2 the complexes were isolated in 39 and 90% yields, respectively, as crystalline solids and were characterized by single-crystal X-ray diffraction, variable-temperature (1)H NMR spectroscopy, elemental analysis, variable-temperature magnetic susceptibility, and UV-visible-NIR spectroscopy. In the case of 3 and 4, the complexes were observed by variable-temperature (1)H NMR spectroscopy but were not isolated as pure materials. Comparison of the equilibrium constants and thermodynamic parameters DeltaH and DeltaS obtained by (1)H NMR titration methods revealed a much stronger U-Ga interaction in 2 than the Nd-Ga interaction in 4. Competition reactions between (CpSiMe(3))(3)U and (CpSiMe(3))(3)Nd indicate that Cp*Ga selectively binds U over Nd in a 93:7 ratio at 19 degrees C and 96:4 at -33 degrees C. For 1 and 3, comparison of (1)H NMR peak intensities suggests that Cp*Al also achieves excellent U(III)/Nd(III) selectivity at 21 degrees C. The solution electronic spectra and solid-state temperature-dependent magnetic susceptibilities of 1 and 2, in addition to X-ray absorption near-edge structure (XANES) measurements from scanning transmission X-ray microscopy (STXM) of 1, are consistent with those observed for other U(III) coordination complexes. DFT calculations using five different functionals were performed on the model complexes Cp(3)M-ECp (M = Nd, U; E = Al, Ga), and empirical fitting of the values for Cp(3)M-ECp allowed the prediction of binding energy estimates for Cp*Al compounds 1 and 3. NBO/NLMO bonding analyses on Cp(3)U-ECp indicate that the bonding consists predominantly of a E-->U sigma-interaction arising from favorable overlap between the diffuse ligand lone pair and the primarily 7s/6d acceptor orbitals on U(III), with negligible U-->E pi-donation. The overall experimental and computational bonding analysis suggests that Cp*Al and Cp*Ga behave as good sigma-donors in these systems.

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Actinium-225 and Bi have been used successfully in targeted alpha therapy (TAT) in preclinical and clinical research. This paper is a continuation of research activities aiming to expand the availability ofAc. The high-energy proton spallation reaction on natural thorium metal targets has been utilized to produce millicurie quantities of Ac. The results of sixteen irradiation experiments of thorium metal at beam energies between 78 and 192MeV are summarized in this work. Irradiations have been conducted at Brookhaven National Laboratory (BNL) and Los Alamos National Laboratory (LANL), while target dissolution and processing was carried out at Oak Ridge National Laboratory (ORNL). Excitation functions for actinium and thorium isotopes, as well as for some of the fission products, are presented. The cross sections for production ofAc range from 3.6 to 16.7mb in the incident proton energy range of 78-192MeV. Based on these data, production of curie quantities of Ac is possible by irradiating a 5.0gcmTh target for 10 days in either BNL or LANL proton irradiation facilities.