No abstract

An approach to obtaining substantial amounts of data from a hazardous starting material that can only be obtained and handled in small quantities is demonstrated by the investigation of a single small-scale reaction of cyclooctatetraene, C8H8, with a solution obtained from the reduction of Cp′3Pu (Cp′ = C5H4SiMe3) with potassium graphite. This one reaction coupled with oxidation of a product has provided single-crystal X-ray structural data on three organoplutonium compounds as well as information on redox chemistry thereby demonstrating an efficient route to new reactivity and structural information on this highly radioactive element. The crystal structures were obtained from the reduction of C8H8 by a putative Pu­(II) complex, (Cp′3PuII)1−, generated in situ, to form the Pu­(III) cyclooctatetraenide complex, [K­(crypt)]­[(C8H8)2PuIII], 1-Pu, and the tetra­(cyclopentadienyl) Pu­(III) complex, [K­(crypt)]­[Cp′4PuIII], 2-Pu. Oxidation of the sample of 1-Pu with Ag­(I) afforded a third organoplutonium complex that has been structurally characterized for the first time, (C8H8)2PuIV, 3-Pu. Complexes 1-Pu and 3-Pu contain Pu sandwiched between parallel (C8H8)2– rings. The (Cp′4PuIII)− anion in 2-Pu features three η5-Cp′ rings and one η1-Cp′ ring, which is a rare example of a formal Pu–C η1-bond. In addition, this study addresses the challenge of small-scale synthesis imparted by radiological and material availability of transuranium isotopes, in particular that of pure metal samples. A route to an anhydrous Pu­(III) starting material from the more readily available PuIVO2 was developed to facilitate reproducible syntheses and allow complete spectroscopic analysis of 1-Pu and 2-Pu. PuIVO2 was converted to PuIIIBr3(DME)2 (DME = CH3OCH2CH2OCH3) and subsequently PuIIIBr3(THF) x , which was used to independently synthesize 1-Pu, 2-Pu, and 3-Pu.

A series of homoleptic tetravalent transition-metal and actinide Schiff-base coordination complexes, ML 2 {M = Zr, Hf, Th, U; L = N,N′-bis[(4,4′diethylamino)salicylidene]-1,2-phenylenediamine}, have been synthesized that feature a rigid phenyl backbone. These complexes create the opportunity for comparing a series of complexes containing metal cations in the formal IV+ oxidation state by structural, spectroscopic, and theoretical analysis that also incorporate the previously reported Ce(IV) and Pu(IV) analogues. X-ray crystallographic analysis reveals that all complexes are isomorphous and feature a co-facial ligand geometry. TD-DFT and other quantum mechanical methods were used to explore bonding differences across between the complexes, and resulting calculated absorbance spectra for ML 2 are in good agreement with the experimental data. The computational results also suggest that U(IV) and Pu(IV) analogs have more covalent character in their bonding than found with the other metal cations reported here.

Two uranyl Schiff-base coordination complexes, UO2L­(MeOH) and UO2Cl2( H2L ) {L = N,N′-bis­[(4,4′-diethylamino)­salicylidene]-1,2-phenylenediamine}, have been synthesized that feature a rigid phenyl backbone. These complexes have been characterized by structural, spectroscopic, and theoretical analysis to offer an electronic structure basis to explain the bonding parameters and stability. Single-crystal X-ray analysis reveals that UO2L­(MeOH) adopts the typical “soft taco confirmation” characteristic of uranyl salophen complexes, whereas UO2Cl2( H2L ) features an unusual neutral ligand coordination that contains an internal hydrogen bond between the phenol and imine. Rate constants calculated from electrochemical experiments confirm a quasi-reversible UO2 2+/UO2 + couple. Single-configurational and multiconfigurational methods were used to explore the bonding in UO2L­(MeOH) and UO2Cl2( H2L ). For UO2Cl2( H2L ), the U–Cl bond exhibits more covalent contributions than U–OL.

PuL and CeL (L = N,N'-bis[(4,4'-diethylamino)salicylidene]-1,2-phenylenediamine) have been synthesized, and characterized by single crystal X-ray diffraction, UV/vis/NIR spectroscopy, and cyclic voltammetry. These studies reveal the enhanced stabilization of Pu(iv) versus Ce(iv) with this Schiff base, and quasi-reversible redox behaviour only with the plutonium complex.